Whole Body Iodine scan is used to examine the function of thyroid tissue. It can show conditions that are not seen using X-rays. This scan is requested on patients who have had an operation to remove cancer of the thyroid.
Radio Active Iodine (RAI) is administered by mouth and images are taken to determine where in the thyroid or other parts of the body the RAI is being taken up. This testing provides information not only about the size and shape of the thyroid gland, but also about its function. In addition to I-131, technetium-99m pertechnetate or iodine-123 (other similar radioactive substances) may also be used. A minimal amount of radioactive substance is used, in order to avoid damaging the thyroid gland. Pictures of the thyroid gland are then obtained at varying time periods (hours to days) after the ingestion of these substances. Thyroid scanning is typically used to evaluate patients for hyperthyroidism or thyroid cancer recurrence.
Patients who have had a total thyroidectomy for thyroid cancer may be sent for RAI scanning with potential ablation. The goal of the scan is to see if there is any remaining normal thyroid tissue (i.e. remnant) or metastatic disease. Even with a total thyroidectomy by an expert surgeon, there is usually a small remnant of thyroid tissue left behind.
Radioactive iodine scans used to be performed routinely for patients with thyroid nodules because "hot" (i.e. hyperactive nodules) were rarely cancer (less than 1%) while "cold" (i.e. underactive nodules) carried a 10% risk of cancer.