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

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering

Background:

• Chemical Exchange Saturation Transfer (CEST) MRI is sensitive to B0 field fluctuations.
• Subject motion during MRI scans can induce significant B0 variations, compromising measurement accuracy.
• Existing methods for B0 correction often require additional scans or complex post-processing.

Purpose of the Study:

• To develop and validate a self-derived, dynamic B0 field map (∆B0) estimation and correction method for CEST MRI.
• To improve CEST measurement accuracy, particularly in the presence of subject motion, without necessitating additional scans.
• To integrate dynamic ∆B0 correction directly into rosette-based CEST acquisition.

Main Methods:

• Dynamic ∆B0 maps were generated by segmenting rosette k-space data from acquired CEST images.
• The accuracy of the rosette-derived ∆B0 maps was validated against standard dual-echo Cartesian GRE ∆B0 maps.
• The method was tested in healthy volunteers at 3T, with and without induced motion, to assess its utility for CEST MRI.

Main Results:

• Dynamic ∆B0 correction significantly improved CEST measurements compared to static correction, especially under motion conditions.
• Mean differences in global Z-spectra between motion-free and motion-corrupted scans were minimal with dynamic correction (0.23% ± 0.06%) but substantial with static correction (3.10% ± 0.70%).
• Dynamic ∆B0-corrected APTw values in motion correlated highly (R ≥ 0.96) with motion-free values, unlike static-corrected values (R ≤ 0.02).

Conclusions:

• The proposed method enables dynamic ∆B0 mapping within rosette-CEST MRI acquisitions.
• This approach enhances the accuracy of CEST measurements by correcting for motion-induced B0 fluctuations.
• The dynamic correction eliminates the need for additional scans or separate alignment of ∆B0 and saturation spectra, streamlining the process.