The metabolically active tumour volume observed in (11)C-methionine PET differs from the volume of MRI by showing areas of infiltrative tumour and distinguishing from non-tumour lesions. Differences in (11)C-methionine PET/MRI integration patterns can be assigned to tumour grades according to the WHO classification. This finding may improve tumour delineation and therapy planning for gliomas 1).
11C methionine positron emission tomography parameters are significantly correlated with histological grade and IDH1 mutation status in patients with glioma. Grade, pathological classification, molecular biomarkers, SUVmax and SUVratio were prognostic factors for PFS in a cohort of patients. The trial was registered with ClinicalTrials.gov (registration: NCT02518061) 2).
The visual assessment showed no significant difference from quantitative assessment of MET-PET with a relevant cut-off value for the differentiation of recurrent brain tumors from radiation-induced necrosis 3).
Mitamura et al., evaluated the uptake of 2-deoxy-18F-Fludeoxyglucose (FDG) and L-[methyl-11C]-methionine (MET) in patients with newly diagnosed intracranial meningiomas and correlated the results with tumor proliferation.
Data from 22 patients with newly diagnosed intracranial meningioma (12 grade I and 10 grade II) who underwent both FDG and MET brain PET/CT studies were retrospectively analyzed. The PET images were evaluated by a qualitative method and semiquantitative analysis using standardized uptake value (SUV) (SUVmax and SUVpeak) and tumor-to-reference tissue ratio (Tmax/N ratio and Tpeak/N ratio). Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens.
MET PET/CT showed a higher detection rate of meningioma than did FDG PET/CT (100 vs. 46%, respectively). The Tmax/N ratio and Tpeak/N ratio on MET PET/CT were significantly higher than those on FDG PET/CT (p < 0.001 and p < 0.001, respectively). There was a significant difference between grades I and II with respect to FDG SUVmax (p = 0.003), FDG SUVpeak (p = 0.003), FDG Tmax/N ratio (p = 0.02), FDG Tpeak/N ratio (p = 0.006), MET SUVmax (p = 0.002), MET SUVpeak (p = 0.002), MET Tmax/N ratio (p = 0.002), and MET Tpeak/N ratio (p = 0.002). There was a significant correlation between Ki-67 index and FDG PET/CT for SUVmax (p = 0.02), SUVpeak (p = 0.005), and Tpeak/N ratio (p = 0.05) and between Ki-67 index and MET PET/CT for SUVmax (p = 0.004), SUVpeak (p = 0.007), Tmax/N ratio (p = 0.002), and Tpeak/N ratio (p = 0.004).
MET PET/CT showed a high sensitivity compared with FDG PET/CT for detection of newly diagnosed WHO grades I and II intracranial meningiomas. Both FDG and MET uptake were found to be useful for evaluating tumor proliferation in meningiomas 4).
MET-PET is a sensitive technique for diagnosing persistent acromegaly and its coregistration with 3T MRI has demonstrated a better definition of the interface, extension and location of the lesion in the management of active postoperative acromegaly 5).