Slice-direction geometric distortion evaluation and correction with reversed slice-select gradient acquisitions

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Neuroimaging

Background:

• Accurate spatial alignment of multi-contrast MRI data is essential but challenging due to differing geometric distortions between acquisitions.
• Single-shot echo-planar imaging (EPI) is susceptible to phase-encoding direction distortion from B0 field inhomogeneities.
• High-resolution ultrahigh-field MRI (e.g., 7T) using low slice-encoding bandwidth can exhibit additional slice-direction geometric distortion.

Purpose of the Study:

• To demonstrate and characterize slice-direction geometric distortion in high-resolution 7T EPI.
• To introduce a novel pulse sequence for acquiring distortion-paired EPI data.
• To validate a gradient reversal-based method for correcting slice-direction distortion.

Main Methods:

• Acquisition of 7T EPI data using a novel pulse sequence with reversible slice-encoding gradient polarity.
• Acquisition of paired images with equal magnitude but opposite polarity slice-direction distortion.
• Application of gradient reversal software, commonly used for phase-encoding distortion, to correct slice-direction distortion.

Main Results:

• Demonstrated the presence of slice-direction geometric distortion in high-resolution 7T EPI.
• Successfully acquired paired EPI images exhibiting symmetric slice-direction distortion with opposite polarity.
• Showed that slice-direction distortion can be effectively corrected using the established gradient reversal method.

Conclusions:

• Slice-direction geometric distortion is a significant issue in high-resolution 7T EPI.
• A novel pulse sequence enables the acquisition of data suitable for distortion correction.
• Gradient reversal techniques can be effectively applied to correct slice-direction distortion, improving MRI data alignment.