Optimization of Flip Angle in Arterial Spin Labeling-based Ultra-Short TE MRI for Brain MR Angiography

Motivation: Ultra-short TE sequences enable better visualization of flow within the vessels; However, optimal flip angle to achieve visualization of both proximal and distal vessels for ASL-based UTE-MRA remains unclear. Goal(s): To quantitatively measure signal intensity and vessel voxel count in key vascular structures, and clarify the FA that maximizes these measures. Approach: UTE MRA were acquired at FAs ranging 1-15. in 1° increments. Signal intensities and voxel counts were measured at the ACA, MCA, vertebral arteries, and carotid arteries. Results: FA 6-8° provided optimal visualization for distal part of ACA and MCA. Higher FAs provided higher signal intensity in proximal vessels. Impact: ASL-based MRA with Ultra-short TE sequence was examined with 1° FA increments and its relationship with vessel signals were quantitatively measured. This provides a guide for improving vessel visualization in UTE-MRA.