Alzheimer's Imaging Consortium.

Area of Science:

• Neuroimaging
• Biomedical Engineering

Background:

• Diffusion MRI aids in detecting neurodegeneration but traditional DTI lacks specificity.
• Multi-dimensional diffusion encoding (MDE) offers improved specificity but often at lower resolution and SNR.
• Current MDE methods face limitations in voxel resolution, hindering detailed brain microstructure analysis.

Purpose of the Study:

• To develop a Multi-dimensional Diffusion Encoding (MDE) MRI protocol with 1.8 mm isotropic resolution and clinically feasible scan time.
• To optimize MDE waveform design and employ an SNR-efficient readout for enhanced brain microstructure mapping.
• To evaluate the scan-rescan reproducibility of the developed MDE protocol for neurodegeneration studies.

Main Methods:

• A customized MDE sequence integrated linear and spherical tensor-valued diffusion encoding (LTE and STE) waveforms.
• An SNR-efficient multi-band multi-shot EPI sequence and reconstruction were utilized for data acquisition.
• Scan-rescan reproducibility was assessed in three elderly subjects across global white/gray matter and specific white matter tracts.

Main Results:

• High-quality quantitative diffusion metric maps (MD, μFA, MKa, MKi) were successfully generated using the developed MDE protocol.
• Excellent scan-rescan reproducibility was demonstrated with high Pearson correlation coefficients (r=0.951-0.995) across regions.
• The protocol achieved 1.8 mm isotropic resolution with substantial slice coverage within a ~13-minute scan time.

Conclusions:

• A novel MDE MRI protocol with 1.8 mm isotropic resolution and high scan-rescan reproducibility has been successfully developed.
• This protocol provides a foundation for more specific mapping of brain microstructure changes, particularly in regions affected by neurodegeneration.
• The combination of high resolution, efficiency, and reproducibility makes this MDE protocol suitable for clinical neuroimaging research.