Quantitative evaluation of microvascular density after stroke in rats using MRI

We investigated vascular changes after stroke using magnetic resonance imaging (MRI) microvascular density (MVD) measurement. T₂ and T ₂ were measured in eight rats before and after injecting an intravascular superparamagnetic iron oxide contrast agent to derive the corresponding transverse relaxation shift. Reliability of MRI for measurement of MVD was compared with corresponding sections immunostained with von Willebrand factor (vWF) 2 weeks after stroke. The intracorrelation coefficient (ICC) and its 95% lower bound (LB) was high in the ischemic recovery region (ICC=0.753), moderate in the contralateral area of normal brain tissue (ICC=0.70), and low in the ischemic core (ICC=0.24). A very good agreement (ICC=0.85) and correlation (r=0.90) were observed using only the recovery region and normal contralateral hemisphere (ICC=0.85; 95% LB=0.78; P<0.05). The mean MRI MVD in the center of the core lesion (26±9 per mm²) was lower than in the recovery region (209±60 per mm²) or contralateral normal hemisphere (313±32 per mm²). However, large errors in MRI MVD were encountered in the ischemic core. Our data demonstrate that MRI MVD measurements can quantitatively evaluate microvascular changes in the brain tissue after stroke, if the MVD is not extremely low as in the ischemic core.