PSF mapping-based correction of eddy-current-induced distortions in diffusion-weighted echo-planar imaging

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Biophysics

Background:

• Diffusion-weighted echo-planar imaging (DW-EPI) is susceptible to geometric distortions caused by eddy currents and magnetic field inhomogeneities.
• Accurate correction of these distortions is crucial for reliable analysis in diffusion tensor imaging (DTI) applications, especially at high magnetic field strengths like 7 Tesla (T).
• Existing methods for eddy-current correction can be time-consuming and may not fully account for complex, nonlinear eddy-current effects.

Purpose of the Study:

• To develop and validate a novel, rapid method for correcting diffusion-encoding direction-dependent eddy-current-induced geometric distortions in DW-EPI at 7T.
• To minimize the calibration time required for eddy-current correction.
• To integrate this correction with existing susceptibility-induced distortion correction methods for comprehensive distortion removal.

Main Methods:

• A point spread function (PSF) mapping-based eddy-current calibration method was developed to precisely determine geometric distortions, including nonlinear effects within the readout window.
• Temporal stability of eddy-current maps was assessed by performing calibrations over a 3-month period.
• Spatial variations were investigated to enable correction for arbitrary diffusion directions without repeated direct calibration. An image-based method was used for comparison.
• The PSF-based eddy-current correction was combined with a previously proposed PSF-based susceptibility-induced distortion correction approach.

Main Results:

• The proposed PSF mapping method allows for very fast 3D eddy-current calibration.
• Eddy-current maps demonstrated high temporal stability, and linear superposition of principal-axes maps yielded similar results.
• High-resolution in vivo brain imaging showed the proposed method achieved more efficient eddy-current correction compared to the image-based approach.
• The combined correction strategy successfully addressed both eddy-current and susceptibility-induced distortions.

Conclusions:

• The combination of PSF-based eddy-current and susceptibility-induced distortion correction effectively eliminates geometric distortions in DW-EPI at 7T.
• This comprehensive distortion correction enables distortion-free images, facilitating reliable analysis in DTI applications.
• The developed method offers a significant improvement in efficiency and accuracy for distortion correction in high-field MRI.