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

## TL;DR

This study shows that CEST MRI at 2 ppm can distinguish between different types of glioma lesions and healthy brain tissue in patients using 7T MRI.

## Contribution

The study provides the first in vivo evidence of the 2 ppm CEST pool's utility in differentiating glioma subregions at 7T.

## Key findings

- The 2 ppm CEST pool showed significant differences between tumor regions and normal tissue across multiple metrics.
- Enhancing and nonenhancing lesions had distinct CEST signals at 2 ppm.
- Nonenhancing lesions differed significantly from healthy white matter in CEST metrics.

## Abstract

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.

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.

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.

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.

We investigated the 7 T MRI 2 ppm CEST pool contrast in (1.) high‐grade and (2.) low‐grade gliomas, finding significant differences between enhancing and nonenhancing lesions (3A,B), and between the healthy appearing white matter and nonenhancing lesions (3C,D). The 2 ppm CEST pool suggests valuable noninvasive contrast for glioma imaging.