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Static imaging of amino acids does not allow differentiation of low versus high grade brain tumours. It has been shown that dynamic imaging of the amino acid analogue 18F-fluoroethyltyrosine (FET) can achieve this goal. In many centres, 11C-methionine (MET) is used for tumour imaging, but no clinical studies on the use of dynamic scanning for grading have been performed. Thirty-four patients with primary brain glioma and histopathological confirmation were retrospectively studied using 40 min dynamic MET–PET with 220 MBq 11C-methionine. In relation to histopathological grading, various metabolic indices and temporal parameters as documented by Poepperl et al. (JNM 2006;47:393–403) were analyzed. None of the evaluated static or temporal parameters allowed discrimination between high and low grade tumours. On average, low grade tumours showed washout after the initial uptake maximum, while both increases and decreases were seen for high grade tumours. Only the relative early versus late uptake ratio showed a trend towards significance (−0.16 ± 0.17 for low grade versus 0.01 ± 0.25 for high grade; p = 0.07). Unlike FET–PET, the uptake characteristics of MET-PET do not allow classification of low and high grade tumours on an individual patient basis. Since literature data indicate that both tracers have a similar performance regarding biopsy location, tumour delineation, and detection of recurrence, FET–PET should be advocated over MET–PET as its uptake mechanism also allows noninvasive grading in glioma. [ABSTRACT FROM AUTHOR]

Purpose: 18F-fluorodeoxyglucose (FDG) and 11C-methionine (MET) PET imaging studies allow the investigation of metabolism and amino acid transport in brain turnouts. Their (relative) usefulness and prognostic value in suspected recurrence or progression of primary brain tumours after previous therapy is an issue of debate. The aim of this study was to compare directly both radioligands in this setting. Methods: Cerebral uptake of FDG and MET was determined sequentially on the same day in 30 patients (21 males, nine females; age 40.4 ± 15.6 years), on average 4.0 years (range 0.1-18) after therapy for a primary brain tumour (23 grade II-IV astrocytomas, four oligodendrogliomas and three mixed oligo-astrocytomas). Images were acquired on a Siemens HR+ dedicated PET camera. Two observers scored FDG and MET scans independently. Semi-quantitative indices defined by the tumour (maximum)-to-background ratio were calculated based on manual ROI delineation and by using MET ROIs for FDG after automated co-registration. Patient follow-up was conducted until the last contact with inconspicuous clinical findings (average 41 months, range 12-62 months after PET) [(n= 10)] or until death (n=20). Results: Overall median survival was 15.0 months. MET showed pathologically increased uptake in 28/30 scans, and FDG in 17/30. The inter-observer agreement was 100% for MET and 73% for FDG. Using Kaplan-Meier survival analysis, significant differences were found for both FDG (cut-off 0.8, log-rank p=0.007) and MET (cutoff 2.2, log-rank p=0.014). The combination of FDG and MET information resulted in the highest prognostic accuracy (p=0.003), while MET alone was the best prognostic predictor in the subgroup of patients with primary astrocytoma (n=23). Conclusion: FDG and MET PET studies provide complementary prognostic information in patients with suspected brain tumour recurrence or progression after primary therapy. MET is considered the single agent of choice in the evaluation of these patients because of its sensitivity and clearer delineation of the suspected recurrence. [ABSTRACT FROM AUTHOR]