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

Abstract

This review article provides an overview of the current status of velocity-selective arterial spin labeling (VSASL) perfusion MRI and is part of a wider effort arising from the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group. Since publication of the 2015 consensus paper on arterial spin labeling (ASL) for cerebral perfusion imaging, important advancements have been made in the field. The ASL community has, therefore, decided to provide an extended perspective on various aspects of technical development and application. Because VSASL has the potential to become a principal ASL method because of its unique advantages over traditional approaches, an in-depth discussion was warranted. VSASL labels blood based on its velocity and creates a magnetic bolus immediately proximal to the microvasculature within the imaging volume. VSASL is, therefore, insensitive to transit delay effects, in contrast to spatially selective pulsed and (pseudo-) continuous ASL approaches. Recent technical developments have improved the robustness and the labeling efficiency of VSASL, making it a potentially moreThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Comparison and optimization of pCASL and VSASL for rat thoracolumbar spinal cord MRI at 9.4 T

“…For VSI, T 2 relaxation reduced the labeling efficiency to ∼0.68 of its maximum theoretical value of 1, and in the SCBF experiments the presaturation pulse further reduced overall labeling efficiency to 0.58. This is consistent with the recommended value of 0.56 for human brain applications of VSI 21 . The true labeling efficiency may be also affected by additional B 0 and $$$ {\mathrm{B}}_1^{+} $$$ imperfections or other effects such as non‐laminar flow.…”

“…A V c of 4 cm/s was used in this study based on its use in vessel suppression, 8 but a V c of 2 cm/s is recommended for VSASL applications. 21 Another limitation for VSASL in this study was the lack of a second velocity encoding module, which is recommended to constrain the width of the bolus for more accurate quantification. We used only a single velocity module because of the short PLDs and transit times.…”

“…This is consistent with the recommended value of 0.56 for human brain applications of VSI. 21 The true labeling efficiency may be also affected by additional B 0 and B + 1 imperfections or other effects such as non-laminar flow.…”

Quantification of blood–brain barrier water exchange and permeability with multidelay diffusion‐weighted pseudo‐continuous arterial spin labeling

“…Velocity-selective ASL labeling may be implemented with MCDW-GRASE readout to minimize quantification error when transit delays are severe. 70 However, sufficient SNR at longer PLD is crucial for reliable individual Ew and PSw measurement, and PSw is likely to be overestimated when Ew is close to 100%. Artery/arteriole compartment was not included in this study.…”

Arterial Spin Labeling Perfusion in Pediatric Brain Tumors: A Review of Techniques, Quality Control, and Quantification

“…The arterial spins are labeled by the VS labeling (label/control) module (VS saturation (VSS)/VS inversion (VSI)) after a saturation time (Tsat). A vascular crushing module (VCM) is then applied, with the same Vcut for acquiring as for labeling, to define the temporal width of the VSASL bolus [32].…”