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Thyroid scan (Radioisotope scan)

What happens during a thyroid scan and why you would have one.

A thyroid scan, sometimes called a radioisotope scan, is an isotope scan or a gamma camera scan. The scan sees if there are thyroid cancer cells in your body.

Doctors can use several different types of radioactive materials (radionuclides) to do the scan. It depends on what information they need. The most common radionuclide used is a form of radioactive iodine.

The amount of radiation is very small so it won’t harm you. The test is painless.

When you have it

It’s used sometimes as a follow up test after surgery to remove the thyroid gland.

Before the scan

For the scan, the doctors give you the radioactive iodine. This is either as an injection into a vein in your arm, or as a liquid or capsule you swallow.

  • For an injection, you’ll have the scan about an hour later.
  • By mouth, you may wait several hours or up to several days to give the iodine time to reach the parts of your body that it needs to.

For some radioisotope thyroid scans, your doctor may give you an injection 2 days before you take the iodine. This injection is a hormone stimulate to help with the uptake of iodine by the thyroid cells.

The scan

You lie on the scanner couch. The gamma camera is put over your neck for a minute or two. 

Thyroid cells are better at picking up iodine than any other cells in the body. The iodine collects in your thyroid cells and the radiation can be seen on your scan.

Some thyroid cancer cells may also pick up the iodine, but not as well as the normal thyroid cells. So thyroid cancers might show up on the scan as areas:

  • with no radiation (cold spots) inside the thyroid gland or
  • with high radiation (hot spots) outside the thyroid gland, if the cancer has spread.

This type of scan might also be used to check whether any cancer cells are left in other parts of the body after radioactive iodine treatment for papillary or follicular thyroid cancer.

After your scan

The test is painless. The amount of radiation is very small so it will not harm you. But the doctors may ask you to take some simple precautions for a few days after your scan. This is to reduce exposing others to radiation as you may be mildly radioactive for a short period of time.

Last reviewed: 
03 May 2018
  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2015

  • Inside Radiotherapy (accessed 03 May 2018)

    Nuclear Medicine Thyroid Scan

    The Royal Australia and New Zealand Radiologists