Positron Emission Tomography

Positron emission tomography (PET) is a non-invasive imaging technique that measures the distribution of positron emitting radiopharmaceuticals. Depending on the radiolabelled tracer used, PET can determine various physiological and biochemical processes in vivo [1]. PET is highly sensitive, with the capacity to detect nanomolar concentrations of radiotracer and provides superior image resolution to conventional gamma camera imaging. Currently, PET can target several biological features of tumours including glucose metabolism, cell proliferation, perfusion and hypoxia [2]. Most malignant tumours are characterized by elevated glucose consumption, which means that their uptake of the glucose analogue [F-18] fluorodeoxyglucose (FDG) increases. The uptake mechanism and biochemical pathway of the glucose analogue [F-18] fluorodeoxyglucose (FDG) has been extensively studied in vitro and in vivo. The transport of the radiotracer through the cell membrane via glucose transport proteins and subsequent intracellular phosphorylation by the enzyme hexokinase have been identified as key steps for subsequent tissue accumulation (for recent review see [3]). As FDG-6-phosphate is not a suitable substrate for glucose-6-phosphate isomerase, and the enzyme level of glucose-6-phosphatase is generally low in tumours, FDG-6-phosphate accumulates in cells and is visualized by PET.

PET imaging using FDG has been applied for staging of cancer patients for more than a decade now. It is generally accepted that imaging the metabolic activity of tumour tissue provides sensitive and specific information about the extent of disease for many types of tumours [4].