Fluorodeoxyglucose Positron Emission Tomography Scanning

Abstract

Positron emission tomography (PET) has become a powerful tool to evaluate various biological processes involving the musculoskeletal system. The positron-emitting radioisotopes commonly used in positron emission tomography in clinical practice (F-18, C-11, and O-15) can be incorporated into a number of physiologic tracers and substrates, with the synthesis of these radiopharmaceuticals taking place in association with a radioisotope-producing cyclotron. The ability of radiopharmaceuticals to function as indicators of specific physiologic processes provides an important measure of an aspect of a disease or repair that might not be apparent on the basis of structural changes alone. The use of positron emission tomography imaging and specific radiopharmaceuticals to measure biological activity of tissue quantitatively and to relate it to structure is unique in the diagnostic imaging process. Radioactive decay involves the emission of a positron (a positive electron) from a proton excess in a radioactive nucleus. The positron travels only a few millimeters in the tissue before colliding with a negative electron. This encounter results in the annihilation of both particles, with the creation of two gamma rays of 511 keV each, the energy equivalent of the two electron masses. These annihilation photons travel in 180° opposite directions from their source (Fig. 1). For positron emission tomography, positron detectors are lined up in a ring formation around the patient and they detect the pair of gamma rays resulting from the positron-electron annihilation. The paired detectors are located on opposite sides of the patient and register a count only if both detect a photon at precisely the same time, a coincidence event (Fig. 2). Computer-controlled image-manipulation techniques are used to reconstruct a cross-sectional image from the electronic information registered from the emission coming from the patient who received an injected radiopharmaceutical for the scan. Fig. 1 In the unstable atomic nucleus, a proton decays to …