Delayed perfusion phenomenon in a rat stroke model at 1.5 T MR: An imaging sign parallel to spontaneous reperfusion and ischemic penumbra?

Abstract

Introduction Delayed perfusion (DP) sign at MR imaging was reported in stroke patients. We sought to experimentally elucidate its relation to spontaneous reperfusion and ischemic penumbra. Methods Stroke was induced by photothrombotic occlusion of middle cerebral artery in eight rats and studied up to 72 h using a 1.5 T MR scanner with T2 weighted imaging (T2WI), diffusion weighted imaging (DWI), and dynamic susceptibility contrast-enhanced perfusion weighted imaging (DSC-PWI). Relative signal intensity (rSI), relative lesion volume (rLV), relative cerebral blood flow (rCBF), PWI rLV–DWI rLV mismatch (penumbra) and DP rLV were quantified and correlated with neurological deficit score (NDS), triphenyl tetrazolium chloride (TTC) staining, microangiography (MA) and histopathology. Results The rSI and rLV characterized this stroke model on different MRI sequences and time points. DSC-PWI reproduced cortical DP in all rats, where rCBF evolved from 88.9% at 1 h through 64.9% at 6 h to 136.3% at 72 h. The PWI rLV–DWI rLV mismatch reached 10 ± 5.4% at 1 h, remained positive through 12 h and decreased to −3.3 ± 4.5% at 72 h. The incidence and rLV of the DP were well correlated with those of the penumbra ( p < 0.01, r 2 = 0.85 and p < 0.0001, r 2 = 0.96, respectively). Shorter DP durations and more collateral arterioles occurred in rats without ( n = 4) than with ( n = 4) cortex involvement ( p < 0.05). Rats without cortex involvement tended to earlier reperfusion and a lower NDS. Microscopy confirmed MRI, MA and TTC findings. Conclusions In this rat stroke model, we reproduced clinically observed DP on DSC-PWI, confirmed spontaneous reperfusion, and identified the penumbra extending to 12 h post-ischemia, which appeared interrelated.