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Unlabelled: Gliomas are regionally heterogeneous tumors. The local relationship between histologic features and radiotracer uptake evaluated by PET should therefore influence analysis and interpretation of PET results on gliomas. This study explored this local relationship as a result of PET guidance of stereotactic biopsies., Methods: Local histology was confronted to the regional uptake of 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG) and 11C-methionine (11C-MET) in 14 patients with high-grade glioma diagnosed during a procedure of PET-guided stereotactic biopsies. We analyzed the uptake of both tracers in regions of interest centered on the stereotactic coordinates of 93 biopsy samples., Results: A semiquantitative analysis revealed a significant regional correlation between 11C-MET and 18F-FDG uptakes. Uptake of both tracers was significantly higher on the site of tumor samples showing anaplastic changes than in the rest of the tumor. Presence of necrosis in anaplastic areas of the tumor significantly reduced the uptake of 11C-MET., Conclusion: PET with 11C-MET and 18F-FDG may help to evaluate, in vivo, the metabolic heterogeneity of human gliomas. Anaplasia is a factor of increased uptake of both tracers, but microscopic necrosis in anaplastic areas influences their uptake differently. This finding probably relates to the differences in tracer uptake by non-neoplastic components of necrotic tumors. These results underline the complementary role of 18F-FDG and 11C-MET for the study of brain tumors and favors their use for stereotactic PET guidance of diagnostic or therapeutic procedures.

Positron emission tomography (PET) with 18F-fluoro-2-deoxy-D-glucose (FDG) is frequently used to study the metabolic correlates of movement and mental disorders. These studies generally focus on changes in the frontal cortex and the basal ganglia. The reproducibility of glucose metabolism estimates in these structures was tested in 13 normal subjects studied at rest using a standard and simple protocol. A reproducible dorsoventral metabolic gradient was demonstrated in the frontal cortex. Such a gradient was not present in the basal ganglia when the upper region of interest in the caudate nucleus, where the lower metabolic rate of glucose was probably attributable to partial volume effects, was not considered. Absolute values of glucose metabolic rates varied by 6.4 to 12.5% in the frontal cortex and by 6.8 to 14.7% in the basal ganglia. Variations in normalized values in the basal ganglia ranged from 4.0 to 8.6%. The number of subjects required to detect statistical differences in group comparison or in test-retest studies was calculated for different anticipated levels of change. With the variability detected in this experiment, less than 10 subjects were expected to be sufficient to detect a 15% change in most regions and in both types of studies.

Three patients were examined using PET with L-methyl-11C-methionine (11C-methionine) and 2-18F-fluoro-2-deoxy-D-glucose (FDG) 20 to 32 days after the occurrence of nontumoral brain hematomas. PET revealed high uptake of 11C-methionine in the area surrounding the hematoma in all three patients. In two patients, discrete spots of moderate uptake of FDG were found at the periphery of a hypometabolic area. PET studies were repeated in two patients 76 and 103 days after the bleeding, respectively, and showed a dramatic decrease in 11C-methionine uptake around the hematoma. The spots of FDG uptake disappeared on the repeated late scans. We hypothesize that the subacute gliotic reaction surrounding brain hematomas is responsible for increased uptake of 11C-methionine and for the presence of spots of FDG uptake. PET studies with 11C-methionine and FDG performed 20 to 32 days after the initial symptom are not helpful in the differentiation between neoplastic and non-neoplastic origins of an intracerebral hemorrhage since tracer uptake at the periphery of the lesion may be increased in both.