Benefits and challenges of multi-delay arterial spin labeling in clinical practice: measuring perfusion and cerebrovascular reactivity in intracranial steno-occlusive disease

Magnetic resonance imaging (MRI) techniques have now widely replaced positron emission tomography (PET) as the modality of choice to assess cerebrovascular reactivity (CVR) and other hemodynamic parameters in intracranial steno-occlusive disease (ISOD), such as moyamoya vasculopathy (MMV). Therefore, radiologists should be aware of the choices in imaging techniques and potential pitfalls in the imaging interpretation. We developed a protocol based on multi-delay arterial spin labeling (ASL), with which, since its implementation in routine clinical practice in 2018, approximately 100 patients have been evaluated for CVR and other parameters. The protocol demonstrates clinical feasibility and utility, allowing detailed cerebral hemodynamic evaluations of individual patients that are useful for clinical decision-making. While multi-delay ASL offers benefits compared to single-delay ASL in patients with arterial transit delays, it is not completely insensitive to transit times, and further methodological improvements could mitigate this issue in the near future. Potential pitfalls in imaging acquisition and interpretation include artefacts due to motion, susceptibility, and misalignment in imaging registration, inadequate labeling, and the effects of anesthesia on CVR. This work serves as a practical guide for clinicians, radiologists, and MRI experts seeking to implement these advanced imaging methods in their institutions. CRITICAL RELEVANCE STATEMENT: Our MRI protocol, based on multi-delay ASL with a vascular challenge of acetazolamide, can be successfully used for hemodynamic assessments of patients with ISOD in clinical settings. KEY POINTS: We developed and implemented a protocol using acetazolamide-augmented multi-delay ASL for hemodynamic assessments in patients with steno-occlusive disease. Obtaining hemodynamic maps from ASL source data requires pre- and post-processing steps using customized toolboxes. CVR, if decreased, indicates hemodynamic compromise. Multi-delay ASL is not completely insensitive to delayed arterial transit, and technical improvements are needed to mitigate this.