Two frame-captured images showing microvascular changes during crisis resolution in the same SCD patient.

Optical magnification, × 4.5; onscreen magnification, × 125. Focusing was aimed at the same location during crisis and crisis resolution, with the same vessel serving as its own reference baseline. (A) During crisis, there is significant reduction in vessel diameter and disappearance of capillaries and arterioles, resulting in extreme avascularity. The arrows point at the three vessels targeted for longitudinal comparison during crisis resolution. (B) An increase in vessel diameter and reappearance of capillaries and arterioles occur during crisis resolution. The vessels indicated by the arrows show a significant increase in vessel diameter. In addition, capillaries and arterioles (arrowheads) reappear during crisis resolution.