Thyroid nuclear medicine scan
A thyroid nuclear medicine scan, also known as a thyroid scintiscan, is a diagnostic imaging technique that utilizes a gamma camera to assess the health and anatomy of the thyroid gland. This scan involves the administration of a radioisotope—commonly iodine 123, iodine 131, or technetium pertechnetate—allowing healthcare providers to evaluate thyroid function and identify potential abnormalities. It is particularly useful for assessing thyroid nodules, masses in the neck, and various types of thyroid cancer, including papillary and follicular cancers.
The procedure is typically noninvasive, with patients often required to discontinue certain medications prior to the scan and may need to fast if the radioisotope is administered orally. By analyzing the radioisotope uptake, which can appear as "hot" or "cold" nodules, clinicians can gather critical information regarding the nature of thyroid growths. While most thyroid abnormalities detected through this imaging technique are benign, the results guide further diagnostic processes and treatment decisions.
Safety measures are in place for specific populations, such as pregnant or breastfeeding women, who are advised against undergoing the scan. Recent advancements in imaging technology and radiative tracers have enhanced the precision and efficacy of thyroid scanning, improving diagnostic accuracy for various thyroid conditions.
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Thyroid nuclear medicine scan
ALSO KNOWN AS: Thyroid scintiscan, technetium thyroid scan
DEFINITION: The thyroid nuclear medicine scan is an imaging technique using a gamma camera to help assess the health and anatomy of the thyroid gland following the administration of a radioisotope, a radiation-emitting form of an element. The radioisotopes most commonly used are iodine 123, iodine 131, and technetium pertechnetate. Other isotopes, such as gallium 67 and thallium 201, are also used for their characteristic correlation in malignancy profiling. Still others have been scrutinized for better visualization of specific thyroid cancers.
Cancers diagnosed: Thyroid cancers (papillary, follicular, medullary, or anaplastic)
Why performed: Thyroid scans are helpful in evaluating masses in the neck area, in defining specific types of hyperthyroidism, and in assessing thyroid nodules, metastatic tumors, and thyroid cancer. They are an important tool in determining the position, size, and structure of the thyroid gland and, together with other tests, help assess thyroid function. Scans are especially helpful in evaluating patients with suspected thyroid nodules. Thyroid nodules are either functioning (hot or warm) or nonfunctioning (cold), which has important implications in assessing malignancy.
The butterfly-shaped thyroid is an endocrine gland consisting of two lobes located on either side of the trachea, connected by bridging tissue called an isthmus. Assessing thyroid health is critical because of its central role in basic human physiology. The iodine-laden hormone produced in the thyroid gland regulates oxygen consumption, body temperature, heart function, skeletal growth, skin function, and carbohydrate, lipid, and fat metabolism.
Patient preparation: The scintiscan may be performed either in an outpatient X-ray center or a hospital department. The patient is instructed to discontinue iodine-containing medications such as thyroid drugs, corticosteroids, phenothiazines, salicylates, anticoagulants, and antihistamines for several weeks to twenty-four hours prior to the scan, depending on the amount of time that the substance takes to clear from the body. If the radioisotope is to be administered orally, the patient should fast after midnight before the test. Fasting is not required for intravenous (IV) injection.
Steps of the procedure: The patient will receive the radioisotope either intravenously or orally. The patient takes the oral medication (iodine 123 or iodine 131) as either a tasteless liquid or a capsule about six hours prior to the initial imaging and twenty-four hours prior to a follow-up imaging, or receives an IV injection (pertechnetate) twenty to thirty minutes before imaging. During the scan, the patient will be lying down with the face up. The camera is then positioned over the thyroid area in the neck, and the radioactive response is displayed on a monitor and recorded on X-ray film. The procedure is usually complete in less than thirty minutes.
When evaluating thyroid function, the radioisotope iodine 123 or iodine 131 is measured at six hours and again at twenty-four hours after dosing.
After the procedure: This is a noninvasive procedure with no special precautions or instructions. Regular eating can resume two hours after imaging.
Risks: The radioactive dose is very small and is generally considered harmless, but pregnant or lactating women, as well as patients allergic to iodine, shellfish, or the tracers used in the imaging, should not undergo the procedure.
Results: Many types of thyroid pathology may be revealed through imaging; fortunately, most are not cancerous. One of the ways in which the scintiscan makes this distinction is through the assessment of thyroid nodules. A thyroid nodule is a nonspecific term for a swelling in the thyroid gland. It might be no more than an accumulation of thyroid cells or a cyst. Even though they are common, they might grow large enough to interfere with swallowing or breathing, or they can produce so much hormone that hyperthyroidism results. They can also become cancerous between 5 and 15 percent of the time.
On scintiscan, the nodules are seen as hot, warm, or cold. An area of increased radionuclide uptake may be called a hot nodule, signifying that a growth has become overactive. An area of decreased radionuclide uptake, representing low thyroid activity, is a cold nodule. A variety of conditions, including cysts, nonfunctioning benign growths, localized inflammation, or cancer, may produce a cold spot. Hot or warm nodules are rarely malignant, while almost all cancerous nodules are cold. A cold nodule is not exclusive to malignancy; however, most benign nodules, cysts, and localized inflammation areas are also cold.
Neoplasms are graded according to cell abnormality and their potential for invasiveness and growth as a guide to treatment options and prognosis. The minimally invasive, encapsulated, and well-circumscribed growth is a grade I neoplasm. As the neoplasm becomes more aggressive and infiltrates the surrounding gland and the cells become more irregular and mitotic, the neoplasm is considered grade II. Grade III describes even more extensive growth, with possible invasiveness beyond the gland and increased cellular irregularity and mitosis. Further classification is done by anatomic staging, which defines the extent of the disease process.
The results of a thyroid nuclear medicine scan serve as a guide and are almost always used in conjunction with other tests to establish a diagnosis. However, advances, including more sophisticated gamma cameras and three-dimensional (3D) imaging techniques, have allowed clinicians to obtain more precise images, leading to more accurate diagnoses. New radiative tracers can also more acutely target the thyroid tissues, also improving the diagnosis of medical conditions.
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