Reduced B₀/B₁ ⁺ sensitivity in velocity-selective inversion arterial spin labeling using adiabatic refocusing pulses.

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Neuroimaging

Background:

• Velocity-selective arterial spin labeling (VSASL) is crucial for non-invasive perfusion imaging.
• Velocity-selective inversion (VSI) pulse trains are sensitive to magnetic field inhomogeneities (B0/B1+).
• Current VSI techniques often require complex dynamic phase-cycling (DPC) to mitigate artifacts.

Purpose of the Study:

• To implement adiabatic refocusing in VSI pulse trains for VSASL.
• To reduce B0/B1+ sensitivity and artifacts in VSI-based perfusion imaging.
• To enable artifact-free imaging using single-pair label-control subtractions, avoiding DPC.

Main Methods:

• Introduction of a Fourier-transform VSI (FT-VSI) train with adiabatic hyperbolic secant refocusing pairs.
• Comparison of FT-VSI with standard composite refocusing trains, with and without DPC.
• Evaluation of simulated velocity-selective profiles, phantom studies, and human subject imaging for artifact assessment and gray matter perfusion heterogeneity.

Main Results:

• Adiabatic refocusing significantly enhances FT-VSI robustness against B0/B1+ inhomogeneity.
• Markedly improved subtraction fidelity in simulations and phantoms compared to non-DPC composite refocusing.
• Elimination of artifacts in human subjects, leading to reduced gray matter perfusion heterogeneity.

Conclusions:

• A novel VSASL labeling train utilizing adiabatic refocusing for VSI effectively minimizes artifacts.
• This approach provides a viable alternative to DPC, overcoming its limitations.
• The new method enhances the applicability and reliability of VSASL perfusion imaging.