The thyroid gland, a small, butterfly-shaped organ in the front of your neck, regulates numerous bodily functions. It produces hormones that control metabolism, influencing energy use and organ function. When thyroid problems arise, understanding its activity is important for diagnosis. Thyroid scintigraphy is a specialized imaging technique offering unique insights into the thyroid’s activity.
Understanding Thyroid Scintigraphy
Thyroid scintigraphy operates on the principle that the thyroid gland naturally absorbs iodine, an element necessary for thyroid hormones. This technique introduces a small amount of a radioactive tracer, typically Technetium-99m pertechnetate or Iodine-123. These tracers mimic iodine, accumulating in thyroid tissue without being incorporated into hormones.
Once absorbed by thyroid cells, the tracer emits gamma rays. A specialized gamma camera detects these emissions, creating detailed images. These images illustrate how the tracer is distributed throughout the thyroid, providing information about its activity and function.
Indications for Thyroid Scintigraphy
Doctors recommend thyroid scintigraphy to gain insight into the gland’s function. A common indication is the evaluation of thyroid nodules. The scan helps determine if these nodules are “hot,” meaning they are highly active, or “cold,” indicating reduced or no tracer uptake. This distinction is important because hot nodules are almost always benign, while cold nodules have a higher chance of being cancerous and may require further investigation, such as a biopsy.
The procedure also diagnoses and manages hyperthyroidism, a condition where the thyroid produces too many hormones. This includes Graves’ disease, which shows diffuse, increased tracer uptake, and toxic multinodular goiter or toxic adenoma, which present with focal areas of increased uptake. Thyroid scintigraphy can also assess the cause of an overactive thyroid, detect ectopic thyroid tissue, and monitor certain thyroid conditions.
The Thyroid Scintigraphy Procedure
Thyroid scintigraphy involves several steps, beginning with preparation. Patients are advised to avoid iodine-containing foods and certain medications like thyroid hormones or antithyroid drugs for a period before the scan. These restrictions are necessary because iodine can interfere with the thyroid’s uptake of the radioactive tracer, leading to inaccurate imaging.
The radioactive tracer is administered, usually intravenously or orally. After administration, there is a waiting period, ranging from minutes to hours, allowing the thyroid to absorb the tracer. Patients may leave the department during this time.
For imaging, the patient lies on an examination table with their head positioned. A gamma camera is placed close to the neck to detect emitted radiation, capturing images. The scanning time lasts between 10 to 30 minutes, during which the patient must remain still. After the scan, patients can resume normal activities and may be instructed to drink plenty of fluids to help eliminate the tracer. Results are usually available within a few days to a week.
Interpreting Scintigraphy Results
A nuclear medicine physician interprets scintigraphy images alongside other clinical data. Interpretation involves identifying areas of varying tracer uptake, described as “hot” or “cold” spots. A normal thyroid gland shows uniform tracer uptake.
“Hot nodules” appear as focal areas that take up more tracer than surrounding tissue, indicating hyperactivity. These nodules are benign and often associated with conditions like toxic adenomas or toxic multinodular goiter. Conversely, “cold nodules” show reduced or absent tracer uptake, suggesting decreased activity. While most cold nodules are also benign, they have a higher chance of being malignant and often warrant further investigation. Diffuse, increased uptake across the entire gland, without specific hot spots, is characteristic of conditions like Graves’ disease, indicating widespread overactivity.
Safety and Patient Considerations
Concerns about radiation exposure are common with imaging tests, but the dose from thyroid scintigraphy is low. The effective radiation dose for a typical thyroid scan using Technetium-99m pertechnetate is approximately 3.2 mSv, comparable to natural background radiation over six months. The diagnostic benefits outweigh these small risks.
The radioactive tracer is eliminated from the body quickly. Side effects are infrequent and usually mild if they occur. However, thyroid scintigraphy is avoided during pregnancy due to potential fetal radiation exposure, as iodine can cross the placenta and be concentrated by the fetal thyroid. For breastfeeding individuals, precautions are advised, such as temporarily discontinuing breastfeeding to prevent infant exposure.