157 Hemodynamic Imaging in Brain Metastases: ASL vs. Hypercapnic BOLD in brain metastases only hemodynamic lag significantly negatively correlated with CVR values (r = -0.73, p = 0.009). For steal regions, longer AAT was significantly related to lower perfusion (r = -0.534, p = .048), but only within GM. See Supplementary Figure 2 for scatterplots of these associations. Figure 3. Group mean values per MRI metric (AAT, CBF, hemodynamic lag and CVR) and per tissue type (GM, WM, edema, brain metastases). Error bars represent the standard deviation. Asterisks indicate significant differences between group values with * p < .05, ** p < .01, *** p < .001. Abbreviations: AAT, arterial arrival time; BM, brain metastases; CBF, cerebral blood flow; CVR, cerebrovascular reactivity; ED, edema; GM, grey matter; WM, white matter. Repeated measures correlation Repeated measures correlations were performed between each MRI metric using either the AAT binned or CBF binned ROIs (Figure 4 and Supplementary Figure 3). In non-steal regions, longer hemodynamic lag time was associated with both longer AAT (rrm = 0.712, p < .001) as well as lower CBF (rrm = -0.822, p < .001). No relationship between either AAT and hemodynamic lag (rrm = 0.063, p = .308) or CBF and hemodynamic lag (rrm = -0.002, p = 0.976) was found for steal regions. Higher CVR was related to shorter AAT (rrm = -0.833, p < .001) as well as higher CBF 6
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