title: Delayed perfusion phenomenon in a rat stroke model at 1.5 T MR: an imaging sign parallel to spontaneous reperfusion and ischemic penumbra?
abstract: BACKGROUND
  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 12h post-ischemia, which appeared interrelated.
authors.affiliation: Department of Radiology, University Hospitals, Catholic University of Leuven, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: Feng
authors.initials: F
authors.lastname: Chen
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Nobuo
authors.initials: N
authors.lastname: Nagai
authors.forename: Xihe
authors.initials: X
authors.lastname: Sun
authors.forename: Walter
authors.initials: W
authors.lastname: Coudyzer
authors.forename: Jie
authors.initials: J
authors.lastname: Yu
authors.forename: Guy
authors.initials: G
authors.lastname: Marchal
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Ni
mesh_terms: D000818:Animals; D002545:Brain Ischemia / Q000175:diagnosis*; D004195:Disease Models, Animal; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000175:diagnosis*; D020521:Stroke / Q000175:diagnosis*; D013997:Time Factors