Positron emission tomography – but not fludeoxyglucose


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Stefano Fanti

University of Bologna, Policlinico, Italy

Abstract

In recent years molecular imaging is acquiring importance for the evaluation of cancer patients, being complementary to conventional imaging methods as CT, MR and US. Among molecular imaging procedures, Positron Emission Tomography (PET) is the most diffuse and rapidly growing, and at present it is routinely used in patients affected by a large variety of malignant neoplastic diseases. Many papers in the literature have already demonstrated the utility of this imaging technique whose capabilities have been furthermore developed by the introduction of hybrid scanners (PET-CT). The combination of functional data (given by PET) and anatomic details (provided by CT) allows to significantly increase diagnostic accuracy, essentially due to a better specificity.

The usefulness of PET relies on its capability of investigating molecular processes by means of specific radiotracers, with the most employed being 18F-DeoxyGlucose (FDG). FDG PET scans give important information about tissues glucose consumption, usually very increased in the great majority of solid malignancies. A number of indications for PET use in clinical oncology have already been validated.

Despite FDG scans representing more than 90% of all PET scans, other positron emitter tracers are available and each one may be specific for different neoplastic diseases. In fact, some malignancies do not show increase in glucose consumption and are almost invisible with FDG: therefore other tracers have been developed to study other metabolic pathways. Tracers already in clinical use include 11C-Choline, a marker of cell membrane metabolism particularly useful for prostate cancer detection; 18F-Tyrosine and 11C-Methionine, which enable to study proteic metabolism and are successfully employed for CNS neoplastic diseases; 11C-Acetate, used for prostate cancer, hepatocellular carcinoma and other liver lesions; 18F-DOPA, suitable for movement disorders as well as for neoplastic diseases; 68Ga-DOTA-NOC, specific for somatostatin receptors overexpressed in neuroendocrine tumours.