Spatial coefficient of variation of arterial spin labeling MRI as a cerebrovascular correlate of carotid occlusive disease.

Henri J M M Mutsaerts,Ronald M Lazar,Randolph S Marshall,Jan Petr,Iris Asllani,Reinoud P H Bokkers,Ona Wu

doi:10.1371/journal.pone.0229444

Abstract

Clinical interpretation of arterial spin labeling (ASL) perfusion MRI in cerebrovascular disease remains challenging mainly because of the method’s sensitivity to concomitant contributions from both intravascular and tissue compartments. While acquisition of multi-delay images can differentiate between the two contributions, the prolonged acquisition is prone to artifacts and not practical for clinical applications. Here, the utility of the spatial coefficient of variation (sCoV) of a single-delay ASL image as a marker of the intravascular contribution was evaluated by testing the hypothesis that sCoV can detect the effects of differences in label arrival times between ipsi- and contra-lateral hemispheres even in the absence of a hemispheric difference in CBF. Hemispheric lateralization values for sCoV and CBF were computed from ASL images acquired on 28 patients (age 73.9 ± 10.2 years, 8 women) with asymptomatic unilateral carotid occlusion. The results showed that sCoV lateralization predicted the occluded side with 96.4% sensitivity, missing only 1 patient. In contrast, the sensitivity of the CBF lateralization was 71.4%, with 8 patients showing no difference in CBF between hemispheres. The findings demonstrate the potential clinical utility of sCoV as a cerebrovascular correlate of large vessel disease. Using sCoV in tandem with CBF, vascular information can be obtained in image processing without the need for additional scan-time.

Highlights

While clinical applications of arterial spin labeling (ASL) are on the rise, interpretation of Cerebral blood flow (CBF) ASL images continues to be hampered by the uncertainty in whether the signal originates from tissue or macrovasculature
When the asymmetry index (AI) was computed between left and right hemispheres, without regard for the side of occlusion, no systematic lateralization was found for either CBF (p = 0.18) or spatial coefficient of variation (sCoV) (p = 0.34)
While predicting the side of occlusion in and of itself has limited clinical value, these findings suggest that sCoV in combination with CBF may extend the clinical utility of ASL as a cerebrovascular marker in carotid occlusive disease

Summary

Introduction

While clinical applications of ASL are on the rise, interpretation of CBF ASL images continues to be hampered by the uncertainty in whether the signal originates from tissue or macrovasculature This complication is especially relevant in diseases such as carotid steno-occlusive where hemodynamic changes are regionally dependent. Carotid occlusive patients provide a unique opportunity for clinical validation of sCoV due to of the gradual collateralization and vascular reconfiguration that occur in the occluded hemisphere [18] These changes are expected to feature a different compartmental distribution—intravascular vs tissue—of the ASL signal compared to the contra-lateral hemisphere, where the intravascular contribution is expected to be lower due to a more efficient label delivery into the tissue [11]. The central hypothesis of the study was that the asymmetry of the intravascular vs. tissue label distribution–i.e., the lateralization of sCoV − is a better predictor of carotid occlusion than the lateralization of the mean CBF

Materials and methods

Results

Discussion

Conclusions