A thyroid scan is a specialized imaging procedure. Typically, a scan is used with nuclear medicine to evaluate the way your thyroid functions. Your thyroid is the gland that controls your metabolism. It’s located in the front part of your neck. Nuclear medicine uses small amounts of radioactive material to diagnose disease.
Radioactive iodine is typically used in thyroid tests, including a thyroid scan. Your thyroid and most types of thyroid cancer absorb iodine naturally. The radioactive iodine builds up in your thyroid tissue. A gamma camera or scanner detects the radioactive emissions. Your doctor will use the results of this test to evaluate how your thyroid is functioning.
Thyroid scans can help your doctor determine if your thyroid is working properly. Radioactive iodine uptake (RAIU) is added to the scan to measure your thyroid’s reaction.
A radioactive material called a radioisotope, or radionuclide “tracer,” is given to you before the test. You may get it by through an injection, a liquid, or a tablet. The tracer releases gamma rays when it’s in your body. A gamma camera or scanner can detect this type of energy from outside your body.
The camera scans your thyroid area. It tracks the tracer and measures how your thyroid processes it. The camera works with a computer to create images that detail the thyroid’s structure and function based on how it interacts with the tracer.
A thyroid scan can be used to evaluate abnormalities found in a physical exam or laboratory test. The images from this test can be used to diagnose:
- lumps, nodules (cysts), or other growths
- inflammation, or swelling
- an overactive thyroid, which is called hyperthyroidism
- an underactive thyroid, which is called hypothyroidism
- goiter, which is an abnormal enlargement of the thyroid
- thyroid cancer
An RAIU evaluates the function of the thyroid gland. When your thyroid absorbs the radioactive iodine, it processes the iodine to make thyroid hormones. By measuring the amount of radioactive iodine in your thyroid gland, your doctor can evaluate the way you’re producing thyroid hormones.
A metastatic survey is a type of thyroid scan. It’s usually reserved for people with thyroid cancer. It can determine whether thyroid cancer has spread by detecting where the iodine is absorbed. The procedure is typically performed after thyroid surgery and ablation, or removal. It can identify pieces of the thyroid that remain after surgery.
Thyroid scans are usually performed on an outpatient basis in the nuclear medicine department of a hospital. It can be administered by a nuclear medicine technologist. Your endocrinologist may or may not be there during the procedure.
Before any thyroid scan, you’ll receive radionuclide in the form of a pill, liquid, or injection. When you’ve waited the necessary amount of time for the radioactive iodine to be absorbed, you’ll return to the nuclear medicine department.
Thyroid Scan Procedure
You’ll lie down on an examination table for a thyroid scan without RAIU. The technologist will tip your head back so that your neck is extended. They’ll then use a scanner or camera to take photos of your thyroid, usually from at least three different angles. You’ll be asked to stay very still while the images are taken. The process takes about 30 minutes.
RAIU is performed six to 24 hours after taking the radionuclide. You’ll sit upright in a chair for an RAIU. The technologist will place a probe over your thyroid gland, where it will measure the radioactivity present. This test takes several minutes.
You’ll return to the nuclear medicine department to have another set of readings taken 24 hours after the test. This allows your doctor to determine the amount of thyroid hormone produced between the two exams.
Metastatic Survey Procedure
You’ll receive radioiodine in pill form for a metastatic survey. You’ll need to wait from two to seven days to allow the iodine to travel throughout your entire body.
On the day of the survey, you’ll lie down on an exam table. Scans of your body will be taken from the front and the back while you lie very still. This can be uncomfortable for some people.
After your thyroid scan, you must contact your physician for instructions on how to resume taking your thyroid medication.
The radioactive iodine in your body is passed when you urinate. You may be advised to drink extra fluids and empty your bladder often to flush out the radionuclide. You may need to be careful to protect others from potential exposure to the material. To do this, your doctor may advise you to flush twice after using the toilet for up to 48 hours after the test.
You can typically resume your normal diet and activities immediately after any thyroid scan.
There’s a small but safe amount of radiation contained in the radionuclide used in any thyroid scan. Your exposure to radiation will be minimal and within the acceptable ranges for diagnostic exams. There are no known long-term complications of having a nuclear medicine procedure.
Allergic reactions to the radionuclide material are extremely rare. The effects are mild when they occur. You may experience mild pain and redness at the injection site for a short time if you receive an injection of the radionuclide.
Even though the radiation exposure is minimal and short-term, thyroid scans are not recommended for pregnant or breastfeeding women. Your doctor may recommend that you avoid becoming pregnant or fathering a child for six months after the test if you have had a metastatic scan.
Tell your physician about any prescription or over-the-counter medications you’re taking. Discuss how they should be used before and during the test.
You may have to discontinue thyroid medication from four to six weeks before your scan. Some heart medications and any medicine containing iodine also may require adjustments.
For any thyroid scan, you may be asked to avoid certain foods that contain iodine for about a week before your procedure. Typically, you shouldn’t eat:
- dairy products
- iodized salt
- seasonings that contain iodized salt
You also should refrain from using:
- cough syrups
- supplements containing iodine
Other drugs that could affect the results of an RAIU are:
- adrenocorticotropic hormone (ACTH)
- Lugol’s solution, which contains iodine
You shouldn’t have any other imaging tests that use radioactive iodine for six weeks before your thyroid scan. A few days before your procedure, your doctor may request a blood test to confirm that your thyroid function is still abnormal. Thyroid scans are used as secondary diagnostic tools to other tests, such as blood work. A scan is not typically used when thyroid functions are normal. An exception to this is when there are nodules or goiters present.
You may have to fast for several hours before your exam. Food can affect the accuracy of the RAIU measurement.
You’ll have to remove any jewelry or other metal accessories before the test. These may interfere with the accuracy of the scan.
A doctor who specializes in nuclear imaging will evaluate the images and results of your thyroid scan. Your results will be sent in a report to your doctor.
Thyroid Scan Results
A normal thyroid scan would show no abnormalities in the size, shape, and location of the thyroid gland. Your thyroid will have an even green color on the image. Red spots on the image indicate abnormal growths in the thyroid. Normal results from a metastatic scan indicate an absence of thyroid tissue and no spread of thyroid cancer.
An abnormal thyroid scan may show a thyroid that’s enlarged or out of position, indicating a possible tumor. Abnormal measurements also may show that your thyroid gland collected too much or too little of the radionuclide.
Abnormal results of a thyroid scan may also indicate:
- colloid nodular goiter, which is a type of thyroid enlargement due to too little iodine
- Graves’ disease, which is a type of hyperthyroidism
- painless thyroiditis, which can involve switching between hyperthyroidism and hypothyroidism
- toxic nodular goiter, which is an enlargement of a nodule on an existing goiter
Metastatic Survey Results
Abnormal results from a metastatic survey will show that there are locations where the thyroid cancer has spread. The study will also show where residual thyroid tissue remains after surgical removal or ablation, which destroyed the gland.
Abnormally high levels of thyroid hormone may indicate:
- the early stage of Hashimoto’s thyroiditis, which is a chronic swelling of the thyroid
- factitious hyperthyroidism, which is an overactive thyroid caused by taking too much thyroid medication
Abnormally low levels of thyroid hormone may indicate:
- iodine overload
- subacute thyroiditis, which is an inflammation of the thyroid gland caused by a virus
- thyroid nodules or goiter
Your doctor will discuss your test results with you. If your tests show that your thyroid is not functioning the way it should, they may order more tests to help them find the right diagnosis. Depending on your condition, they might give you medications to either increase your thyroid hormone levels or decrease them. Careful follow-up is necessary to ensure that your hormone levels are normal. This will also help you avoid any health complications.