Rodent stroke induced by photochemical occlusion of proximal middle cerebral artery: Evolution monitored with MR imaging and histopathology

Abstract

Purpose To longitudinally investigate stroke in rats after photothrombotic occlusion of proximal middle cerebral artery (MCA) with magnetic resonance imaging (MRI) in correlation with histopathology. Materials and methods Forty-two rats were subjected to photochemical MCA occlusion and MRI at 1.5 T, and sacrificed in seven groups ( n = 6 each) at the following time points: 1, 3, 6 and 12 h, and at day 1, 3 and 9. T2-weighted (T2WI) and diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) map was performed in all rats. Contrast-enhanced T1-weighted imaging (CE-T1WI) was compared to intravital staining with Evans blue in one group for assessing blood–brain barrier (BBB) integrity. The brain was stained histochemically with triphenyl tetrazolium chloride (TTC) and processed for pathological assessment. The evolutional changes of relative lesion volume, signal intensity (SI), and the BBB integrity on MRI with corresponding histopathology were evaluated. Results The ischemic lesion volume reached a maximum around 12 h to day 1 as visualized successively by DWI, ADC map and T2WI, implicating the evolving pathology from cytotoxic edema through vasogenic edema to tissue death. The ADC of brain infarction underwent a significant reversion after 12 h, reflecting the colliquative necrosis. On CE-T1WI, BBB leakage peaked at 6 h and at day 3 with a transitional partial recovery around 24 h. The infarct volume on T2WI, DWI and ADC map matched well with that on TTC staining at 12 h and at day 1 ( p > 0.05). Conclusion The evolution of the present photothrombotic stroke model in rats could be characterized by MRI. The obtained information may help longitudinal studies of cerebral ischemia and anti-stroke agents using the same model.