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BACKGROUND:Because magnetic resonance diffusion-weighted imaging is sensitive to water molecule movement,it has particular advantages for early diagnosis of cerebral infarction.However,the relationship between apparent diffusion coefficient changes with ischemia time,particularly relative apparent diffusion coefficient and tissue pathological changes remains controversial.OBJECTIVE:To explore the correlation between apparent diffusion coefficient changes and pathologic changes in hyperacute cerebral infarction.DESIGN,TIME AND SETTING:A randomized,controlled,animal experiment of neuroimaging.The study was performed at the Laboratory of Radiology Department,Longgang Central Hospital of Shenzhen from October 2007 to October 2008.MATERIALS:Magnetic resonance scanner was purchased from Philips Medical Systems,Best,the Netherlands.METHODS:A total of 42 healthy,adult,New Zealand rabbits were randomly assigned into sham-operation,ischemia 0.5-,1-,2-,3-,4-,and 6-hour groups,with six animals in each group.Local cerebral ischemia model was established by right middle cerebral artery occlusion,and cranial MRI scanning and pathologic observation were performed,respectively,at 0.5,1,2,3,4,and 6 hours following ischemia.The middle cerebral artery of sham-operation group was only exposed,but not occluded.Images at the above-mentioned time points were also collected.MAIN OUTCOME MEASURES:Apparent diffusion coefficient and relative apparent diffusion coefficient values of abnormal signal on diffusion-weighted imaging were calculated and compared with pathological changes in the ischemic region.RESULTS:No abnormal diffusion-weighted imaging signals or pathological changes were observed in the sham-operation group.Abnormal signal intensity on diffusion-weighted imaging was first observed in the 0.5-hour group.Apparent diffusion coefficient and relative apparent diffusion coefficient values decreased in all middle cerebral artery occlusion rabbits and reached lowest levels at 3 hours,followed by a gradual increase.The right ischemic basal ganglia region with high signal intensity on diffusion-weighted imaging extended with increasing time of occlusion,and the pathologic outcome corresponded with MRI changes.CONCLUSION:Relative apparent diffusion coefficient values changed regularly with ischemia time and displayed good correspondence to pathological manifestations.