Creatine mapping of the brain at 3T by CEST MRI

作者：Wang, Kexin; Huang, Jianpan; Ju, Licheng; Xu, Su; Gullapalli, Rao P.; Liang, Yajie; Rogers, Joshua; Li, Yuguo; van Zijl, Peter C. M.; Weiss, Robert G.; Chan, Kannie W. Y.; Xu, Jiadi^*

来源：Magnetic Resonance in Medicine, 2023.

DOI：10.1002/mrm.29876

• amideCEST
• arginine CEST (ArgCEST)
• chemical exchange saturation transfer (CEST)
• concentration
• creatine CEST (CrCEST)
• exchange rate
• guanidino or guanidinium CEST (GuanCEST)
• high spectral resolution (HSR) CEST
• pH mapping
• polynomial Lorentzian line-shape fitting (PLOF)
• two-step Bloch-McConnell (BM) fitting

Purpose: To assess the feasibility of CEST-based creatine (Cr) mapping in brain at 3T using the guanidino (Guan) proton resonance.Methods: Wild type and knockout mice with guanidinoacetate N-methyltransferase deficiency and low Cr and phosphocreatine (PCr) concentrations in the brain were used to assign the Cr and protein-based arginine contributions to the GuanCEST signal at 2.0 ppm. To quantify the Cr proton exchange rate, two-step Bloch-McConnell fitting was used to fit the extracted CrCEST line-shape and multi-B1 Z-spectral data. The pH response of GuanCEST was simulated to demonstrate its potential for pH mapping.Results: Brain Z-spectra of wild type and guanidinoacetate N-methyltransferase deficiency mice show a clear Guan proton peak at 2.0 ppm at 3T. The CrCEST signal contributes similar to 23% to the GuanCEST signal at B-1 = 0.8 mu T, where a maximum CrCEST effect of 0.007 was detected. An exchange rate range of 200-300 s(-1) was estimated for the Cr Guan protons. As revealed by the simulation, an elevated GuanCEST in the brain is observed when B-1 is less than 0.4 mu T at 3T, when intracellular pH reduces by 0.2. Conversely, the GuanCEST decreases when B-1 is greater than 0.4 mu T with the same pH drop.Conclusions: CrCEST mapping is possible at 3T, which has potential for detecting intracellular pH and Cr concentration in brain.