Introduction to imaging brain tumor metabolism with positron emission tomography (PET)

The need for prompt and detailed evaluation of cancers and their treatment is requiring increasingly sophisticated methodologies for in vivo assessment. Morphological detail as provided by CT and MRI has yielded significant advances in diagnostic medicine. In spite of such advances, the means of achieving the clinical goals of improved quality and quantity of life in many cancer patients remain elusive. It is becoming increasingly evident that only with the addition of complementary physiological and biochemical data will further advances occur. While neither in vivo morphological imaging with CT or MRI nor physiological imaging with PET or MRS can provide the resolution of microscopic or cellular level assessment, all can provide macroscopic or regional data. With PET, however, exploration of the kinetics or chemical processes occurring at the cellular level is providing a "biological resolution" not heretofore achieved with in vivo imaging. Application of this complementary morphological and biochemical diagnostic information will likely lead to significant advances in patient management in the immediate future, most of which would probably not be achievable using any individual technique. Efficacy studies should be performed, however, when introducing any new high-technology methodology into clinical practice. A number of retrospective and prospective trials on PET applications in clinical oncology are ongoing sponsored by organizations such as the Institute for Clinical PET and the Western PET Association. Detailed studies also are underway to estimate the "cost" of delivery of PET services to the community (146). Numerous PET feasibility studies in animal models have demonstrated that no one radiotracer serves as the best agent for tumor imaging in all cases. Such studies with radiolabeled amino acids, sugars, and nucleoside derivatives, representatives of the major classes of biomolecules, have demonstrated variable tumor uptake dependent on such parameters as the type of cancer, organ of origin, animal host, and chemical structure of the radioligand. Detailed analysis of tracer uptake using multiple ligands in a variety of animal tumor models and clinical patients suggests that while given types of cancers may be better imaged with certain radiotracers, the use of multitracer imaging provides the specific details necessary for appropriate interpretation of tumor status. In addition, in cases where the diagnosis is uncertain, such information could have a significant impact on patient management by reducing the diagnostic differential. In spite of the many successes achieved with FDG in brain tumor imaging, the most well-known example of the problems that can arise with PET image interpretation is with the use of this agent.(ABSTRACT TRUNCATED AT 400 WORDS)