Implementation of vascular-space-occupancy MRI at 7T

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging
• Physiology

Background:

• Vascular-space-occupancy (VASO) MRI measures cerebral blood volume by exploiting T1 differences between blood and tissue.
• Higher magnetic fields (7T) present challenges for VASO due to converging T1 values, increased BOLD contamination, geometric distortions, and power deposition.
• Non-steady-state blood spin effects are also significant at 7T with head coils.

Purpose of the Study:

• To develop and validate an optimized VASO MRI sequence for 7T.
• To overcome the technical limitations of VASO imaging at higher magnetic fields.
• To improve signal-to-noise ratio and reduce artifacts in 7T VASO functional MRI.

Main Methods:

• Implemented a magnetization-transfer-enhanced-VASO approach to maximize tissue-blood signal difference.
• Utilized a 3D fast gradient-echo sequence (low flip angle, short echo time) to minimize BOLD effects, distortion, and power deposition.
• Combined magnetization-reset with motion-sensitized-driven-equilibrium to suppress non-steady-state spins.

Main Results:

• Magnetization-transfer-enhanced-VASO boosted signal-to-noise ratio by 149% ± 13% compared to standard VASO.
• The optimized 7T VASO sequence demonstrated improved signal-to-noise ratio over 3T VASO in initial human brain fMRI results.
• The sequence successfully minimized BOLD effects, image distortion, and power deposition.

Conclusions:

• The developed VASO MRI sequence effectively addresses challenges at 7T.
• This optimized approach significantly enhances signal-to-noise ratio and image quality for functional MRI at higher magnetic fields.
• The findings suggest improved capabilities for studying brain function using VASO MRI at 7T.