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

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), PWIrLV-DWIrLV mismatch (penumbra) and DPrLV 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 It through 64.9% at 6 h to 136.3% at 72 h. The PWIrLV-DWIrLV 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. (C) 2006 Elsevier Ireland Ltd. All rights reserved.