High-resolution whole-brain diffusion MRI at 7T using radiofrequency parallel transmission

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Diffusion MRI (dMRI)

Background:

• High-resolution whole-brain diffusion MRI (dMRI) at 7 Tesla (7T) faces challenges with signal uniformity and scan time.
• Existing methods struggle to balance resolution, coverage, and acquisition speed.

Purpose of the Study:

• To investigate the utility of radiofrequency parallel transmission (pTx) for Human Connectome Project (HCP)-style whole-brain dMRI at 7T.
• To assess if pTx can overcome limitations in signal uniformity and acceleration for advanced dMRI acquisition.

Main Methods:

• Healthy subjects underwent dMRI scans using both pTx and single-transmit (1Tx) modes at 7T.
• Multiband (MB) pTx pulses were designed for sagittal slice imaging, acquiring HCP-style dMRI data and data with higher accelerations (MB3, MB4).

Main Results:

• pTx significantly improved signal uniformity across the brain, increasing temporal signal-to-noise ratio (tSNR) by ~19% compared to 1Tx.
• Enhanced fiber orientation estimation (21% decrease in dispersion) and substantially lower power deposition were achieved with pTx, enabling higher accelerations.
• Scan time was reduced by 1/3 or 1/2, or more data was acquired within the same time.

Conclusions:

• pTx addresses key limitations in slice-accelerated, high-resolution whole-brain dMRI at 7T.
• It improves flip-angle uniformity and allows for higher slice acceleration than current methods.
• pTx offers significant advantages for rapid, high-quality, high-resolution whole-brain dMRI acquisition.