Nuclear medicine is a specialized area of radiology, which is the medical specialty that uses imaging to diagnose and treat diseases. In this branch of radiology, tiny amounts of radioactive material are used to assess organ structure and function. Nuclear imaging combines the study of medicine, chemistry, physics, mathematics, and computer technology, to help diagnose and treat abnormalities very early in a disease’s progression.
Because X-rays pass through the body’s tissues, such as muscles, intestines, and blood vessels, these tissues are difficult to visualize on an X-ray—unless a contrast dye is injected using cardiac catheterization. However, nuclear imaging allows doctors to see and analyze organ and tissue structure as well as their functions.
To do this, a very small amount of a radioactive substance is used. The substance is called a radiopharmaceutical (also referred to as a radionuclide or radioactive tracer). There are different types of radiopharmaceuticals including forms of the elements thallium, technetium, gallium, iodine, and xenon. The type of radiopharmaceutical used depends on the body part and type of study necessary.
After a radiopharmaceutical has been administered using an intravenous (IV) line, and collected in the area under study, radiation will be given off; this is monitored by a radiation detector, and the most common type of detector is called a gamma camera. When this special camera detects radiation during a nuclear scan, digital signals are sent to a computer. The areas where the radiation collects in larger amounts, appearing brighter on the scan image, are called "hot spots.” And the areas that do not absorb as much radiation, and appear less bright, are "cold spots."
In result, doctors can better analyze, diagnose, and treat conditions such as heart disease, various cancers, tumors, cysts, abscesses, hematomas, or organ enlargement. A nuclear scan can also be used to examine organ function and blood circulation.
In planar, or flat, imaging, the gamma camera remains stationary, resulting in two-dimensional (2D) images of the area being studied. Single photon emission computed tomography (or SPECT) produces axial images—or slices—of an area, because the camera rotates around the patient. These slices are similar to those performed by a computerized tomography (CT) scan. In certain scans, such as positron emission tomography (PET) scans, three-dimensional (3D) images can be produced using SPECT data.
There are several types of nuclear scans including those that analyze how the heart wall moves as well as whether the heart is both getting and expelling enough blood. For example, a PET scan provides information about blood flow through the coronary arteries (or blood vessels) that supply the heart. A PET F-18 FDG (fluorodeoxyglucose) scan uses glucose in determining if any heart tissue has had permanent damage due to decreased blood flow, helping decide which procedure, such as an angioplasty, stenting, or valve surgery, may be appropriate.
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