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Glossary of terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All 

abdominal aorta
The portion of the largest artery in the body that runs through the abdomen; it supplies oxygenated blood to the abdominal and pelvic organs and the legs.

abdominal aortic aneurysm (AAA)
Sometimes called triple A.
A ballooning out of a segment of artery caused by disease or weakness in the vessel wall (called an aneurysm) that occurs in the portion of the aorta that runs through the abdomen. For more information, see the Abdominal aortic aneurysm page.

abdominoperineal resection
A surgical procedure in which cancer cells in the anus, rectum and part of the large intestine are removed through an incision made in the abdomen.

See radiofrequency ablation.

A localized infection consisting of pus surrounded by inflamed tissue.

absence seizure
See petit mal seizure.


  1. In radiology, the uptake of energy from radiation by the tissue or medium through which it passes.
  2. In radiation or medical physics, the number of disintegrations per second of a radionuclide.

A drug that reduces pain and fever but not inflammation. A member of the family of drugs called analgesics, it is found in many over-the-counter medications, such as Tylenol®.

acquired immunodeficiency syndrome (AIDS)
A stage of human immunodeficiency virus (HIV) infection in which the immune system is so badly damaged the body is unable to fight off infections and disease.

Referring to the rapid onset of a disease or condition.

Also called brentuximab vedotin
A treatment for Hodgkin lymphoma that combines a chemotherapy drug with a monoclonal antibody that attaches to a specific molecule on the cancer cells.

adjuvant therapy
Treatment designed to be contributory or complementary to primary therapy. See also definitive treatment.

adrenal glands
Small glands that sit atop each kidney and produce hormones important in regulating metabolism, blood pressure and response to stress.

afterloaded implant
A brachytherapy treatment in which a remote-controlled machine pushes radioactive material through a delivery device to the site of a tumor.

A hypersensitive reaction to common, often harmless substances, most of which are found in the environment.

Involving genetically similar but not identical donor in a medical procedure such as a stem cell transplant.

Tissue graft from a separate donor.

A drug that lowers an elevated level of uric acid in the blood caused by some cancer treatments.

Alpha-1 antitrypsin (A1AT)
A protein that protects the lung. A1AT deficiency puts a person at risk of developing emphysema or chronic obstructive pulmonary disease (COPD).

Alpha-1 antitrypsin deficiency (A1AD)
A genetic disorder caused by low levels of alpha-1 antitrypsin, a protein that protects the lungs. Alpha-1 antitrypsin deficiency (A1AD) puts a person at risk of developing emphysema or chronic obstructive pulmonary disease (COPD). See the COPD page for additional information.

Tiny air sacs located at the end of the respiratory tract in the lungs that allow inhaled oxygen to enter the bloodstream and carbon dioxide to leave the bloodstream with exhalation.

The suction of fluid from the amniotic sac through the use of a needle inserted through the abdomen.

See amniotic sac.

amniotic sac
Membrane filled with fluid within the abdomen that holds the embryo/fetus.

A drug that relieves pain.

A group of hormones produced by both men and women. They are present in much higher levels in men and govern the growth and development of the male reproductive system. In women, they are converted to hormones called estrogens.

A condition in which too few red blood cells are in the bloodstream, resulting in insufficient oxygen to tissues and organs. For additional information see the Anemia page.

Drugs used to induce loss of sensation for the patient in preparation for operative procedures.

A physician specializing in the controlled loss of sensation through anesthesia.

Drugs used to induce loss of sensation for the patient in preparation for operative procedures.

A ballooning out of a segment of blood vessel caused by disease or weakness in the vessel wall. It may lead to rupture and serious or fatal bleeding.

Cramp-like pain that comes and goes, and is made worse by physical effort. It is a sign that the tissue or organ supplied by a narrowed artery is not getting enough blood or oxygen. For more information see the Angina Pectoris page.

X-ray imaging of the heart, coronary arteries and/or great vessels made visible by injection of a dye directly into the vessel via a catheter. In other instances, CT or MRI can be used to create three-dimensional pictures of blood vessels.

Formation of new blood vessels.

angiogenesis inhibitors
Drugs that interfere with the growth of blood vessels in the tumor, thus starving the tumor of the nutrients and oxygen it needs to grow. Also called angiostatic therapy.

In a conventional angiogram, a dye is injected into the bloodstream and x-rays are taken to visualize the blood vessels. In other instances, CT or MRI can be used to create three-dimensional pictures of blood vessels.

Relating to or utilizing angiography.

An examination of blood vessels that uses X-ray, CT or MR imaging and an injection of a radiopaque contrast material to image arteries in the brain, heart, kidneys, gastrointestinal tract, aorta, neck, chest, limbs and pulmonary circulatory system.

Reconstitution or reopening of a blood vessel; may involve balloon dilation, mechanical stripping of the inside of the blood vessel, forceful injection of a elastic filamentous protein, or placement of a stent. For details see the Angioplasty and Vascular Stenting page.

angiostatic therapy
See angiogenesis inhibitors.

The outer layer of intervertebral discs, sponge-like cushions between the vertebrae, or bones, of the spine.

The process of removing all indentifiers or codes that directly or indirectly link a sample or data to a specific identifiable person.

anterior fibromuscular stroma
The anterior surface of the prostate.

A class of medications used to treat bacterial infections by killing or inhibiting the growth of bacteria.

Substances that neutralize body toxins and bacteria.

anticoagulant therapy
The use of anticoagulant drugs (blood-thinners) to treat blood clots, including those due to pulmonary embolism and deep venous thrombosis in the calf.

A drug used to prevent or reduce the severity of seizures associated with epilepsy or other seizure disorders.

antiplatelet drug
A medication that interferes with the normal function of blood platelets and thereby reduces the tendency for blood to clot; commonly called a blood thinner.

The opening at the end of the gastrointestinal tract through which stool, or solid waste, leaves the body.

The largest artery in the body; it distributes blood from the heart to the entire body via the circulatory system.

aortic aneurysm
A ballooning-out of a segment of artery caused by disease or weakness in the vessel wall (called an aneurysm) the largest artery in the body, the aorta.

appendiceal lumen
Inside of the appendix where mucus, created by the appendix, travels and empties into the large intestines.

An inflammation (swelling) of the appendix, usually caused by a blockage at the opening of the appendix and a subsequent infection. See the appendicitis page for additional information.

A stone, calcification or calcific deposit in the appendix.

A wormlike "pouch" several inches long located near the beginning of the large intestine, in the lower right portion of the abdomen. At this time, the role the appendix plays in the human body is not known.

arachnoid membrane
A thin membrane enclosing the brain and spinal cord.

argon gas
A colorless, odorless gas found in the air and used in its liquefied state in cryosurgery to freeze and destroy diseased tissue, including cancer cells.

An abnormal rhythm of the heart.

Hardening of the arteries; types generally recognized are: atherosclerosis, Mönckeberg's arteriosclerosis, and arteriolosclerosis.

arteriovenous fistula
An abnormal connection between an artery and a vein. This can be surgically created for hemodialysis (see dialysis arteriovenous fistula) but can also be caused by trauma. These fistulas can commonly be treated by interventional radiologists.

arteriovenous malformation (AVM)

  1. An abnormal connection between arteries and veins that allows blood flow to bypass the small vessels where oxygen and tissue nutrients are exchanged. These unusual malformations may be present at birth or may result from injury or infection. They are often found in the brain and spinal cord, but may occur anywhere in the body.
  2. A tangle of dilated blood vessels that disrupts normal blood flow in the brain.

Vessels that carry blood away from the heart.

Inflammation (swelling) of a joint or a state characterized by inflammation of joints. See the Arthritis page for additional information.

An imaging study of a joint that uses a contrast material and either magnetic resonance imaging (MRI) or a special form of real-time x-ray imaging called fluoroscopy.

In radiology, something artificial that appears on a medical image but is not a part of the living tissue being examined. The image distortion could be due to an obstruction, such as a surgical metal clip, or to a problem with the imaging equipment.

A group of potentially dangerous, naturally occurring minerals with long, thin fibers; asbestos was once extensively used in building materials and commercial products. Asbestos inhalation can cause a variety of health problems (e.g., asbestosis, pleural effusion, mesothelioma or lung cancer).

A condition in which fluid accumulates in the abdomen and causes swelling; it may be caused by cirrhosis (chronic liver disease), cancer, heart failure, kidney failure, tuberculosis and/or pancreatic disease.

A member of the family of drugs called nonsteroidal anti-inflammatory agents (NSAID) that reduces pain, fever, inflammation, and blood clotting.

A condition of the lungs characterized by a narrowing of the airways and excessive mucus; can cause difficulty breathing, wheezing and coughing.

Having no signs or symptoms.

A minimally invasive treatment for blocked arteries that uses a catheter with a sharp blade or laser on the end to remove plaque from a blood vessel.

Arteriosclerosis characterized by irregularly distributed lipid deposits, or plaque, in large and medium-sized arteries; such deposits provoke fibrosis and calcification (hardening of the tissues).

A wasting away or gradual decline of tissues, organs, or the entire body.

Loss of energy of a beam of radiant energy due to absorption, scattering, beam divergence, and other causes as the beam propagates through a medium.

An information system log that keeps a record of all user activity by user identification.

A visual disturbance, such as flashing lights, wavy lines, blurry vision or blind spots, that sometimes occurs prior to the onset of a migraine headache.

Verifying the identity of a person/user to a computer system or assuring that a computer program is a trusted one.

Access controls that restrict access to a system to only authorized users; access control assigns right and privileges of users to resources via single sign-on databases; auto logoff to prevent someone other than the valid user from continuing a session; physical access control for critical computers to prevent console-based malicious attacks, power interruptions or other threats to security of the systems.

autoimmune disease
Any disorder that causes the immune system to attack the body’s own tissues.

Involving one individual as both donor and recipient in a medical procedure such as a stem cell transplant.

automatic spring-loaded needle
Also called core needle.
A spring-loaded device that cuts and retrieves a small tissue specimen in its collecting chamber. It is used for biopsy of many different organs in the body.

axillary lymph node dissection
Surgical exploration and removal of lymph nodes from the armpit area, as a part of breast cancer surgery. Some or all of these lymph nodes are examined under a microscope by a pathologist (a physician specializing in the examination of cells and tissues) to see if cancer cells are present.

axillary lymph nodes
Numerous nodes around the axillary (below the shoulder joint) veins which receive the lymphatic drainage from the upper limb, scapular region and pectoral region (including mammary gland); they drain into the subclavian trunk.

See nerve fibers.

B cell
A type of white blood cell (called a lymphocyte) that is an essential component of the immune system. Non Hodgkin B cell lymphoma begins in B cells.

balloon angioplasty
An image-guided procedure in which a balloon-tipped catheter, a long thin, hollow plastic tube, is guided into an artery and advanced to a blockage or narrowing in a blood vessel. The balloon is then inflated to open the vessel, deflated and removed.

balloon assistance
A vascular treatment technique that uses catheter-guided balloons to open narrowed blood vessels.

barium (Ba)
A naturally occurring metal that is used in barium sulfate, a contrast material. Barium is most commonly used for studying the gastrointestinal (GI) tract.

barium sulfate
A white insoluble radiopaque powder that is used as a contrast material to make certain body parts more visible in x-ray images. Radiopaque substances limit the penetration of x-rays and other forms of radiation.

barium swallow
Also called an esophagram.
An x-ray examination that uses a barium sulfate contrast material to assess both the pharynx and esophagus in the upper gastrointestinal tract.

Barrett’s esophagus
A condition in which the cells lining the esophagus undergo change due to damage from repeated exposure to stomach acid. These changes increase the risk of esophageal cancer. Treatments include antacids, proton pump inhibitors, dietary changes and surgery.


becquerel (Bq)
The SI unit of measurement of radioactivity, equal to 1 disintegration per second;;
1 Bq = 0.027 × 10-9 Ci.

Not cancerous. May also be defined as non-malignant. Benign is also used to describe medical conditions that have a mild course.

benign prostatic hyperplasia (BPH)
An enlarged prostate gland, a common problem among older men. See the Benign Prostatic Hyperplasia page for additional information.

beta blocker
A type of medicine used to lower blood pressure, treat chest pain and heart failure, and to prevent a heart attack.

beta-amyloid plaque
Thick deposits of proteins in the brain considered one of the hallmarks of Alzheimer’s disease (AD).

An iodine-131 agent used in radioimmuniotherapy to treat non-Hodgkin lymphoma.

A greenish-yellow fluid secreted by the liver, stored in the gallbladder and released through tubular passageways called bile ducts into the bowel to help digest fat and carry away waste.

bile ducts
Tubular structures that course through the liver and carry bile – a greenish-yellow fluid – to the gallbladder and small intestine where it is used to help digest fat.

biliary atresia
A condition present at birth in which there is a blockage in the ducts that carry bile from the liver to the gallbladder.

biliary system
See biliary tract.

biliary tract
Also called the biliary system.
Includes the gallbladder and tubular structures called ducts that course through the liver. Bile, a greenish-yellow fluid secreted by the liver, is stored in the gallbladder and released into the bowel through bile ducts to help the small intestine digest fat and carry away waste.

biologic therapy
Also called biotherapy
A treatment that involves natural or laboratory-made substances designed to boost, direct or restore the body's natural defenses against cancer.

biologically active coils
A type of coil, made of soft platinum wire smaller than a strand of hair and available in different diameters and lengths, used in a procedure called a detachable coil embolization to treat an aneurysm (a bulge) or a blood vessel malformation called a fistula (a false passageway) that occurs in the brain and other parts of the body. Using image guidance, the coils are placed at the site of a bulge or passageway, where it helps block the flow of blood and prevents a rupture of the vessel.

Biometrics requires a user to provide a unique identifier, such as a fingerprint or voice sample, which is compared to a stored record before the user can gain access to the computer.


  1. Process of removing tissue from living patients for diagnostic examination.
  2. A specimen obtained by biopsy.

See the Biopsies page for additional information.

Also called biologic therapy
A treatment that involves natural or laboratory-made substances designed to boost, direct or restore the body's natural defenses against cancer.

A balloon-like organ where urine is stored before being passed from the body.

bleeding disorder
A condition in which the body's blood clotting mechanism, which turns blood from a free-flowing liquid to a thickened state, is defective.

blood clot
A thickened mass of blood. For additional information see the Blood Clots page.

blood clotting
See blood coagulation.

blood coagulation
Also called blood clotting.
A process in which blood changes from a free-flowing liquid to a semi-solid gel.

blood oxygenation
The level of oxygen in the blood.

blood thinning agents
Also known as blood thinners. Medicine used to prevent blood clots from forming or getting larger.

bone marrow
The soft tissue that fills the cavities of bones in which blood cells are produced.

bone scan
An imaging test in which a radiotracer called technetium-99m is injected into a vein and travels to the bone where it is detected by a special camera.

The center of the cylindrical shaped magnet (often referred to as a doughnut) within an magnetic resonance imaging (MRI) scanner.

The part of the digestive system distal to the stomach, consisting of the small and large intestines, that digest and eliminate food.

bowel cancer
See colorectal cancer.

Also called internal radiation therapy.
A type of radiation therapy used to treat cancer, involving the placement of a radioactive material, either temporarily or permanently, directly inside the body. For more information please refer to the Brachytherapy page.

brain herniation
An often fatal condition that results when brain tissue, fluid or blood vessels are pushed outside the skull.

brain mapping
A medical imaging study of the brain's surface using small electrodes to stimulate a nerve so its electrical response can be measured. By determining the role of specific nerves in a patient, this technique helps surgeons avoid damage to sensitive areas while operating on the brain.

The base of the brain consisting of stems connected to the spinal cord.

BRCA1 and BRCA 2
Human genes that belong to a class of genes known as tumor suppressors. A mutation of these genes has been linked to hereditary breast and ovarian cancers.

breast coil
A wire coil placed around the breast that sends and receives radio waves within the magnetic field of an MRI unit to create images.

breast density
A measure of the proportions of fat, connective tissue and breast tissue within the breast. A dense breast has a greater amount of ducts, glands, fibrous tissue and less fat. When mammography is performed, many cancers can be difficult to see in patients with dense breast.

brentuximab vedotin
See Adcetris®.

The large air passages that lead from the trachea (windpipe) to the lungs.

bronchial tubes
Tubes that carry air from the windpipe into the lungs.

A dilation (widening) of the bronchi (the "breathing tubes"), often caused by infection. Serious complications may occur, and some patients require surgical removal of the affected part of the lungs.

Inflammation (swelling) of the mucous membrane of the two subdivisions of the trachea (air tube) that conveys air to and from the lungs.

An instrument used to examine the trachea and bronchi.

Visual inspection of the inside of the trachea and the bronchial passages of the lungs, using a rigid or flexible tube or catheter called a bronchoscope.

An abnormal sound heard when listening with a stethoscope over an organ or blood vessel such as the carotid artery in the neck.

Budd-Chiari syndrome
A blockage of one or more hepatic veins, which carry blood from the liver back toward the heart.

bulla, pl. bullae
A thin-walled air "cyst" within the lung, found in patients with emphysema.

bursa, pl. bursae
A closed sac or envelope lined with a membrane and containing lubricating fluid, usually found or formed in areas subject to friction; e.g., over an exposed or prominent part or where a tendon passes over a bone.

C-11 PIB
Carbon-11-labeled Pittsburgh Compound B, (C-11 PIB), is a radiotracer used with positron emission tomography (PET) scanning to image the build-up of beta-amyloid plaques in the brain, which are associated with Alzheimer’s disease.

A blood test used to measure levels of a protein that is found in greater concentrations in tumor cells.

See computer-aided detection (CAD)

The process by which noncellular material in the body becomes hardened due to deposits of calcium and other materials.

calcium score
A number reflecting the degree and extent of calcium deposits in the walls of the coronary arteries, as demonstrated by cardiac computed tomography.

General term frequently used to indicate any of various types of malignant neoplasms, most of which invade surrounding tissues, may metastasize to several sites, and are likely to recur after attempted removal and to cause death of the patient unless adequately treated.

carcinoembryonic antigen
A protein normally found in the tissue of developing babies, but can also be produced by certain types of cancers in adults.

cardiac catheterization
A diagnostic procedure in which a catheter is placed in a large vein in the leg or arm and advanced to the heart to check for blood pressure within the heart, oxygen in the blood, and/or pumping ability of the heart muscle. (Also see angiography and angioplasty.)

cardiac pacemaker
An electrical device, often implanted, that maintains a normal heart rhythm by stimulating the heart muscle.

A physician specializing in the diagnosis and treatment of heart disease.

An x-ray image intensifier.

carotid artery
One of the two major arteries running through either side of the neck, which supply blood to the brain.

carotid endarterectomy
A surgical procedure in which plaque buildup is removed from the carotid arteries.

CAT scan
See computed tomography (CT).

A clouding of the lens in the eye that affects vision.

A substance that causes evacuation of the bowel.


  1. A tubular instrument to allow passage of fluid from or into a body cavity. It is often used to drain abscesses.
  2. A tube that is inserted through the urethra into the bladder to drain it of retained urine.
  3. A flexible, hollow plastic or rubber tube that may be passed into a blood vessel to withdraw fluids or inject medicine or contrast materials.

catheter angiography
An examination of blood vessels by injecting contrast material directly into an artery through a small plastic tube.

For details see the Catheter Angiography page.

catheter-directed thrombolysis
A procedure in which a catheter is inserted through the skin into a vessel and directed to a blood clot in a fistula or graft of a hemodialysis patient. A medication or mechanical device delivered via the catheter is used to break up the clot and restore blood flow. See the Catheter-directed Thrombolysis page for more details.

To use heat, usually from radiofrequency energy or a laser, to destroy tissue or seal blood vessels to prevent infection.

CEA assay
A test that measures the level of a protein called carcinoembryonic antigen in the blood, which is often elevated in cases of cancer.

A saclike pouch connecting to the point where the small and large intestines join.

celiac disease

Also known as gluten intolerance.
A condition in which sensitivity to gluten (a protein found in wheat, barley and rye) may cause pain, diarrhea, inflammation and damage to the small intestine, and inability to absorb certain vitamins.

The measurement of the head.

Relating to the brain.

cerebral embolism
See embolic stroke.

cerebrospinal fluid
Fluid that surrounds the brain and spinal cord and helps to cushion and protect them.

Refers to the neck region of the spinal column which includes seven bones, or vertebrae, labeled C-1 through C-7. It can also refer to the cervix as it relates to cervical cancer.

The lower part of the uterus, connecting the uterus with the vagina.

Treatment of disease by means of chemical substances or drugs; usually used in reference to neoplastic (cancer) disease.

Chiari malformation
A condition in which brain tissue involving the part of the brain called the cerebellum protrudes into the spinal canal.

An inflammation (swelling) of the gallbladder that causes abdominal pain. See the Cholecystitis page for additional information.

A compound found in most body tissues and an important component of cell membranes. High concentrations in the blood, derived mainly from animal fats in the diet, are thought to promote atherosclerosis.

chronic obstructive pulmonary disease (COPD)
A general term for chronic diseases such as bronchitis and emphysema that cause the airways in the lung to become narrowed, limiting airflow to and from the lungs and causing shortness of breath. For more information see the Chronic Obstructive Pulmonary Disease (COPD) page.

Pain, fatigue and cramping in the legs brought on by walking that goes away when at rest.

A morbid fear of being in a confined place.

Also called Plavix®
One of a class of medications called antiplatelet drugs that help prevent harmful blood clots that may cause heart attacks or strokes.

closed bone biopsy
Also called needle bone biopsy.
An image-guided procedure in which a needle is used to remove a small sample of bone from the body to be examined under a microscope.

To coagulate or turn from a free-flowing liquid to a thickened or semi-solid state.

An enlargement of the fingertips, which may occur as a result of advanced diffuse interstitial lung disease.

cluster headache
Headaches that occur in groups, or clusters, over a period of several weeks or months separated by headache-free periods of months or years. Cluster headaches include sharp, penetrating pain around or behind one eye, watering of the eye and a stuffy nose.

CNS prophylaxis
Chemotherapy or radiation therapy that is delivered to the central nervous system (CNS) by means of a lumbar puncture as preventive cancer treatment. Also referred to as central nervous system (CNS) sanctuary therapy.

To change from a liquid to a thickened or solid state. Blood that does not flow smoothly through a vessel can coagulate or clot by turning from a free-flowing liquid to a semi-solid gel.

cobalt (Co)
A steel-gray metallic element, atomic no. 27, atomic wt. 58.93320; a bioelement and a constituent of vitamin B12; certain of its compounds are pigments, e.g., cobalt blue.

cobalt-60 radiation therapy
Cobalt-60-based or photon radiation therapy machines are used exclusively to treat brain tumors and abnormalities. See also Gamma Knife.

A device used in proton therapy to narrow the beam of particles being delivered to cancerous tissue. For details see the Proton Therapy page.

A liquid that, on evaporation, leaves a protective film over cuts.

Part of the body’s digestive tract and a component of the digestive system. The colon is comprised roughly of the first five or six feet of the large intestine.

colon adenoma
A type of potentially precancerous polyp, an abnormal growth that protrudes from the inner wall of the colon. The majority of colorectal cancers develop from adenomas.

A long flexible tube with a tiny camera at the end used in a procedure called a colonoscopy, which captures images of the interior of the colon and rectum.

Visual examination of the inner surface of the colon by means of a lighted, flexible tubular instrument inserted into the colon through the rectum.

color Doppler
Color Doppler uses a computer to convert the Doppler measurements into an array of colors. This color visualization is combined with a standard ultrasound picture of a blood vessel to show the speed and direction of blood flow through the vessel.

colorectal cancer
Colorectal cancer is cancer that forms in the large intestine (colon or rectum), in the lower part of the body’s digestive tract, a long twisting tube that extends from the mouth to the anus. This tract is part of the digestive system, a complex process that enables the body to break down and absorb food and eliminate waste. For more information see the Colorectal Cancer Treatment and Colorectal Cancer Screening pages.

Establishment of an artificial opening into the colon.

A state of deep unconsciousness that lasts for a prolonged or indefinite period, caused by severe injury or illness.

computed tomography (CT)
Sometimes referred to as CAT scan (computerized axial tomography).

Imaging anatomical information from a cross-sectional plane of the body, each image generated by a computer synthesis of x-ray transmission data obtained in many different directions in a given plane.

Developed in 1967 by British electronics engineer Godfrey Hounsfield, CT has revolutionized diagnostic medicine. Hounsfield linked x-ray sensors to a computer and worked out a mathematical technique called algebraic reconstruction for assembling images from transmission data. In 1973, the Mayo Clinic began operating the first machine in the U.S. Early machines yielded digital images with at least 100 times the clarity of normal x-rays. Subsequently, the speed and accuracy of machines has improved many times over. CT scans reveal both bone and soft tissues, including organs, muscles, and tumors. Image tones can be adjusted to highlight tissues of similar density, and, through graphics software, the data from multiple cross-sections can be assembled into 3-D images. CT aids diagnosis and surgery or other treatment, including radiation therapy, in which effective dosage is highly dependent on the precise density, size, and location of a tumor.

computed tomography (CT) angiography
A method of examining blood vessels utilizing x-rays and injection of iodine-rich contrast material (dye).

For details see the CT Angiography page.

computer-aided detection (CAD)
CAD is computer software that is used to highlight suspicious features on an image and bring them to the attention of the radiologist.

Also known as mild traumatic brain injury.
An injury to the brain that occurs when the head or body is struck hard enough that the brain bounces against the skull.

conformal radiation therapy
Use of a CT image to tailor the radiotherapy beam to the exact size and shape of a tumor.

Existing at birth.

congenital heart disease
A heart problem that has existed since birth.

congestive heart failure
A condition in which the heart cannot adequately pump blood forward, leading to a back-up of blood in vessels and an accumulation of fluid in body tissues including the lungs.

conization (cone biopsy)
A surgical procedure used to diagnose cervical cancer that involves removal of a cone-shaped wedge of tissue from the cervix.

A condition in which bowel movements are infrequent or incomplete.

contrast agent
See contrast material.

contrast material
Also referred to as contrast agent or contrast medium. Any internally administered substance that has a different opacity from soft tissue on radiography or computed tomography. Includes:

  • Barium or water, used to make parts of the gastrointestinal tract opaque.
  • Iodine in water, used for arthrography.
  • Water soluble iodine, used to make blood vessels opaque; to demonstrate the inner structures of the urinary tract (kidneys, ureters and bladder); and to outline joints (the spaces between two bones).
  • Iodine mixed with water or oil may be used to evaluate the fallopian tubes and lining of the uterus.
  • Sterile saline (salt water) is used during hysterosonography.
  • May refer to air occurring naturally or introduced into the body.
  • Paramagnetic substances used in magnetic resonance imaging.

For more information see the Contrast Meterials page.

contrast medium
See contrast material.

A bruise resulting from trauma in which blood seeps into surrounding tissue.

core needle biopsy
A type of biopsy in which a large hollow needle is inserted through the skin to the site of an abnormal growth to collect and remove a sample of cells for analysis. This procedure uses an automated needle, which obtains one sample of tissue at a time and is re-inserted several times.

coronary arteries
The arteries that supply freshly oxygenated blood to the heart muscle.

coronary artery bypass graft surgery
This surgery increases blood flow to the heart by using a vein, or an artery from elsewhere in the body, and using it to divert blood around the area of narrowing or blockage in the coronary arteries of the heart.

coronary artery disease
A condition involving the narrowing of the coronary arteries that carry blood and oxygen to the heart muscle.

coronary bypass surgery
A surgical means of rerouting blood in the coronary artery system around diseased vessels.

A brand name for warfarin.

Cowden syndrome
A disorder characterized by non-cancerous, tumor-like growths and an increased risk of developing certain cancers.

Related to the bony skull known as the cranium that holds the brain.

Relating to the face and the cranium (skull that protects the brain).

Crohn's disease
Also known as regional enteritis.
A moderately severe chronic inflammation (swelling) of the intestine, especially of the small intestine, of unknown cause, involving the obstruction of the lower part of the small intestine and less frequently other parts of the gastrointestinal tract. It is characterized by patchy deep ulcers that may cause abnormal passages within the bowel, and narrowing and thickening of the bowel. Symptoms include fever, diarrhea, cramping abdominal pain, and weight loss.

See cryosurgery.

An instrument used to apply extreme cold to a selected anatomic area.

Also known as cryotherapy, cryoablation or targeted cryoablation therapy.
A minimally invasive treatment that uses extreme cold in the form of liquid nitrogen or argon gas to freeze and destroy diseased tissue, including cancer cells. See the Cryotherapy page for more information.

See cryosurgery.

CT colonography (CTC)
Also called virtual colonoscopy.
A procedure in which computed tomography (CT) scanning is used to produce detailed pictures of the inside of the colon and rectum.

CT enteroclysis
CT enteroclysis is a special type of computed tomography (CT) imaging that produces detailed images of the small bowel by infusing contrast material through a tube positioned in the upper small bowel.

CT enterography
CT enterography is a special type of computed tomography (CT) imaging performed with contrast material to produce images of the small intestine. See the CT Enterography page for more information.

See dilation and curettage (D&C).

curie (C, c, Ci)
A unit of measurement of radioactivity, 3.70 ×1010 disintegrations per second; formerly defined as the radioactivity of the amount of radon in equilibrium with 1 gm. of radium; superseded by the S.I. unit, the becquerel (1 disintegration per second). Origin [Marie (1867-1934) and Pierre (1859-1906) Curie, French chemists and physicists and Nobel laureates]

A blue coloration in the lips, skin and fingernails as a result of reduced oxygen levels in the blood.

A type of particle accelerator in which charged particles are propelled by an alternating electric field between two large electrodes in a constant magnetic field created by two large magnets. The particles are injected at the center of the magnet and spiral outward as their energy increases. Protons produced in a cyclotron can be used to treat cancer, and cyclotron-produced protons can create radioisotopes for nuclear medical procedures.

cystic fibrosis
An inherited disease in which the lungs, intestines and pancreas become clogged with thick mucus, interfering with normal digestion and breathing.

Radiography of the bladder, following injection of a radiopaque substance. For more information, see the Voiding Cystourethrogram page.

This procedure uses a special camera at the end of a tube that allows the doctor to see inside the bladder.

Abnormal sacs containing gas, fluid, or a semisolid material, with a membranous lining.

data integrity
When transferring information, it is necessary to verify that the information arrived exactly as it was sent and was not modified.

To reduce the size of a tumor without completely eliminating it, by surgical or other means. This often makes the tumor more responsive to chemotherapy or radiotherapy.

deep sedation
See sedation, deep.

deep vein thrombosis
A condition in which a blood clot forms in a main vein that returns blood flow from the extremities back to the heart and lungs. This type of clot may grow big enough to completely block the vein or can pose a serious risk if part of it breaks off and travels to the lungs.

Also called implanted cardiac defibrillator (ICD). A pacemaker-like device that continuously monitors the heart rhythm and delivers lifesaving shocks if a dangerous heart rhythm is detected.

definitive treatment
Primary treatment designed to provide a disease cure.

The process of modifying identifiers within medical data so that the information does not include protected health information (PHI).

delivery device
In brachytherapy treatment of cancer, a means of delivering a sealed radioactive substance to the site of a tumor inside the body, such as a catheter, tiny needle or applicator.

A method for imaging density.

Thickness or mass.

deoxyribonucleic acid (DNA)
Acid found in cell nuclei that is the basis of heredity.

diabetes (diabetes mellitus)
AA metabolic disease in which carbohydrate utilization is reduced while lipid and protein usage is enhanced; it is caused by a complete or relative deficiency of insulin and is characterized in more severe cases by chronic hyperglycemia, glycosuria, water and electrolyte loss, ketoacidosis, and coma. Long-term complications include: development of disorders of the nervous system, eyes and kidneys; generalized degenerative changes in large and small blood vessels; and an increased susceptibility to infection.

diagnostic ultrasound
Procedure that uses - a transducer (probe) to generate high frequency sound waves (2-12MHz) to produce images of the body’s internal structures for medical diagnostic purposes.

A method of removing waste materials from the body when the kidneys are not working properly.

dialysis arteriovenous fistula
A surgically created connection between an artery and vein in the arm of patients who need to undergo hemodialysis, a process in which blood is removed from the body, cleansed and then returned to the body. The fistula causes the vein to become enlarged, and allows blood to be easily withdrawn and replaced during dialysis.


  1. A plate-like muscular structure that separates the chest from the abdominal cavity.
  2. The dividing membrane between the chest and abdominal cavity.

diaphragmatic hiatus
An abnormal opening in the diaphragm.

An abnormally frequent discharge of semisolid or fluid fecal matter from the bowel.

Dietitians work with patients to help maintain nutrition. They monitor patients' weight and nutritional problems. Dietitians educate patients and may provide them with recipes and nutritional supplements to improve their nutritional status before, during and after treatment. Dietitians attend four years of college then usually take part in a one-year internship. The American Dietetic Association registers dietitians who have passed a professional examination.

diffuse axonal injury
See shear injury.

diffusion tensor imaging (DTI)
A variation of conventional magnetic resonance imaging (MRI) that creates vivid color pictures of the paths of innumerable nerve fibers in the white matter of the brain by analyzing the movement of water molecules along the fibers. Pictures of these fiber pathways can be helpful in assessing damage to brain by many disease processes, including trauma and brain tumors.

digestive system
A complex process that enables the body to break down and absorb food and eliminate waste; it includes the digestive tract, a long twisting tube that extends from the mouth to the anus (the digestive tract) and various organs.

digestive tract
A series of hollow organs joined in a long, twisting tube from the mouth to the anus that is part of the digestive system, a complex process that enables the body to break down and absorb food and eliminate waste.

digital certificate
A special secure data file that accompanies an electronic message to verify the identity of the user sending the message, and enabling the user to encrypt the message so that it can only be read by its intended recipient.

digital rectal exam
An examination of the lower rectum and the prostate gland in males to check for abnormalities. The term "digital" refers to the clinician's use of a lubricated finger to conduct the exam.

dilation and curettage (D&C)
A procedure in which the cervix is dilated and the inner lining of the uterus is scraped to remove the uterine contents.

A device or substance used to enlarge a hollow structure or opening.

A tear in the wall of a blood vessel that allows blood under pressure to flow between the layers of the wall, making the tear worse.

An inflammation or infection of the diverticulum.

A pouch or a pocket-like opening in the bowel wall, usually in the colon. You might think of it as a "bubble" through a weak point in the bowel wall.

See deoxyribonucleic acid (DNA).

Doppler ultrasound
An application of diagnostic ultrasound used to detect moving blood cells or other moving structures and measure their direction and speed of movement. The Doppler effect is used to evaluate movement by measuring changes in frequency of the echoes reflected from moving structures.

In many instances, Doppler ultrasound has replaced x-ray methods such as angiography, as a method to evaluate blood vessels and blood flow. Doppler ultrasound permits real-time viewing of blood flow that cannot be obtained by other methods. Doppler ultrasound has proved a boon in all areas of ultrasound, aiding in the evaluation of the major arteries and veins of the body, the heart, and in obstetrics for fetal monitoring.

Types of Doppler ultrasound include:

Dosimetrists carefully calculate the dose of radiation to make sure the tumor gets enough radiation. They develop a number of treatment plans that can best destroy the tumor while sparing the normal tissues. Many of these treatment plans are very complex. Dosimetrists work with the doctor and the medical physicist to choose the treatment plan that is just right for each patient. Many dosimetrists start as radiation therapists, then, with very intensive training, become dosimetrists. Others are graduates of one-to-two-year dosimetry programs. The Medical Dosimetrist Certification Board certifies dosimetrists.

Double-contrast barium enema (DCBE)
Also called lower GI tract radiography
A test in which a barium solution and air are introduced into the colon and a series of x-rays are taken of the entire colon and rectum. A single-contrast barium enema without air also is available.

A medication that is injected into the membranes lining the pleural cavity, causing an inflammatory reaction that shrinks the space between the lungs and chest wall to minimize the buildup of fluid in the cavity.

drug-eluting stent
A semi-rigid, tube-like device used to keep an artery open after angioplasty. The stent is made of metal and coated with medication that is slowly released (eluted) to help prevent the growth of scar tissue in the artery lining.

ductal carcinoma in situ (DCIS)
A breast cancer that has not spread beyond the lining (epithelium) of the milk ducts into the surrounding breast tissue. While DCIS must be treated to prevent it from developing into an invasive breast cancer, it is not harmful at this stage.

The first part of the small intestine immediately below the stomach.

dura mater
The outermost layer of three meninges, or membranes, that surround the spinal cord and the brain. In Latin, it means "tough mother." The name is apt, because the membrane is thick and strong, and normally firmly attached to the inner side of the skull.

Impaired swallowing.

This test uses a small transducer that produces high-frequency sound waves, which create detailed images of the heart.

ectopic pregnancy
A pregnancy in which the fetus develops outside the uterus, typically in a fallopian tube.

An accumulation of an excessive amount of watery fluid in cells, tissues, or serous cavities.

Also called EKG or ECG.
A test that records the electrical activity of the heart; it is used to help diagnose certain heart abnormalities.

electromagnetic radiation
Radiation consisting of electric and magnetic waves that travel at the speed of light, such as light, radio waves, gamma rays and x-rays.

electronic detector
The part of a digital imaging system that captures and converts x-rays as they pass through a patient into digital signals which are in turn sent to a computer to produce images.

electronic media
Storage media in PCs and removable/transportable digital media such as magnetic tapes or disks, CDs, pen, flash drives, optical disks, or digital memory cards; or transmission media such as the intranet, dial-up lines, and/or private networks.

electronic medical information
Patient information, including radiological images, lab test results, medications, clinical history, etc., stored on electronic media.

electronic medical record (EMR)
Also called electronic health record.
A computer information system that stores patients’ medical information such as demographics (name, date of birth, address), clinical history, medical images, lab test results, medications, and allergies; it electronically allows healthcare providers to view the information on a computer.

embolic agent
A material used to block off blood flow through a vessel.

embolic stroke
Also called a cerebral embolism
This type of stroke occurs when a blood clot that has formed elsewhere in the body breaks away and travels to a blood vessel in the brain, blocking the flow of oxygen-carrying blood.

A blood clot (a thickened mass of blood), mass of bacteria or other tissue, air or foreign body that breaks loose, travels through the bloodstream and lodges in either an organ or artery forming a complete or partial blockage in blood flow.

The movement of a blood clot, piece of tissue, or pocket of air or gas from where it forms through the bloodstream until it lodges in place, cutting off the flow of blood with its oxygen and tissue nutrients. Catheter embolization is the deliberate introduction of foreign ("embolic") material such as gelatin sponge or metal coils to stop bleeding or cut off blood flowing to a tumor or arteriovenous malformation.

embolus, pl. emboli
A plug, composed of a detached blood clot, mass of bacteria or other tissue, air or other foreign body, completely or partially blocking a vessel.

In humans, the developing organism from conception until approximately the end of the second month; developmental stages from this time to birth are commonly designated as fetal.

A common type of chronic obstructive pulmonary disease (COPD). It occurs when the linings of the air sacs within the lungs are damaged and air pockets develop as a result. Once the air becomes trapped, the lungs slowly increase in size and lose their elasticity, which makes breathing difficult because the lungs cannot exhale completely. See the COPD page for additional information.

An abscess or infection in the space between the lung and the chest wall (pleural space).

An acute inflammation of the brain caused by a viral infection.

Radiographic representation of the brain.

An alteration of normal brain function that can lead to confusion.

The process of transforming or coding information to make it unreadable to anyone except those possessing special knowledge or the key to decrypt the data.

endocrine gland

  1. A gland that produces and secretes hormones into the blood or lymph nodes, exerting powerful effects on specific tissues throughout the body.
  2. An organ consisting of specialized cells that produces and sends hormones into the bloodstream, affecting various processes throughout the body.

Referring to the inside.

endometrial ablation
A treatment for abnormal vaginal bleeding in which the lining of a woman's uterus (called the endometrium) is destroyed.

endometrial biopsy
A procedure in which a sample of tissue from the lining of the uterus, called the endometrium, is removed and examined for abnormal cells under a microscope.

endometrial cavity
The space within the walls of the endometrium.

The mucous membrane that forms the inner layer of the uterine wall; the thickness of the endometrium undergoes marked changes with the menstrual cycle.

endorectal coil
A wire coil that is inserted through a small plastic tube into the rectum as part of a magnetic resonance imaging (MRI) exam to obtain more detailed images of the prostate gland or other internal body structures.

endorectal MRI
A magnetic resonance imaging (MRI) performed from the inside of the rectum.

An illuminated optical instrument used to examine inside the body.

endoscopic mucosal resection
A procedure in which an early stage cancer of the esophagus is removed using a thin tube called an endoscope that is inserted into the throat.

endoscopic retrograde cholangiopancreatography (ERCP)
An endoscope, an illuminated optical instrument, is inserted through the mouth and threaded through the esophagus to the small intestine to allow the bile duct, liver, gallbladder, and pancreas to be examined. A contrast material is then injected into the small intestine and x-rays are taken.

endoscopic treatments
Treatment methods that involve the use of an endoscope, an illuminated optical instrument used to examine inside the body.

The use of an illuminated optical instrument to visualize the interior of the body and its organs.

Within the vagina (the genital canal in the female, extending from the uterus to the vulva).

endovaginal ultrasonography
Pelvic ultrasonography using a probe inserted into the vagina.

endovascular surgery
A procedure to repair an aneurysm in the abdominal aorta in which a synthetic tube called a stent graft is attached to the end of a catheter, inserted through an artery in the leg and positioned inside the aneurysm and fastened in place with small hooks.

endovascular therapy
Minimally invasive procedures used to improve blood flow in the brain's arteries and veins. In these treatments, an image-guided catheter is navigated through the body’s blood vessels to the brain to deliver medications or devices that dissolve or remove blood clots and other debris, or to repair damaged blood vessels.

Within the vein.

endovenous ablation
A minimally invasive treatment that uses heat to cauterize or burn enlarged veins in the legs, a condition called varicose veins.

A preparation that involves injecting liquid into the intestine through the rectum, or administering drugs or food to help clear the bowel.

A protein that regulates chemical changes in other substances.

A long, tightly coiled tube that lies behind each testicle. The epididymis collects the sperm made by the testicles.

An inflammation of the epididymis.

epidural analgesia
Injection of a local anesthetic into the epidural space of the spine to prevent or eliminate pelvic pain.

epidural hematoma
May be intracranial (in the skull) or in the spine.

  1. In this type of hematoma, a blood vessel outside the brain, usually in a groove on the inner side of the skull bursts. Because it is usually an artery that is involved, blood begins to rapidly accumulate between the inside of the skull and the strong outer covering of the brain (called dura mater). The pressure of the blood clot strips the dura mater away from its normal firm attachment to the inside of the skull. The blood clot then can press on the brain, causing injury, and if not diagnosed and treated promptly, may be fatal.
  2. In spinal epidural hematoma, the bleeding into the space between the spinal column and the outer lining of the spinal cord may be a result of trauma, bleeding disorders, underlying vascular abnormalities or may occur spontaneously.

See red blood cells.

esophageal reflux
A condition in which stomach contents (food or acids) move up into the esophagus, the passageway between the stomach and the mouth, and is tasted in the mouth.

A surgical procedure in which a portion of the diseased esophagus and nearby lymph nodes are removed and the remaining esophagus is reconnected to the stomach using a plastic tube or part of the patient’s gastrointestinal (GI) tract.

Inflammation of the esophagus, the tube-like structure connecting the throat with the stomach.

A surgical procedure in which a portion of the diseased esophagus nearby lymph nodes and the diseased part of the stomach are removed and the remaining esophagus is reconnected to the stomach using a plastic tube or part of the patient’s gastrointestinal (GI) tract.

A long, narrow tube with a light and lens that is used for examining the throat and esophagus.

Also called a barium swallow.
An x-ray examination that uses a barium sulfate contrast material to assess both the pharynx and esophagus in the upper gastrointestinal tract.

The "food tube" which connects the mouth to the stomach.

excisional biopsy
A type of surgical biopsy in which an entire lesion or abnormal group of cells and tissue as well as a surrounding margin of normal-appearing tissue are removed.

exercise cardiac stress test
(also called a cardiac stress test or exercise electrocardiogram)
A test that involves walking on a treadmill or pedaling a stationary bike at increasing levels of difficulty while heart rate and rhythm, blood pressure and the electrical activity of the heart (using electrocardiography) are monitored to determine if there is adequate blood flow to the heart when the heart is stressed.

external beam therapy
Also called external radiation therapy.
A method whereby highly focused beams of high-energy x-rays are targeted at the tumor site to destroy cancer cells while sparing surrounding normal tissues. See the External Beam Therapy page for additional information.

fallopian tube
One of the two tubes extending from the uterus to the ovaries, providing a path by which the ovum, or egg, travels from the ovary to the uterus during ovulation.

false negative test result
A test result that indicates a disease is not present, when in fact it is present.

false positive test result
A test result that indicates cancer is present when it is not.

fecal immunochemical test (FIT)
A test that checks for hidden blood in fecal material (stool).

fecal occult blood test (FOBT)
A test that checks for hidden blood in fecal material (stool).

femoral artery
A major artery that supplies blood to the lower extremity.

Prefix designating the presence of metallic iron.

The presence of metallic iron or of the divalent ion Fe2+ that possesses magnetism.

In humans, the product of conception from the end of the eighth week to the moment of birth.

A benign tumor usually occurring in breast tissue.

Composed of fibrocartilage, the fibers that appear between tendons, ligaments or bones.

A common and benign (non-cancerous) condition of cysts in the breast, characterized by lumpiness and sometimes discomfort.

Resembling or composed of fibers or fibrous tissue.

fibroid tumor
Masses of fiber and muscle tissue in the wall of the uterus, also known as myomas.

fiducial marker
A small metal (typically gold) sphere, coil or cylinder about the size of a grain of rice that is placed in or near a tumor to help guide the placement of radiation beams during radiation therapy treatment.

fine needle aspiration
A type of biopsy in which a small needle is inserted through the skin to the site of an abnormal growth to collect and remove a sample of cells for analysis.

A program or hardware device that filters information coming through an Internet connection into a computer system. If the incoming information packet is flagged by the filters it is not allowed through.

A groove or tear.

An abnormal connection or false passageway between the body's organs and or blood vessels.

A device that projects radiographic (x-ray) images in a movie-like sequence onto a screen monitor.

A form of real-time x-ray that employs a fluoroscope to examine the tissues and deep structures within the body.

focal seizure
Also known as partial seizure.
A type of seizure or convulsion often associated with epilepsy in which abnormal electrical activity occurs in a specific area of the brain, often producing symptoms that affect one area of the body.

Foley catheter
A flexible plastic tube (a catheter) inserted into the bladder to provide continuous urinary drainage.

The incompletely formed gap between bones of a skull in a fetus or an infant, also known as a soft spot.

The process of administering a dose of radiation in smaller units over time, as opposed to a single large dose, to minimize tissue damage.

A partial or complete break in a bone.

An element used in contrast media for magnetic resonance imaging.

A pear-shaped receptacle that is located along the anterior and inferior surfaces of the liver just beneath the lower rib cage; it stores bile produced by the liver and releases it into the small intestine to aid in the digestion of fats.

Small stone-like objects made of cholesterol or other substances that form in the gallbladder or bile ducts. For more information see the Gallstones page.

gamma camera
A camera that records the distribution of radiation emitted from a chemical containing a radionuclide that is attracted to a specific organ or tissue of interest.

Gamma Knife
A cobalt-60 based radiation therapy machine used to treat brain tumors and abnormalities. The Gamma Knife delivers 201 beams of highly focused gamma rays to the treatment site. See the Gamma Knife page for additional information.

gamma radiation
(Also called gamma rays.) A very high frequency form of electromagnetic radiation that consists of photons emitted by radioactive elements. Gamma rays can injure and destroy body cells and tissue, especially cell nuclei.

gamma ray
See gamma radiation.

Necrosis (death of one or more cells, or of a portion of tissue or organ) due to obstruction, loss, or diminution of blood supply; it may be localized to a small area or involve an entire extremity or organ (such as the bowel), and may be wet or dry.

A frame housing the x-ray tube, collimators, and detectors in a CT or radiation therapy machine, with a large opening into which the patient is inserted; a mechanical support for mounting a device to be moved in a circular path.

gastroesophageal junction
The point at which the esophagus and the stomach join.

Gastroesophageal reflux disease (GERD)
A condition in which stomach acid leaks into the esophagus. Heartburn is the most common symptom. Left untreated, the disease can cause changes to the tissue lining the esophagus and increase the risk of esophageal cancer.

gastrointestinal (GI)
Relating to the stomach and intestines.

A disease or any condition that affects the stomach.

Establishment of a new opening into the stomach.

The use of an electronic signal from the pumping of the heart to obtain images of heart contractions.

gene therapy
Treatment based on alteration of genetic material.

general anesthesia
The use of medications (intravenous or gases), called anesthetics, that cause unconsciousness and help patients tolerate a medical or surgical procedure. General anesthetics are always administered under the care of an anesthesiologist or nurse anesthetist.

genetic marker
A specific gene or other identifiable portion of DNA that can be used to identify an individual disease or trait.

genetically engineered tumor vaccines
A DNA molecule that is broken into fragments and then rearranged to create an altered microorganism that when administered, induces immunity.

A group of cells that secrete a substance needed by the body.

Of or relating to elated to a gland, a group of cells that secrete a substance needed by the body.

glenoid labrum
A rim of fibrocartilaginous tissue attached to the scapula, or shoulder blade, that provides a deeper socket for the head of the humerus, or upper arm bone. The labrum is a common site of injuries: it can be damaged in falls and from repetitive use, as in throwing and weightlifting.

glial cells
The most abundant cell type in the central nervous system; glial cells surround and support neurons.

A category of brain and spinal cord tumors that begin in glial cells.

Glucophage® (Metformin)
Medication prescribed for diabetics to help the body respond better to its own insulin and decrease glucose production by the liver, ultimately helping to control a patient's blood sugar level. Bristol-Myers Squibb, the manufacturer of Glucophage, recommends that:

  • Glucophage should be stopped at the time of or prior to the procedure.
  • Glucophage should then be withheld for 48 hours after the procedure.
  • Once renal function is found to be normal, Glucophage therapy can be started again.

A major source of energy for human function. During the digestive process, carbohydrates break down into this sugar. It is then carried through the bloodstream to the body’s cells where it is converted to energy or stored.

gluten intolerance
See Celiac disease .

An enlarged thyroid gland, usually evident as a pronounced swelling in the neck.

A patented commercial product known as a waterproof laminate that has multiple uses, including as a material for surgical implants.


  1. Any free (unattached) tissue or organ for transplantation.
  2. To transplant an organ or unattached tissue.
  3. An artificial blood vessel connection used to facilitate kidney dialysis.

grand mal seizure
Also known as tonic–clonic seizure.
A type of seizure or convulsion often associated with epilepsy in which the patient shakes violently and loses consciousness.

Graves' disease
A condition, also called hyperthyroidism, in which the thyroid gland produces more thyroid hormone than the body needs. Symptoms include an enlarged thyroid gland, rapid heart rate, and high blood pressure.

great saphenous vein
The longest vein in the body extending from the foot up the inner thigh to the groin.

guide wire
A thin wire used to guide the placement of a catheter within the body during a minimally invasive procedure.

Guillain-Barre syndrome
An autoimmune illness, often occurring after a viral infection, that causes severe nerve damage.

A physician who specializes in functions and conditions of the female reproductive system.

Raised birthmarks that consist of a clump of blood vessels that did not grow normally. They are often found on the face in many sizes and shapes and are usually blue, red, or purple.

A collection of blood formed when small blood vessels are damaged, causing bleeding into the tissues.

A procedure often required at regular intervals by patients whose kidneys no longer are able to remove waste materials from the blood. A machine performs this function instead and the cleansed blood then is returned to the patient.

The iron-rich protein that carries oxygen inside the red blood cells and gives blood its red color.

The flow of blood from a ruptured blood vessel.

hemorrhagic stroke
A stroke in which blood flow to part of the brain is interrupted as a result of a ruptured blood vessel.

Excess blood in the pleural space caused by a chest injury, tumor or other bleeding problems.

A drug that thins the blood and helps to prevent abnormal blood clotting.

hepatic vein
There are three hepatic veins: the right, middle, and left hepatic veins drain blood from the liver back toward the heart.

hepatobiliary system
The liver, gall bladder and bile ducts. The liver produces and secretes bile which is stored in the gallbladder and released through tubular passageways called bile ducts into the bowel to help digest fat and carry away waste.

hepatocellular carcinoma
The most common type of primary liver cancer that starts in the main cells of the liver.

Short for hepatocellular carcinoma.
The most common type of primary liver cancer that originates from the main cells of the liver.

hereditary diffuse gastric cancer
A hereditary condition associated with an increased risk of stomach cancer.

hereditary disorders
Medical conditions that are passed on genetically from parent to child.

herniated disk
Protrusion of a degenerated or fragmented vertebral disk with potential compression of nerves in the spine.

hiatal hernia
An abnormality in which part of the stomach protrudes through the diaphragm.

high-dose rate (HDR) brachytherapy
One of two types of temporary brachytherapy, a radiation therapy treatment for cancer that involves the placement of a radioactive material directly inside the body, in or near a tumor, for a specific amount of time and then withdrawn. In HDR brachytherapy, a high dose of radiation is delivered to the tumor in a short burst, lasting only a few minutes. This treatment may be repeated several times in a day or a number of times over one or more weeks.

HIPAA – Health Insurance Portability and Accountability Act; Federal Law as of 1996.

HIPAA security standards

The Federal Government's requirements for handling electronic media and protected health information. The standards address the following:

  1. Ensuring confidentiality, integrity and availability of all electronic protected health information (ePHI) created, received, maintained, or transmitted by a healthcare entity.
  2. Protecting against any reasonably anticipated threats or hazards to security or integrity of ePHI.
  3. Protecting against any reasonably anticipated uses or disclosures of ePHI that are not permitted or required for the care of the patient.
  4. Ensuring compliance by the workforce.

Confined, short-term elevation or irregular fluid-filled spot on the skin, slightly reddened, often changing in size and shape and extending to adjacent areas. Hives suddenly erupt and are usually accompanied by intense itching; usually produced by exposure to allergenic substances in susceptible persons.

Hodgkin lymphoma (HL)
One of two major types of lymphoma, a cancer that develops in the white blood cells (lymphocytes) of the lymphatic system, which is part of the body’s immune system.

A complex chemical substance produced in one part or organ of the body that sets the pace for the activity of an organ or group of cells in another part of the body.

A family-centered system of care that attempts to keep chronically ill and terminal patients as comfortable and active as possible.

hospital information system (HIS)
Also called an EMR (Electronic Medical Record) or EHR (Electronic Health Record). See Electronic Medical Record.

human immunodeficiency virus (HIV)
A virus spread through body fluids that affects specific cells of the immune system and can lead to acquired immunodeficiency syndrome (AIDS).

human papilloma virus (HPV)
A collection of infectious viruses that are spread through intercourse. HPV is the most common sexually transmitted disease (STD).

A condition marked by an excessive accumulation of fluid resulting in enlarging of the brain cavities and raised pressure within the skull; may also result in enlargement of the skull and wasting of the brain.

A condition characterized by high levels of calcium in the blood, typically the result of overactive parathyroid glands. Some cases are caused by an inherited condition called familial hypocalciuric hypercalcemia.

The process of administering a dose of radiation in smaller units two to three times a day, as opposed to a larger amount once a day.

An excessive hormone production by the parathyroid gland(s).

A condition, also called Graves' disease, in which the thyroid gland produces more thyroid hormone than the body needs. Symptoms include an enlarged thyroid gland, rapid heart rate, and high blood pressure.

A condition in which the thyroid gland does not produce enough thyroid hormone for the body's needs. Symptoms include weight gain, energy loss, and dry skin.

Surgical removal of the uterus.

An x-ray examination of the uterus and fallopian tubes performed after the injection of a contrast material.

A narrow lighted tube with an optical instrument or viewing device on the end that is used to examine the inside of the uterus.

An examination of the uterus using a hysteroscope, a narrow lighted tube with an optical instrument or viewing device on the end that is inserted into the vagina.

A non-steroidal anti-inflammatory drug (NSAID) available over-the-counter.

A surgical procedure to attach the ileum (a portion of the small intestine) to an opening made in the abdomen.

The third portion of the small intestine.

image recording plate
Part of an electronic detector used in a digital imaging system. An x-ray machine produces a small burst of radiation that passes through the body, recording an image either on photographic film or, in a digital system, on the image recording plate of an electronic detector, a device that converts the x-rays into digital signals which are in turn sent to a computer to produce images.

image-guided biopsy
The use of imaging modalities, such as ultrasound, CT, x-ray or MRI, to assist in targeting a lesion too small to be felt so that cells can be removed from the suspicious area and examined under a microscope to determine whether the abnormality is cancerous.

image-guided radiation therapy (IGRT)
A technique for external beam therapy in which more precise radiation doses are delivered to a malignant tumor or even specific areas within the tumor. Often used in conjunction with intensity-modulated radiation therapy (IMRT). For details see the IGRT page.

immunoreactive trypsinogen (IRT)
A chemical released by the pancreas. High levels of IRT can be an indication of cystic fibrosis.


  1. The practice of giving small amounts of an allergy-producing substance in order to stimulate the formation of antibody that will neutralize it.
  2. Use of the body's immune system to fight tumors.


  1. A tooth compressed between the jaw and another tooth that fails to fully erupt through the surface of the gums.
  2. An immobile mass of stool that does not easily pass from the rectum.

A painful condition that occurs when the tendons of the rotator cuff muscles and the bursa, or fluid-filled sacs, in the shoulder joint become irritated and inflamed due to compression of soft tissues. Impingement can result in weakness and loss of movement at the shoulder.


  1. To graft or insert.
  2. Material inserted or grafted into tissues.
  3. In dentistry, a graft or insert set in or onto the tooth socket prepared for its insertion.
  4. In orthopedics, a metallic or plastic device employed in joint reconstruction.

implanted cardiac defibrillator (ICD)
See defibrillator.

implanted port
A quarter-sized disk that is placed either surgically or by an interventional radiologist just beneath the skin in the chest or abdomen. The disk is connected to a catheter that is inserted into a large vein. Fluids, drugs, or blood products can be infused or blood drawn through a needle that is inserted into the disk through the skin. Examples of manufacturer's names: Port-o-cath, Infusaport, Lifeport.

Inability of the male to maintain erection and engage in sexual intercourse.

in situ breast cancer
The early stage of cancer when it is confined to the ducts of the breast where it began and has not invaded the surrounding fatty tissues.

incentive spirometer
A breathing apparatus that helps patients inflate their lungs and exercise breathing muscles to prevent the onset of pneumonia following surgery.

incisional biopsy
A type of surgical biopsy in which part of a lesion or abnormal group of cells is removed.

Inability to prevent the discharge of urine or feces.

Slow to develop or progress.

The death of tissue in the body caused by an obstruction in the tissue's blood supply, a lack of oxygen or both factors.

inferior vena cava
The large vein that returns blood from the legs and abdomen to the heart.

inferior vena cava (IVC) filter
A device that is implanted in the inferior vena cava, the large vein that returns blood from the legs to the heart, to prevent blood clots in the lower body from traveling to the heart or lungs.

The protective response of body tissues to irritation or injury. Signs include redness, heat, swelling and pain.

inflammatory bowel disease (IBD)
A group of inflammatory conditions affecting the colon and small intestine. The two major types are Crohn’s disease and ulcerative colitis.

Manufacturer's name. See implanted port.

Introduction of a fluid, nutrient, or medication directly into a vein by means of gravity flow.

infusion catheter
A catheter that is inserted into a large vein or artery directly into the bloodstream. Fluids, drugs or blood products can be infused or blood drawn through the catheter.

institutional review board (IRB)
A review body established to protect the welfare of human participants recruited for biomedical research.

intensity-modulated radiation therapy (IMRT)
A delivery technique for external beam therapy that uses special devices called collimators to regulate the intensity of the radiation beams, allowing different areas of a tumor and nearby tissues to receive different doses of radiation. For details see the IMRT page.

A drug used in biologic therapy to affect the division of cancer cells and slow tumor growth.

internal jugular vein
One of a pair of neck veins that collect blood from the brain and face and convey it toward the heart.

internal radiation therapy
See brachytherapy.

A physician specializing in the diagnosis and treatment of disorders of the internal organs.

interstitial lung disease
A respiratory disorder causing shortness of breath on effort. In time the lung tissue may become severely scarred. While some patients recover, others develop respiratory failure or heart failure.

The scaffolding of the lung that supports the tiny air sacs (alveoli) in the lung.

interventional radiologist
A radiologist who specializes in the use of fluoroscopy, CT, and ultrasound to guide passage through the skin by needle puncture, including introduction of wires and catheters for performing procedures such as biopsies, draining fluids, inserting catheters, or dilating or stenting narrowed ducts or vessels.

interventional radiology
The clinical subspecialty that uses fluoroscopy, CT, and ultrasound to guide percutaneous (through the skin) procedures such as performing biopsies, draining fluids, inserting catheters, or dilating or stenting narrowed ducts or vessels.

intervertebral disks
Disk-shaped pads of fibrous tissue that are interposed between the vertebrae.

intestinal obstruction
Partial or total blockage of movement of food or stool through the intestines.

One of the two innermost layers of the walls of the carotid arteries.

Within the skull.

intracranial aneurysm
A ballooning out of the wall of an artery inside the brain; it may lead the vessel to rupture and bleed heavily.

intracranial pressure (ICP)
The pressure inside the skull, in brain tissue and in the cerebrospinal fluid.

intractable ascites
A condition in which excess fluid continually builds up in the abdominal or peritoneal cavity despite appropriate medical therapy.

During surgery.

intraoperative cryotherapy
Cryotherapy is a minimally invasive treatment that uses extreme cold to freeze and destroy diseased tissue, including cancer cells. In an intraoperative cryotherapy procedure, tissue inside the body is treated by inserting a cryoprobe or a series of small needles through the skin and delivering liquid nitrogen or argon gas to the site of the diseased tissue.

intraoperative radiation therapy
Radiation treatment of cancer or other diseases done during surgery.

Within the mouth.

Situated within, occurring within, or administered by entering a bone.

intraosseous venography
A procedure in which an x-ray, or venogram, is taken of a bone after a special dye is injected into bone marrow, the soft substance that fills the hollow center of most bones.

intraperitoneal therapy
A minimally invasive procedure in which anti-cancer drugs are delivered into the peritoneal cavity through a catheter connected to a peritoneal port, a small reservoir or chamber surgically implanted under the skin near the abdomen.

Within the uterus.

intravenous ('inside a vein')
Frequently a needle will be placed in a vein, often a large arm vein, to deliver fluids and medications, withdraw blood samples, and transfuse blood.

intravenous pyelography (IVP)
Radiography of kidneys, ureters, and bladder following injection of contrast medium into a peripheral vein. For details see the Intravenous Pyelogram page.

intraventricular hemorrhage (IVH)
Bleeding into the ventricles within the brain.

A serious disorder in which one part of the intestine slides into another part of the intestine, similar to a folding telescope, creating an obstruction and causing swelling and inflammation. For information about diagnosis and treatment see the Therapeutic Enema for intussusception page.

An invasive procedure is typically an "open" operation, such as appendectomy, which requires a surgical incision for exposure of deep structures or organs for performance of an intervention.

invasive breast cancer
Cancer that has spread beyond the layer of tissue in which it first developed and is growing into surrounding, healthy tissues.

involved site radiation
A type of radiation therapy in which a patient receives radiation only to the parts of the body known to be cancerous.

A non-metallic element found in table salt, seawater and in plants and animals that grow in the sea. The human body requires small amounts of iodine for healthy growth and development. This element is present in many radiographic contrast materials.

ionizing radiation
Radiation of sufficient energy to dissociate atoms or molecules into electrically charged atoms or radicals in the irradiated material.


  1. The subjective enlargement of a bright object seen against a dark background.
  2. Exposure to the action of electromagnetic radiation (e.g., heat, light, x-rays).

irritable bowel syndrome
Characterized by abdominal pain and altered bowel function - alternating bouts of constipation and diarrhea.

An inadequate blood supply to an organ or part of the body.

ischemic stroke
A brain event that occurs when a blood vessel carrying blood to the brain is blocked or restricted by severely narrowed arteries or a thickened mass of blood called a blood clot.

One of two or more nuclides that are chemically identical, having the same number of protons, yet differ in mass number, since their nuclei contain different numbers of neutrons; individual isotopes are named with the inclusion of their mass number in the superior position (12C) and the atomic number (nuclear protons) in the inferior position (6C). In former usage, the mass numbers follow the chemical symbol (C-12).

A condition in which the skin and whites of the eyes turn a yellowish color caused by abnormal levels of bilirubin, a yellow/orange pigment, in the bile and liver.

The middle section of the small intestine.

One of the two bean-shaped organs that excrete urine; typically about 11 cm long, 5 cm wide, 3 cm thick, and located on either side of the backbone.

A torn wound or cut.

A thin, tube-like instrument with an attached light and a lens for viewing the inside of the abdominal cavity.

laparoscopic cholecystectomy
Gallbladder removal using small abdominal incisions and a laparoscope, a thin, tube-like instrument with a light and a lens for viewing the inside of the abdominal cavity.


  1. Examination of a body cavity such as the pelvis using an illuminated tube that is inserted through a small incision.
  2. Examination of the lining of the abdominal wall with a laparoscope.

In this exploratory procedure, the surgeon makes a large incision in the abdomen and investigates the internal organs to help determine the cause and extent of a disease.

large intestine
Part of the lower gastrointestinal tract and the last part of the digestive system where water is absorbed from food matter and waste material is passed through the rectum.

A device emitting intense, focused light energy that can destroy tissues as an alternative to conventional surgical removal.

lateral view
A visual perspective from the side.


  1. Mildly cathartic; having the action of loosening the bowels.
  2. A mild cathartic; a remedy that moves the bowels slightly without pain or violent action.

A benign tumor derived from smooth muscle. In the uterus, commonly called a fibroid.

An area of abnormal tissue on the skin or within the body caused by injury or disease. A lesion may be benign (noncancerous) or malignant (cancerous).

Water frozen -40°C (-40°F) or less, which kills cells.

Cancer of the blood cells that starts in the bone marrow, the soft tissue inside most bones.

Manufacturer's name. See implanted port.

Li-Fraumeni syndrome
A rare hereditary condition that increases a person’s risk of a wide range of tumors, including breast cancer and sarcomas of soft tissue.

linear accelerator (LINAC)
A device imparting high velocity and energy to atomic and subatomic particles; an important device for radiation therapy. See the Linear Accelerator page for more information.

liquid nitrogen
Nitrogen gas in a liquid state. The extreme cold of liquid nitrogen at -196°C is used in cryosurgery to freeze and destroy diseased tissue, including cancer cells.

The crushing of a stone in the renal pelvis, ureter, or bladder, by mechanical force or sound waves.

The largest gland of the body, lying beneath the diaphragm; it is of irregular shape and weighs from 1 to 2 kg (2 to 4 pounds). It secretes the bile and is also of great importance in both carbohydrate and protein metabolism.

Glands that make breast milk.

local anesthesia
The use of medications called anesthetics to produce a temporary loss of sensation in a specific area of the body during a surgical or other medical procedure. While the local area affected by the anesthetic becomes numb, the patient remains awake and responsive.

local anesthetic
Also called numbing agent.
A medication used to produce a temporary loss of sensation in a specific area of the body during a surgical or other medical procedure; It may be administered as an injection under the skin, applied as a topical cream or a patch to the surface of the skin.


  1. Limitation to a definite area.
  2. The reference of a sensation to its point of origin.
  3. The determination of the location of a tumor, disease or other morbid process.

Low dose rate (LDR) brachytherapy
A radiation therapy treatment for cancer that involves the placement of a radioactive material directly inside the body, in or near a tumor, for a specific amount of time and then withdrawn. In LDR brachytherapy, the patient is treated with a low dose of radiation for hours at a time.

low-dose computed tomography (LDCT)
Computed tomography (CT) scanning combines special x-ray equipment with sophisticated computers to produce multiple, cross-sectional images or pictures of the inside of the body. Low-dose CT or LDCT uses less ionizing radiation than a conventional CT scan.

Refers to the low back region of the spinal column, which includes five bones, or vertebrae, labeled L-1 through L-5.

lumbar puncture
Also called spinal tap.
A minimally invasive diagnostic test that involves the removal of a small amount of cerebrospinal fluid—the fluid that surrounds the brain and spinal cord—or an injection of medication or another substance into the lumbar (or lower) region of the spinal column.

lumen, pl. lumina, lumens
The space in the interior of a tubular structure, such as an artery or the intestine.

See lumens.

The surgical removal of a small tumor (a lump). Lumpectomy generally refers to the removal of a lump from the breast as an alternative to mastectomy, which is the removal of the entire breast including the lump.

One of a pair of organs of respiration in the chest in which aeration of the blood takes place. As a rule, the right lung is slightly larger than the left and is divided into three lobes (an upper, a middle, and a lower), while the left has but two lobes (an upper and a lower). Each lung is irregularly conical in shape, presenting a blunt upper extremity (the apex), a concave base following the curve of the diaphragm, an outer convex surface following the inner curve of the ribs, an inner or mediastinal surface, a thin and sharp anterior border, and a thick and rounded posterior border.

lung volume reduction surgery
The removal of part of the damaged lung, which creates additional space for the remaining healthy lung tissue to expand more easily. This surgery is only used for those with severe emphysema.

A clear, transparent, sometimes faintly yellow and slightly opalescent fluid that is collected from the tissues throughout the body, flows in the lymphatic vessels (through the lymph nodes), and is eventually added to the venous blood circulation. Lymph consists of a clear liquid portion, varying numbers of white blood cells (chiefly lymphocytes), and a few red blood cells.

lymph node biopsy
The removal of all or part of a lymph node to be examined under a microscope by a pathologist (a physician specializing in the examination of cells and tissues) to see if cancer cells are present.

lymph nodes
Small structures throughout the body that filter lymph fluid and collect inflammatory cells in order to keep them from spreading infection.

An x-ray examination of the lymphatic system. This procedure has been replaced by lymphoscintigraphy.

lymphatic system
A network of small channels similar to blood vessels that circulate fluid (called lymph) and cells (lymphocytes) of the immune system throughout the body.

A condition in which tissue fluid does not drain normally through the lymphatic system but instead builds up in the body’s soft tissues and causes swelling, usually of a leg or arm.

White blood cells of the lymphatic system, which is part of the body’s immune system. The two major subgroups of lymphocytes are: B cells that produce antibodies and T cells that destroy disease-causing pathogens.

A group of cancers that involve the cells of the immune system, called lymphocytes. There are two major categories of lymphoma: Hodgkin (HL) and non-Hodgkin (NHL).

A special type of noninvasive nuclear medicine imaging that provides pictures called scintigrams of the lymphatic system. See the Lymphoscintigraphy page for more information.

magnetic field gradient
In magnetic resonance imaging, a magnetic field that varies with location, superimposed on the main uniform field of the magnet, to alter the resonant frequency of nuclei and allow detection of their spatial position.

magnetic resonance angiography (MRA)
A method of angiography utilizing the magnetic properties of tissues and body fluids rather than x-rays to record images. For details see the MR Angiography page.

magnetic resonance cholangiopancreatography (MRCP)
A special type of magnetic resonance imaging (MRI) exam that produces detailed images of the hepatobiliary and pancreatic systems, including the liver, gallbladder, bile ducts, pancreas and pancreatic duct. See the MRCP page for additional information.

magnetic resonance imaging (MRI)
A diagnostic radiologic modality, in which the nuclei of the hydrogen atoms in a patient are aligned in a strong, uniform magnetic field, absorb energy from tuned radio pulses, then emit radio signals. These signals are converted into images which appear as cross-sectional slices of the patient’s body.

Cancerous cells, also called a tumor, able to grow into surrounding tissue, spread to other parts of the body and destroy normal cells. Malignant is also less commonly used to describe other medical conditions that are severe and becoming progressively worse.

Imaging examination of the breast by means of x-rays, used for screening and diagnosis of breast disease. Ultrasound and magnetic resonance may also be used to image the breast. For details see the Mammography page.

The lower jaw.

Also called a surgical margin.
A small amount of healthy tissue surrounding a tumor that may be surgically removed with diseased tissue.

The upper jaw.

One of the two innermost layers of the walls of the carotid arteries.

The central part of the chest cavity, behind the sternum and between the two lungs. This space is mostly occupied by the heart and its major blood vessels, and by the trachea and esophagus.

medical radiation physicists
Qualified medical physicists work directly with the doctor in the treatment planning and delivery. They oversee the work of the dosimetrist and help ensure that complex treatments are properly tailored for each patient.

Qualified medical physicists are responsible for developing and directing quality control programs for equipment and procedures. They are responsible for making sure the equipment works properly. Medical radiation physicists take precise measurements of radiation beam characteristics and do other safety tests on a regular basis.

Qualified medical physicists have doctorates or master's degrees. Qualified medical physicists have completed four years of college, two to four years of graduate school and typically one to two years of clinical physics training. They are certified by the American Board of Radiology or the American Board of Medical Physics.

A malignant tumor, usually in the skin, that develops from a pigmented lesion over a period of months or years.

A thin layer of tissue that covers a surface, lines a cavity, or divides space in the body.

Thin layers of tissue, or membrane, that surround and cover the brain and spinal cord.

Inflammation in the meninges, the covering of the brain and spinal cord, often caused by a virus or bacteria.

The point in a woman's life when she stops menstruating, or having periods.

menstrual cycle
A recurring cycle during a woman’s reproductive life in which the lining of the uterus prepares for pregnancy; if pregnancy does not occur the lining is shed.

A cyclical shedding of the lining, or endometrium, of a woman’s uterus when no pregnancy occurs. Women typically experience menstruation (also called a period) on a monthly basis throughout their sexually reproductive years, from puberty until menopause, except when pregnant or breastfeeding.

Abdominal membrane that connects the intestines to the abdominal cavity.

metabolic rate
The amount of energy or heat expended by the body in a given unit of time as a result of the body's metabolism, or all of its chemical processes.

The sum total of all chemical processes in the body that result in growth, energy, waste elimination and other body functions following food digestion and the distribution of nutrients in the blood.

The spread of a disease process from one part of the body to another, as in the appearance of abnormal tissue growths (malignant or nonmalignant) in parts of the body remote from the site of the primary tumor.

To spread to another part of the body, usually through the blood vessels, lymph channels, or spinal fluid.

metastatic tumor
A cancerous tumor formed when cancer cells located elsewhere in the body break away and spread to a new site.

See Glucophage.

A small wire mesh tube-like device used to hold open an artery following balloon angioplasty.

midline catheter
A special type of catheter used in a vascular access procedure that is inserted inside a major vein for a period of weeks so that blood can be repeatedly drawn or medication and nutrients can be injected into the patient’s bloodstream on regular basis. Unlike a standard intravenous catheter (IV) which is for short term use, a vascular access catheter is more durable and does not easily become blocked or infected. The midline catheter is 4-6 inches in length.

migraine headache
A type of headache that may include intense, throbbing pain often on one side of the head, nausea, vomiting and sensitivity to light, sound and exertion, as well as a visual disturbance called an aura.

mild cognitive impairment (MCI)
A condition in which memory or other cognitive functions are below normal but do not interfere with daily functioning. MCI is considered a transitional state between normal forgetfulness and dementia.

mild traumatic brain injury
See concussion.

milk ducts
Small tubes within the breast that carry breast milk from the lobule to the nipple.

One-thousandth of a roentgen (the international unit of exposure dose for x-rays or gamma rays).

mini stroke
See Transient Ischemic Attack (TIA).

minimal and moderate sedation
See sedation, minimal and moderate.

minimally invasive
A minimally invasive procedure requires a small skin puncture or very limited incision to perform the intervention, which typically involves the insertion of miniaturized instruments. Common examples of minimally invasive procedures would be stereotactic breast biopsy, heart catheterization or temporary placement of an implanted port for chemotherapy.

A form of application or employment of a therapeutic agent or regimen.

monoclonal antibodies
A laboratory-produced molecule that is engineered to recognize and bind to the surface of cancer cells. Monoclonal antibodies mimic the antibodies naturally produced by the body's immune system that attack invading foreign substances, such as bacteria and viruses.

monoclonal antibody therapy
Also called targeted therapy
A treatment involving laboratory-produced molecules called monoclonal antibodies that are engineered to recognize and bind to the surface of cancer cells. When combined with a chemotherapy drug or radioactive material, monoclonal antibodies are able to deliver the cancer-killing agent directly to the cancer cell.

The rate of death from a particular disease or condition in a defined population.

MR enterography
A special type of magnetic resonance imaging (MRI) performed with a contrast material to produce detailed images of the small intestine.

MR spectroscopy (MRS)
A variation of conventional magnetic resonance imaging (MRI). This diagnostic imaging technique measures the concentration of metabolites, which are produced by chemical reactions in the brain and other areas of the body, and displays the results as a graph. The peaks in the graph represent various metabolites. The concentration of these metabolites can be altered by many diseases, including tumor, infections and trauma.

A slimy substance secreted by glands in mucous membranes. Mucous helps protect and lubricate surfaces within the body.

multi-detector computed tomography (MDCT)
A form of computed tomography technology with a two-dimensional (2-D) detector that produces multiple, thinner slices in a single rotation and a shorter period of time allowing for more detail and additional view capabilities.

multiple myeloma
An uncommon disease that occurs more frequently in men than in women and is associated with anemia, hemorrhage, recurrent infections, and weakness.

multiple sclerosis
A degenerative disease affecting the central nervous system in which the sheaths around nerve fibers in the brain and spinal cord are damaged.

Relating to muscles and to the skeleton, as, for example, the musculoskeletal system.

An x-ray taken after injecting contrast material into the space surrounding the spinal cord. Its purpose is to identify spinal lesions caused by disease or injury.

A radiographic procedure using contrast material to visualize the spinal column and its contents. See the Myelography page for more information.

A tumor of the bone marrow. Multiple myeloma is an uncommon cancer of the white blood cells in the bone marrow that is associated with anemia, hemorrhage, recurrent infections, and weakness.

myocardial infarction
Also known as a heart attack, it occurs when the supply of blood to the heart is blocked. If blood flow is not quickly restored, the section of the heart wall involved may begin to die.

myocardial perfusion scan
The most common cardiac nuclear medicine procedure, which results in imaging of blood-flow patterns to the heart muscles.

Masses of fiber and muscle tissue in the wall of the uterus, also known as leiomyomas or fibroid tumors. Although these tumors are not cancerous, they may cause heavy menstrual bleeding, pain in the pelvic region and pressure on the bladder or bowel.

The surgical removal of fibroids from a woman’s uterus.

The muscular walls of the uterus.

A muscle disease characterized by muscle weakness that usually results in the deterioration of muscle.

A substance that is used medically to relive pain and/or produce a state of drowsiness or sleep.

nasal cavity
A system of air channels connecting the nose with the back of the throat.

natural background exposure
Radiation is a natural part of life. It has existed since the beginning of time and is an integral part of the universe in which we live. Life as we know it on earth has evolved in the presence of radiation. Radiation comes to us from many sources both natural and man-made. These sources include cosmic radiation from outer space, radiation from the soil and buildings, and natural isotopes in our own bodies. Cosmic radiation and terrestrial radiation vary with location.

The death of living tissue.

needle aspiration
The removal of living tissue for microscopic examination by suction through a fine needle attached to a syringe. The procedure is used primarily to obtain cells from a lesion containing fluid.

needle biopsy
Removal of tissue or suspensions of cells from living patients through a small needle for diagnostic examination.

needle electrode
A fine wire through which electrical current may flow when attached to a power source; used to carry high frequency electrical currents that create heat or destroy diseased tissue (called radiofrequency ablation) or seal blood vessels. There are two types of needle electrodes: a simple straight needle; and a straight, hollow needle that contains several retractable electrodes that extend when needed. Needle electrodes may also be a part of devices that monitor electrical activity for diagnostic purposes such as in the performance of electromyography and nerve conduction studies.

neoadjuvant treatment
A treatment given prior to the main or primary treatment.

neonatal intensive care unit (NICU)
An intensive care unit containing specialized equipment to treat and care for premature or critically ill newborn babies.

An abnormal tissue that grows by cellular proliferation more rapidly than normal and continues to grow after the stimuli that initiated the new growth cease. Neoplasms show partial or complete lack of structural organization and functional coordination with the normal tissue, and usually form a distinct mass of tissue, which may be either benign (benign tumor) or malignant (cancer).

Of or related to the kidney.

nephrogenic systemic fibrosis
A rare complication that may occur in some patients with kidney disease who undergo an MRI with contrast material. It causes a thickening of the skin, organs and other tissues.

Damage to or disease of the kidney.

nerve cell
See neuron.

nerve fibers
Also called axons.
Threadlike extensions from a nerve cell.

neuroendovascular treatments
Procedures in which miniature instruments or a catheter containing medications are inserted into a blood vessel in the brain to treat vascular disease or abnormalities.

neurofibrillary tangles
Abnormal structures that form inside neurons considered one of the hallmarks of Alzheimer’s disease (AD).

Pertaining to the nervous system and its disorders.

A physician who specializes in the diagnosis and treatment of diseases and conditions related to the brain and nervous system.

Also called a nerve cell.
A specialized cell in the brain and nervous system that receives and sends electrical impulses through networks of connections.

A doctor who specializes in diagnosing and treating brain tumors and other tumors of the nervous system.

The clinical subspecialty concerned with the diagnostic radiology of diseases of the central nervous system, head, and neck.

Devices that are implanted into the spine and connected to internal or external generators to stimulate the nerves as a means of disrupting pain signals or causing organs to function more efficiently.

A small, solid lump. A lump can be benign or malignant.

non-Hodgkin lymphoma
One of two major categories of lymphoma, a cancer of the blood, that begins in either the B cells or T cells of the immune system.

A noninvasive procedure does not require any skin incision or the insertion of any instruments or medical devices. Examples include CT and MR scanning and ultrasound.

non-pharmacological sedation
See sedation, non-pharmacological.

Not related to radiology.

Nonrepudiation ensures that a party cannot argue the validity of a statement or contract, that a transferred message has been sent and received by the parties claiming to have sent and received the message; methods include digital signature, the use of public and private keys, and auditing of all user activity.

A non-steroidal anti-inflammatory drug that reduces swelling and pain, such as aspirin and ibuprofen.

nuclear medicine
The clinical discipline concerned with the diagnostic and therapeutic uses of radionuclides (an isotope of artificial or natural origin that exhibits radioactivity), excluding the therapeutic use of sealed radiation sources.

Certain imaging procedures, including PET scanning, employ radionuclides to provide real-time visuals of biochemical processes. One device, a nuclear imaging machine, employs a scintillation camera, which can rotate around the body to pick up radiation emitted by an injected substance (e.g., radioactive iodine, which localizes in the thyroid, or radioactive thallium, which localizes in the heart). A digitized image of a particular organ, or the whole body, is produced.

The center part of intervertebral discs, sponge-like cushions between the vertebrae, or bones, of the spine. The nucleus is filled with a soft, rubber-like material.

numbing agent
See local anesthetic ("numbing agent").


An injury or disease is said to be occult when it is hidden, difficult to see or unaccompanied by readily discernible signs and symptoms.

Relating to oncology, the study of cancer and the branch of medicine devoted to the diagnosis and treatment of cancer.

A medical doctor who specializes in oncology—the study and treatment of tumors and cancer.

The study and treatment of neoplasms (abnormal tissue growths), tumors and cancers, including their causes and development.

The surgical removal of one or both ovaries.

Impervious to light or radiation; not transparent or only slightly so.

optionally retrievable filters
A device that is temporarily implanted in and then removed from the inferior vena cava, the large vein that returns blood from the legs to the heart, to prevent blood clots in the lower body from traveling to the heart or lungs.

The bony cavity containing the eyeball.

Related to orthodontics, a specialty within dentistry to prevent and correct teeth irregularities.

The medical specialty concerned with the preservation, restoration, and development of form and function of the musculoskeletal system, extremities, spine, and associated structures by medical, surgical, and physical methods.

orthopedic cement
An acrylic cement such as polymethylmethacrylate (PMMA) used to repair bone fractures and in other orthopedic surgeries.

Movement of a solution through the membrane of a cell.

A common condition that usually starts in middle age and is characterized by degenerative changes in the bone and cartilage of one or more joints.

Bone infection.

Reduction in bone mineral density to below-normal levels; the first stage of bone loss; an early-warning sign pointing to an increased risk of developing full-blown osteoporosis.

A condition of reduced bone mass, with decreased outer thickness and a decrease in the number and size of the spongy structures in the bone (but normal chemical composition), resulting in increased fracture incidence. Osteoporosis is primarily classified as an age-related decline in bone mineral density. Secondary osteoporosis results from an identifiable disease (for example, diseases of the parathyroid glands, or, for instance, certain medications). See the Osteoporosis page for additional information.

One of two female reproductive glands that contain the ova, or eggs, that are released during ovulation; the fallopian tubes connect the ovaries and the uterus.

The release of an ovum, or egg, from the ovary, which then travels through the fallopian tube to the uterus to be fertilized by a sperm

See cardiac pacemaker.

A measure of an individual's cigarette smoking history calculated by multiplying the number of cigarette packs smoked per day by the number of years the individual has smoked.

Paget disease
A genetic or viral condition characterized by excessive breakdown and formation of bone tissue that can lead to enlarged or misshapen bones.

palliative treatment
Treatment designed to relieve or control symptoms rather than to cure disease.


  1. Able to be felt; perceptible to touch
  2. Evident; plain

A gland that produces several hormones and secretes digestive enzymes, or proteins that act as a catalyst for the breakdown of food, through the pancreatic duct that connects the gland to the intestine. The pancreas also secretes hormones, most importantly insulin, into the blood to regulate metabolism of the body.

pancreatic duct
A tubular passageway that connects the pancreas to the intestine.

Inflammation (swelling) of the pancreas.

An imaging examination of the pancreatic ducts. For x-ray pancreatography, the examination requires direct injection of contrast material into the pancreatic ducts. For MRI, pancreatography is performed without a direct contrast material injection, however an intravenous injection of contrast material may be used.

Pap test
Also known as Pap smear.
The removal of cells from the surface or interior of a woman’s cervix for examination under a microscope; used to help detect cervical cancer.

A tumor, usually benign, that may appear on a mucous membrane or the surface of the skin.

A minimally invasive procedure in which a thin needle or tube is inserted into the abdomen to remove excess fluid from the peritoneal cavity.

Alongside the nose.

paranasal sinuses
Four pairs of hollow, air-filled spaces located within the bones of the face that surround the nasal cavity and are connected to the nose by small openings. They are named the frontal, maxillary, ethmoid, and sphenoid sinuses.

parathyroid glands
Typically four small raisin-sized glands in the neck primarily involved in the regulation of calcium and phosphorus levels in the body.

parathyroid imaging
Evaluation of the parathyroid glands, accomplished with a nuclear medicine technique using a material called Sestamibi, or the parathyroid glands can be imaged with ultrasound, CT or MRI.

partial bowel resection
See partial colectomy.

partial colectomy
Removal of part of the colon.

particle beam radiation therapy
Particle or proton beam radiation therapy is a type of radiation therapy that uses protons as the source of radiation rather than x-rays. Protons can pass through healthy tissue without damaging it. See the Proton Therapy page for more information.

particulate agents
Synthetic materials that are suspended in liquid and injected into a blood vessel to form a permanent barrier to blood flow. They are used in embolization procedures to stop bleeding or block arteries that provide blood flow to a tumor.

The state of being freely open or exposed.

Morbid or diseased; resulting from disease.

A physician specializing in the examination of cells and tissues.

The study of disease processes.

pelvic floor dysfunction
(Also called pelvic floor disorders).
A group of conditions in which the stretching or tearing of the pelvic floor leads to one or more of the pelvic organs falling out of position (also called prolapse), incontinence, pelvic pain and/or constipation.

penetrating injury
An injury in which the skin is broken as the result of a cut (laceration).

A passing through the skin, as in absorption of an ointment containing the active ingredient; also passage through the skin by needle puncture, including introduction of wires and catheters.

percutaneous transhepatic cholangiography (PTC)
An x-ray procedure that involves the injection of a contrast material directly into the liver to produce pictures of the bile ducts.

A hole in the walls of an organ or structure of the body that develops from a weak spot in the organ or from a deep penetrating wound caused by trauma.

The flow of blood or other fluid to an organ.

pericardial effusion
Excessive fluid within the sac surrounding the heart, usually due to inflammation.

The surface of the body between the anus and the scrotum in men and between the anus and the vulva in women.

periodontal disease
Disease that affects the tissue and bone surrounding the teeth.

peripheral artery disease (PAD)
Also called peripheral vascular disease (PVD).
Arterial disease that occurs outside of the heart or brain in which arteries in the extremities (legs and arms) become narrowed or blocked, usually as a result of atherosclerosis or plaque. The most common form of PAD affects the large vessels supplying the legs, which can cause severe pain on walking and may in time make a patient immobile. See the Peripheral Artery Disease page for more information.

peripheral vascular disease (PVD)
See peripheral artery disease (PAD)..

peripherally inserted central catheter (PICC)
A long catheter that extends from an arm or leg vein into the largest vein (superior vena cava or inferior vena cava) near the heart and typically provides central IV access for several weeks. Unlike a standard intravenous catheter (IV) which is for short term use, a PICC is more durable and does not easily become blocked or infected. It may remain in place for several months so that blood can be repeatedly drawn or medication and nutrients can be routinely injected into the patient’s bloodstream.

peritoneal cavity
Also called abdominal cavity.
The space within the peritoneum not occupied by the abdominal organs. In most circumstances, this space is empty and the cavity is collapsed. In certain disease, this space can become filled with fluid. In other circumstances, this space may be intentionally inflated with carbon dioxide for laparoscopic surgery, or with a sterile solution for peritoneal dialysis.

peritoneal port
A small reservoir or chamber about the size of a quarter that is surgically implanted under the skin near the abdomen. The port has a silicone rubber top that can be penetrated by a needle and an attached catheter that is designed to hang down into the abdominal or peritoneal cavity.

A thin layer of connective tissue that lines the abdominal cavity.

Inflammation of the thin tissues that line the abdomen and the abdominal organs.

periventricular leukomalacia (PVL)
Damage to white matter brain tissue as a result of a lack of oxygen or blood flow to the brain prior, during or after birth.

permanent brachytherapy
Also called seed implantation.
A radiation therapy treatment for cancer in which a sealed pellet (or “seed”) containing radioactive material is permanently placed inside the body in or near a tumor.

Also known as hydrogen peroxide, a liquid bleaching agent used as a disinfectant.

petit mal seizure
Also called an absence seizure.
A type of seizure or convulsion often associated with epilepsy in which the patient stares into space for a short period of time.

Related to the pharynx, or throat.

Also known as the throat, the passageway that extends from immediately behind the mouth and nasal cavity to the esophagus and stomach.

Removal of a vein segment, sometimes performed for the treatment of varicose veins.

Painful inflammation (swelling) of the veins.

photodynamic therapy
A form of treatment in which a drug is administered and then activated by light.

photon radiation therapy
See cobalt-60 radiation therapy.

A specialist in the science of physics.

Picture Archiving and Communication System (PACS)
A computer system for acquiring, storing, viewing, and managing digital medical imaging studies and related information.

pituitary adenoma
A common, benign tumor of the pituitary gland that may affect hormonal levels.

pituitary gland
An endocrine gland located beneath the brain that supplies numerous hormones that govern many vital processes in the body.

An accumulation of fat and other substances on the inner wall of a blood vessel that, over time, may build up and limit or block blood flow through the vessel.

Particles that are formed in bone marrow and circulate in the blood. They bind at the site of a wound to begin the clotting process.

platinum coils
A type of coil, made of soft platinum wire smaller than a strand of hair, used in a procedure called a detachable coil embolization to treat an aneurysm or an artificial blood vessel connection called a fistula that may occur in the brain or other parts of the body. Using imaging guidance, the coils are placed at the site of an aneurysm or fistula to help block the flow of blood or prevent a rupture of the vessel.

A brand name for clopidogrel, an antiplatelet drug prescribed to help prevent blood clots.

pleural effusion
An excess of fluid in the pleural cavity, the space that surrounds the lungs and lies underneath the chest wall.

pleural membrane
A thin layer of tissue that lines the pleural cavity, the space that surrounds the lungs and lies underneath the chest wall.

pleural space
Also called pleural cavity.
The cavity that exists between the lungs and underneath the chest wall. It is normally empty, with the lung immediately against the inside of the chest wall. In some diseases, fluid can build up in this space (a pleural effusion). In trauma, air can enter this space (a pneumothorax). Under either condition, excessive fluid or air in the pleural space can cause difficulty breathing since the lung is prevented from inflating fully.

Inflammation of the membrame encasing the lungs.

An infection that causes inflammation in one or both of the lungs; may be caused by a virus, bacteria, fungi or other germs. See the Pneumonia page for more information.

A condition in which air enters and collects within in the pleural space and may cause the lung to collapse. It occurs during heart or lung surgery or as a result of a trauma (such as a gunshot or stab wound) to the chest, but also may occur spontaneously, particularly with violent coughing.

A condition in which air enters and collects within in the pleural space and may cause the lung to collapse. It occurs during heart or lung surgery or as a result of a trauma (such as a gunshot or stab wound) to the chest, but also may occur spontaneously, particularly with violent coughing.

A disorder in which there is an abnormal increase in the number of red blood cells in the blood.

polymethylmethacrylate (PMMA)
An acrylic cement used to repair bone fractures and in other orthopedic procedures.

A usually benign growth that bulges outward from the surface of normal tissue, usually appearing as an irregular mound- or mushroom-like structure growing from a broad base or a slender stalk.

A procedure using an endoscope in which abnormal growths called polyps are removed from the inner walls of the colon and rectum.

Having small holes or pores.

portal hypertension
Blockage of normal blood flow through the liver, usually the result of cirrhosis, which can lead to back-pressure on the veins of the portal (intestinal) circulation, variceal bleeding and ascites.

portal vein
Also called the hepatic portal vein.
The main vein that carries blood from the digestive tract to the liver.

Manufacturer's name. See implanted port.

Imaging of the portal circulation by x-rays, using contrast material, usually introduced into the spleen or into the portal vein at operation.

positron emission tomography (PET)
Positron emission tomography, also called PET or a PET scan, is a diagnostic examination that uses small amounts of radioactive materials called radiotracers, a special camera and a computer to help evaluate your organ and tissue functions. By identifying body changes at the cellular level, PET may detect the early onset of disease before it is evident on other imaging tests. See the PET/CT page for additional information.

post-embolization syndrome
A condition that includes pain, nausea, vomiting and low-grade fever that many patients experience following an embolization procedure. to prevent blood from flowing to the area.

posteroanterior view
A term typically denoting the direction of x-rays, from posterior to anterior, through a body part.

power Doppler
An ultrasound technique that is used to obtain images that are difficult or impossible to obtain using standard color Doppler and to provide greater detail of blood flow, especially in vessels that are located inside organs. Power Doppler is more sensitive than color Doppler for the detection and demonstration of blood flow, but provides no information about the direction of flow. Color and spectral Doppler both reveal the direction of blood flow which can be valuable information.

Abnormal tissue changes that often are found before cancer develops.

primary aldosteronism
A condition in which the adrenal glands produce too much of the hormone aldosterone, leading to high blood pressure.

primary headache
One of the two major types of headaches. Primary headaches, which include cluster, migraine and tension headaches, are not associated with a medical condition or disease.

primary tumor
A tumor that originates at its location. See also tumor.


  1. A slender rod of flexible material, with blunt bulbous tip, used for exploring sinuses, fistulas, other cavities, or wounds.
  2. A device or agent used to detect or explore a substance; e.g., a molecule used to detect the presence of a specific fragment of DNA or RNA or of a specific bacterial colony.
  3. To enter and explore, as with a probe.

A surgical procedure to remove the rectum and part or the entire colon.

This procedure uses a special camera at the end of a tube that allows the doctor to see inside the rectum.

Related to a medical prognosis, a prediction of the course and likely outcome of a disease.

prophylactic cranial radiation
Exposure of the brain to low-dose radiation in a cancer patient in order to prevent the tumor from spreading to this site.

prostate cancer
A tumor of the prostate gland, which is located in front of a man's rectum and below the bladder.

prostate gland
A walnut-size gland in men that surrounds the urethra (the duct that transports urine out of the body) and the base of the bladder. The prostate, part of the male reproductive system, makes some of the milky fluid called semen that carries sperm.

prostate-specific antigen (PSA)
A protein produced by the prostate gland. A PSA Test is used to determine the level of PSA in the blood. Higher levels of PSA in the blood are sometimes – but not always – indicative of prostate cancer.

An inflammation (swelling) of the prostate gland.

protected health information (PHI)

Any information relating to a patient's physical or mental health, the details of one's care, or the payment for that health care. The U.S. Department of Health and Human Services (HHS) defines all of the following as individually identifiable health information:

  1. Names and addresses
  2. Identifying Dates – date of birth, date of admission, date of examination.
  3. Specific age if over 89 years old.
  4. Telephone and fax numbers, Social Security numbers, medical record or account numbers, employee numbers, health plan numbers, email addresses, vehicle identifiers, license numbers.
  5. Full face images or biometric identifiers such as finger and/or voice prints.
  6. Any unique identification numbers, codes or characteristics that may be traced back to an individual.

A positively charged particle that is a fundamental component of the nucleus of all atoms.

proton beam radiation therapy
See particle beam radiation therapy.

Related to the lungs or the respiratory system.

pulmonary edema
A build-up of fluid in the lungs and a swelling of lung tissue.

pulmonary embolism
Blockage of the arteries in the lungs, most frequently by detached fragments of a blood clot from a leg or pelvic vein, commonly when that clot follows an operation or confinement to bed.

pulmonary hypertension
A type of high blood pressure within the network of blood vessels between the heart and lungs.

A physician who specializes in pulmonology (pulmonary disease), which deals with lung and respiratory tract disease.

pulse oximetry
A test that involves a small device placed on a finger tip to measure the oxygen saturation of the blood.

Radiologic study of the kidney, ureters, and usually the bladder, performed with the aid of a contrast material either injected intravenously, or directly from below via the urethra, or from above through the kidney (either via a direct puncture or through a previously placed catheter).

A bacterial infection of the kidney that may occur when a urinary tract infection (UTI) spreads beyond the bladder to the ureters and kidneys.

The passage from the stomach into the small intestines.

Also known as radiation absorbed dose.
The scientific unit of measurement for the amount of radiant energy absorbed in a certain amount of tissue. See the Radiation Dose in X-ray and CT Exam page for additional information.

Radiant energy from waves or subatomic particles.

radiation dermatosis
Skin changes at the site of ionizing radiation, particularly redness of the skin due to capillary dilatation in the acute stage, temporary or permanent loss of hair, and chronic changes in the epidermis and dermis resembling a premalignant wart-like lesion.

radiation oncologist
Doctors who oversee the care of each cancer patient undergoing radiation treatment. They develop and prescribe each cancer patient's treatment plan, they make sure that every treatment is accurately given, and they monitor the patient's progress and adjust treatment to make sure patients get quality care throughout treatment. Radiation oncologists also help identify and treat any side effects of radiation therapy and work closely with all members of the radiation oncology team. Radiation oncologists have completed four years of college, four years of medical school, one year of general medical internship, then four years of residency (specialty training in radiation oncology). They have extensive training in the safe use of radiation to treat disease. If they pass a special examination, they are certified by the American Board of Radiology. Patients should ask if their doctor is board certified.

radiation oncology
Also known as radiation therapy.
The study and use of x-rays or radionuclides to treat abnormal tissue growths (malignant or nonmalignant).

radiation oncology nurses
Nurses work with the radiation team to care for patients during the course of treatment. They help evaluate the patient before treatment begins and talk to the patient about their treatment, the potential side effects and their management. During the course of radiation treatments patients may be evaluated weekly, or more frequently by the nurse to assess problems and concerns. Radiation oncology nurses are registered nurses. Most nurses in radiation therapy have additional accreditation in the specialty of oncology nursing. Advanced practice nurses in oncology, which include clinical nurse specialists and nurse practitioners, have completed a master's degree program.

radiation pneumonitis
Inflammation of lung tissue caused by exposure to radiation therapy.

radiation therapist
Radiation therapists work with radiation oncologists. They administer the daily radiation treatment under the doctor's prescription and supervision, maintain daily records and regularly check the treatment machines to make sure they are working properly. Radiation therapists go through a two-to-four year educational program following high school or college, then take a special examination and must be certified by the American Registry of Radiologic Technologists. In addition, many states require that radiation therapists be licensed.

radiation therapy
Also known as radiotherapy.
The study and use of x-rays or radionuclides to treat abnormal tissue growths (malignant or nonmalignant).

Radiation Units
There are a number of units to measure radiation dose and exposure:

  • rad or radiation absorbed dose
    The amount of radiant energy absorbed in a certain amount of tissue.
  • gray (Gy)
    A unit of absorbed radiation equal to the dose of one joule of energy absorbed per kilogram of matter, or 100 rad. The unit is named for the British physician L. Harold Gray (1905-1965), an authority on the use of radiation in the treatment of cancer.
  • milligray (mGy)
    A unit of absorbed radiation equal to one thousandth of a gray, or 0.1 rad.
  • rem or roentgen-equivalent-man
    A unit of measurement that takes into account different biological responses to different kinds of radiation. The radiation quantity measured by the rem is called equivalent dose.
  • millirem
    One thousandth of a rem, the unit for measuring equivalent dose.
  • roentgen (R, r) (rent-gen, rent-chen)
    The international unit of exposure dose for x-rays or gamma rays. Roentgens are named after Professor Wilhelm Konrad Roentgen, the man who discovered x-rays in 1895.
  • sievert (Sv) (see-vert)
    The unit for measuring ionizing radiation effective dose, which accounts for relative sensitivities of different tissues and organs exposed to radiation. The radiation quantity measured by the sievert is called effective dose.
  • millisievert (mSv) (mill-i-see-vert)
    One thousandth of a sievert, the unit for measuring effective dose.

radical trachelectomy
Surgical removal of the cervix.

Giving off radiation.

radioactive disintegration
The decrease in the amount of any radioactive material with the passage of time due to the spontaneous emission of radiation from an atomic nucleus.

radioactive iodine I-131
Also called radioiodine I-131.
A radioactive isotope created from iodine to emit radiation for medical use. See also radioactive iodine therapy.

radioactive iodine I-131 therapy
radioactive iodine I-131 therapy. The use of radioactive iodine I-131 to treat an overactive thyroid, a condition called hyperthyroidism. When a small amount of I-131 is swallowed, it is absorbed into the bloodstream in the gastrointestinal (GI) tract and concentrated from the blood by the thyroid gland, where it begins destroying the gland’s cells.

radioactive iodine uptake test (RAIU)
See thyroid uptake.

radioactive material
Also called radioactive substance.
As used in the brachytherapy treatment of cancer, a radioactive material is sealed inside a seed or pellet and placed inside the body, in or near a tumor. The radiation material used in brachytherapy comes from radioactive iodine 125, strontium 89, phosphorous, palladium, cesium, iridium, phosphate, or cobalt.

radioactive substance
See radioactive material.

radiodense markers
Small pieces of radiodense, or radiopaque, material placed inside the body near a tumor to help the treatment team direct radiation beams at the cancerous cells. Radiodense markers are made from materials that cannot be penetrated by x-rays or any other form of radiation.

radiofrequency ablation
A treatment technique that uses high-frequency alternating electrical current to destroy tissue cells by heating them.

radiofrequency electrodes
A type of electrode (a fine wire through which electrical current may flow when attached to a power source) that carries high frequency electromagnetic waves that create heat to ablate or destroy tissue (called radiofrequency ablation) or to seal blood vessels.

Referring to the examination of any part of the body for diagnostic purposes by means of x-rays.

Examination of any part of the body for diagnostic purposes by means of x-rays with the findings usually recorded digitally or on film.

A combination of radiation therapy and immunotherapy that delivers a high dose of radiation directly to a tumor.

radioiodine I-131
See radioactive iodine I-131.

An isotope that changes to a more stable state by emitting radiation.

radioisotope bone scan
A nuclear imaging examination that produces pictures of bones to help detect abnormalities caused by disease or injury. During a bone scan, a small amount of radioactive material is injected into the body and collects in the bones.

A physician trained in the diagnostic and/or therapeutic use of x-rays and radionuclides, radiation physics, and biology; a diagnostic radiologist may also be trained in diagnostic ultrasound and magnetic resonance imaging and applicable physics.


  1. The science of high energy radiation and of the sources and the chemical, physical, and biologic effects of such radiation; the term usually refers to the diagnosis and treatment of disease.
  2. The scientific discipline of medical imaging using ionizing radiation, radionuclides, nuclear magnetic resonance, and ultrasound.

Radiology Information System (RIS)
A special case of a hospital information system (HIS) tailored to radiological imaging, containing information such as imaging examination orders, schedules on imaging modalities, imaging device parameters, billing codes and information.

Almost completely transparent to x-rays.

An isotope of artificial or natural origin that exhibits radioactivity.

Radionuclides serve as agents in nuclear medicine and genetic engineering, play a role in computer imaging for diagnosis and experiment, and account for a percentage of background radiation to which humans are exposed. In cancer therapy, radionuclides are used to destroy tumors.

Impenetrable by x-rays or any other form of radiation.

radiopaque dye
See contrast material.

A drug that emits radioactivity. Also called a radiotracer.

Drugs that enhance the effect of radiation on cancer cells.

One who practices radiotherapy or is versed in radiotherapeutics.

The medical specialty concerned with the use of electromagnetic or particulate radiation in the treatment of disease.

See radiopharmaceutical.

A radioactive gas without odor, taste or color that occurs naturally with the decay of uranium and thorium, metallic chemicals found in rocks and soil. Radon ingestion or inhalation can cause health problems (e.g., lung cancer).

A scan pattern in which an area is scanned in a rectangular pattern from side-to-side in lines from top to bottom to create an image that is projected on a cathode-ray tube and displayed on a screen.

reactive airway disease
An asthma-like syndrome due to muscle spasms in the airways. It can cause wheezing, chest tightness, coughing and difficulty breathing. This includes patients with asthma.

rectal prolapse
A medical condition found most often in young children and the elderly where part of the rectum wall falls out of and protrudes from the anus.

The lower part of the large intestine where water is absorbed from the gut and where stool is formed.

red blood cells

Also known as erythrocytes.
Cells found in the blood that contain hemoglobin and carry oxygen to and carbon dioxide from body tissues.

Reed-Sternberg cell
A cell that distinguishes diseased tissue as Hodgkin lymphoma.

referring physician
Usually a non-radiologist physician who sends a patient to a specialist for more information or treatment.

regional anesthesia
The injection of a local anesthetic, a medication that produce a temporary loss of sensation, near a specific group of nerves in order to block sensation in a larger, but still limited, area of the body supplied by those nerves.

regional enteritis (Crohn's disease)
See Crohn's disease.

The backward flow of undigested food from the esophagus to the mouth.

renal artery
The major artery supplying the kidney.

renal hypertension
High blood pressure caused by a narrowing of the kidney arteries

Relating to the system of organs and parts used in reproduction. In the male, this consists of the testes, penis, seminal vesicles, prostate, and urethra. In the female, this consists of the ovaries, fallopian tubes, uterus, vagina, and vulva.

Surgical removal of part or all of an organ or an area of diseased tissue.

Related to the process of moving air into and out of the lungs, exchanging oxygen and carbon dioxide within the body's tissues.

respiratory therapy
Treatment to preserve or improve lung function.

The gradual re-closing of an artery after it has been widened through a procedure such as angioplasty.

A tumor of the retina, occurring in children.

rheumatoid arthritis
A chronic autoimmune disease that occurs when the immune system attacks the lining, cartilage, bones, and supporting structures of multiple joints.

A monoclonal antibody used in the immunotherapy treatment of non-Hodgkin lymphoma; it binds to a protein found on the surface of normal and abnormal B cells.

roentgen (R, r)
The international unit of exposure dose for x-rays or gamma rays; that quantity of radiation that will produce in 1 cc of air at standard temperature pressure, or 0.001293 g of air, 2.08 ×109 positive and negative ions , each totaling 1 electrostatic unit (e.s.u.) of charge; in the MKS system this is 2.58 ×10-4 coulombs per kg of air.

rotator cuff
A group of muscles around the shoulder joint that help stabilize and move the upper arm.

sacroiliac joint
joint in the pelvis between the sacrum and the ilium of the pelvis

Salt water.

Surgical removal of the ovaries and fallopian tubes.

A malignant or cancerous tumor that occurs in the connective tissues of the body, including the bones, cartilage, tendons and soft tissues.


  1. To survey by traversing with an active or passive sensing device.
  2. The image, record, or data obtained by scanning, usually identified by the technology or device employed; e.g., CT scan, radionuclide scan, ultrasound scan.
  3. Abbreviated form of scintiscan (scintigram), usually identified by the organ or structure examined; e.g., brain scan, bone scan.

A general term for pain related to the sciatic nerve; it may result from a herniated intervertebral disc in the spine.

A diagnostic procedure consisting of the administration of a radionuclide that accumulates in the organ or tissue of interest, followed by recording the distribution of the radioactivity with a stationary or scanning external scintillation camera.

Causing scarring. Liquid chemicals or alcohols used to destroy blood vessels in an embolization procedure. Sclerosing damages the inner lining of a vessel and causes blood clots (a thickened mass of blood) to form, thus preventing blood flow through the vessel.

sclerosing cholangitis
Inflammation of the bile ducts.

Treatment involving the injection of a sclerosing (hardening) solution into vessels or tissues.

A side-to-side curvature of the spine that usually develops in childhood or adolescence.

screening mammography
Imaging examination of the breast by means of x-rays, of individuals usually without symptoms, to detect unsuspected breast cancer.

A muscular sac that contains the testes.

secondary headache
One of the two major types of headaches. Secondary headaches are caused by an injury or underlying illness, such as bleeding in the brain, an infection or a brain tumor.

secondary hyperparathyroidism
A condition in which one or more of the body’s four parathyroid glands produces too much parathyroid hormone due to low calcium levels in the blood. Symptoms include bone and joint pain.

secure sockets layer (SSL)
A cryptographic communications protocol that provides secure transmissions on the Internet by encoding/decoding the data transfers.

sedation, deep
A level of sedation in which patients will generally sleep during the procedure without responding to painful stimulation. Patients will be able to breathe on their own and in many cases will receive oxygen from a face mask. See sedation, minimal and moderate.

sedation, minimal and moderate
Levels of sedation in which the patient receives a drug to relax but remains responsive to verbal questions and painful stimulation. Patient is able to breathe independently during a surgical or medical procedure. See sedation, deep.

sedation, non-pharmacological
Approaches that guide a patient to a state of relaxation by focusing attention on pleasant thoughts. Guidance is provided by specially trained radiology or other medical personnel. This condition may be achieved via distraction techniques or self-hypnotic relaxation.

A drug that allows you to relax during a procedure like angiography, often without putting you to sleep.

seed implantation
See permanent brachytherapy.

A sudden, uncontrollable wave of electrical activity in the brain that causes involuntary bodily movement, a change in attention or a loss of consciousness.

seizure disorders
A condition marked by sudden, uncontrollable waves of electrical activity in the brain, causing involuntary movement or loss of consciousness.

A thick white fluid, made and stored in male testicles, that carries sperm out of the body through the penis during ejaculation.

sentinel lymph node
The first lymph node in a lymph node bed to receive drainage from a tumor site.

serial paracentesis
A minimally invasive procedure in which excess fluids in the abdomen are repeatedly withdrawn, either through a needle inserted directly into the peritoneal cavity or through a catheter connected to a peritoneal port, a small reservoir or chamber surgically implanted under the skin near the abdomen.

sexually transmitted diseases (STDs)
Any infectious disease that is passed from one person to another during sexual contact.

shear injury
Also known as diffuse axonal injury.
Stretched or torn nerve fibers in the brain.

A short, hollow plastic tube inserted through the skin into a blood vessel or tissue through which other instruments, such as a guide wire and balloon-tipped catheter are advanced.

short-bore MRI system
A type of magnetic resonance imaging (MRI) unit. The traditional MRI unit is a large doughnut-shaped magnet with a tube-like central opening. The patient lies on a moveable examination table that slides into the center of the magnet. While the body part that is being scanned must remain in the magnet, the short-bore nature of the magnet allows the part of the body not being scanned to potentially be "outside" of the magnet. Patients often report the short-bore MRI system produces less claustrophobia than a traditional MRI unit.

sickle-cell anemia
A severe, chronic type of anemia caused by an abnormal form of hemoglobin that distorts the red blood cells. These abnormal red blood cells sometimes plug the blood vessels, causing damage to the organ downstream.

sigmoid colon
The lower part of the colon.

A thin flexible tube with a tiny camera at the end used in a procedure called a sigmoidoscopy, which captures images of the interior of the lower large intestine and rectum.

An examination in which a flexible tube with a tiny camera at the end called a sigmoidoscope is inserted into the colon to capture images of the interior of the lower colon and rectum.

Use of a radiographic system or computer to plan radiation therapy. See also treatment planning.

single-photon emission-computed tomography (SPECT)
An imaging test that uses a gamma camera and a computer to create three-dimensional (3-D) images of the distribution of a radiotracer in the body. SPECT is used to study blood flow through the heart muscle, and to study the brain, bones and to detect infection and certain types of tumors.

sinus (sinuses)
Hollow, air-filled spaces located within the bones of the face surrounding the nasal cavity. There are four pairs of cavities, called paranasal sinuses, each of which is connected to the nose by small openings.

Infection or inflammation of one or more of the sinuses.

The process in which dead tissue becomes separated from living anatomic structures.

small intestine
The section of the gastrointestinal tract that digests food and absorbs nutrients after they have passed through the stomach.

A device similar to a credit card that contains electronic information or tokens that identify and validate a user in conjunction with biometric or password information.

social workers
Social workers may be available to provide practical help and counseling to patients or members of their families and can help them to cope. They also may help arrange for home health care and other services. Social workers may be licensed. Licensed social workers must have a master's degree and must pass an examination.

A pulse of ultrasonic energy used to heat up and destroy diseased tissue.

An allied health professional who has been specifically trained to perform ultrasound examinations. Many sonographers are certified by a registry of sonographers, provided they meet strict training requirements and pass examinations in basic ultrasound science and clinical applications.

Syn: ultrasonography.
The imaging of body structures by measuring the reflection or transmission of high frequency sound waves. Computer calculation of the distance to the sound-reflecting or -absorbing surface plus the known orientation of the sound beam gives a two- or three-dimensional image.

Sonography of the uterus and fallopian tubes using a transvaginal probe following the injection of sterile saline into the uterus via a thin catheter inserted through the cervix.

spectral Doppler
Instead of displaying Doppler measurements visually as in the color and power Doppler methods, spectral Doppler displays the blood flow measurements graphically, displaying flow velocities recorded over time.

An instrument for enlarging the opening of a canal or cavity in order to facilitate inspection of its interior; most frequently used with Pap tests.

Sperm (or spermatozoa) is the male reproductive cell carried by semen through the penis when a man ejaculates.

A ring-like muscle that surrounds and is able to contract or close a bodily passage or opening.

A procedure in which a small incision is made in the opening of the bile duct to allow bile and small gallstones to drain.

spinal anesthesia
Administration of a local anesthetic into the subarachnoid space surrounding the spinal cord. Generally used to prevent pain and movement in areas below the chest and extending to the feet.

spinal canal
The cavity within the vertebral column through which the spinal cord passes.

spinal cord
A cylindrical bundle of nerves, lying within the vertebral column, that carries sensory messages from peripheral nerves to the brain, and motor impulses from the brain to the body's muscles.

spinal fusion
Surgical fixation of an unstable segment of the spine.

A device that measures the volume of air that moves in and out of the lungs.

A test of lung function using a spirometer, a device that measures the volume of air that moves in and out of the lungs.

A large organ located in the left, upper abdomen, beside the stomach; as part of the immune system, it produces white blood cells and acts as a blood filter.

Introduction of radiopaque material into the spleen to obtain an x-ray visualization of the portal vessel of the portal circulation.

spontaneous pneumothorax
A condition in which a collection of air in the pleural space causes the lung to collapse, occurs in the absence of disease or injury.

spot films
X-rays of a localized region, usually under study by fluoroscopy.

A mixture of saliva and mucus coughed up from the respiratory tract.

sputum cytology
A diagnostic test in which a sample of sputum (mucus) is examined under a microscope to determine whether abnormal cells are present.

squamous cell carcinoma
A cancer that develops in the thin, flat cells (called squamous) that make up the outer layer of the skin.

Extent or progression of a disease such as cancer.

Determining the extent or progression of a disease such as cancer.

stem cell transplant
In this treatment, diseased bone marrow is replaced with the patient's own healthy stem cells or the stem cells of a donor in order to help new bone marrow grow.

stenosis, pl. stenoses
Also called a stricture

  1. An abnormal narrowing of any canal; for example, a narrowing of one of the cardiac valves.
  2. Narrowing of an opening or passageway in the body. Stenosis of an artery may reduce blood flow through the vessel.

Slender thread, rod, or catheter, lying within the space in the interior of a tubular structure, such as an artery or the intestine. Used to provide support during or after opening surgically, or to assure the opening of an intact but contracted lumen.

stent graft
A synthetic tube-like device used to replace a portion of an artery that has weakened and bulged (called an aneurysm).

The act of placing a stent.

stereotactic biopsy
An x-ray procedure that uses multiple coordinates to precisely determine the location of a tumor or nodule so that a tissue sample may be obtained.

stereotactic radiosurgery
A highly precise form of radiation therapy that directs narrow beams of radiation from different angles at a brain tumor or abnormality. Using a device that keeps the head completely still, this treatment minimizes the amount of radiation to healthy brain tissue. For more information see the Stereotactic Radiosurgery page. See also stereotactic radiotherapy.

stereotactic radiotherapy
A form of stereotactic radiosurgery using fractionated radiation dose (smaller dose over a period of days or weeks) or hyperfractioned dose (smaller dose two to three times a day), as opposed to a single large dose, to minimize tissue damage. Also see stereotactic radiosurgery.

The breastbone (the long, flat bone that forms the front of the chest cage).

See: Gallstones or Kidney and Bladder Stones.

stress echocardiography
A test in which ultrasound is used to create moving pictures of the heart before and after the heart is stressed either through exercise or a medication that stimulates the heart.

stress test
A heart monitoring test to discover how well the heart works, usually performed via physical exercise, sometimes via drugs to simulate heart stress.

A stroke occurs when a blood vessel that carries oxygen and nutrients to the brain is either blocked by a clot or bursts, interrupting blood flow to an area of the brain. When either of these happens, brain cells begin to die and brain damage occurs. See the Stroke page for more information.

subarachnoid hemorrhage
Blood collection between middle (arachnoid) and inner (pia mater) linings of the brain. It can be a result of trauma, or a bursting (ruptured) aneurysm. An aneurysm is a small area of weakness of the wall of an artery, which may be congenital, or less commonly, due to other causes, such as an infection.

subarachnoid space
The space between the membrane covering the spinal cord and the cord itself.

subclavian vein
A major vein running under the collarbone (clavicle) which receives blood from the large vein of the upper arm and returns toward the heart.

subcutaneous port
A special device used in a vascular access procedure that is inserted inside a major vein for a period of months or years so that blood can be repeatedly drawn or medication and nutrients can be injected into the patient’s bloodstream on regular basis. The subcutaneous implantable port is a permanent device that consists of a catheter, a long, thin, hollow plastic tube, attached to a small reservoir, both of which are placed under the skin.

subdural hematoma
In this type of hematoma, a blood vessel (usually a vein) bursts in a space just outside of the brain. Blood begins to pool along the surface of the brain, between membranes that cover the brain. Because subdural hematomas arise from low pressure venous bleeding, it may take some time for symptoms to appear after the injury. By contrast, an epidural hematoma, which is blood bleeding between the skull and a tough membrane normally firmly attached to the skull, called the dura mater, usually arises from an artery torn by a skull fracture. The higher pressure arterial blood accumulates much more quickly, usually resulting in a rapid appearance of symptoms (e.g., headache, paralysis, disturbance of consciousness).

superior vena cava
One of the largest veins in the body, it returns blood from the entire upper half of the body directly to the right atrium, one of the heart chambers.

surgical shunt
A surgically created passageway to allow blood or other bodily fluids to flow between two locations. A shunt may be used to move fluid from one part of the body to another or to divert blood flow from one route to another.

Stitches used to hold tissue together or to close a wound.

A cyclic particle accelerator in which the magnetic field (to turn the particles so they circulate) and the electric field (to accelerate the particles) are synchronized with the traveling particle beam. While the cyclotron uses a constant magnetic field and a constant frequency electric field, both are varied in the synchrotron. This allows for construction of large rings that can accelerate particles to much higher energies than a cyclotron which has a limited magnet size. The synchrotron uses multiple separate bending magnets and narrow bore tubes to connect them. It can be used to produce high energy protons and other particles such as carbon ions that are used to treat cancer. In addition the energy of the particles can be varied as needed which is very difficult in a cyclotron.

A sexually transmitted disease that can cause lesions of the central nervous and cardiovascular systems.

targeted cryoablation therapy
See cryosurgery.

targeted therapy
See monoclonal antibody therapy.

A radiotracer commonly used in nuclear medicine for many different types of examination. It decays within 24 hours, leaving no residual radiation.

One trained in and using the techniques of a profession, art, or science.

temporary brachytherapy
A radiation therapy treatment for cancer in which a sealed pellet (or “seed”) containing radioactive material is placed inside the body in or near a tumor for a specified amount of time and then withdrawn; can be administered at a low dose rate (LDR) or high dose rate (HDR).

temporomandibular joint disorder
Also known as TMJ.
A group of disorders associated with pain in the face affecting the jaw muscles, temporomandibular joints (upper temporal bone and lower mandible jaw bone that form the joint) and nerves.

tension headache
A headache in which pressure and a band-like tightness begins in the back of the head and upper neck and gradually encircles the head.

testicular torsion
The twisting of the spermatic cord that contains the vessels that supply blood to the testicles.

testis (pl. testes)
One of the two male reproductive glands that produce spermatozoa (sperm) and male hormones (testosterone). The testes are located behind the penis in the scrotum.

therapeutic radiology
A medical specialty and the study of radiation treatment of abnormal tissue (nonmalignant or cancerous) through the use of x-rays or radionuclides.

One professionally trained and/or skilled in the practice of a particular type of therapy.

Refers to the chest or ribs region of the spinal column, which includes twelve bones, or vertebrae labeled T-1 through T-12.

three-dimensional conformal radiation therapy (3D-CRT)
A form of external beam therapy that more precisely conforms the radiation to the tumor, allowing a higher radiation dose to be safely delivered.

See catheter-directed thrombolysis.

thrombolytic agent
One of a group of medications used to dissolve clots within the blood vessels of the body.

thrombolytic therapy
The use of medication used to break up or dissolve clots within blood vessels.

Inflamation of a vein that results when a blood clot, a thickened mass of blood, forms along the wall of a blood vessel.

The blocking of a blood vessel by a blood clot (or thrombus) that forms in a blood vessel or organ.

thrombotic stroke
A stroke that occurs when a blood clot forms in a cerebral blood vessel that is already very narrow.

thyroid gland
One of nine endocrine glands in the body, located in front of the neck just below the Adam's apple. It is shaped like a butterfly, with two lobes on either side of the neck connected by a narrow band of tissue. The thyroid gland produces thyroid hormones that set the rate the body carries on its necessary functions (metabolic rate). Some of the functions controlled by thyroid hormones include heart rate, cholesterol level, body weight, energy level, muscle strength, skin condition and vision.

thyroid scan
A nuclear medicine examination that helps evaluate the structure of the thyroid. The thyroid is a gland in the neck that controls metabolism, a chemical process that regulates the rate at which the body functions.

thyroid uptake
Also known as radioactive iodine uptake test (RAIU).
A nuclear medicine examination that helps evaluate the function of the thyroid. The thyroid is a gland in the neck that controls metabolism, a chemical process that regulates the rate at which the body functions.

tissue plasminogen activator (t-PA)
A blood clot-busting drug used to reduce the severity of an ischemic stroke if given within a short window of time following the onset of the stroke.

Making a radiographic image of a selected plane by means of reciprocal linear or curved motion of the x-ray tube and film cassette; images of all other planes are blurred ("out of focus") by being relatively displaced on the film.

tonic-clonic seizure
See grand mal seizure.

total body irradiation
A type of radiation therapy in which the entire body receives radiation prior to chemotherapy and a stem cell or bone marrow transplant.

total nodal irradiation
A type of radiation therapy that involves the delivery of radiation to all the lymph nodes in the body.

Also known as the windpipe, the tube that connects the lungs and mouth.

Through or across the abdomen.

A hand-held device that sends and receives ultrasound signals.

transient ischemic attack (TIA)
Often referred to as a mini stroke, a TIA is a temporary blockage in blood flow to parts of the brain, usually due to plaque or a blood clot. Symptoms typically go away within a day.

transjugular intrahepatic portosystemic shunt (TIPS)
A procedure that uses imaging guidance to connect the portal vein to the hepatic vein in the liver. A small metal device called a stent is placed to keep the connection open and allow it to bring blood draining from the bowel back to the heart while avoiding the liver. See the Transjugular Intrahepatic Portosystemic Shunt (TIPS) page for additional information.


  1. To transfer from one part to another, as in grafting and transplantation.
  2. The tissue or organ in grafting and transplantation.

Passing through or performed by way of the rectum.

Across or through the vagina (the genital canal in the female, extending from the uterus to the vulva).

treatment planning
Establishment of procedures to carry out effective radiation therapy with minimal risk to healthy tissue. See also simulation.

triple A
See abdominal aortic aneurysm (AAA).

A hollow needle with a sharply pointed end that is inserted into a blood vessel, body cavity or bone. Needles, tubes or other instruments are then inserted through the trocar be inserted to reach the treatment area.

A highly contagious infection transmitted through the air that attacks the lungs and other parts of the body.

A growth of abnormal cells that are either malignant or benign.

tumor ablation
The removal of a tumor.

tunneled cathether
A special type of catheter used in a vascular access procedure that is inserted inside a major vein for a period of weeks, or months so that blood can be repeatedly drawn or medication and nutrients can be injected into the patient’s bloodstream on regular basis. Unlike a standard intravenous catheter (IV) which is for short term use, a vascular access catheter is more durable and does not easily become blocked or infected. The tunneled catheter, which has a cuff at one end that stimulates tissue growth to help hold it in place, is used when access to the vein is needed for longer than three months and many times each day. This catheter is commonly used for patients requiring dialysis.

Veins that carry blood from throughout the body to the heart rely on a series of valves that work like gates to prevent blood from flowing backwards. When valves are not working properly, the normal flow of blood slows and creates pockets of backflow, called turgidity, where clots can develop.

ulcerative colitis
A chronic disease of unknown cause characterized by ulceration of the colon and rectum, with rectal bleeding, abdominal pain, and diarrhea; frequently causes anemia and electrolyte imbalance, and is less frequently complicated by peritonitis inflammation of the abdominal membrane, toxic megacolon (a condition of extreme dilation and hypertrophy of the colon), or cancer of the colon.

ulcers (of the skin)
An open sore or irritation on the skin.

ulcers (of the stomach)
A sore or erosion in the lining of the stomach.

See sonography.

ultrasound, diagnostic
Ultrasound imaging, also known as ultrasound scanning or sonography, is a method of obtaining images from inside the human body through the use of high frequency sound waves. The soundwaves' echoes are recorded and displayed as a real-time, visual image. No ionizing radiation is involved in ultrasound imaging.

Denoting electromagnetic rays at higher frequency than the violet end of the visible spectrum.

undescended testicle
A testicle that hasn't descended from the body.

uranium (U)
A radioactive metallic element, atomic no. 92, atomic wt. 238.0289, occurring mainly in pitchblende and notable for its two isotopes: 238U and 235U (99.2745% and 0.720%, respectively, the rest being made up by 234U), 235U being the first substance ever shown capable of supporting a self-sustaining chain reaction.

The tube that carries urine from each kidney to empty into the bladder.

A tube that carries urine from the bladder out of the body. In men, the urethra carries semen from the prostate and other sex glands out of the body through the penis.

A procedure that simultaneously measures pressures in urinary bladder and urethra.

uric acid
A waste product left over from normal chemical processes in the body and found in the urine and blood.

Relating to the organs involved in producing and passing urine.

Radiography of any part (kidneys, ureters, or bladder) of the urinary tract.

A medical doctor who specializes in the diagnosis and treatment of genitourinary tract diseases.

Relating to the uterus.

uterine cavity
The space within the uterus.

uterine fibroid embolization
A minimally invasive treatment for fibroid tumors of the uterus, , in which a synthetic material called an embolic agent is placed inside one or more of the blood vessels that supply the tumors with blood. As the vessels close off, the fibroid tissue shrinks. See the Uterine Fibroid Embolization (UFE) page for more information.

A hollow muscular organ in which a fertilized ovum (egg) develops into a fetus; located in a woman’s lower abdomen.

V/Q Lung scan
A nuclear medicine exam that uses a small amount of radioactive material (called a radiotracer). The radiotracer is injected into the bloodstream and collected in the blood vessels of the lungs. A special camera takes pictures to show how blood and air are flowing throughout the lungs.

vacuum-assisted biopsy
A type of biopsy in which a vacuum-powered instrument is inserted through the skin to the site of an abnormal growth to collect and remove a sample of cells for analysis. Using vacuum pressure, the abnormal cells and tissue are removed without having to withdraw the probe after each sampling as in core needle biopsy.

The genital canal in the female, extending from the uterus to the vulva.

vagus nerve
One of two nerves that run on opposite sides of the body from the brainstem through the neck and chest to the abdomen. The vagus nerves are involved in bodily functions that are not under voluntary control, such as breathing and digestion, as well as regulation of the heart rate.

vagus nerve stimulation (VNS)
A procedure in which a device similar to a heart pacemaker is implanted under the skin and sends regular impulses of electrical energy to the brain through the vagus nerve to prevent or reduce seizures.

vagus nerve stimulator
A device similar to a heart pacemaker that is implanted under the skin and sends regular impulses of electrical energy through an electrode placed near the vagus nerve to prevent or reduce seizures. The vagus nerve sends these seizure-reducing impulses to the brain.

variceal bleeding
Bleeding from any of the veins that normally drain the stomach, esophagus, or intestines into the liver.

Dilated, fragile veins that are prone to bleeding because of the high pressure caused by portal hypertension. Varices typically arise at the junction of the esophagus and stomach, but can arise anywhere along the gastrointestinal tract.

An abnormal enlargement of a vein in the scrotum draining the testicles.

Abnormally swollen and enlarged.

varicose veins
When veins, typically in the legs, become less elastic and the one-way valves that normally prevent blood from flowing backward malfunction, blood pools in the vessels resulting in varicose or enlarged and knotty veins.

Relating to or containing blood vessels.

vascular disease
Any condition that affects the (circulatory) system of blood vessels that carries blood from the heart throughout the rest of the body. This includes diseases of the arteries, veins, and lymph vessels and blood disorders that affect circulation.

vascular stenting
Often performed with angioplasty, a procedure in which a small wire mesh tube called a stent is permanently placed in a newly opened artery to help it stay open. For details see the Angioplasty and Vascular Stenting page.

Radiography of the the secretory duct of the testicle (vas deferens), to determine patency (the state of being freely open), by injecting contrast medium into its opening either through the urethra or by incision into the vas deferens.

The narrowing of a blood vessel due to excessive contraction of the vessel wall.

One of a large system of branching vessels that collect blood which the arteries have distributed to body tissues and returns it to the heart and then the lungs.

vein stripping
A procedure in which varicose veins, abnormally swollen and enlarged blood vessels, are removed surgically, usually from the leg.

X-ray imaging of the veins following contrast material injection into the veins.

A type of x-ray in which contrast material is injected into a vein to show the details of its structure and any abnormality that may be present.

venous insufficiency
Enlarged veins with faulty valves that permit blood to pool by gravity instead of returning to the heart for re-circulation.


  1. Replacement of air or other gas in a space by fresh air or gas.
  2. Movement of gas(es) into and out of the lungs.


  1. In the brain, the hollow cavities containing cerebrospinal fluid (CSF).
  2. The main pumping chambers in the heart.

An individual bone in the column of bones that extends from the base of the skull to the pelvis which permits us to stand upright and serves to enclose and protect the spinal cord.

The bony segments of the spinal column which contain and protect the spinal cord.

vertebral compression fractures
Fractures of the vertebrae caused by the compression, or excessive pushing, of one bone against another.

An image-guided, minimally invasive, nonsurgical therapy that uses an injection of bone cement to strengthen a broken vertebra (spinal bone) that has been weakened by osteoporosis or, less commonly, cancer. See the Vertebroplasty & Kyphoplasty page for additional information.

From the bladder to the ureter – typically, the abnormal passage of urine from the bladder back into a ureter.

video capsule endoscopy
A procedure in which the patient swallows a tiny capsule holding a video camera and light. Over a period of hours, the camera sends images of the small intestine to a video recorder.

virtual private network (VPN)
A computer network in which links between computers or other hardware devices are carried on an open connection or over the Internet instead of being directly connected by physical wires; software encryption ensures that only authorized users can access the network.

An organ of the digestive, respiratory, urogenital, and endocrine systems, as well as the spleen, the heart, and great vessels; hollow and multilayered walled organs.

volumetric modulated arc therapy (VMAT)
Volumetric Arc Therapy (VMAT) is an advanced form of intensity-modulated radiotherapy (IMRT) that delivers a targeted three-dimensional dose of radiation to a tumor in one or more treatments.

Also called Coumadin®
One of a class of medications called anticoagulants, or blood thinners, which work by decreasing the clotting ability of the blood.

white blood cells
Also known as lymphocytes.
Cells that circulate in the blood and are responsible for both directly and indirectly fighting infection by attacking foreign invaders of the body.

wire localization
Guided by an imaging modality such as magnetic resonance imaging, a wire is inserted through a hollow needle to a lesion, or suspicious area of cells and tissue. The wire then guides the surgeon to the area so that the abnormal tissue can be surgically removed for examination.


  1. The ionizing electromagnetic radiation emitted from a vacuum tube, resulting from the bombardment of the target anode with a stream of electrons from a heated cathode.
  2. Ionizing electromagnetic radiation produced by the excitation of the inner orbital electrons of an atom by other processes, such as nuclear delay and its sequelae.
  3. A radiograph.

x-ray therapy
A medical specialty and the study of radiation treatment of abnormal tissue (nonmalignant or cancerous) through the use of x-rays or radionuclides.

Yttrium Y-90
A radioactive form of rare earth metal yttrium used in radiation therapy and immunotherapy.

A Yttrium-90 agent used in radioimmuniotherapy to treat non-Hodgkin lymphoma.