In thyroid nuclear scan, a small amount of radioactive material is introduced into your body, and a special type of camera records the absorption of the radiotracer by the thyroid gland. (Usually, a form of radioactive iodine is given by mouth.) The camera data are translated by a computer into two-dimensional images that are displayed on a viewing monitor and recorded on film.
Thyroid nuclear scan is most often done to examine a thyroid growth, or nodule, that was detected on another imaging test or by palpating the gland.
Purpose of the Thyroid Nuclear Scan
- To evaluate the size, structure, position, and function of the thyroid gland, usually in conjunction with other thyroid tests
- To detect thyroid growths, or nodules, and aid in determining whether they are benign or malignant
- To assess thyroid gland function
- To help diagnose overactive thyroid gland (hyperthyroidism), thyroid cancer or other growths, and other thyroid problems
- To locate lumps (nodules) or inflammation in the thyroid gland
- To determine whether thyroid cancer has spread beyond the thyroid
- To monitor changes in the thyroid gland after treatment, including surgery, radiotherapy and chemotherapy
Who Performs Thyroid Nuclear Scan
- A physician, a nurse, or a nuclear medicine technician
Special Concerns about Thyroid Nuclear Scan
- People with allergies to iodine or shellfish may experience a severe allergic reaction to radioactive iodine; another radiotracer will be used.
- Women who are pregnant or nursing should not undergo this test because exposure to the radiotracer may harm the fetus or infant.
- A diet deficient in iodine can cause increased uptake of radioactive iodine; on the other hand, ingestion of iodine-containing foods such as iodized salt or shellfish can interfere with its uptake. Recent exposure to x-ray contrast dyes may also affect test results because these agents may contain large quantities of iodine.
- The presence of kidney disease, severe diarrhea, or vomiting, as well as various medications (including thyroid drugs, cough medicines, multivitamins, some oral contraceptives, phenothiazines, and corticosteroids) may affect test results.
Before the Thyroid Nuclear Scan
- Inform your doctor if you have an allergy to iodine or shellfish, and whether you have undergone any contrast x-ray procedures or nuclear scans in the previous 60 days.
- Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain of these agents for a specified period before the test.
- Tell your doctor if you are pregnant or breastfeeding or you may be pregnant.
- Tell your doctor if you had an x-ray, CT scan, other test, or another treatment of surgery involving iodinated contrast material within the last two months.
- You will be instructed to avoid ingesting iodized salt, iodinated salt substitutes, and seafood for 1 week before the test.
- If this test requires you to take radioactive iodine orally, you will be asked to fast for 12 hours beforehand.
- On the day of the test, wear a comfortable, loose-fitting shirt.
- Immediately before the scan, you will be asked to remove your dentures and any jewelry that could interfere with visualization of the thyroid.
What You Experience
- You will ingest an oral radiotracer either in a beverage or in pill form, and you will be asked to return for the scanning procedure 4 to 24 hours later.
- You will lie on your back on an examination table with your neck pushed forward, or hyperextended. (A pillow is placed under your neck to make this position more comfortable.)
- A scanning camera is placed over your neck to record the gamma rays emitted by the radiotracer in the thyroid. The device projects images of the gland on a viewing screen, and these pictures are recorded on x-ray film. Several views will be obtained from different angles.
- The scanning procedure itself takes about 20 or 30 minutes.
Risks and Complications
- The trace amount of radioactive material used in this test is not associated with any significant risks or complications.
After the Thyroid Nuclear Scan
- Resume your normal diet and any medications withheld before the test, according to your doctor’s instructions.
Results of Thyroid Nuclear Scan
- A physician will examine the scans for evidence of abnormalities. Nodules exhibiting increased iodine uptake are deemed “hot spots” (indicating a possible benign tumor), while nodules that take up little or no iodine, or “cold spots,” may be cysts, cancer, or another abnormality. Diffuse increased uptake may indicate hyperthyroidism (overactive thyroid).
- If a definitive diagnosis can be made, appropriate therapy will be started.
- In most cases, a diagnosis must be confirmed with blood tests for thyroid hormones, ultrasound, or a biopsy.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media