| Background and purpose: Cerebral infarction is a universal cerebrovascular disease, which has been threatening human health and has a significant morbility, deformity and recurrence rate. Early diagnosis is the precondition of early therapy for cerebral infarction. The main goal of clinical therapy for cerebral infarction is to protect the ischemic penumbra(IP) and prevent it from developing towards irreversible cerebral infarction .Therefore the identification of IP and following its evolution has great importance for guiding the clinical therapy. MR diffusion weight imaging (DWI) and perfusion weighted imaging (PWI) sequence provide a new method to the early diagnosis of IP. DWI is the only imaging technique to evaluate the diffusion movement of the water molecules in vivo. When cerebral ischemia occurs, the water diffusion in focal ischemic tissue is limited.Hence there will be high signal intensity on DWI and low signal intensity on apparent diffusion coefficient (ADC) map. PWI can alter the magnetic ratio of the focal tissue and MR signal intensity by used echo planar imaging(EPI) sequence and susceptibility contrast agent, Thus the ischemic brain tissue showed relatively high signal intensity on PWI . Therefore MRI can assess IP of the superacute cerebral infarction by combining DWI with PWI. The purpose of our research was to establish an easy and stable middle cerebral artery occlusion model (MCAO) in rabbit, and to exploit the identification of IP , its maintaining time and volume by DWI and PWI sequence studies within 12 hours.A comparison of the MRI and the pathomorphological results of microscopy and electrical microscopy was carried out in order to provide a theoretical foundation for the guidance of the clinical therapy and evaluating the prognosis and curative effect.Objects and methods: 35 New Zealand rabbits regardless of male or female were randomized into two groups, 28 rabbits were included in the experimental group and 7 rabbits were classified as control group. For the experimental group, a transobital electrocoagulation was carried out to occlude the middle cerebral artery, whereas the control group only exposed the middle cerebral artery, and no electrocoagulation was performed. Coronal 5-mm thickness sections were performed with a Marconi 1.5T MRI system, and its b value was 1000s/mm2,2000s/mm2and 3000s/mm2 respectively.After MCAO, the rabbits in the experimental group and control group were examined by MR scanner at 0.5h, Ih, 2h, 4h, 6h, 8h and 12h respectively, 4 rabbits of each experimental group and 1 rabbit of each control group were classified as the above time point. The scan sequences included SE sequence TiWI, T2WI, DWI and PWI. The rabbits were rapidly decapitated after MRI scan. 2 specimens of the brain tissue in each time point which were obtained correspondently to MRI scans were taken into cut brain tissue slices every 5 mm for TTC staining. When observing their colour changes and measured their areas and photos were taken. The other 2 specimens of the brain tissue in each time point which were obtained correspondently to The MRI scans were observed by microscopy and electrical microscopy respectively.All of the MR images were processed in the work station. Artificial colour were performed for MR DWI and PWI in 0.5h, Ih, 2h, 4h, 6h, 8h and 12h after MCAO, and the volumes of abnormal signal intensity were measured on T2WI , ADC map, DWIand PWI , and ADC, rADC values were obtained on ADC maps.Statistical analysis was executed by SPSS 10.0 software packages. Enumeration data between experimental group and control group was assessed by Student's t test, and multigroup enumeration data assessed by analysis of variance. P < 0.05 was deemed significant.Results: (1) The contrast ratio of frontoparietal cortex and basal ganglia on DWI was similar to that on T2WI when b value is 1000s/mm2, and the signal intensity of frontoparietal cortex was slightly higher than that of the basal ganglia. When b value increased, the contrast ratio is also in... |
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