Comparison of F-18-FET PET and perfusion-weighted MRI for glioma grading: a hybrid PET/MR study

Purpose Both perfusion-weighted MR imaging (PWI) and O-(2-F-18-fluoroethyl)-L-tyrosine PET (F-18-FET) provide grading information in cerebral gliomas. The aim of this study was to compare the diagnostic value of F-18-FET PET and PWI for tumor grading in a series of patients with newly diagnosed, untreated gliomas using an integrated PET/MR scanner. Methods Seventy-two patients with untreated gliomas [22 low-grade gliomas (LGG), and 50 high-grade gliomas (HGG)] were investigated with F-18-FET PET and PWI using a hybrid PET/MR scanner. After visual inspection of PET and PWI maps (rCBV, rCBF, MTT), volumes of interest (VOIs) with a diameter of 16 mm were centered upon the maximum of abnormality in the tumor area in each modality and the contralateral unaffected hemisphere. Mean and maximum tumor-to-brain ratios (TBRmean, TBRmax) were calculated. In addition, Time-to-Peak (TTP) and slopes of time-activity curves were calculated for F-18-FET PET. Diagnostic accuracies of F-18-FET PET and PWI for differentiating low-grade glioma (LGG) from high-grade glioma (HGG) were evaluated by receiver operating characteristic analyses (area under the curve; AUC). Results The diagnostic accuracy of F-18-FET PET and PWI to discriminate LGG from HGG was similar with highest AUC values for TBRmean and TBRmax of F-18-FET PET uptake (0.80, 0.83) and for TBRmean and TBRmax of rCBV (0.80, 0.81). In case of increased signal in the tumor area with both methods (n = 32), local hot-spots were incongruent in 25 patients (78%) with a mean distance of 10.6 +/- 9.5 mm. Dynamic FET PET and combination of different parameters did not further improve diagnostic accuracy. Conclusions Both F-18-FET PET and PWI discriminate LGG from HGG with similar diagnostic performance. Regional abnormalities in the tumor area are usually not congruent indicating that tumor grading by F-18-FET PET and PWI is based on different pathophysiological phenomena