18F-FDG Imaging: Molecular or Functional?

olecular imaging in oncology is defined as the noninvasive imaging of the key molecules and molecular-based events that are fundamental to the malignant state. By this definition, there is no doubt that 18F-FDG PET imaging is molecular imaging. The biologic basis for 18F-FDG PET in oncology is the Warburg effect (1). Technically, this is an increase in glycolysis under aerobic conditions and is characteristic of the malignant state. FDG is an analog for glucose and is taken up by the cell on glucose transporters and phos-phorylated by hexokinase to the glucose-6 phosphate. The FDG-6P is not a good substrate for further enzyme action by more distal enzymes of the glycolytic chain. Glucose-6-phosphate can be broken down by glucose 6-phosphatase, but this enzyme is markedly downregulate