A thyroid scan is a diagnostic imaging test that uses a small amount of radioactive material to create images of the thyroid gland. This procedure, a form of nuclear medicine, provides insights into the structure and functional activity of the thyroid, a gland located in the front of the neck that plays a role in metabolism. It helps visualize how the thyroid is working.
Purpose of a Thyroid Scan
A thyroid scan investigates conditions affecting the thyroid gland. The test helps determine if the thyroid is functioning properly, especially when there are concerns about an overactive or underactive thyroid. It is often ordered to evaluate thyroid nodules (lumps or growths within the gland).
A scan differentiates causes of hyperthyroidism (too much hormone production). It also aids in diagnosing hypothyroidism (insufficient hormone production) or an enlarged thyroid (goiter). While not typically a primary tool for initial cancer diagnosis, a thyroid scan can assist in assessing the spread of thyroid cancer or evaluating changes in the gland after medication adjustments or surgery.
Undergoing a Thyroid Scan
Preparation for a thyroid scan involves specific instructions. Patients might be advised to avoid certain medications (like thyroid hormones or antithyroid drugs) and to limit iodine-rich foods, supplements, or recent exposure to iodine-containing contrast agents. Fasting for several hours may also be necessary, particularly if a radioactive iodine uptake (RAIU) test is performed. Inform the medical team about any possibility of pregnancy or if breastfeeding, as precautions are taken due to the radioactive tracer.
During the procedure, a small amount of a radioactive tracer (e.g., iodine-123 or technetium-99m) is administered. This tracer is given as a pill, liquid, or injection. After a waiting period (minutes to 24 hours depending on the tracer), the patient lies on an examination table. A gamma camera then detects the gamma rays emitted by the tracer as it accumulates in the thyroid gland, creating images. Patients must remain still during the 10 to 30-minute scanning time for clear images.
The amount of radiation involved is small and generally considered safe for diagnostic purposes, with benefits usually outweighing risks. After the scan, patients are encouraged to drink extra fluids to help eliminate the tracer from their body.
What Scan Results Show
Thyroid scan images provide information about the thyroid gland’s size, shape, and position. They also reveal how different areas of the gland function by showing where the radioactive tracer has been absorbed. Areas with increased tracer uptake appear as “hot spots,” indicating highly active thyroid tissue. These hot nodules are usually benign and often produce excess thyroid hormones.
Conversely, areas with decreased or no tracer uptake are known as “cold spots.” These regions signify less active tissue. While most cold nodules are also benign, they have a slightly higher chance of being malignant compared to hot nodules. Therefore, cold spots may require further evaluation, such as a biopsy, to determine their cause. A nuclear medicine physician interprets these findings, and the results are conveyed to the referring medical professional to guide further management.