Arterial Spin Labeling (ASL) in Neuroradiological Diagnostics – Methodological Overview and Use Cases

Abstract

Background Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI)-based technique using labeled blood-water of the brain-feeding arteries as an endogenous tracer to derive information about brain perfusion. It enables the assessment of cerebral blood flow (CBF). Method This review aims to provide a methodological and technical overview of ASL techniques, and to give examples of clinical use cases for various diseases affecting the central nervous system (CNS). There is a special focus on recent developments including super-selective ASL (ssASL) and time-resolved ASL-based magnetic resonance angiography (MRA) and on diseases commonly not leading to characteristic alterations on conventional structural MRI (e. g., concussion or migraine). Results ASL-derived CBF may represent a clinically relevant parameter in various pathologies such as cerebrovascular diseases, neoplasms, or neurodegenerative diseases. Furthermore, ASL has also been used to investigate CBF in mild traumatic brain injury or migraine, potentially leading to the establishment of imaging-based biomarkers. Recent advances made possible the acquisition of ssASL by selective labeling of single brain-feeding arteries, enabling spatial perfusion territory mapping dependent on blood flow of a specific preselected artery. Furthermore, ASL-based MRA has been introduced, providing time-resolved delineation of single intracranial vessels. Conclusion Perfusion imaging by ASL has shown promise in various diseases of the CNS. Given that ASL does not require intravenous administration of a gadolinium-based contrast agent, it may be of particular interest for investigations in pediatric cohorts, patients with impaired kidney function, patients with relevant allergies, or patients that undergo serial MRI for clinical indications such as disease monitoring. Key Points:

Acute cerebral blood flow and its connectivity in patients with anti-LGI1 encephalitis: an arterial spin labeling study

“…Notably, the cost of 18 F-FDG-PET is prohibitive for its widespread clinical utilization, and pseudocontinuous arterial spin labeling (PCASL) is being increasingly utilized as an innovative functional method. This noninvasive MRI technique utilizes magnetically labeled arterial blood water as a natural tracer to measure cerebral blood ow (CBF) [12][13][14][15][16][17] . The clinical implementation of ASL has been further re ned since the release of a consensus by the Perfusion Study Group of the International Society for Magnetic Resonance in Medicine (ISMRM) and the European Consortium for ASL in Dementia in 2015, facilitating its transition to broader clinical application 16 .…”

Evaluation of the contribution of individual arteries to the cerebral blood supply in patients with Moyamoya angiopathy: comparison of vessel-encoded arterial spin labeling and digital subtraction angiography

“…In recent years, MRI-based techniques gained importance in assessment of the cerebral perfusion without the need for application of contrast agent [1,[5][6][7][8][9]. Namely, arterial spin labeling (ASL) became increasingly important in the last few years [10][11][12][13]. ASL uses blood water as an endogenous tracer by spatially selectively inverting the longitudinal magnetization of the blood supplying the brain [5,10,14].…”