Thyroid Scan

Introduction:-
A thyroid scan uses a radioactive tracer and a special camera to measure how much tracer the thyroid gland absorbs from the blood. A thyroid scan is done to find problems with the thyroid gland. A thyroid scan may be done to check for thyroid nodules, or it may be done with a radioactive iodine uptake test (RAIU) to check how well the thyroid gland is working.

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A thyroid scan can show the size, shape, and location of the thyroid gland. It can also find areas of the thyroid gland that are overactive or underactive. The camera takes pictures of the thyroid gland from three different angles. The radioactive tracer used in this test is either iodine or technetium.

A radioactive iodine uptake test measures the amount of radioactivity in your thyroid after you’ve been given a relatively small dose of radioactive iodine in pill form. Your thyroid gland absorbs iodine and uses it to make hormones. Therefore, the amount of radioactive iodine detected in your thyroid gland corresponds with the amount of hormone your thyroid is producing.

Another type of thyroid scan, a whole-body thyroid scan, may be done for people who have had thyroid cancer that has been treated. The whole-body scan can check to see if cancer has spread to other areas of the body.

Why It Is Done:-
A thyroid scan is done to:

*See whether thyroid nodules are present.
*Find the cause of an overactive thyroid gland (hyperthyroidism).
*See whether thyroid cancer has spread outside the thyroid gland. A whole-body thyroid scan will usually be done for this evaluation.

How To Prepare:-
For about a week before a thyroid scan, your doctor may ask you to avoid certain foods and medicines that can interfere with the results, including thyroid hormones and shellfish (which contain iodine). You might have to fast entirely for several hours beforehand if you’ll be given a radioactive iodine pill for the test.You might also need to have blood tests that check thyroid function.

The preparation for a radioactive iodine uptake test is almost the same as for a thyroid scan. However, because you are given radioactive iodine in pill form for an uptake test, you need to wait four to six hours, and possibly as long as a day, before having the scan. (This gives the radioactive iodine time to reach your thyroid.)

Tell your doctor if you:

*Take any medicines regularly. Be sure your doctor knows the names and doses of all your medicines. Your doctor will instruct you if and when you need to stop taking any of the following medicines that can change the thyroid scan test results.

*Thyroid hormones

*Antithyroid medicines

*Medicines that have iodine, such as iodized salt, kelp, cough syrups, multivitamins, or the heart medicine amiodarone (Cordarone, Pacerone)

*Are allergic to any medicines, such as iodine. But even if you are allergic to iodine, you will likely be able to have this test because the amount used in the tracer is so small that your chance of an allergic reaction is very low.

*Have ever had a serious allergic reaction (anaphylaxis) from any substance, such as the venom from a bee sting or from eating shellfish.

*Have had bleeding problems or take blood thinners, such as aspirin or warfarin (Coumadin).

*Have had any test using radioactive materials or iodine dye 4 weeks before the thyroid scan. These other tests may change the results of the thyroid scan.

*Are or might be pregnant.

*Are breast-feeding.

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Before a thyroid scan, blood tests may be done to measure the amount of thyroid hormones (TSH, T3, and T4) in your blood.

To prepare for a thyroid scan:

*Do not eat for 2 hours before the test.

*Do not take any antithyroid medicine for 5 to 7 days before the test.

Your doctor may ask you to eat a low-iodine diet, especially if this test is being done to check for thyroid cancer.

Just before the test, you will remove your dentures (if you wear them) and all jewelry or metal objects from around your neck and upper body.

Before a thyroid scan, you need to sign a consent form that says you understand the risks of the thyroid scan and agree to have it done. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .

How It Is Done
A thyroid scan is done in the nuclear medicine section of a hospital’s radiology department by a person trained in nuclear medicine (nuclear medicine technologist).

A radionuclide is either injected into a vein or given to you as a pill. Timing of the test then depends on the type of radionuclide your doctor uses, and whether you will also have an uptake test. If you are having only a thyroid scan and your doctor prefers to give a radionuclide by intravenous injection, the scan can be done within 30-60 minutes. If you are given radioactive iodine in pill form, you need to wait four to six hours, and possibly as long as a day, before having the scan. (This gives the radioactive iodine time to reach your thyroid.) If you’re having both a scan and the uptake test, you are likely to receive radioactive iodine in pill form. This allows one radionuclide to be used for both the scan and uptake test, instead of two, and eliminates the need for an injection.

After you’ve received the radionuclide and have waited the appropriate amount of time, a technician places a radioactivity detector-a camera specially designed to take pictures of radioactive objects – against your neck and takes several images. The camera itself doesn’t expose you to any radiation. This portion of the test usually takes about half an hour.

An uptake test only takes several minutes and is performed while you are sitting up. Using a device that resembles a Geiger counter, the doctor or technician places a probe several inches in front of your neck, where the thyroid gland is located, and measures the percentage of radioactivity that is retained by the thyroid gland. You return the next day for follow-up testing to obtain a second set of uptake readings, which are then compared with the first set to determine how much hormone has been formed and secreted in the interim.

If you get technetium, you may feel warm, flushed, and nauseated when it is given. Taking deep breaths to relax may relieve these feelings.

For this test, you will lie on your back with your head tipped backward and your neck extended. It is important to lie still during this test. A special camera (called a gamma scintillation camera) takes pictures of your thyroid gland from three different angles 4 to 6 hours after you took the iodine. The test takes about 10 minutes. Another scan is done again in 24 hours.

After a thyroid scan, you can do your regular activities. But you will be asked to take special precautions when you urinate. This is because your body gets rid of the radioactive tracer through your urine. This takes about 24 hours. It is important to flush the toilet and wash your hands thoroughly after each time you urinate.

How It Feels
You may find it uncomfortable to lie still with your head tipped backward.

Results:
How long is it before the result of the test is known?
For the thyroid scan, it takes an hour or more for the pictures to be developed and additional time for a radiologist to examine them. Your doctor will probably receive a report within a day or two. The scan will show the outline, shape, and position of your thyroid so that the doctor can determine whether it is enlarged and whether there are any suspicious growths or nodules. The scan also provides a rough measure of thyroid activity, although this has to be confirmed with a radioactive iodine uptake test.

Uptake test results are available immediately, but because the initial and follow-up readings must be compared, it may take your doctor a day or two to get back to you. To obtain results, your doctor determines an uptake value, which is the net result of how much iodine is picked up by the thyroid, how much is converted to hormone since the time of administration, and how much is either leaked or secreted into the bloodstream. (The thyroid normally secretes hormone in an orderly fashion based on physical needs; leakage is less controlled and indicates that the gland is damaged.) A low reading of radioactivity suggests that your thyroid gland has retained only a small amount of iodine. This generally indicates that the thyroid gland is not producing excess thyroid hormone, but has become inflamed and is unable to properly store the hormone, which then leaks into the bloodstream. A high reading suggests that your thyroid is overactive, producing an excessive amount of thyroid hormone.

A thyroid scan uses a radioactive tracer and a special camera to make a picture of the thyroid gland. The radioactive tracer used in this test is usually iodine or technetium. A thyroid scan is done to help find problems with the thyroid gland.

Thyroid scanĀ  Normal: A normal thyroid scan shows a small butterfly-shaped thyroid gland about 2in. long and 2in. wide with an even spread of radioactive tracer in the gland.

Thyroid scan Abnormal: An abnormal thyroid scan shows a thyroid gland that is smaller or larger than normal. It can also show areas in the thyroid gland where the activity is less than normal (cold nodules) or more than normal (hot nodules). Cold nodules may be related to thyroid cancer.

A whole-body scan will show whether iodine is in bone or other tissue (iodine uptake) after the thyroid gland has been removed for cancer. The whole-body scan can check to see if cancer has spread to other areas of the body.
Resources:
https://www.health.harvard.edu/fhg/diagnostics/thyroid-scan.shtml
http://www.webmd.com/a-to-z-guides/thyroid-scan

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