Whole-Brain 4D MRA With Improved Vessel Delineation Using Undersampled Multiple Overlapping Thin-Slab Radial Acquisition.

Time-resolved arterial spin labeling (ASL)-based noncontrast 4D MRA enables visualization of cerebral arterial flow dynamic patterns and holds great potential for evaluating cerebrovascular disease. However, conventional ASL 4D MRA implementations using look-locker acquisitions are susceptible to progressive RF saturation during extended readouts, leading to substantial ASL signal attenuation and loss of vessel delineation in distal arteries. These limitations potentially hinder a wider clinical translation of 4D MRA, especially when assessment of whole-brain vascular anatomy and flow dynamics is needed. This study introduces a practical and reliable ASL 4D MRA technique for whole-brain or large volumetric imaging by integrating pulsed ASL with undersampled multiple overlapping thin-slab stack-of-stars (SOS) golden-angle radial acquisition. The proposed method was evaluated against conventional single-slab 4D MRA, 3D time-of-flight magnetic resonance angiography (TOF-MRA), and pseudocontinuous ASL (pCASL)-based 4D MRA in terms of vessel delineation, blood flow dynamics, and image quality. Compared to the other methods, the proposed method substantially reduced RF saturation effects and preserved signal intensities in distal small arteries, resulting in significantly improved vessel continuity and contrast throughout the cerebral vasculature, as well as reliably capturing complete inflow-to-outflow arterial flow dynamics with good scan efficiency and image quality. The proposed technique enables high-quality, time-resolved whole-brain angiography, offering a promising noncontrast imaging tool for comprehensive assessment of cerebral arterial hemodynamics in clinical and research applications.