A nuclear medicine thyroid scan uses radioactive iodine to measure thyroid function and diagnose conditions such as hyperthyroidism, goiter, and thyroid cancer. The patient takes a pill containing the tracer, and the scan measures how quickly the thyroid absorbs it. A second scan is usually done after 18 hours for a detailed insight into thyroid function. If abnormalities are found, other diagnostic tools are needed for a final diagnosis.
A nuclear medicine thyroid scan is a diagnostic tool used to determine a patient’s thyroid function. The test is needed to detect a number of conditions, including hyperthyroidism, goiter and thyroid cancer. The test requires a patient to ingest a small amount of radioactive iodine several hours before the test. The procedure takes only a few minutes and causes little or no discomfort to the patient.
If a patient has symptoms suggestive of a thyroid disorder, a physician must determine whether the cause is benign or harmful. A nuclear medicine thyroid scan is needed to diagnose the specific disorder. Unlike other forms of medical imaging, such as MRI or PET scans, nuclear medicine scans have the advantage of showing metabolic function in real time. For a nuclear medicine thyroid scan, the scan measures how quickly the thyroid absorbs iodine.
Hours before the scan, the patient takes a pill containing a small amount of radioactive iodine, a tracer that detects the scan. The body, unable to distinguish the tracer from normal iodine, sends it to the thyroid to be transformed into thyroid hormones. Only when this process is ongoing can the test accurately measure thyroid function.
The first scan occurs about four to six hours after the patient has ingested the radioactive iodine. He or she lies on a table, the image scanner placed directly above her neck. Within minutes, the scanner records the radioactivity emitted by the iodine tracer that has reached the thyroid gland. In a healthy adult, the scanner produces an image of the thyroid gland as shaded areas on a white background. Shading also indicates normal iodine intake.
Regardless of the result of the first test, a second one is usually done after 18 hours. Comparing the two images gives doctors a detailed insight into thyroid function. If the thyroid in the first image is particularly dark, it indicates hyperthyroidism; the thyroid is overactive. An unusually clear picture occurs due to hypothyroidism. An enlarged or misshapen thyroid suggests a tumor or goiter.
If a doctor discovers abnormalities in the results of a nuclear medicine thyroid scan, other diagnostic tools are needed to make a final diagnosis. For example, a tumor and a goiter can create a similar picture on a scan. In these cases, a surgeon takes a biopsy to determine the nature of the mass.
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