Whole-Brain Intracellular PH Mapping of Gliomas Using High-Resolution P MR Spectroscopic Imaging at 7.0 T

Malignant tumors commonly exhibit a reversed pH gradient compared with normal tissue, with a more acidic extracellular pH and an alkaline intracellular pH (pH). In this prospective study, pH values in gliomas were quantified using high-resolution phosphorous 31 (P) spectroscopic MRI at 7.0 T and were used to correlate pH alterations with histopathologic findings. A total of 12 participants (mean age, 58 years ± 18 [SD]; seven male, five female) with histopathologically proven, newly diagnosed glioma were included between September 2018 and November 2019. The P spectroscopic MRI scans were acquired using a double-resonant P/H phased-array head coil together with a three-dimensional (3D) P chemical shift imaging sequence (5.7-mL voxel volume) performed with a 7.0-T whole-body system. The 3D volumetric segmentations were performed for the whole-tumor volumes (WTVs); tumor subcompartments of necrosis, gadolinium enhancement, and nonenhancing T2 (NCE T2) hyperintensity; and normal-appearing white matter (NAWM), and pH values were compared. Spearman correlation was used to assess association between pH and the proliferation index Ki-67. For all study participants, mean pH values were higher in the WTV (7.057 ± 0.024) compared with NAWM (7.006 ± 0.012; < .001). In eight participants with high-grade gliomas, pH was increased in all tumor subcompartments (necrosis, 7.075 ± 0.033; gadolinium enhancement, 7.075 ± 0.024; NCE T2 hyperintensity, 7.043 ± 0.015) compared with NAWM (7.004 ± 0.014; all < .01). The pH values of WTV positively correlated with Ki-67 ( = 0.74, = 0.78, = .001). In conclusion, P spectroscopic MRI at 7.0 T enabled high-resolution quantification of pH in gliomas, with pH alteration associated with the Ki-67 proliferation index, and may aid in diagnosis and treatment monitoring. P MRSI, pH, Glioma, Glioblastoma, Ultra-High-Field MRI, Imaging Biomarker, 7 Tesla © RSNA, 2023.