Cardiac Nuclear Medicine
Cardiac nuclear medicine imaging evaluates the heart for coronary artery disease and cardiomyopathy (diseases of the heart muscle). It also may be used to help determine whether the heart has been damaged by chemotherapy or radiotherapy. Nuclear medicine uses small amounts of radioactive materials called radiotracers that are typically injected into the bloodstream, inhaled or swallowed. The radiotracer travels through the area being examined and gives off energy in the form of gamma rays which are detected by a special camera and a computer to create images of the inside of your body. Nuclear medicine imaging provides unique information that often cannot be obtained using other imaging procedures.
Tell your doctor if there's a possibility you are pregnant or if you are breastfeeding and discuss any recent illnesses, medical conditions, allergies and medications you're taking. Depending on the type of exam, your doctor will instruct you on what you may eat or drink beforehand, especially if sedation is to be used. Leave jewelry at home and wear loose, comfortable clothing. You may be asked to wear a gown.
- What is Cardiac Nuclear Medicine?
- What are some common uses of the procedure?
- How should I prepare?
- What does the equipment look like?
- How does the procedure work?
- How is the procedure performed?
- What will I experience during and after procedure?
- Who interprets the results and how do I get them?
- What are the benefits vs. risks?
- What are the limitations of Cardiac Nuclear Medicine?
What is Cardiac Nuclear Medicine?
Nuclear medicine imaging uses small amounts of radioactive material to diagnose, evaluate or treat a variety of diseases. These include many types of cancers, heart disease, gastrointestinal, endocrine or neurological disorders and other abnormalities. Because nuclear medicine exams can pinpoint molecular activity, they have the potential to identify disease in its earliest stages. They can also show whether a patient is responding to treatment.
Cardiac nuclear medicine is useful in diagnosing and assessing coronary artery disease. It is also used to evaluate cardiomyopathy and identify possible damage to the heart from chemotherapy or radiotherapy.
Nuclear medicine imaging procedures are noninvasive. With the exception of intravenous injections, they are usually painless. These tests use radioactive materials called radiopharmaceuticals or radiotracers to help doctors diagnose and evaluate medical conditions.
Radiotracers are molecules linked to, or "labeled" with, a small amount of radioactive material that can be detected on the PET scan. Radiotracers accumulate in tumors or regions of inflammation. They can also bind to specific proteins in the body. The most commonly used radiotracer is F-18 fluorodeoxyglucose, or FDG, a molecule similar to glucose. Cancer cells are more metabolically active and may absorb glucose at a higher rate. This higher rate can be seen on PET scans. This allows your doctor to identify disease before it may be seen on other imaging tests. FDG is just one of many radiotracers in use or in development.
Depending on the type of exam, the radiotracer is injected, swallowed or inhaled as a gas. It eventually accumulates in the area of the body under examination. A special camera or imaging device detects radioactive emissions from the radiotracer. The camera or device produces pictures and provides molecular information.
Many centers superimpose nuclear medicine images with computed tomography (CT) or magnetic resonance imaging (MRI) to produce special views. This is known as image fusion or co-registration. These views allow the doctor to correlate and interpret information from two different exams on one image This leads to more precise information and accurate diagnoses. Single photon emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/computed tomography (PET/CT) units can perform both exams at the same time. PET/MRI is an emerging imaging technology. However, it is not universally available at this time.
Cardiac nuclear medicine exams provide pictures of the distribution of blood flow to the heart muscle and can be used to visualize the function of the heart.
What are some common uses of the procedure?
Physicians use cardiac nuclear medicine studies to help diagnose cardiac disease. The symptoms include:
- unexplained chest pain.
- chest pain brought on by exercise (called angina).
- shortness of breath with exertion.
- abnormal electrocardiogram.
Cardiac nuclear medicine imaging is also performed:
- to visualize blood flow patterns to the heart walls, called a myocardial perfusion scan.
- to evaluate the presence and extent of suspected or known coronary artery disease.
- to determine the extent of injury to the heart following a heart attack, or myocardial infarction.
- to evaluate the results of bypass surgery or other revascularization procedures designed to restore blood supply to the heart.
- in conjunction with an electrocardiogram (ECG), to evaluate heart-wall movement and overall heart function with a technique called cardiac gating.
How should I prepare?
You may wear a gown during the exam or be allowed to wear your own clothing.
Women should always tell their doctor and technologist if there is any possibility that they are pregnant or they are breastfeeding. See the Safety in X-ray, Interventional Radiology and Nuclear Medicine Procedures page for more information about pregnancy and breastfeeding related to nuclear medicine imaging.
Tell the doctor and the technologist performing your exam about any medications you are taking, including vitamins and herbal supplements. List any allergies, recent illnesses and other medical conditions.
You should inform your physician if you are pregnant or breastfeeding and/or if you have:
- had a recent heart attack or myocardial infarction
- heart failure
- chronic lung disease
- conduction abnormalities within the heart (such as AV block), aortic stenosis or other abnormalities with the valves of your heart
- any abnormality with the heart and lungs
Also, if you have problems with your knees, hips or keeping your balance, tell your doctor as this may limit your ability to perform the exercise needed for this procedure. You should wear comfortable clothing and walking shoes. Do not apply oil, lotion, or cream to your skin the day of the exam. If you use an inhaler for asthma or other breathing problems, bring it to the test and make sure the health care team monitoring your stress test knows that you use an inhaler.
Leave jewelry and other metallic accessories at home or remove them prior to the exam. Such objects may interfere with the procedure.
You should avoid caffeine (caffeinated as well as decaffeinated coffee, hot and cold tea, caffeinated soft drinks, energy drinks, chocolate and medications containing caffeine, etc.) and smoking for up to 48 hours before your examination. Your physician or radiologist may give you more specific instructions.
You should not eat or drink anything after midnight on the day of your procedure, but you may continue taking medications with small amounts of water unless your physician says otherwise. If you take beta-blocker or calcium channel blocker medication (Inderal, metoprolol, Norvasc, etc.) you should specifically ask your physician about temporary discontinuation. If you are diabetic, check with your physician about specific instructions for your diabetes medication on the day of the exam.
What does the equipment look like?
The special camera and imaging techniques used in nuclear medicine include the gamma camera and single-photon emission-computed tomography (SPECT).
The gamma camera, also called a scintillation camera, detects radioactive energy that is emitted from the patient's body and converts it into an image. The gamma camera itself does not emit any radiation. The gamma camera is composed of radiation detectors, called gamma camera heads, which are encased in metal and plastic and most often shaped like a box, attached to a round circular donut shaped gantry. The patient lies on the examination table which slides in between two parallel gamma camera heads that are positioned above the patient. Sometimes, the gamma camera heads are oriented at a 90 degree angle and placed over the patient's body.
SPECT involves the rotation of the gamma camera heads around the patient's body to produce more detailed, three-dimensional images.
Most nuclear medicine procedures use a gamma camera. Some nuclear medicine equipment has CT capabilities that help improve the images and increase the ability to combine functional imaging (nuclear medicine) and anatomic imaging (CT).
A computer helps create the images from the data obtained by the gamma camera.
How does the procedure work?
Ordinary x-ray exams create an image by passing x-rays through the body. Nuclear medicine exams use a radioactive material called a radiopharmaceutical or radiotracer. This material is injected into the bloodstream, swallowed or inhaled as a gas. The material accumulates in the area of your body under examination, where it gives off a small amount of energy in the form of gamma rays. Special cameras detect this energy and, with the help of a computer, create pictures that offer details on the structure and function of organs and tissues.
In order to evaluate the coronary arteries, heart scans are often performed immediately after patients have engaged in physical exercise (called a stress test) so that blood flow throughout the heart is maximized, making any blockages of the coronary arteries easier to detect. These images of the heart are compared with heart images taken while the patient is at rest. Patients who are unable to exercise are given a drug that increases blood flow to the heart.
How is the procedure performed?
Nuclear medicine imaging is performed on outpatients and hospitalized patients.
The exam will usually begin with an injection of tracer while you are resting. Within the first hour after the tracer is injected, you will lie on a moveable imaging table with your arms (or in some cases your left arm only) over your head for about 15 to 20 minutes while images are recorded. Following imaging, you will undergo a stress test, which requires you to exercise either by walking on a treadmill or pedaling a stationary bicycle for a few minutes. While you exercise, the electrical activity of your heart will be monitored by electrocardiography (ECG) and your blood pressure will be frequently measured. When blood flow to the heart has reached its peak, you will be given the radiotracer through your IV. After you complete the stress test, you may be asked to drink some water. You will be placed on the imaging table a second time so a second series of images can be recorded. At this time, an ECG will also be placed to image the motion of your heart.
If you are unable to use a treadmill or bicycle, you will not exercise but you will be given a drug that will increase blood flow to the heart.
Actual scanning time for each heart scan varies from 15 to 30 minutes, depending on the type of scanner used. Total time in the nuclear medicine department will be approximately two to four hours.
If the SPECT scanner has CT capabilities, a short CT scan of your heart will be obtained. The CT may be obtained before or after each of the nuclear medicine imaging procedures. You will not have to get up or change positions on the table for this part of the exam as the CT is part of the nuclear medicine equipment, but you will be asked to stay very still for this portion of the exam.
When the examination is complete, you may be asked to wait until the technologist checks the images in case more images are needed. Sometimes, more images are obtained to clarify or better visualize certain areas or structures. The need for more images does not necessarily mean there was a problem with the exam or that something abnormal was found. It should not cause you concern.
If you had an intravenous (IV) line inserted for the procedure, it will usually be removed unless you are scheduled for another procedure that same day that requires an IV line.
What will I experience during and after the procedure?
Except for intravenous injections, most nuclear medicine procedures are painless. They are rarely associated with significant discomfort or side effects.
When the radiotracer is given intravenously, you will feel a slight pin prick when the needle is inserted into your vein for the intravenous line. You may feel a cold sensation moving up your arm when the radiotracer is injected. Generally, there are no other side effects.
You will be asked to exercise until you are either too tired to continue or short of breath, or if you experience chest pain, leg pain, or other discomfort that causes you to want to stop.
If you are given a medication to increase blood flow because you are unable to exercise, the medication may induce a brief period of feeling anxious, dizzy, nauseous, shaky or short of breath. Mild chest discomfort may also occur. Any symptoms that do develop typically resolve as soon as the infusion is complete. In rare instances, if the side effects of the medication are severe or make you too uncomfortable, other drugs can be given to stop the effects.
It is important to remain still during the exam. Nuclear imaging itself causes no pain. However, having to remain still or to stay in one particular position during imaging may cause discomfort.
Unless your doctor tells you otherwise, you may resume your normal activities after your exam. A technologist, nurse or doctor will provide you with any necessary special instructions before you leave.
The small amount of radiotracer in your body will lose its radioactivity over time through the natural process of radioactive decay. It may also pass out of your body through your urine or stool during the first few hours or days following the test. Drink plenty of water to help flush the radioactive material out of your body.
Who interprets the results and how do I get them?
A radiologist or other doctor specially trained in nuclear medicine will interpret the images and send a report to your referring physician.
What are the benefits vs. risks?
- Nuclear medicine examinations provide unique information—including details on the function and anatomy of body structures—that is often unattainable using other imaging procedures.
- Nuclear medicine scans provide the most useful diagnostic or treatment information for many diseases.
- A nuclear medicine scan is less expensive and may yield more precise information than exploratory surgery.
- If you have coronary artery disease, it is possible that you could experience chest pain during exercise or when a drug is given for the stress test. However, your heart will be monitored and if necessary, medication can be given for your chest pain.
- If life threatening cardiac disease is suspected because of the test findings, your cardiologist may consider same-day cardiovascular intervention.
- Because only a small dose of radiotracer is used, nuclear medicine exams have a relatively low radiation exposure. This is acceptable for diagnostic exams. Thus, the radiation risk is very low when compared with the potential benefits.
- Nuclear medicine diagnostic procedures have been used for more than five decades, and there are no known long-term adverse effects from such low-dose exposure.
- Treatment risks are always weighed against the potential benefits for nuclear medicine therapeutic procedures. Your doctor will inform you of all significant risks prior to the treatment and give you an opportunity to ask questions.
- Allergic reactions to radiotracers are extremely rare and usually mild. Always tell the nuclear medicine personnel of any allergies you may have or other problems that may have occurred during a previous nuclear medicine exam.
- Injection of the radiotracer may cause slight pain and redness. This should rapidly resolve.
- Women should always tell their doctor and radiology technologist if there is any possibility that they are pregnant or they are breastfeeding. See the Safety in X-ray, Interventional Radiology and Nuclear Medicine Procedures page for more information about pregnancy, breastfeeding and nuclear medicine imaging.
What are the limitations of Cardiac Nuclear Medicine?
Nuclear medicine procedures can be time consuming. It can take several hours to days for the radiotracer to accumulate in the area of interest, and imaging may take up to several hours to perform. In some cases, newer equipment can substantially shorten the procedure time.
The image resolution of nuclear medicine images may not be as high as that of CT or MRI. However, nuclear medicine scans are more sensitive for a variety of indications, and the functional information they yield is often unobtainable by other imaging techniques.
This page was reviewed on March 18, 2020