Establishment Of Cerebral Microembolic Model In Rabbits And Dynamic Changes Study Of Hemodynamics By CT Perfusion Imaging

Establishment of cerebral microembolic model in rabbits and dynamic changes study of hemodynamics by CT perfusion imagingCerebral infarct is the common disease leading to death and disability,there is no effective therapy method except thrombolytic presently.And the diagnosis,time window and approach of thrombolysis and the changes of pathology,physiology after therapy are needed further investigation,which also shows the significance and instancy of investigating cerebral infarct.The cerebral vessel blocked by embolus is the crucial mechanism leading to cerebral infarct.And establishing a stable embolic model of brain could provide a reliable tool for clinical study.The cerebral vascular anatomy of rabbit is similar to that of humans and the volume of brain is larger than rat,so it is suitable for the study of nervous system.In the other hand,the figure of rabbit is moderate and the temper is mild which is convenient for surgery and operation,therefore,the rabbit could be used to establish cerebral ischemic model.The model of middle cerebral artery occlusion by an intraluminal thread was applied broadly;however,the limitation of this method was that it only could lead to broad cerebral infarct in the area supplied by middle cerebral artery.Establishing the cerebral microembolic model could simulate the falling of microembolus in humans,observe the cerebral injury caused by microembolus and evaluate the pathology,physiology and medical imaging of cerebral microembolism.CT perfusion imaging has a number of practical advantages:1) It can be performed easily no special equipment,except a power injector,is required;2) examination time is considerably short;3) it has a higher spatial and temporal resolution.On the other hand, compared with MR perfusion imaging,the functional maps of CT perfusion are better and more stable;therefore,CT perfusion imaging was applied in our study.PartⅠMulti-slice spiral CT perfusion imaging in cerebral hemodynamies of normal rabbitsPurpose:To evaluate the application of multi-slice spiral CT perfusion imaging in normal rabbits of cerebral hemodynamics.Materials and Methods:CT perfusion imaging(CTPI) was performed in twenty normal New Zealand rabbits(2.5～3.0 kg) with GE Light Speed 16 multi-slice spiral CT scanner.Firstly,routine CT scans were performed,and then CTPI study was made by selecting the basal ganglia slice and its adjacent slice.Scanning was performed at 120 kV,150 mA,with a 512×512 matrix, 9.6-cm FOV,and 2.5-mm section thickness.5ml of iodinated contrast agent(omnipaque, 300mg/ml) was bolus injected through femoral vein at rate of 1.5 ml/s,and multilayer of dynamic scan was performed for 30 seconds at a delayed time of 5 seconds.Four hundred and seventy-two maps at an interval of 0.5 second were acquired.The post-processing was performed with GE perfusion3.0 cerebral perfusion software.Cerebral blood flow, cerebral blood volume and mean transit time maps were acquired.The specific region of interest in both sides of frontal,temporal,parietal lobes,basal ganglia,cerebral stem and cerebellum were selected,the values of CBF,CBV,and MTT were measured,and quantitative analysis was performed.The data was analyzed using the software of SPSS 11.0 and P＜0.05 was taken to indicate statistical difference.Results:Twenty rabbits all entered the auto-regulated threshold value interface and the acquired maps of CBF, CBV,and MTT had no abnormal perfusion,including mostly cerebral tissue from frontal lobe to cerebellum.By paired-samples t test,there was no significant difference in the both sides of CBV(t=0.517,P=-0.608),CBV(t=1.581,P=0.120),and MTT(t=-0.541, P=-0.591).By one-way ANOVA,the perfusion in basal ganglia and cerebral stem was higher than in frontal,temporal,parietal lobes and cerebellum.And in different lotions, the values of CBF(F= 3.059,P=0.013)and MTT(F= 2.493,P=0.036)have significant difference,while the value of CBV has no significant difference(F = 1.189,P=0.320).In normal brain of rabbits,the values of CBF,CBV,and MTT are(115.45±36.83) ml/(min·100g),(3.85±1.20) ml/100g and(2.43±0.81)s respectively.Conclusion:The satisfying perfusion image could be obtained by injecting contrast material through femoral vein.MSCTPI provides a new noninvasive imaging method for measuring the cerebral hemodynamics in normal rabbits.And the acquired values of cerebral hemodynamics are reproducible which established basis for the CT perfusion investigation in all kinds of diseases cerebral mode of rabbits. PartⅡEstablishment of acute cerebral microembolic model in rabbits and evaluation by CT perfusion imagingPurpose:To establish a highly stable microembolic model of brain in rabbits,provide a reliable tool for investigating the pathology,physiology and medical imaging of cerebral embolism,and to evaluate the application of computed tomography perfusion imaging in acute ischemic cerebrovascular disease.Materials and Methods:Thirty normal New Zealand white rabbits(2.5～3.0 kg) were randomly divided into two groups:Group A(n = 5) underwent sham operation,group B(n = 25) underwent an operation of microembolic brain injury.Right cervical vessels were separated in thirty New Zealand white rabbits,the anatomy and variations of the rabbit carotid artery were recorded,and about ten SiO2 grains(D=0.5mm) were injected into internal carotid artery by external carotid artery in group B.After 30 minutes,CT perfusion imaging was performed.After 24 hours,the brain was removed,fixed in 10%formalin.After one week,the brain was cut into 5-mm sections and HE stain was performed.The CT imaging procedures and post-processing are same to the part one.Values of CBF,CBV,and MTT were measured in the lesions and the normal contra-lateral regions and statistic analysis was performed. The results of CTPI were compared with HE stain,and the curves of receiver operating characteristic of CBV,CBV and MTT were performed by SPSS11.0 statistic software, the accuracy of diagnosing acute cerebral ischemia was evaluated.Results:The right common carotid artery is divided into internal carotid artery and external carotid artery in gonial.Internal carotid artery is thinner than external carotid artery and the dilated carotid sinus is seen in the origination of internal carotid artery.In our study,origins of the internal carotid artery in thirty rabbits are all typeⅠ(lateral origin).Subtype A(the occipital artery origins from the external carotid artery) accounts for 73.3%(22/30),and subtype B(the occipital artery origins proximal on the internal carotid artery) accounts for 26.7%(8/30).The mean diameters of internal carotid artery and external carotid artery are 1.15±0.27mm and 1.93±0.32mm respectively.No abnormity was seen on CTPI in group A.Among group B,three rabbits were died during the experiment,CTPI was defeated in one rabbit because of the failure of puncture of femoral vein,and CTPI was succeeded in twenty-one rabbits,including abnormal perfusion in eighteen rabbits and normal perfusion in three rabbits.By HE stain,among the rabbits of abnormal perfusion,ten rabbits were cerebral infarct,seven rabbits were cerebral ischemia and one rabbit was normal.While among the rabbits of normal perfusion,one rabbit was slightly ischemic and two rabbits were normal.Reduced CBF,prolonged MTT and slightly low or high CBV were found on CT perfusion maps.There was broad low perfusion in right frontal and temporal lobes in five rabbits,broad low perfusion in right frontal and temporal lobes,basal ganglia and cerebral stem in four rabbits,local low perfusion in right temporal lobe in seven rabbits and local low perfusion in both side of frontal and temporal lobes in two rabbits.By paired-samples t test,there are significant difference between abnormal side and normal side for CBF(t=-7.286,P=0.000) and MTT(t=5.556, P=0.000),but for CBV,there is no significant difference(t=-1.080,P=0.287).The CBF value in abnormal side was decreased to 38.7%±23.7%(1%～83%),and MTT was delayed 6.22±5.36s(0.08s～18.33s).The accuracy of MTT in diagnosing acute cerebral ischemia is slightly higher than CBF,and the accuracy of both CBF and MTT are remarkably higher than CBV.If the value of CBF is less than 67.06ml/(min.100g),the sensitivity is 84.6%and the specificity is 84.6%in diagnosing cerebral ischemia.If the value of CBV is less than 3.08 ml/100g,the sensitivity is 74.4%and the specificity is 74.4%.And if the value of MTT is more than 4.58s,the sensitivity is 87.2%and the specificity is 87.2%.Conclusions.The cerebral vascular anatomy of rabbit is similar to that of humans and the volume of brain is larger than rat,furthermore,the figure of rabbit is moderate and the temper is mild which is convenient for surgery and operation, therefore,the rabbit could be used to establish cerebral ischemic model.The stable acute cerebral microembolic model in rabbits can be established by injecting microembolus from external carotid artery to internal carotid artery.CBF and MTT have high accuracy in diagnosing cerebral ischemia and CTPI can be as an accurate and non-invasive method in evaluating the acute ischemic cerebrovascular disease.PartⅢSerial changes in CT perfusion parameters of acute microembolic cerebral ischemic model in rabbits.Purpose:To discuss the serial changes in CT perfusion parameters during the first twenty-four hours of microembolic cerebral ischemic model in rabbits and to evaluate the application of computed tomography perfusion imaging in identifying acute cerebral ischemia and cerebral infarct.Materials and Methods:Eighteen rabbits which had abnormal perfusion in 30 minutes after embolism were further studied.CT perfusion imaging was performed continuously in 3 hours,6 hours,12 hours,and 24 hours after embolism.According to the results of HE stain,the rabbits were divided into cerebral ischemia and cerebral infarct.The serial changes in CT perfusion parameters of cerebral ischemia and cerebral infarct were discussed respectively.The CT imaging procedures and post-processing are same to the part one.Values of CBF,CBV,and MTT were measured in the lesions and the normal contra-lateral regions at each time point.The curves of receiver operating characteristic of CBV,CBV and MTT were performed by SPSS 11.0 statistic software and the accuracy of diagnosing cerebral infarct was evaluated. Results:In 30 minutes,the cerebral ischemia had low perfusion with different degrees, and reduced CBF,prolonged MTT and slightly high or normal CBV were found on CT perfusion maps.During 3～6 hours,the descended perfusion was further aggravated,the value of CBV was slightly descended.During 12～24 hours,the low perfusion was lightened.In different time points,there were remarkable difference for CBF and MTT (F=20.08,P=0.001;F=13.22,P=0.002),but for CBV,the difference had no statistic meaning(F=1.34,P=0.267).For CBV,there was no statistic difference between ischemia side and normal contra-lateral side at 30minutes,3,6,12 and 24hours.And for CBF and MTT,the difference between ischemia side and normal contra-lateral side at 30minutes,3, 6 and 12 hours had statistic meaning,but at 24 hours,the difference had no statistic meaning.The cerebral infarct had evidently low perfusion in 30 minutes which showed remarkably descended CBF and CBV,evidently prolonged MTT.Three rabbits had lightened low perfusion in 3 hours,6 hours and 12 hours respectively and in the next time, the perfusion was descended rapidly again and further aggravated along with time. Another seven rabbits had evidently low perfusion and the degree of low perfusion was aggravated gradually or fluctuated slightly at a certain level.In different time points,the difference of CBF and CBV had no statistic meaning(F=2.01,P=0.097;F=2.399, P=0.054),but for MTT,there was remarkable difference(F=5.39,P=0.001).For CBF, CBV and MTT,there were statistic difference between infarct side and normal contra-lateral side at 30minutes,3,6,12 and 24hours.The mean values of CBF,CBV and MTT in cerebral ischemia and cerebral infarct were(58.08±20.81)ml/(min·100g), (3.29±0.62)ml/100g,(6.03±2.50)s and(16.47±14.91)ml/(min·100g),(1.87±1.04)ml/100g, (13.69±5.15)s respectively,and the difference has statistic meaning.The accuracy of CBF in diagnosing cerebral infarct is remarkably higher than CBV and the accuracy of MTT is slightly higher than CBF.If the value of CBF is less than 27.07ml/(min·100g),the sensitivity is 82.8%and the specificity is 82.3%in diagnosing cerebral infarct.If the value of CBV is less than 2.48 ml/100g,the sensitivity is 73.8%and the specificity is 74.2%.And if the value of MTT is more than 7.77s,the sensitivity is 89.3%and the specificity is 85.5%.Conclusions:The cerebral ischemia has most evidently low perfusion during 3～6 hours and the low perfusion was lightened during 12～24 hours, while the cerebral infarct showed that the low perfusion was gradually aggravated along with time or descended rapidly again after lightened with different degree.The cerebral ischemia and cerebral infarct have different features of CT perfusion imaging.The cerebral ischemia was characterized by mismatch in CBF and CBV values which showed a significantly reduced CBF but slightly elevated or reduced or normal CBV,whereas the cerebral infarct showed a matched significant decrease in both CBF and CBV values.The values of CBF＜27.07ml/(min.100g) and MTT＞7.77s could identify cerebral ischemia and cerebral infarct,and it has very high accuracy in diagnosing cerebral infarct.