[Nuclear magnetic resonance and positron emission tomography: diagnostic potential in tissue characterization]

Nuclear magnetic resonance (NMR) and positron emission tomography (PET) are among the most advanced methodologies providing, with different physical approaches, diagnostic images of the body. In this framework, NMR and PET are particularly well known, not only for the high quality of their present results, but also for the expectations of further developments at clinical and diagnostic level. Common feature of NMR and PET is the capability of associating the anatomical image with information on the physico-chemical and/or biochemical properties of tissues. NMR imaging (MRI) is in fact based upon the acquisition of signals, whose intensities indirectly but closely depend upon particular physico-chemical and biophysical properties of biological tissues. NMR spectroscopy (MRS) and PET allow, on the other hand, quantitative studies on metabolic reactions, as they occur in intact tissues, in vivo and in situ. This review is aimed at summarizing the basic principles of tissue characterization by NMR and PET and discussing their perspectives of clinical application. Emphasis will be given to the special requirements of tissue characterization by these methodologies, referring to the need of improving accuracy and precision of measurements, as well as at evaluating, on a quantitative basis, the performance of the equipment.