Functional Collateral Scores by MRI Arterial Spin Labeling in Stroke application

Abstract

Introduction: Arterial Spin Labeling (ASL) is a non-invasive perfusion technique utilizing magnetically labeled blood as endogenous tracers. However absolute quantification is confounded by several practical issues. Since ASL is sensitive to arterial transit time, any late-arriving spins due to sluggish flow or collaterals would show linear/serpiginous high signals, known as Arterial Transit Artifacts (ATA). It is found to be of high diagnostic values in cerebrovascular diseases.2. For this reason, Collateral Scores (CS)3 based on ATA has been proposed by Zaharchuk et al. (2011) to characterize the collateral stataus. In this study, we attempted to illustrate the clinical use of CS in interpreting the perfusion status by case examples taken from our cohort of stroke patients. Methods: Consecutive 136 patients with stroke symptoms from March 2015 to June 2015 with MRI and pseudo-continuous ASL examinations done in a 3T scanner (Achieva, Philips Healthcare) were retrospectively reviewed. Pseudo-continuous ASL were acquired by 2D EPI (TR = 4000 ms, TE = 11 ms, labeling-duration = 1600 ms, post-labeling-delay = 1525 ms, 17 slices with spatial resolution of 3.5 x 3.5 x 7 mm). CS is rated in regions of interest according to ASPECTS methodology as described in figure 1. Results: Two examples were shown in figure 2 and figure 3 with CS system showing different degrees of perfusion impairment and collaterals recruitment. Findings reflected different degrees of stroke severity which could assist the clinicians in diagnosis and risk stratification without resorting to the computation of cerebral perfusion. Conclusion: CS could assess cerebral perfusion semi-quantitatively and determine the patterns of perfusion deficits. Identifying perfusion abnormalities would be desirable as it could suggest pathophysiologic changes not detected by structural imaging. 4 CS might help in stroke interpretation in the acute clinical setting. Future validation of its efficacy is deemed necessary for its popularization.