目的　阻断狗大脑中动脉建立急性脑梗塞动物模型，观察早期 Ｍ Ｒ Ｉ表现及其病理改变。方法　将 １６ 只成年狗随机分为实验组（１０ 只）和对照组（６ 只）。经颞开颅阻断一侧大脑中动脉（ Ｍ Ｃ Ａ），造成 Ｍ Ｃ Ａ 供应区急性缺血性脑梗塞，术后 ４、６、８、１２ｈ 行 Ｍ Ｒ Ｉ薄层扫描；取出动物大脑观察病理改变，测定不同时相梗塞区 Ｔ２ 时间和组织水含量。结果　梗塞 ２ｈ Ｍ Ｒ Ｉ Ｔ２ 加权可见尾状核头部、豆状核信号增高；６ｈ Ｍ Ｒ Ｉ可见尾状核、豆状核形成明确梗塞，并出现占位征象。２ｈ 电镜下已有缺血水肿改变，４ｈ 光镜下出现脑缺血水肿改变，电镜下见到血脑屏障受损。相关分析表明：病灶区 Ｔ２ 时间变化与组织水含量变化在时序上有密切关系（ｒ＝ ０．９５３７， Ｐ＜ ０．０１）。结论　 Ｍ Ｒ Ｉ可用于脑梗塞早期的诊断。急性脑梗塞早期 Ｍ Ｒ Ｉ表现的病理基础是脑水肿。 Objective To establish an animal model of acute cerebral infarction by blocking middle cerebral artery (MCAO) in dogs and observe the expression of M R I and its pathological changes in early stage. Methods Sixteen adult dogs were randomly divided into experimental group (n = 10) and control group (n = 6). One side of the middle cerebral artery (M C A) was blocked by temporal craniotomy, which caused acute ischemic cerebral infarction in the M C A supply area. M R I thin layer scanning was performed at 4, 6, 8 and 12 h after the operation. The pathological changes were observed and the infarct zone T2 at different time points and the tissue water content were measured. Results The infarction 2h M R I T2 weighted head of caudate nucleus, somatic nucleus signal increased; 6h M R I visible caudate nucleus, lentiform nucleus formed a clear infarction, and the appearance of signs. 2h electron microscopy has been ischemic edema, 4h light microscopy changes in cerebral ischemia and edema, under the electron microscope to see the blood-brain barrier damage. Correlation analysis showed that the temporal change of lesion area T2 was closely related to the change of tissue water content (r = 0.9537, P <0.01). Conclusion M R I can be used in the early diagnosis of cerebral infarction. The pathological basis for the early manifestation of M R I in acute cerebral infarction is cerebral edema.