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Introduction. The radiotracer L-[methyl-11C]methionine (Met) has long been considered the tracer of choice in CNS tumors diagnosis using positron emission tomography, combined with computed tomography (PET/CT). However, there are more and more logistic arguments for the introduction of fluorinated amino acids into diagnostics, in particular, O-2-[18F]fluoroethyl-L-tyrosine (FET), for which our institute has developed its own method of radiochemical synthesis. The aim of the study was to compare amino acid radiotracers L-[methyl-11C]methionine (Met) and O-2-[18F]fluoroethyl-L-tyrosine (FET) in the imaging of cerebral gliomasusing PET/CT. Materials and methods. PET/CT studies using Met and FET were performed in 36 patients (15 men and 21 women) aged 28 to 73 years with suspected intracerebral tumor before surgery of biopsy. Pathohistologicalstudy verified gliomas(n-31) or other tumors (n=3), inflammatory process (n=2). The analysis of results included visual comparison of images, calculation of the tumor-to-brainratio (TBR) and metabolic tumor volume for Met and PET. Results. Visual and quantitative analysis of the scans revealed that tumor uptake pattern of FET was similar to those of Met. No significant differences were found in the TBR of both radiotracers in tumors of different grades of malignancy. A strong significant correlation (r=0,9) was revealed between the TBR of Met and FET in gliomas. There were no significant differences between tumor metabolic volumes when using the same cutoff values for both radiotracers. The ROC analysis established the same diagnostic value of Met and FET in differentiating low and high grade gliomas (area under curve 0,884 and 0,881, respectively). Conclusion. Amino acid radiotracers provide comparable diagnostic information in preoperative imaging of gliomas using PET/CT, which makes it possible to recommend FET as an adequate alternative to Met for PET centers without on-site cyclotron.

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The purpose of the study was to explore the correlation between 11С-methionine (Met) uptake measured by combined positron emission and computed tomography (PET/CT) in newly diagnosed cerebral gliomas and tumor proliferative activity as measured by Ki-67 labeling index (Ki-67 LI).The results of PET/CT with 11С-methionine (PET-Met) of 236 adult patients with pretreated glial brain tumors were included in retrospective analysis. The final diagnosis of glioma according to WHO classification of CNS tumors (2007) was based on both histology and immunohistochemistry using Ki-67 antibodies. On PET-Met tumor-to normal brain uptake ratio (TBR) was calculated by dividing maximum Met uptake in the tumor (hot spot 10 mm in diameter) to activity concentration in the contralateral cortex. The Spearmen rank correlation test was used to analyze the relationships between TBR and Ki-67 LI.PET-Met analysis showed that TBR increases with an increase in the aggressiveness of the glial tumor. The differences of TBR values between gliomas grade II vs III and grade III vs IV were significant (p < 0,001). Among grades II-III gliomas Met uptake was significantly higher in oligodendroglial and mixed gliomas than in astrocytomas (p < 0,001), but the differences did not depend on Ki-67 LI.Correlation analysis demonstrated significant correlation between Ki-67 LI and TBR values (r = 0,49, p < 0,05, Spearman rank test). With analyzing glioma subgroups TBR values correlated with Ki-67 LI in diffuse astrocytomas (r = 0,52, p < 0,05), oligodendrogliomas (r = 0,40, p < 0,05), oligoastrocytomas (r = 0,47, p < 0,05) and in high-grade gliomas (r = 0,45, p < 0,05) but not in low-grade gliomas. Comparison between TBR value and Ki-67 LI in each glioma showed a lack of coincidence in 22 % of cases (high Met uptake but low Ki-67 LI and vice versa). The main reasons for such discrepancies were tumor molecular biology or incorrect biopsy target.Met uptake in diffuse gliomas correlates with proliferative activity which justifies the use of PET-Met for glioma grading. In case of mismatch between two biomarkers one should rely on the indicator that implies a higher aggressiveness of the glioma.

The aim of the study was to assess the diagnostic value of MR diffusion imaging (DWI) and hybrid positron emission and computed tomography (PET/CT) with [11C]methionine for glioma grading and to compare the spatial distribution of diffusion restriction and [11C]methionine uptake abnormalities within a tumor.Material and methods: MRI with diffusion sequences and PET/CT with [11C]methionine were performed for 46 patients with untreated histologically proven brain gliomas. Quantitative evaluation included the minimal apparent diffusion coefficient value (ADCmin) in the tumor and maximum [11C]methionine uptake ratio, measured as ratio of highest tumor count density to that of the brain cortex(tumor-to-cortex-T/Cmax). Mean measurements of ADC (ADCmean) and T/C (T/Cmean) were obtained for each tumor. The ADC and T/Cratio values for glioma grading were assessed and correlations were evaluated. In addition PET and ADC images were coregistered to each other.Results: The T/Cmax and ADCmin values were significantly negatively correlated (r=–0,82). The T/Cmean and ADCmean measurements also demonstrated the significant negative correlation (r=0,56). The T/Cmax showed best accuracy in glioma grading. Sites of maximal radiotracer uptake and minimal ADC did not match in 34% of cases and in 66% of tumors the match was partial.Conclusion: Diagnostic accuracy of PET/CT using [11C]methionine in glioma grading exceeds DWI-MRI, and for both methods it is preferable to analyze a small tumor volume. The T/C ratios and ADC measurements demonstrate the significant inverse correlations. High rate of mismatch between spatial distribution of increased [11C]methionine uptake and low ADC areas within a tumor could be a result of different biological features registered by PET and DWI.