A PET scan is an NMI test that involves the combined use of positron-emitting radionuclides and emission CT (PET/CT). PET technology generates high-resolution images of body function and metabolism. PET uses radiopharmaceutical agents that are the basic elements of biologic substances. In this way, normal and abnormal biologic function of cells and organs can be determined. It produces images of molecular-level physiologic function, including glucose metabolism, oxygen utilization, blood flow, and tissue perfusion. The radiopharmaceutical agent dose is injected and emits radioactivity in the form of positrons, which are detected and transformed into a visual display by computer.
A broad spectrum of radiopharmaceutical agents are used for a PET scan. A main advantage of a PET scan derives from the positron-emitting isotopes themselves: carbon 11 (11Ca), nitrogen 13 (13N), and oxygen 15 (15O), which are present in organic molecules, and 18F, which can be substituted for hydrogen. Typically, radionuclides used in PET scans have very short half-lives (2 minutes to 2 hours).
18F is used for several purposes. Its half-life is long enough to trace biochemical reactions. It can be used to label a glucose compound, permitting imaging of a variety of tissues. 18F is administered primarily in a glucose form called fluorodeoxyglucose (FDG). FDG is highly sensitive. Neoplastic cells are hypermetabolic and appear to have an FDG affinity that results in high contrast. FDG has more than 90% specificity for myocardial viability, neoplastic processes, and infection. FDG is an outstanding tracer that can be used in many areas of the body. It is a glucose analogue and has a broad application because every cell uses glucose as fuel.
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