What is a parathyroid 4DCT scan?

Four-dimensional parathyroid computed tomography (4DCT) is an advanced method for detecting enlarged parathyroid glands in the neck.

Computed tomography, more commonly known as a CT or CAT scan, is a diagnostic medical imaging test. Like traditional x-rays, it produces multiple images or pictures of the inside of the body. The cross-sectional images generated during a CT scan can be reformatted in multiple planes. They can even generate three-dimensional images.

In 4DCT, time represents the fourth dimension of the image. Contrast material is given at specific rates and images are taken at specific times. This gives a clearer picture and better distinguishes abnormal tissue from normal tissue.

What are some common uses of the procedure?

A 4DCT exam is used to identify enlarged parathyroid glands and plan surgery. It is a very sensitive study with better resolution than any other diagnostic study utilized for the detection of the parathyroid glands. This study is particularly useful in cases where the other diagnostic tests such as ultrasound and nuclear medicine scans have been negative, or with more complicated cases such as history of prior surgery or recurrent parathyroid disease.

The parathyroid glands are four pea-sized glands located behind or near the thyroid gland in the neck. The glands produce parathyroid hormone (PTH). This hormone helps maintain the correct balance of calcium in the body. When one or more of the glands is diseased, the body may have abnormal levels of calcium. This can lead to health problems like kidney stones, heart abnormalities and loss of bone over time.

Parathyroid disease can affect one or more of the parathyroid glands. Treatment often involves removal of the diseased glands. Locating the abnormal gland(s) can be very difficult. Doctors most often use ultrasound or nuclear medicine imaging. If neither of these methods is effective, 4DCT may be used.

A 4DCT scan is also used to help plan for parathyroid surgery. This may allow the doctor to avoid more invasive surgery and reduce the risk of complications.

Who interprets the results and how do I get them?

A radiologist, a doctor specially trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send an official report to the doctor who ordered the exam.

What are the benefits vs. risks?

Benefits:

• Parathyroid 4DCT has a greater ability to locate diseased glands. This may lead to better treatment results.
• Parathyroid 4DCT has a higher image resolution than any other type of parathyroid scan.
• Parathyroid 4DCT is particularly useful when other imaging studies have failed to identify the abnormal parathyroid gland.
• By determining the precise location of the enlarged parathyroid gland, 4DCT can help avoid more invasive surgery and its associated complications.
• Parathyroid 4DCT can make re-operative surgery both faster and more successful. This is particularly true in challenging cases where multiple abnormal parathyroid glands are causing the disease.

Risks

The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare, and radiology departments are well-equipped to deal with them.

Patients undergoing 4DCT scan do receive a larger amount of radiation compared to a routine neck CT.

While there is no conclusive evidence that the small doses of radiation delivered by a CT scan cause cancer, large population studies have shown a slight increase in cancer from much larger amounts of radiation, such as from radiation therapy. Thus, there is always concern that this risk may apply to the amounts of radiation delivered by a 4DCT exam. When your doctor recommends a 4DCT, the expected benefit of the test outweighs the potential risk from radiation. Discuss the benefits versus the risks of your 4DCT scan with your doctor or radiologist. Ask whether other imaging tests may be used to diagnose your condition.

• The radiation dose for this procedure varies. See the Radiation Dose page for more information.
• Women should always tell their doctor and x-ray or CT technologist if there is any chance they are pregnant. See the Radiation Safety page for more information about pregnancy and x-rays.
• Doctors do not generally recommend CT scanning for pregnant women unless medically necessary because of potential risk to the unborn baby.
• IV contrast manufacturers indicate mothers should not breastfeed their babies for 24-48 hours after contrast material is given. However, the most recent American College of Radiology (ACR) Manual on Contrast Media reports that studies show the amount of contrast absorbed by the infant during breastfeeding is extremely low. For further information please consult the ACR Manual on Contrast Media and its references.

What are the limitations of a parathyroid 4DCT scan?

Patients with impaired kidney (renal) function should be given special consideration before receiving iodine-based contrast materials by vein or artery. Such patients are at risk for developing contrast-induced nephropathy (CIN), a condition in which already-impaired kidney function worsens within a few days of contrast material administration. Much of the research linking CIN with iodine-based contrast material is based on older contrast agents that are no longer used. Some recent studies have found no increased risk of CIN in patients who received iodine-based contrast material. If you have impaired kidney function, your doctor will weigh the benefits of contrast-enhanced CT against any risks.