Insights Into CEST Contrast at 2 ppm in Enhancing and Nonenhancing Lesions From Glioma Patients Scanned at 7 T.

INTRODUCTION: Chemical exchange saturation transfer (CEST) has been demonstrated to provide a noninvasive opportunity to image gliomas. Preclinical ultrahigh-field MRI studies have shown the value of the 2 ppm pool; however, in vivo studies in glioma patients are currently lacking. This study aimed to explore the 7 T MRI CEST contrast of the 2 ppm in gliomas and the tumor's different components. METHODS: Twenty-one glioma patients treated at two tertiary referral centers for brain tumors in the Netherlands were scanned. Regions of interest were defined as contrast-enhancing (CE-lesion), nonenhancing (NE-lesion) tumor, and the contralateral normal-appearing white matter (CL NAWM). Magnetization transfer ratio asymmetry (MTRasym), Lorentzian difference (LD), spillover and magnetization transfer-corrected inverse difference (REX), and relaxation-compensated (AREX) were calculated for all regions of interest. RESULTS: The 2 ppm CEST pool signal between tumor regions and normal-appearing tissue was found to be significantly different for all four CEST quantification methods (MTRasym p = 0.001; LD p < 0.001; REX p = 0.008; AREX p = 0.001). The CE and NE lesions showed significantly different 2 ppm pool CEST MTRasym (p = 0.034) and LD (p = 0.052). Significantly different 2 ppm CEST REX (p = 0.005) and AREX (p = 0.001) were found between the CL NAWM and the NE lesions. CONCLUSIONS: CEST 2 ppm pool contrast was distinctive between normal-appearing white matter, enhancing and nonenhancing tumor lesions, independently of the metric used. These findings suggest that the CEST pool at 2 ppm provides a valuable noninvasive contrast for imaging gliomas.