Iodide I-123

Iodide I-123 (as sodium Iodide I-123) is a radioactive isotope of iodine used in nuclear medicine for the diagnostic study of thyroid disease. Following oral administration, I-123 is absorbed through the gastrointestinal tract and is taken up by the thyroid gland. After incorporation, a gamma camera is used to detect the decay by electron capture to tellurium-123.

Iodine is commonly used in thyroid function diagnostic tests as this gland normally absorbs iodine through the diet for formation of the thyroid hormones triiodothyronine (T3) and its prohormone, thyroxine (T4). Radioactive I-123 in particular is effective for this use as its half-life of approximately 13.13 h (hours) is ideal for the 24-h (hour) iodine uptake test and it has a reduced radiation burden as compared to I-131.