Mean microvessel segment length and radius after embolic stroke: Comparison of magnetic resonance imaging (MRI) and laser scanning confocal microscopy (LSCM)

We offer a new means of noninvasively assessing mean microvessel segment length and radius after ischemic stroke. This method involves measuring changes in T₂ and T₂^* after injecting an intravascular superparamagnetic iron oxide contrast agent and result was verified using laser scanning confocal microscopy (LSCM) of both normal brain tissue and the ischemic recovery region. Embolic stroke was induced in 8 male Wistar rats and magnetic resonance imaging (MRI) performed 1 day and 6 weeks later. On MRI taken at 6 weeks, MRI of the recovery region revealed a significant increase in mean vessel size index (VSI) (5.75 ± 0.54 vs 4.81 ± 0.39 μm; p < 0.001) and decrease in mean segment length (MSL) (16.61 ± 2.33 vs 26.52 ± 3.20 μm; p < 0.001) compared to the normal contralateral hemisphere, comparable with published values. There was also a significant correlation between MSL and VSI measured by MRI vs LSCM in the recovery region and normal contralateral hemisphere (p < 0.001). Our data suggest that a) morphological changes in the microvasculature can be measured noninvasively using MRI, and b) both MRI and LSCM give comparable information about both of these important parameters.