PET in Tumors of the Digestive Tract
The basic principle of positron emission tomography (PET) is the use of pharmaceuticals labeled with positron-emitting isotopes. These agents are such that they can be integrated into one of the body’s metabolic pathways. Positron-emitting isotopes are characterized by a beta plus-decay, in which a positron is emitted. This positron collides with any of the numerous shell electrons of neighboring atoms and the resulting annihilation produces two 511-keV gamma rays. These two photons are detected in coincidence by the PET scanner. Additionally, the use of an integrated PET/computed tomography (CT) machine allows PET and CT images of the patient to be acquired in the same imaging session. The clinically and most widely evaluated of the labeled pharmaceuticals is fluorine-18 fluoro-2-deoxy-D-glucose (18F-FDG). This glucose analogue is transported into the cell by specific transporters and phosphorylated by hexokinase to 18F-FDG-6 phosphate. The latter is inert to further metabolic processing or to transmembrane back-transport outside the cell and therefore accumulates intracellularly.
KeywordsPositron Emission Tomography Rectal Cancer Standard Uptake Value National Comprehensive Cancer Network Primary Gastric Lymphoma
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