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18F-fluorodeoxyglucose PET/CT in cancer imaging.

By far the most widely used and successful PET radiotracer is 18F-fluorodeoxyglucose (FDG). Most PET radiotracers, including FDG, require a cyclotron for generation. Other PET radiotracers have limited clinical usefulness as they have very short physical half lives (Table 1). Fluorine-18 has a physical half-life of 110 minutes, allowing distribution of FDG to sites in reasonable proximity to the supplying cyclotron. Metabolically active cells including tumours accumulate FDG within the cytoplasm. FDG is taken into cells via glucose transporter proteins and phosphorylated by hexokinase. It is then ‘trapped’ within the cell as it is resistant to further glycolysis; its strong negative charge prevents passage back across the cell membrane. FDG is also taken up by activated macrophages, leading to positive uptake in a range of benign infectious and inflammatory pathologies (Table 2).