Reportage on PET imaging at the Antoine-Lacassagne Cancer centre in Nice, France. Positron Emission Tomography, or PET scan, is used in diagnosing and monitoring patients with cancer. This method enables tumours to be detected using a radioactive tracer, which accumulates heavily in cells that present a pathological hypermetabolism. Injecting the radioactive tracer. The tracer is a glucose derivative marked with a fluorine -18 molecule.