HU decreases the volume of brain tissue with elevated OEF in the border zone. The average white matter OEF map for each cohort was thresholded at 40% (dark teal), 42.5% (light teal), and 45% (white) OEF to identify the brain regions with peak oxygen metabolic stress, as a potential index of elevated stroke risk. The figure shows the average OEF map for each cohort (left), paired with the thresholded regions overlaid on a T1 atlas (right). There is a decrease in thresholded brain tissue in the cohort treated with HU when compared with those not receiving disease-modifying therapy across all thresholds, but the cohort receiving CTT has a significantly lower volume of at risk tissue compared with the HU cohort.