Grading of glioma and prediction of IDH mutation status via longitudinal relaxation time in rotating frame mapping on 5-T magnetic resonance imaging: added value to amide proton transfer-weighted imaging

Background: Accurate preoperative glioma grading and isocitrate dehydrogenase (IDH) mutation status prediction via conventional magnetic resonance imaging (MRI) remain challenging. We aimed to evaluate the performance of longitudinal relaxation time in rotating frame (T1rho) mapping and amide proton transfer (APT)-weighted chemical exchange saturation transfer (CEST) for grading gliomas and predicting IDH mutation status using 5-T MRI. Methods: Fifty patients with histopathologically confirmed glioma underwent 5-T MRI, including T2-weighted, T1-weighted, T1rho mapping, APT-weighted, and contrast-enhanced T1-weighted imaging. The T1rho and APT parameters were measured at the solid tumor portion, peritumoral edema, and contralateral normal-appearing white matter. In addition to absolute lesion values, the relative values (rT1rho and rAPT) were defined as the difference between the lesion and white matter. Differences between low-grade glioma (LGG) and high-grade glioma (HGG) and between IDH mutant-type and IDH wild-type were evaluated via the Mann-Whitney U test. Receiver operating characteristic (ROC) analyses were performed to assess the performance of each parameter and T1rho-plus-APT combination. Results: Among the 50 patients, 12 had LGG, 38 had HGG, 19 had the IDH mutant type, and 31 had IDH wild type. Compared with LGGs, HGGs exhibited significantly greater T1rho, rT1rho, APT, and rAPT values in both tumor and edema areas (P≤0.036). ROC analysis of individual parameters revealed that T1rho in edema achieved the highest area under the curve (AUC) in differentiating HGG from LGG (AUC, 0.974; sensitivity, 97.4%; specificity, 91.7%). With the combination of T1rho in edema and rAPT in tumor, the AUC further improved to 0.978 (sensitivity, 92.1%; specificity, 100%). Compared with the IDH mutant-type group, the IDH wild-type group had significantly greater T1rho and rT1rho values in tumor, T1rho and rT1rho values in edema, and APT and rAPT values in tumor (P≤0.003). T1rho in the edema achieved the highest AUC (0.883) in differentiating IDH wild type from IDH mutant type (sensitivity, 90.3%; specificity, 89.5%). Significant differences were noted between grade 2, 3, and 4 gliomas (P≤0.007). Conclusions: Both T1rho mapping and APT-CEST can be used to grade gliomas and differentiate IDH mutational status. Combining these two techniques further aids in the differentiation of HGG from LGG.