Grade and IDH genotype prediction in glioma by a hybrid PET/MR with FET-PET and DSC-PWI

Objectives: According to the revised World Health Organization (WHO) Classification of gliomas in 2016, the isocitrate dehydrogenase (IDH) mutation have been demonstrated to be essential for the diagnosis and prognosis of glioma. Both O-(2-¹⁸F-fluoroethyl)-L-tyrosine (¹⁸F-FET) PET and dynamic susceptibility contrast perfusion-weighted imaging (DSC-PWI) play a pivotal role in glioma assessment. We aimed to investigate the predictive value of FET-PET and relative cerebral blood volume (rCBV) for glioma grades and with or without IDH mutation using a hybrid PET/MR.

Methods: Fifty-two patients with newly diagnosed and untreated gliomas who underwent simultaneous ¹⁸F-FET PET scan and DSC-PWI on a hybrid PET/MR were enrolled in this retrospective study. Mean and max tumor-to-background ratios (TBR) and normalized rCBV (nCBV) were calculated based on whole tumor volume segmentation with reference to FET-PET and FLAIR images. Predictive efficacy of FET-PET and rCBV in glioma according to the 2016 WHO classification was evaluated by receiver operating characteristics analyses with the area under the curve (AUC).

Results: TBRmean, TBRmax, nCBVmean, and nCBVmax discriminated between low- and high-grade gliomas, with the highest AUC value of nCBVmean (0.920). TBRmax and nCBVmean showed significant differences between gliomas with and without IDH mutation (P < 0.05). Furthermore, TBRmean, TBRmax and nCBVmean discriminated between IDH-wildtype glioblastomas and IDH-mutated astrocytomas (P < 0.05). The combination of TBRmax and nCBVmean showed the best predictive performance (AUC, 0.903). Only nCBVmean differentiated IDH-mutated with 1p/19q codeletion oligodendrogliomas from IDH-wildtype glioblastomas (P < 0.001) (AUC, 0.829), and none of the parameters discriminated between oligodendrogliomas and astrocytomas.

Conclusions: Both FET-PET and rCBV may serve as noninvasive predictors for grades and IDH mutation status in gliomas. The combination of FET-PET with DSC-PWI parameters could improve the differentiation of IDH-mutated astrocytomas and IDH-wildtype glioblastomas. However, FET-PET and DSC-PWI demonstrated limited predictive potential in differentiating oligodendrogliomas from astrocytomas and glioblastomas.

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