Reducing voxel bleed in Hadamard-encoded MRI and MRS

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Signal Processing in Medical Imaging

Background:

• Hadamard encoding in MRI is susceptible to practical limitations, deviating from ideal point spread function (PSF) profiles.
• Finite radiofrequency (RF) pulse length and gradient strength introduce slice profile imperfections, causing significant cross-talk (voxel bleed).
• Voxel bleed can reach up to 17%, potentially compromising MRI-based localization, quantification, and clinical applications.

Purpose of the Study:

• To address the issue of voxel bleed in Hadamard encoding.
• To propose and validate a modified Hadamard RF pulse synthesis method.
• To improve the point spread function (PSF) and reduce cross-talk in MRI.

Main Methods:

• Developed a modified Hadamard RF pulse synthesis technique.
• Utilized computer simulations to model PSF and voxel bleed.
• Conducted in vitro and in vivo experiments to validate the proposed method.

Main Results:

• The modified Hadamard RF pulse synthesis markedly improved the PSF.
• Voxel bleed was significantly reduced from approximately 17% to below 5% per Hadamard-encoded direction.
• The proposed modification effectively mitigates practical limitations causing cross-talk.

Conclusions:

• A simple modification to Hadamard RF pulse synthesis can substantially improve the PSF.
• The enhanced method effectively reduces voxel bleed, improving localization and quantification in MRI.
• This technique offers a promising solution for increasing the clinical usefulness of Hadamard encoding in MRI.