Accelerated diffusion-weighted magnetic resonance imaging at 7 T: Joint reconstruction for shift-encoded...

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Biophysics

Background:

• Ultra-high field (7T+) MRI is crucial for detailed brain microstructure and function studies.
• High spatial-angular-temporal resolution in diffusion-weighted MRI (DW-MRI) faces challenges like short T2 relaxation and high specific absorption rate (SAR).
• Existing high-resolution DW-MRI methods often use fully-sampled multi-shot EPI, leading to long scan times and high SAR.

Purpose of the Study:

• To develop a novel technique, NAViEPI, for overcoming technical challenges in ultra-high field DW-MRI.
• To enable clinically feasible high-resolution sub-millimeter DW-MRI protocols.
• To improve signal-to-noise ratio (SNR) and reduce undersampling artifacts in DW-MRI.

Main Methods:

• Developed navigator-based interleaved EPI (NAViEPI) with matched echo spacing for imaging and navigator echoes.
• Implemented kY-shift encoding across diffusion encodings for complementary k-q-space sampling.
• Introduced JETS-NAViEPI, a joint reconstruction method with overlapping locally low-rank regularization for multi-band multi-shot acquisition.

Main Results:

• NAViEPI demonstrated simplified shot-to-shot phase variation correction due to no distortion mismatch.
• The method allows for a high number of shots with undersampled iEPI, enabling sub-millimeter resolution protocols.
• Experimental results showed 1 mm isotropic resolution multi-b-value DWI and sub-millimeter in-plane resolution fast TRACE acquisition.

Conclusions:

• NAViEPI is a promising technique for achieving high-resolution DW-MRI at ultra-high fields.
• The developed JETS-NAViEPI reconstruction effectively addresses SNR and artifact reduction.
• This advancement facilitates more detailed in vivo brain imaging for research and clinical applications.