Work

Human liver CEST imaging at 7 T: Impact of B1+ shimming

Year: 2025

Type: article

Abstract: Purpose To explore the feasibility of CEST imaging in the human liver at 7 T with shimming. Methods CEST MRI was performed on a 7 T whole‐body scanner with a parallel transmission (pTx) system in five healthy volunteers. Static pTx ( shimming) was applied to locally maximize the magnitude per input power within a given region of interest (ROI) of approximately 30 mm diameter (ROI shim ). Relaxation‐compensated inverse magnetization transfer ratio (MTR Rex ) values were quantified for amide protons, guanidino protons, and relayed nuclear Overhauser effect signals based on five‐pool Lorentzian fit analysis. MTR Rex values were corrected for B 1 inhomogeneities using an absolute, accurate MR fingerprinting–based mapping technique. Results Within the ROI shim , reliable MTR Rex values could be calculated for an average of 85% of voxels. The mean MTR Rex values and corresponding coefficient of variations across the group are: 0.113 ± 0.009, 8.8% for amide; 0.167 ± 0.010, 6.3% for nuclear Overhauser effect; and 0.079 ± 0.010, 12.9% for guanidino. MTR Rex values exhibit low variation between subjects, as reflected by low coefficient of variations. Conclusion In this study, we have demonstrated for the first time the feasibility of acquiring and quantifying relaxation‐compensated CEST contrasts in the human liver at ultrahigh field. The application of static pTx effectively eliminates dropouts and allows for accurate CEST contrast quantification within the selected ROI. In addition, the proposed mapping technique shows efficacy for enhanced MTR Rex B 1 corrections in the abdomen.

Source: Magnetic Resonance in Medicine

DOI: 10.1002/mrm.30557