Spatial dependency and the role of local susceptibility for velocity selective arterial spin labeling (VS‐ASL) relative tagging efficiency using accelerated 3D radial sampling with a BIR‐8 preparation

Abstract

Purpose: Velocity selective arterial spin labeling (VS-ASL) is a promising approach for non-contrast perfusion imaging that provides robustness to vascular geometry and transit times; however, VS-ASL assumes spatially uniform tagging efficiency. This work presents a mapping approach to investigate VS-ASL relative tagging efficiency including the impact of local susceptibility effects on a BIR-8 preparation. Methods: Numerical simulations of tagging efficiency were performed to evaluate sensitivity to regionally varying local susceptibility gradients and blood velocity. Tagging efficiency mapping was performed in susceptibility phantoms and healthy human subjects (N = 7) using a VS-ASL preparation module followed by a short, high spatial resolution 3D radial-based image acquisition. Tagging efficiency maps were compared to 4D-flow, B 1 , and B 0 maps acquired in the same imaging session for six of the seven subjects. Results: Numerical simulations were found to predict reduced tagging efficiency with the combination of high blood velocity and local gradient fields. Phantom experiments corroborated numerical results. Relative efficiency mapping in normal volunteers showed unique efficiency patterns depending on individual subject anatomy and physiology. Uniform tagging efficiency was generally observed in vivo, but reduced efficiency was noted in regions of high blood velocity and local susceptibility gradients. Conclusion: We demonstrate an approach to map the relative tagging efficiency and show application of this methodology to a novel BIR-8 preparation recently proposed in the literature. We present results showing rapid flow in the presence of local susceptibility gradients can lead to complicated signal modulations in both tag and control images and reduced tagging efficiency.

Velocity‐selective arterial spin labeling perfusion MRI: A review of the state of the art and recommendations for clinical implementation

“…These effects are likely to apply for all VS labeling pulses and merit further investigation. VSMRA with 0 TI can help assess the labeling efficiency in large vessels 28,42,43 …”

“…Other factors may also contribute to labeling efficiency loss, such as temporal variations of velocities 15 and rapid flow of large vessels in the presence of local susceptibility gradients 42 . These effects are likely to apply for all VS labeling pulses and merit further investigation.…”

Recent Technical Developments in ASL: A Review of the State of the Art

“…Radial trajectories have been used fairly extensively for ASL angiography (see below), and more recently for assessing the labeling efficiency of velocity‐selective ASL preparations 26 ; however, a few new methods have also explored their use for ASL perfusion imaging. In the Combined Angiography and Perfusion using Radial Imaging and ASL (CAPRIA) approach, 27 a PCASL preparation is followed by a continuous golden ratio readout.…”

Velocity‐selective excitation: Principles and applications

“…VS magnetization preparation in most VSASL studies is based on sinusoidal excitation pulses, similar to the pulse sequence of Figure 3A with α = 90° 13–16,18,20–25,27,29,31–37 . The resultant M z profile follows a cosine function of velocity (see Figure 3D, rightmost column).…”