What is a thyroid scan?
Iodine is the natural molecule used by the thyroid gland to make thyroid hormone, which performs various important roles in the body. Technetium- 99m is a radioactive analogue of iodine that has less radiation than conventional radioactive iodine. Both however can be used to image the thyroid gland using a special machine called a gamma camera.
The amount of technetium uptake and/or iodine uptake can actually be measured using various imaging methods. This allows us to confirm when the thyroid gland is overactive and also allows us to determine the radio-iodine dose needed when treating the patient.
Radioiodine is also used for whole body imaging in thyroid cancer patients – see cancer staging scan.
What can I expect to happen?
The tracer is injected, and imaging of the thyroid is performed 20 minutes afterwards. Various views are taken.
If any cold areas are noted, this implies that there is non-thyroidal tissue in the thyroid gland. Normally these are benign, but cancer must be excluded. If a cold area is seen a second tracer may be indicated. This tracer is 99mTc-Sestamibi – a non-specific tumour agent. Regardless of whether the second tracer is given or not, an ultrasound is indicated, and the cold area may have to be biopsied.
