What information does a radioactive iodine scan provide?

In the setting of recurrent differentiated thyroid cancer, radioactive iodine scans may be used to perform functional imaging.

Functional imaging differs slightly from anatomic imaging. With anatomic imaging, pictures reveal the inner structure of a specific region of the body. With functional imaging, pictures reflect the metabolic activity of certain cells in the body.

With most types of functional imaging, special tracers are administered that may be taken up and retained by certain types of normal or abnormal cells located in different parts of the body. These tracers are radioactive, releasing small bursts of energy that can be detected with imaging instruments to generate special pictures. These pictures, which tend to be of lower resolution than anatomic pictures, may show areas of tracer uptake that reflect the metabolic activity of abnormal cells.

Radioactive iodine scans performed in the setting of recurrent thyroid cancer use 131-Iodine as a tracer. Differentiated thyroid cancer cells that have retained the ability to take up iodine may also take up 131-Iodine from the bloodstream. If a whole-body scan is performed after a patient receives a tracer dose of 131-Iodine, the images that are obtained can be examined to look for abnormal areas of increased uptake that may indicate the presence of thyroid cancer cells. A whole-body scan may reveal abnormal areas of uptake that are concerning for thyroid cancer that has spread or metastasized to the lymph nodes, the lungs, the bones, or to the central nervous system.

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