Arterial Spin Labeling MR Perfusion in Acute Ischemic Stroke in the Era of Expanding Endovascular Therapy: ASFNR State of Practice

BACKGROUND: The therapeutic landscape of acute ischemic stroke (AIS) has been transformed by expanding endovascular therapy (EVT) criteria. With the incorporation of MR perfusion imaging in the 2026 AHA/ASA Guidelines for the early management of patients with AIS to support EVT patient selection, there is renewed energy and focus on the clinical applications of different MR perfusion techniques in AIS. A reliable, contrast-free perfusion technique with acceptable acquisition time and capability to identify salvageable tissue and assess collateral status may be utilized in certain clinical contexts. Arterial spin labeling (ASL) is a clinically feasible technique that can be considered as a valuable modality within stroke workflows and MRI-based EVT selection protocols, particularly in patients with renal insufficiency, contrast allergy, and contrast-limited settings. Although ASL has been investigated in multiple previous studies, its systematic integration into contemporary acute stroke clinical workflows has yet to be routinely adopted and standardized practical guidance in this regard is lacking. Furthermore, ASL is not yet validated in prospective EVT-selection trials to support timely reperfusion decisions. METHODS AND PURPOSE: This state-of-practice paper was developed on behalf of the American Society of Functional Neuroradiology (ASFNR) by an expert panel of neuroradiologists with expertise in cerebrovascular imaging and MR perfusion. We appraise the current evidence, clinical applications, implications for therapeutic decision-making, and translational barriers of ASL in AIS triage and EVT patient selection. We also discuss ASL challenges related to workforce capacity and reimbursement, and propose recommendations for future clinical validation and implementation. CONCLUSION: ASL may serve as a valuable adjunct within MRI-based stroke workflows by providing complementary information on ischemic penumbra and collateral status. However, validation through multicenter prospective studies for EVT patient selection, standardized acquisition protocols, and automated postprocessing quantification pipelines are needed before ASL can be routinely integrated into time-sensitive stroke workflows.