Click here for Frequently Asked Questions on Radionucleotide Scans.
Radioactive isotopes, such as 123-I or 99-Tc may be taken up by the thyroid, and used to visualize the functional anatomy of the thyroid. Regions of the thyroid that are functioning and actively incorporating the isotope will be detected with a counter, forming an image of the thyroid that reflects the ability of specific regions of the thyroid to trap the isotope.Regions of the thyroid that are not functioning normally, or are filled with fluid, will not take up the isotope, and will appear as 'cold' or hypofunctioning regions on the thyroid scan.Imaging studies should be avoided in pregnant women or in women who may be uncertain as to whether they are pregnant. When doubt arises, a pregnancy test is recommended prior to the scan.
Quantification of the amount of iodine that a thyroid gland can take up may be obtained from an iodine uptake test. This test does not generate a picture of the thyroid, but involves ascertaining the percentage of radioactive iodine localized to the thyroid after a small amount of the isotope is administered. In most centers, the amount of radioactive iodine taken up is assessed a few hours after it is administered, and again 24 hrs later. This test is commonly obtained to differentiate various forms of hyperthyroidism, such as Grave's Disease, versus thyroiditis.
FAQs
Are these imaging studies using radioactive materials safe for children?
There have been no long term reports of increased thyroid problems following use of 131-I. In fact, there have been studies showing no increased incidence of thyroid cancer after diagnostic scanning in children. See Thyroid cancer after diagnostic administration of iodine-131 in childhood. Radiat Res. 2001 Jul;156(1):61-70.
I have renal failure and I am on dialysis-Can I still have a diagnostic test or treatment with radioactive iodine?
Although a pre-test or pre-treatment assessment should be done to estimate dosing, these types of tests and treatments can be safely administered to patients with kidney failure on dialysis. See Nuclear medicine studies in the dialysis patient. Semin Dial. 2002 Jul-Aug;15(4):269-76.
Is any preparation required for the scan?
Try and avoid inadvertent exposure to exogenous iodine in the form of supplements, contrast dye, kelp, or some drugs. Similarly, the utility of the scan my be compromised in patients taking thyroid hormone