Self-Derived Dynamic Field Map Estimation and Correction in CEST MRI

To demonstrate a self-derived, dynamic field map (∆B₀) estimation and correction method for improved CEST measurements without additional scans, especially in the presence of subject motion.

Dynamic ∆B₀ maps were derived directly from the CEST images acquired with rosette readout trajectories by segmenting the rosette k-space data. The rosette ∆B₀ mapping accuracy was validated against standard dual-echo Cartesian GRE ∆B₀ maps. The utility of dynamic ∆B₀ estimation and correction for CEST MRI was demonstrated in healthy volunteers at 3 T with and without the presence of motion.

Self-derived dynamic ∆B₀ correction substantially improved the CEST measurements compared to static ∆B₀ correction, particularly under conditions of motion. The mean differences between the motion-free and motion-corrupted global Z-spectra were 0.23% ± 0.06% (p > 0.2) and 3.10% ± 0.70% (p < 0.03) with dynamic and static ΔB₀ correction, respectively. Dynamic ΔB₀-corrected APTw values in the presence of motion also showed very high correlation (R ≥ 0.96) with motion-free values, whereas static ΔB₀-corrected APTw values showed very poor correlation (R ≤ 0.02).

By enabling dynamic ΔB₀ mapping, rosette-CEST MRI enhances the accuracy of CEST measurements in the presence of subject motion-induced B₀ fluctuations, eliminating the need for additional scans or separate alignment of ΔB₀ and saturation spectra.