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

Purpose: Both perfusion-weighted MR imaging (PWI) and O-(2- ¹⁸ F-fluoroethyl)-L-tyrosine PET ( ¹⁸ F-FET) provide grading information in cerebral gliomas. The aim of this study was to compare the diagnostic value of ¹⁸ F-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 ¹⁸ F-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 (TBR _mean , TBR _max ) were calculated. In addition, Time-to-Peak (TTP) and slopes of time-activity curves were calculated for ¹⁸ F-FET PET. Diagnostic accuracies of ¹⁸ F-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 ¹⁸ F-FET PET and PWI to discriminate LGG from HGG was similar with highest AUC values for TBR _mean and TBR _max of ¹⁸ F-FET PET uptake (0.80, 0.83) and for TBR _mean and TBR _max 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 ¹⁸ F-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 ¹⁸ F-FET PET and PWI is based on different pathophysiological phenomena.