Hadamard slice encoding for reduced-FOV diffusion-weighted imaging.

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging (MRI)

Background:

• High spatial resolution is crucial for Diffusion-Weighted Imaging (DWI) but challenging for small structures like the spinal cord.
• A novel reduced field-of-view method using 2D echo-planar radiofrequency (RF) excitation was developed for high-resolution DWI.
• This study proposes a Hadamard slice-encoding scheme to enhance slice coverage by leveraging the periodicity of the 2D echo-planar RF excitation profile.

Purpose of the Study:

• To improve the clinical utility of DWI by extending slice coverage.
• To enhance the application of high-resolution reduced field-of-view DWI techniques.

Main Methods:

• Designed 2D echo-planar RF pulse and multiband refocusing RF pulses using the Shinnar-Le Roux algorithm.
• Employed variable-rate selective excitation to shorten pulse durations.
• Utilized Hadamard-encoded images resolved through phase-preserving image reconstruction and evaluated via simulations, phantom, and in vivo experiments.

Main Results:

• The proposed Hadamard scheme successfully extended slice coverage while maintaining the original method's excitation profile and fat suppression.
• Achieved an in-plane resolution of 0.7 × 0.7 mm² with 16 slices for in vivo axial DWI of the spinal cord.

Conclusions:

• The Hadamard slice-encoding scheme effectively doubles the slice coverage for the 2D echo-planar RF reduced field-of-view DWI method.
• This enhancement is achieved without increasing the scan time, offering a significant advantage for clinical applications.