PET scan technique

PET imaging involves the use of specialised radiation sensitive cameras which detect specific radioactive isotopes that decay by positron emission. Most of the common molecules involved in organic processes can be labelled with positron emitting isotopes. Atoms of low atomic number such as carbon, oxygen, nitrogen, and fluorine have positron emitting isotopes. Molecules of specific functional import, labelled with positron emitting isotopes, can be injected intravenously into patients and an image of their distribution can be obtained using a PET camera. Although many different tracers can be manufactured and have been utilised to evaluate malignancy, this review will focus on the use of one tracer, ¹⁸F-fluorodeoxyglucose (FDG), which is the most widely used for detection of malignancy.

Malignant tumours usually demonstrate rapid cell proliferation with a proportionally increased cellular metabolism. Physiologically, this translates into increased glucose metabolism in malignant cells, a finding first reported in the 1930s.1-3 Comparable enhancements of glucose and FDG uptake in malignant cells have permitted the identification of malignancy using PET imaging.4 A unique feature of FDG as a marker of glucose metabolism is the fact that, after FDG phosphorylation, FDG-6-PO₄ does not proceed further in the metabolic pathway but remains trapped within tumour cells, thus becoming a marker of metabolism. This persistence of the tracer …