Background
Positron emission tomography (PET) scanning is a noninvasive nuclear medicine diagnostic tool that is used for quantifying regional blood flow and tissue glucose metabolism in vivo. In a PET scan, radiotracers like 2-deoxy-2-[18F] fluoro-D-glucose (FDG) emit positrons—positive antiparticles of electrons—which then undergo radioactive decay. They collide with electrons to produce 2 photons, which are emitted at 180° angles. The PET scanner then detects these photons and reconstructs an image of spatial density that highlights the functional data and reveals blood flow changes. PET scans are particularly useful for studying normal versus abnormal brain activity and are most commonly used for diagnosing and monitoring neurologic disorders, certain cancers, and heart disease; however, research suggests that they may also serve a role in assessing skeletal muscle activity and identifying articular conditions like rheumatoid arthritis and osteoarthritis affecting the hand and/or wrist.1-3
Historical Overview
PET imaging was based on discoveries dating back to the late 1800s, when the physiology of brain circulation first became appreciated. The evolution from theory to medical practice did not occur until the 1950s, when modern radiotracers and technologically advanced scanning devices were introduced. After World War II, nuclear research transitioned from the Manhattan Project to scientific particle pursuits, which led to the development of safe radioisotopes and brought PET imaging closer to fruition. In 1961, Lassen and Ingvar utilized radiotracer 133 Xe to localize sensory, motor, and mental functions in a human brain. Color-coded patterns tracked brain blood flow as it related to function, which became the standard visual representation of cerebral PET images. The first large-scale use of a human positron-imaging device was developed in the 1950s to detect brain tumors with sodium iodide. Refinements led to increased sensitivity and to multiple detectors, and in 1972, one of the first PET imaging devices called PC-I was unveiled. Then, in 1975, Phelps and Hoffman constructed and introduced an improved PET scanner with hexagonal detectors. A ring-shaped PCR-I (1985) and a cylindrical shaped PCR-II (1988) detector eventually provided even better resolution and sensitivity for PET scanning.1
Description
Before the PET scan is performed, the patient is given a tracer that has been tagged with a radioactive atom that breaks down quickly to release positrons. The most commonly used tracer is FDG, which is injected, inhaled, or swallowed. Approximately 30-60 minutes after the tracer is administered, the patient is asked to lie on the scanner table that moves into the scanning ring. The PET scan may take anywhere from 30 minutes to 2 hours, during which time the patient must remain still to ensure that the images produced are clear.2,3
