RF Pulse Designs for Velocity-Selective MRA at Low Field Strengths

Velocity‐selective (VS) RF pulses can differentiate flowing blood from background tissue, and have been utilized for non-contrast intracranial, abdominal, and peripheral angiography at 3T. Here, we explore RF pulse designs for intracranial VS-MRA at low field strengths including 0.55T. We evaluate pulse performance using simulations that incorporate realistic levels of B₀ variation, B₁⁺ variation, and gradient distortions. Compared to 3T, simulations indicate 22% - 38% sharper velocity transitions and/or 50% - 60% less signal loss at 0.55T. We also show that gradient distortions can lead to “stripe” artifacts and can be mitigated with pre-emphasis.