Clinical application and utility of arterial spin labeling MR perfusion imaging in stroke

Abstract

Arterial spin labeling (ASL) is a non-invasive perfusion technique that does not use any contrast agents. Due to its exquisite sensitivity to arterial transit time, this form of perfusion imaging might have a potential role at different stages of stroke application, from diagnosis to prognostication and treatment decisions. Despite this potential, little research to date has explored the application of this technique. This small-scale pilot study conducted retrospectively set out to investigate the clinical utility of ASL perfusion imaging in stroke and transient ischemic attack (TIA) applications.

In the stroke cohort, a newly proposed Collateral Scores (CS) system was used and evaluated. The hypothesis is that CS could indirectly characterize the collateral circulation and act as a functional indicator of the perfusion status. It could reflect the stroke severity and assist the radiologists in risk stratification and prognostication. Its associations with other MRI imaging findings – such as cerebral perfusion, degree of atherosclerosis and stroke subtypes – were also investigated. The results showed that CS could assess cerebral perfusion semi-quantitatively and could identify the collaterals and perfusion deficits. This information would be desirable as it could suggest pathophysiologic changes not detected by structural imaging.

In the TIA cohort, the association between the cerebral perfusion and small vessel disease (SVD) was investigated. The hypothesis is that SVD might be associated with general perfusion impairments involving not only the deep white matter but also the cortical grey matter. Although SVD has been commonly regarded as an incidental or subclinical finding if there are no overt neurological symptoms, the underlying cerebrovascular pathologies must be clearly characterized as they might have a critical role in cerebrovascular accidents. The results matched well with those in other studies in the literature. Hypoperfusion might be a critical contributor to the SVD severity. This association also supports the validity of the newly proposed total SVD burden scheme. It opens up the possibility that perfusion status and SVD could be used as the baseline imaging markers of brain health, which could be correlated with other information to have a more complete picture of cerebrovascular accidents.

This study demonstrated that ASL is feasible in both stroke and TIA evaluation and could be a useful adjunct for stroke risk assessment; its role in prognostication needs to be explored in future longitudinal studies. However, the current sample size is too small to draw any firm conclusions, and more work is needed. Although the primary purpose of this study was for research, we believe that these findings could increase the public awareness of SVD and perfusion imaging in clinical practice. In the future, such imaging information could be incorporated into longitudinal studies in order to clarify the prognostic values and associations with individual clinical features. (452 words)