Introduction: Vessel-encoded arterial spin labeling (ASL) perfusion MRI is a new non-invasive method that is able to assess collateral blood flow and the perfusion territories of the brain feeding arteries.
Hypothesis: Collateral blood flow imaging with ASL MRI is feasible in acute stroke patients and can be used to study the relationship between infarct location, perfusion territories and collateral patterns, together with dynamic changes after treatment.
Method: Consecutive acute stroke patients were imaged within 24 hours of onset. Follow-up imaging was performed at discharge and/or 30 days to assess changes in vascular distribution and final infarct size. The imaging protocol contained a vessel-encoded pseudo-continuous ASL, DWI and MRA sequence.
Results: Twenty stroke patients were included (NIHSS, 10; range, 0-23). Twelve patients were treated with tPA and 3 with additional endovascular therapy. Median time from initial imaging to follow-up was 25 days (range, 3-36). 80% of the exams were interpretable. Thirteen subjects (70%) had an ischemic lesion within the expected perfusion territory; 12 within the internal carotid artery (ICA) territory and 3 from basilar artery. In 5 patients (25%), the infarct zone was fed through collateral pathways. Figure A demonstrates a patient with a left ICA occlusion and collateral flow through the anterior and posterior-communicating artery. In 2 of the 5 patients with collaterals there was a shift in the vascular distribution at FU with decline of collateralisation. Figure B shows a patient with a right-sided ICA dissection directly post endovascular therapy with collateral flow from the basilar artery and normalization of the vascular distribution after 30 days.
Conclusion: ASL can access perfusion territories and collateral blood flow in acute stroke. It may potentially be used to identify brain tissue without adequate collateral blood flow and stratify patients suitable for appropriate (endovascular) therapy.