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Thyroid Nuclear Medicine Scan
Procedure: Nm
Bodypart: Head
Patient Group: Female Male Child
Technique
What it is
Other terms: Thyroid Radionuclide Scan
A thyroid nuclear medicine scan is a diagnostic procedure to evaluate the thyroid
gland, which is located in the front of the neck and controls the metabolism of the
body. A radioactive substance that concentrates in the thyroid is taken orally or
injected into a vein (intravenously), or both. There are three types of radioactive
iodine used in these scans. A special camera is used to take an image of the
distribution of the radioactive substance in and around the thyroid gland. This is
interpreted to evaluate thyroid function and to diagnose abnormalities. Although
other imaging methods exist for evaluating thyroid disease, thyroid scanning is
the most commonly used and is the most cost-effective.
A gamma scan of the human thyroid gland revealing
cancer
© eNotes (Custom Medical Stock Photo. Reproduced
by permission.)
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Purpose
A thyroid scan can help assess the overall structure and function of the thyroid. It can be used to identify benign cancers,
to assess nodules, to evaluate masses, to locate the source of a painful gland, to assess gland size, to find differentiated
carcinomas, and to identify thyroid tissue. A thyroid scan may be ordered by a physician when the gland becomes abnormally
large, especially if the enlargement is greater on one side, or when hard lumps (nodules) are felt. The scan can be helpful in
determining whether the enlargement is caused by a diffuse increase in the total amount of thyroid tissue or by a nodule or
nodules. The thyroid scan plays a critical role in the diagnosis of thyroid cancer.
When other laboratory studies show an overactive thyroid (hyperthyroidism) or an underactive thyroid (hypothyroidism), a
radioactive iodine uptake scan is often used to confirm the diagnosis. A thyroid scan is often performed in conjunction with this
scan. Thyroid radionuclide scanning is being considered as a means to screen individuals at risk for thyroid disease following
radiation therapy.
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Procedure
Persons
A nuclear medicine technologist administers the radioactive substance to the patient and operates the equipment that produces
the scan. The nuclear medicine technologist obtains pertinent medical history from the patient and will explain the nature of the
test. All data collected by the technologist are interpreted by a physician who is a specialist in nuclear medicine or a radiologist.
Patients usually obtain the test results from their physician or the physician who requested the thyroid tests.
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Preparation
Certain medications can interfere with iodine uptake. These include certain cough medicines, some oral contraceptives, and
thyroid medications. The patient is usually instructed to stop taking these medicines for a period of time before the test. This
period may range from several days up to three to four weeks, depending on the amount of time the medicine takes to clear
from the body.
Other nuclear medicine scans and x ray studies using contrast material performed within the past 60 days may affect this test.
Therefore, patients should tell their doctors if they have had either of these types of studies before the thyroid scan is begun,
to avoid inaccurate results.
Some institutions prefer that the patient have nothing to eat or drink after midnight on the day before the radioactive liquid or
capsule is to be taken. A normal diet can usually be resumed two hours after the radioisotope is taken. Dentures, jewelry, and
other metallic objects must be removed before the scanning is performed. No other physical preparation is needed.
The patient should understand that there is no danger of radiation exposure to themselves or others. Only very small amounts
of radioisotope are used. The total amount of radiation absorbed is often less than the dose received from ordinary x rays. The
scanner or camera does not emit any radiation, but detects and records it from the patient.
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Precautions
Women who are pregnant should not have this test. Any person with a history of allergy to iodine, such as those with shellfish
allergies, should notify the physician before the procedure is performed.
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Process
This test is performed in a radiology facility, either in an outpatient x ray center or a hospital department. Most often, the patient
is given the radioactive substance in the form of a tasteless liquid or capsule. It may be injected into a vein (intravenously)
in some instances. Images will be taken at a specified amount of time after this, depending on the radioisotope used. Most
often, scanning is done 24 hours later, if the radioisotope is given orally. If it is given intravenously, the scan is performed
approximately 20 minutes later.
For a thyroid scan, the patient is positioned lying down on his or her back, with the head tilted back. The radionuclide scanner,
also called a gamma camera, is positioned above the thyroid area as it scans. This takes 30-60 minutes.
The uptake study may be done with the patient sitting upright in a chair or lying down. The procedure is otherwise the same as
described for the thyroid scan. It takes approximately 15 minutes. There is no discomfort involved with either study.
A thyroid scan may also be referred to as a thyroid scintiscan. The name of the radioactive substance used may be incorporated
and the study called a technetium thyroid scan or an iodine thyroid scan. The radioactive iodine uptake scan may be called by
its initials, an RAIU test, or an iodine uptake test.
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After procedure
No isolation or special precautions are needed after a thyroid scan. The patient should check with his or her physician about
restarting any medications that were stopped before the scan.
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Results
Normal results
A normal scan will show a thyroid of normal size, shape, and position. The amount of radionuclide uptake by the thyroid will be
normal according to established laboratory figures. There will be no areas where radionuclide uptake is increased or decreased.
Abnormal results
An area of increased radionuclide uptake may be called a hot nodule or "hot spot." This means that a benign growth is overactive.
Despite the name, hot nodules are unlikely to be caused by cancer.
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An area of decreased radionuclide uptake may be called a cold nodule or "cold spot." This indicates that this area of the thyroid
gland is underactive. A variety of conditions, including cysts, nonfunctioning benign growths, localized inflammation, or cancer
may produce a cold spot.
A thyroid nuclear medicine scan is rarely sufficient to establish a clear diagnosis. Frequently, the information revealed will need
to be combined with data from other studies to determine the problem.
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Consideration
Importance
Although other imaging methods exist for evaluating thyroid disease, thyroid scanning is the most commonly used and is the
most cost-effective.
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Risks
There are no risks with this procedure.
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Citations
114 - "Thyroid Nuclear Medicine Scan." Encyclopedia of Medicine. Ed. Jacqueline L. Longe. Thomson Gale, 2002. eNotes.com.
2006. 5 Mar, 2007 <http://health.enotes.com/medicine-encyclopedia/thyroid-nuclear-medicine-scan>
115 - "Thyroid Nuclear Medicine Scan." Encyclopedia of Cancer. Ed. Ellen Thackery. Thomson Gale, 2002. eNotes.com. 2006.
5 Mar, 2007 <http://health.enotes.com/cancer-encyclopedia/thyroid-nuclear-medicine-scan>
116 - "Thyroid Radionuclide Scan." Encyclopedia of Nursing & Allied Health. Ed. Kristine Krapp. Thomson Gale, 2002.
eNotes.com. 2006. 5 Mar, 2007 <http://health.enotes.com/nursing-encyclopedia/thyroid-radionuclide-scan>
114, 115, 116
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