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

ABSTRACT Purpose To demonstrate a self‐derived, dynamic field map (∆B 0 ) estimation and correction method for improved CEST measurements without additional scans, especially in the presence of subject motion. Methods Dynamic ∆B 0 maps were derived directly from the CEST images acquired with rosette readout trajectories by segmenting the rosette k‐space data. The rosette ∆B 0 mapping accuracy was validated against standard dual‐echo Cartesian GRE ∆B 0 maps. The utility of dynamic ∆B 0 estimation and correction for CEST MRI was demonstrated in healthy volunteers at 3 T with and without the presence of motion. Results Self‐derived dynamic ∆B 0 correction substantially improved the CEST measurements compared to static ∆B 0 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 ΔB 0 correction, respectively. Dynamic ΔB 0 ‐corrected APTw values in the presence of motion also showed very high correlation ( R ≥ 0.96) with motion‐free values, whereas static ΔB 0 ‐corrected APTw values showed very poor correlation ( R ≤ 0.02). Conclusion By enabling dynamic ΔB 0 mapping, rosette‐CEST MRI enhances the accuracy of CEST measurements in the presence of subject motion‐induced B 0 fluctuations, eliminating the need for additional scans or separate alignment of ΔB 0 and saturation spectra.