In 1951 Cassen reported the successful imaging of the thyroid gland by means of compounds containing radioactive iodine and a mechanical moving detector. The many technical advances in radioisotope detectors which has occurred since then, as well as our greater knowledge of thyroid pathophysiology, have improved the thyroid scan so that today it is an important diagnostic tool in the evaluation of thyroid disease. The thyroid scan can be used for in vivo determination of thyroid size, location, function, and position.
The most common type of radiation detector for thyroid imaging is the rectilinear scanner with a focusing collimator. The patient is given a tracer dose of a compound containing thyroid-seeking radioisotope. The detector moves stepwise over the neck of the patient and records, point by point, the distribution of radioactivity. The data is displayed as dots or dashes on paper or as varying degrees of density