High slew-rate head-only gradient for improving distortion in echo planar imaging: Preliminary experience

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Gradient Coil Technology

Background:

• Echo planar imaging (EPI) is susceptible to image distortions.
• Conventional whole-body gradient coils limit achievable slew rates for EPI.
• Reducing EPI distortion is crucial for accurate in vivo human brain imaging.

Purpose of the Study:

• To evaluate the impact of high gradient slew rates (up to 700 T/m/s) on EPI distortion.
• To assess the effectiveness of a dedicated, head-only gradient coil for reducing EPI artifacts.
• To demonstrate the feasibility of high-resolution, whole-brain EPI with reduced distortion.

Main Methods:

• Performed simulation studies to predict echo spacing and distortion reduction.
• Installed a 42-cm inner diameter, asymmetric transverse coil head gradient in a 3T MRI system.
• Conducted in vivo human brain imaging on five subjects at various gradient slew rates.

Main Results:

• Reduced EPI echo spacing by 48% compared to whole-body gradient coils.
• Achieved up to 25-26% (simulation) and 19% (in vivo) improvement in signal dropout.
• Demonstrated whole-brain imaging at 1.5 mm isotropic resolution with good coverage, linearity, and low distortion.

Conclusions:

• High slew rate EPI using a compact head gradient coil substantially reduces image distortion in human brain imaging.
• This technique offers potential benefits for non-EPI pulse sequences.
• The findings support improved diagnostic accuracy and advanced neuroimaging applications.