Is a Thyroid Scan?
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.
of a Thyroid Scan
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
- lumps, nodules (cysts), or other growths
- inflammation, or swelling
- an overactive thyroid, which is called
- an underactive thyroid, which is called
- goiter, which is an abnormal enlargement of the
- 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.
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
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.
from a Thyroid Scan
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.
of a 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.
for a Thyroid Scan
Tell your physician about any prescription or over-the-counter
medications you’re taking. Discuss how they should be used before and during
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.
of a Thyroid 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
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
- 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