Test Details & Preparation
A thyroid scan is a type of nuclear medicine imaging. The radioactive iodine uptake test (RAIU) is also known as a thyroid uptake. It is a measurement of thyroid function, but does not involve imaging.
Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive material to diagnose and determine the severity of or treat a variety of diseases, including many types of cancers, heart disease, gastrointestinal, endocrine, neurological disorders and other abnormalities within the body. Because nuclear medicine procedures are able to pinpoint molecular activity within the body, they offer the potential to identify disease in its earliest stages as well as a patient’s immediate response to therapeutic interventions.
Nuclear medicine imaging procedures are non-invasive and, with the exception of intravenous injections, are usually painless medical tests that help physicians diagnose and evaluate medical conditions. These imaging scans use radioactive materials called radiopharmaceuticals or radiotracers.
The thyroid scan and thyroid uptake provide information about the structure and function of the thyroid. The thyroid is a gland in the neck that controls metabolism, a chemical process that regulates the rate at which the body converts food to energy.
The thyroid scan is used to determine the size, shape and position of the thyroid gland. The thyroid uptake is performed to evaluate the function of the gland. A whole-body thyroid scan is typically performed on people who have or had thyroid cancer. A physician may perform these imaging tests to determine if the gland is working properly help diagnose problems with the thyroid gland, such as an overactive thyroid gland, a condition called hyperthyroidism, cancer or other growths assess the nature of a nodule discovered in the gland detect areas of abnormality, such as lumps (nodules) or inflammation determine whether thyroid cancer has spread beyond the thyroid gland evaluate changes in the gland following medication use, surgery, radiotherapy or chemotherapy.
You will be given radioactive iodine (I-123 or I-131) in liquid or capsule form to swallow. The thyroid uptake will begin several hours to 24 hours later. Often, two separate uptake measurements are obtained at different times. For example, you may have uptake measurements at four to six hours and 24 hours.
When it is time for the imaging to begin, you will sit in a chair facing a stationary probe positioned over the thyroid gland in the neck. When the examination is completed, you may be asked to wait until the technologist checks the images in case additional images are needed. Occasionally, more images are obtained for clarification or better visualization of certain areas or structures. The need for additional images does not necessarily mean there was a problem with the exam or that something abnormal was found, and should not be a cause of concern for you. Actual scanning time for each thyroid uptake is five minutes or less. A radiologist or other physician who has specialized training in nuclear medicine will interpret the images and forward a report to your referring physician.