兔脑微栓塞模型脑血流动力学的CT灌注动态变化

Changes of cerebral hemodynamics in CT perfusion imaging of rabbit models with cerebral microembolism

目的探讨兔脑微栓塞模型CT灌注成像(CT perfusion imaging,CTPI)脑血流动力学的动态变化规律。方法 30只新西兰兔,随机分成两组,A组:假手术对照组5只,B组:微栓塞组25只。经颈外动脉向颈内动脉注入直径约0.5 mm的SiO2颗粒10枚,分别于栓塞后30 min、3 h、6 h、12 h及24 h行CTPI,24 h处死动物取脑组织行HE染色。根据HE染色结果将模型分为缺血组和梗死组,分别观察其脑血流量(cerebral blood flow,CBF)、脑血容积(cerebral blood volume,CBV)和平均通过时间(mean transit time,MTT)的动态变化规律。结果 A组CTPI及HE染色均未见明显异常。B组3只因实验意外死亡,1只因下肢静脉穿刺失败导致CTPI失败,21只行CTPI,其中18只灌注异常,3只未见明显异常。18只灌注异常的兔中,HE染色10只脑梗死,7只脑缺血,1只未见明显异常。30 min时7只缺血兔脑不同程度低灌注,表现为CBF降低,MTT延长,CBV无显著变化,3～6 h低灌注进一步加重,CBV值略降低,12 h低灌注不同程度恢复,24 h进一步恢复。30 min时10只梗死兔脑明显低灌注,表现为CBF及CBV显著降低,MTT显著延长,3只兔低灌注分别在3 h、6 h及12 h不同程度恢复,然后下一时间又迅速降低并随着时间延长进一步加剧,其余7只兔低灌注程度随时间延长逐渐加剧或在一定水平上波动。结论脑缺血3～6 h低灌注最明显,12～24 h低灌注不同程度恢复,而脑梗死随时间延长低灌注程度不断加重或一过性恢复后再次加重。脑缺血的特征是CBF和CBV的不匹配,缺血组织CBF显著降低,CBV无显著变化,而脑梗死则表现为这两个参数的一致性下降。

Objective To study the changes of cerebral hemodynamics revealed by CT perfusion imaging（CTPI） in rabbit models of cerebral microembolism.Methods Thirty normal New Zealand rabbits were randomly divided into two groups： Group A（n =5） underwent sham operation,group B（n =25） underwent an operation of microembolism.About ten SiO2 grains（D=0.5 mm） were injected into the internal carotid artery from external carotid artery.CTPI was performed continuously at 30 minutes,3,6,12,and 24 hours after embolization.At 24 hours after embolism,the rabbits were sacrificed and the brain was removed and prepared for histopathology with HE staining.According to the results of HE staining,the rabbits were divided into cerebral ischemia and cerebral infarction subgroups.The serial changes in cerebral blood flow（CBF）,cerebral blood volume（CBV） and mean transit time（MTT） were discussed respectively.Results No abnormality was seen on both CTPI and HE staining pathology in the group A.In the group B,three rabbits died during the experiment,CTPI was failed in one rabbit because of the failure of femoral vein puncture,and CTPI was succeeded in twenty-one rabbits,including abnormal perfusion in eighteen rabbits and normal perfusion in three rabbits.By HE staining,among the rabbits of abnormal perfusion,ten rabbits were of cerebral infarction,seven rabbits were of cerebral ischemia and one rabbit was normal.At 30 minutes after embolization,the ischemic brain had low perfusion to a different degree,reduced CBF,prolonged MTT and almost normal CBV.During 3 to 6 after embolization,the descended perfusion was further aggravated,the value of CBV was slightly descended.During 12 to 24 hours,the low perfusion was lightened.The cerebral infarction had evidently low perfusion in 30 minutes which showed remarkably descended CBF and CBV,and significantly prolonged MTT.Three rabbits had lightened low perfusion at 3 hours,6 hours and 12 hours,respectively,but in the subsequent time,the perfusion was descended rapidly again and further aggravated along with time.Another seven rabbits had evidently low perfusion and the degree was aggravated gradually or fluctuated slightly at a certain level.Conclusions The cerebral ischemia has most evidently low perfusion during 3 to 6 hours and the low perfusion is lightened during 12 to 24 hours,while the cerebral infarction show that the low perfusion is gradually aggravated along with the time or descended rapidly again after lightened to a different degree.The cerebral ischemia is characterized by mismatch in CBF and CBV values which show a significantly reduced CBF but almost normal CBV,whereas the cerebral infarction shows a matched significant decrease in both CBF and CBV values.