Your health care professional may order one or more imaging tests to diagnose and find the cause of thyroid disease. A trained technician usually does these tests in your doctor’s office, outpatient center, or hospital. A radiologist, a doctor who specializes in medical imaging, reviews the images and sends a report for your health care professional to discuss with you.
Ultrasound
Ultrasound of the thyroid is most often used to look for, or more closely at, thyroid nodules. Thyroid nodules are lumps in your neck. Ultrasound can help your doctor tell if the nodules are more likely to be cancerous.
For an ultrasound, you will lie on an exam table and a technician will run a device called a transducer over your neck. The transducer bounces safe, painless sound waves off your neck to make pictures of your thyroid. The ultrasound usually takes around 30 minutes.
Thyroid scan
Health care professionals use a thyroid scan to look at the size, shape, and position of the thyroid gland. This test uses a small amount of radioactive iodine to help find the cause of hyperthyroidism and check for thyroid nodules. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.
For the scan, a technician injects a small amount of radioactive iodine or a similar substance into your vein. You also may swallow the substance in liquid or capsule form. The scan takes place 30 minutes after an injection, or up to 24 hours after you swallow the substance, so your thyroid has enough time to absorb it.
During the scan, you will lie on an exam table while a special camera takes pictures of your thyroid. The scan usually takes 30 minutes or less.
Thyroid nodules that make too much thyroid hormone show up clearly in the pictures. Radioactive iodine that shows up over the whole thyroid could mean you have Graves’ disease.
Even though only a small amount of radiation is needed for a thyroid scan and it is thought to be safe, you should not have this test if you are pregnant or breastfeeding.
Radioactive iodine uptake test
A radioactive iodine uptake test, also called a thyroid uptake test, can help check thyroid function and find the cause of hyperthyroidism. The thyroid “takes up” iodine from the blood to make thyroid hormones, which is why this is called an uptake test. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.
For this test, you will swallow a small amount of radioactive iodine in liquid or capsule form. During the test, you will sit in a chair while a technician places a device called a gamma probe in front of your neck, near your thyroid gland. The probe measures how much radioactive iodine your thyroid takes up from your blood. Measurements are often taken 4 to 6 hours after you swallow the radioactive iodine and again at 24 hours. The test takes only a few minutes.
If your thyroid collects a large amount of radioactive iodine, you may have Graves’ disease, or one or more nodules that make too much thyroid hormone. You may have this test at the same time as a thyroid scan.
Even though the test uses a small amount of radiation and is thought to be safe, you should not have this test if you are pregnant or breastfeeding.