Objectives: Collateral blood flow is accepted as a predictive factor of tissue fate in ischemic stroke. Thus, we aimed to evaluate a new method derived from MR perfusion source images to assess collateral flow in patients with ICA/MCA occlusions.
Methods: A total of 132 patients of the prospective 1000+ study were examined. MR perfusion source images were assessed according to Δimg_n = img_n + 1 - img_n - 1 using the five-grade Higashida collateral flow rating system. Higashida scores were correlated to mismatch (MM) volume, mismatch ratio, day 6 FLAIR lesion volumes and day 90 mRS.
Results: Patients with Higashida scores 3 and 4 had significantly lower admission NIHSS, smaller FLAIR day 6 lesion volumes (p < 0.001) and higher rates of better long-term outcome (mRS 0-2, p = 0.002). There was a linear trend for the association of Higashida grade 1 (p = 0.002) and 2 (p = 0.001) with unfavourable outcome (day 90 mRS 3-6), but no significant association was found for MM volume, MM ratio and day 90 mRS. Inter-rater agreement was 0.58 (95% CI 0.43-0.73) on day 1, 0.70 (95% CI 0.58-0.81) on day 2.
Conclusion: sMRP-SI Higashida score offers a non-invasive collateral vessel and tissue perfusion assessment of ischemic tissue. The predictive value of Higashida rating proved superior to MM with regard to day 90 mRS.
Key points: • Assessment of collateral flow using subtracted dynamic MR perfusion source imaging (sMRP-SI). • sMRP-SI offers additional information about morphological characteristics of ischemic brain tissue. • sMRP-SI collateral flow assessment proves superior to mismatch volume. • Better collateral flow was significantly associated with better outcome (day 90 mRS).
Keywords: Collateral circulation; MRI; Outcome assessment; Perfusion; Stroke.