A thyroid nuclear scan is a medical imaging procedure providing insights into thyroid function and structure. It uses small amounts of radioactive material called radiotracers. Its purpose is to assess thyroid function and identify structural abnormalities. It helps diagnose conditions like overactive or underactive thyroid, or to investigate lumps and nodules. This scan offers information often not attainable through other imaging methods.
Preparing for Your Scan
Preparation for a thyroid nuclear scan ensures accurate results. Patients often adjust medications, particularly thyroid hormone replacements like levothyroxine, which may be paused for several weeks before the scan. Anti-thyroid medications and iodine-containing drugs (e.g., amiodarone, cough syrups, multivitamins) require specific discontinuation periods, ranging from days to months. Recent imaging with iodine contrast (e.g., CT scans) can interfere with tracer uptake, requiring rescheduling several weeks later.
A low-iodine diet (LID) is prescribed one to two weeks before the scan. This diet reduces the body’s iodine stores, allowing the tracer to be more effectively absorbed by the thyroid. Avoid foods high in iodine, such as iodized salt, seafood, dairy products, and processed foods. Fresh fruits, vegetables, unsalted meats, and egg whites are permissible.
Patients fast for a few hours before their appointment; water is often permitted. Inform the medical team about pregnancy or breastfeeding status, as tracers are not recommended for pregnant individuals due to fetal risks. Breastfeeding mothers may need to temporarily stop nursing and discard milk after the scan to prevent infant exposure. Remove all metal jewelry and accessories around the head and neck, as these can interfere with the imaging equipment.
During the Thyroid Nuclear Scan
The thyroid nuclear scan begins with the administration of a small amount of a radioactive tracer, also known as a radiopharmaceutical. The type of tracer used dictates the method of administration; radioactive iodine (I-123) is typically given orally as a capsule or liquid, while Technetium-99m (Tc-99m) is usually administered intravenously through an injection into a vein in the arm. The injection itself is generally painless, similar to a blood draw.
Following tracer administration, there is a waiting period to allow the thyroid gland to absorb the radioactive material. If radioactive iodine is used, this waiting period can range from four to six hours, with some scans requiring a return visit 24 hours later for additional measurements, reflecting the thyroid’s iodine uptake over time. When Technetium-99m is injected, the waiting period is much shorter, usually 15 to 30 minutes, before imaging can begin. During this time, patients might be asked to drink water to help clear the tracer from other areas of the body, such as the salivary glands.
For the imaging phase, the patient lies on an examination table, often with the head gently tilted back to extend the neck, allowing for clear visualization of the thyroid. A specialized device called a gamma camera is then positioned closely over the neck, without making physical contact. This camera is designed to detect the gamma rays emitted by the radioactive tracer that has concentrated within the thyroid gland.
The gamma camera captures a series of images from various angles, such as anterior and oblique views, to create a comprehensive picture of the thyroid’s size, shape, and the distribution of the tracer. Maintaining stillness throughout this process is important, as any movement can blur the images and impact their diagnostic clarity. The actual scanning time is relatively brief, typically lasting between 10 and 30 minutes, after which the collected data is processed by a computer to generate detailed images.
After the Scan: What to Expect
After the thyroid nuclear scan is complete, patients can generally resume their normal activities, diet, and medications, though it is important to confirm with their doctor regarding the reintroduction of any thyroid-related drugs. A primary instruction following the scan is to increase fluid intake, as drinking plenty of water helps the body excrete the small amount of radioactive tracer through urine. This process aids in minimizing residual radioactivity within the body.
While the radiation dose from a diagnostic thyroid scan is low and considered safe, some precautions are advised to limit exposure to others. Patients may be instructed to limit prolonged close contact with pregnant individuals and young children for a period, typically 24 hours, to prevent unnecessary radiation exposure. This is a temporary measure as the radiotracer naturally decays and is eliminated from the body within a short timeframe.
Once the images are acquired, a nuclear medicine specialist or radiologist interprets the results, assessing the thyroid’s function and structure. A detailed report is then sent to the referring physician, usually within several business days to a week. Patients typically receive their scan results and discuss the findings, as well as any next steps, directly with their referring doctor during a follow-up appointment.