Slow‐Flow‐Sensitive Artery‐Vein‐Separated Velocity Mapping ( SAM ) Phase Contrast MR Angiography: Initial Evaluation of Hand Vasculature

PURPOSE: To develop a non-contrast-enhanced MR angiography method for imaging slow-flow hand vessels that enables flow velocity measurement and artery-vein separation. METHODS: A slow-flow-sensitive artery-vein-separated velocity mapping phase-contrast MR angiography (SAM PC-MRA) technique was developed, employing multiple velocity encodings (VENCs). Ultra-low VENC acquisitions enhanced visualization of slow-flow vasculature, while high-VENC acquisitions enabled velocity mapping and artery-vein separation based on flow direction. MRA was performed on a 5 T MR system in 20 healthy volunteers and one patient with vasculitis. Vessel delineation scores, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and vascular morphology metrics were compared with conventional 3D PC-MRA at VENCs of 5 and 10 cm/s. Flow velocity measurements were validated against 2D PC. RESULTS: SAM-PC demonstrated superior visualization of small vessels with reliable artery-vein separation and flow velocity mapping. Across healthy volunteers, vessel delineation scores were significantly higher with SAM-PC compared with 3D PC at VENCs of 5 and 10 cm/s (3.9 vs. 3.3 vs. 2.9, p < 0.001), with average SNR increasing by 37.6% and 74.8% and CNR by 69.8% and 131.2%. More vessels were detected (16 571 vs. 10 132 vs. 7856, p < 0.001), and flow velocity showed no significant difference from 2D PC (p = 0.389, r = 0.835). SAM-PC in the vasculitis patient demonstrated an absence of blood flow in the necrotic fingers. CONCLUSIONS: SAM PC-MRA enables high-resolution visualization of slow-flow hand vessels with accurate time-averaged flow quantification and artery-vein separation.