猪心梗模型MRI心肌首过灌注及DE-MRI、cTnI实验研究

【作者】 赵新湘；

【导师】 杨达宽； 闫东； 袁曙光； 杨绍军；

【作者基本信息】 昆明医学院 ， 外科学， 2010， 博士

【摘要】 研究目的心肌灌注减低发生于心电图(ECG)变化和临床出现心绞痛等综合征之前,因此心肌灌注异常对冠心病的诊断有积极的意义。通过对猪心梗模型MRI心肌首过灌注成像(Fist-pass-perfusion MRI),探讨缺血心肌灌注曲线(时间-信号强度曲线)变化与局部心肌的存活情况,并对其目前应用中存在的局限性进行探讨。方法:制备成功10只心梗模型猪行术前及术后MRI心肌首过灌注检查,观察灌注图像有无灌注缺损或减低,并经图像后处理软件绘制灌注缺损区及周围、心肌下壁和侧壁时间信号强度曲线,对曲线峰值时间、峰值信号强度进行分析。MR工检查结束后处死实验猪,取出心脏,行心肌TTC组织化学检查和常规病理检查。结果:①符合实验研究10只猪术前未见心肌灌注减低或缺损。②术后8只在前壁和(或)前间壁见心肌灌注减低和缺损,灌注缺损区曲线未见明显的波峰,在正常心肌灌注时间内为低灌注表现,后期曲线呈轻度上升表现;灌注缺损周围时间-信号强度曲线可见波峰,但峰值信号强度低于正常侧壁和下壁心肌(P<0.05),峰值时间较正常侧壁和下壁心肌延迟(P<0.05)。③切片后行TTC染色和病理检查灌注缺损区均可见心肌梗死,灌注缺损周围心肌纤维见水肿、变性;无灌注缺损2只猪TTC染色和病理检查见小灶性心肌坏死区。结论:MRI心肌首过灌注检查可对心肌活性和缺血情况进行评估,灌注曲线可发现灌注图不能识别的缺血心肌;灌注曲线的不同走势和变化客观反映了局部心肌血流生理情况,心肌微循环灌注的改变以及生理病理的即时信息,但临床应用中还存在一定的局限性。目的MR延迟增强技术(Delayed-Enhancement MRI,DE-MRI)在对心肌活性的评价中,正快速成为一种突出有效的检查手段,相对于MRI心肌首过灌注,它具有更高的空间分辨率和CNR,并能扫描完整的心肌;但对DE-MRI高信号是否就是失活心肌还存在争议;同时临床更关注心梗节段的透壁程度对治疗的反应,而目前尚无心梗透壁程度与组织学的比较,多是测量心梗体积或面积;本研究通过对猪心梗模型DE-MRI和基础病理对照研究,旨在对上述问题进行探讨:研究其评价失活心肌的准确性、对心梗节段透壁程度判断的一致性,为DE-MRI临床运用提供更有力的实验依据。方法10只制备成功的猪急性心肌梗死模型分别于术前及术后24 h、72 h、1周分组行心脏DE-MR检查,观察DE-MRI图像上高信号部位、节段数与透壁程度;MRI检查完后,处死试验猪,取出心脏行TTC染色和病理检查,并对DE-MRI和TTC两者检测的梗死心肌节段、部位及透壁程度行统计学分析。结果①10只猪心梗模型制作成功,术前DE-MRI检查未见异常高信号节段。②10只心梗模型猪术后DE-MRI均发现异常高信号心肌节段,共检测到30个高信号心肌节段,其检测的高信号心肌节段数及部位与TTC染色组所诊断心梗节段数及部位相比,差别统计学意义(McNemar Test,P>0.05)。③对梗死心肌节段透壁程度的判断,DE-MRI和TTC染色两种方法诊断结果有关(Chi-Square test,P<0.05),且一致性较好(Kappa>0.75),但DE-MRI高信号节段透壁程度分级高于TTC染色组心梗透壁程度分级(McNemar Test,P<0.05)。④DE-MRI高信号(TTC染色梗死区域)24小时病理表现为心肌细胞胞浆嗜酸性增强,呈均质样,核固缩。72小时病理表现为心肌纤维多灶性、不规则溶解消失,代之以大量增生的纤维母细胞。1周病理表现为心肌纤维溶解消失,间质纤维母细胞及毛细血管增生、炎细胞浸润,小血管扩张、充血。DE-MRI稍高信号区(TTC染色无梗死区域)见间质局灶水肿明显、部分心肌纤维显著水肿变性,胞浆淡然,气球样变。结论DE-MRI能准确检测失活心肌(梗死心肌),并能清楚描述失活心肌的透壁程度,其判断的心梗透壁程度与TTC染色相比一致性较好,这对于CAD的临床评价和治疗都非常重要;但应注意急性期DE-MRI显示高信号区会“放大”失活心肌,急性期心肌梗死DE-MRI高信号并非完全是失活心肌,少部分源于心肌纤维水样变性和间质局灶水肿导致的Gd造影剂分布容积增加,但部分高信号节段水肿区与梗死区亮度不一致,梗死区信号亮度更高。目的目前,在临床评价心肌活性手段中,DE-MRI正有望成为检测不可逆心肌新的金标准,而心脏肌钙蛋白(cTnT或cTnI)是目前临床上评价和判断患者心肌损伤最好的检测标志物,但临床上用于检测的心肌坏死标记物的试剂盒是针对人的血清,其是否适用于猪的血清?其检测的cTnI值与DE-MRI所判断的心梗损伤程度相关性如何?本研究拟在对上述问题进行探讨,并与组织病理进行对照研究。方法10只制备成功的猪急性心肌梗死模型分别术前、术后1小时、术后2小时、术后5小时、24小时、48小时、72小时、1周采血,行心肌肌钙蛋白(cTnI)检测;并分组行术后24 h、72 h、1周心脏DE-MR检查,对DE-MRI所显示的心肌梗死程度进行评分;MRI检查完后,处死试验猪,取出心脏行TTC染色和免疫组化肌动蛋白(HHF35)、肌红蛋白(Mb)、结蛋白(Dm)检查。对cTnI峰值和DE-MRI、TTC染色所判断的心肌梗死程度评分Correlate(Bivariate)行相关分析。结果①心肌钙蛋白(cTnI)术后1小时可见上升,于24小时达高峰,此后逐渐下降,1周后回复至术前水平。②10例免疫组织化均证实心肌梗死:24h组缺血坏死区显示HHF35、Myoglobin、Desmin三种蛋白显著减少,呈大片淡染,周围正常心肌细胞呈棕褐色阳性反应;72h组三种蛋白缺失较24h组明显,呈大片缺染表现,与周围正常染色阳性的棕褐色心肌分界清楚;1w组与72h组相比无明显变化。③24小时TnI峰值与TTC和DE-MRI两者检测的心梗损伤程度评分高度相关,散点图可见有明显的直线相关关系,相关系数分别为0.85和0.84,P<0.05,有显著的统计学意义。结论临床上用于检测的人血清心肌坏死标记物的试剂盒对猪血清cTnI术前及术后检测,可反映心肌损伤;其24小时峰值与DE-MRI所判断的心肌损伤程度高度相关;DE-MRI是目前临床正开展的检测心肌活性一种非常有效、无创、并具有高空间分辨率、高信号对比(SNR)优势的一项检查技术,cTnI与DE-MRI的联合应用有助于结果的相互应证和互为补充,可更好准确地评价心肌梗死。更多还原

【Abstract】 Objectives:The reduce of myocardial perfusion occurs before the electrocardiogram(ECG) changes and clinical syndrome(angina),so myocardial perfusion abnormalities have a positive meaning in the diagnosis of coronary artery disease.The aim of this study is to explore the value of the first-pass myocardial perfusion MR imaging in evaluating the ischemic myocardial perfusion and viability.Especially,to investigate to perfusion curves(time-signal intensity curves) changes of the ischemic myocardium.In addition, to explore the limitations existing in the current MR first-pass perfusion imaging study.Materials and Methods:Ten porcine model with myocardial infarction had the preoperative and postoperative MR first-pass myocardial perfusion imaging examination.The perfusion reduce or defects on the MR myocardial perfusion imaging were observed. And the time-signal intensity curves in the regions with the perfusion reduce or defects and normal regions were drawed by the image post-processing software.The peak time,peak signal intensity of curve were statistical analyzed.After MRI examination,the experimental pigs were executed and its heart been had the TTC staining and pathological examination.Results:The preoperative myocardial perfusion in the all of the 10 pigs is nomal,but there is myocardial perfusion decrease and defect in 8 experimental pigs after operation.The curves in the area with perfusion defects have no obvious peak and have a sligtly increase in late time.The curves in the area around perfusion defect can be seen the peak,but the peak signal intensity is lower than normal inferior and lateral myocardial wall(P<0.05);and the peak time is delayed compared with normal inferior and lateral myocardial wall(P<0.05).There are myocardial infarction in the perfusion defects areas and its were certified by TTC staining and pathological examination.The interstitial edema and myocardial degeneration can be seen in the perfusion reduced areas.Conclusion:MRI fist-pass myocardial perfusion imaging combined with time-signal intensity curves analysis can evaluate perfusion changes of the regional myocardial microcirculation.It may be useful in assessing the ischemic myocardial viability.But there are some limitations in the the clinical application. Objectives:Delayed-enhancement MR imaging(DE-MRI) is rapidly becoming a prominent and effective means in the evaluation of myocardial viability,but there is a question about it,that is "bringt is dead"? This study aimed to explore the accuracy and question in assessment of myocardial viability by delayed-enhanced MR imaging.Materials and MethodsA total of 15 pigs were used to make the acute myocardial infarction(MI) models,and then ten successful models were underwent delayed-enhancement MR imaging at preoperation,]postoperative 24 h,72 h and 1 W,respectively.The hyperenhanced regions and segments as well as their transmural extent on DE-MRI were observed. After MR examination,2,3,5-triphenyltetrazolium chlorid(TTC) staining and pathological examination were performed.The segments with MI detected by the DE-MRI and TTC staning were made statistical analysis.Results①Ten MI models were made,and no abnormal signals were found on pre-operative DE-MRI.②The abnormal high signal myocardial segments were found in the all of 10 pigs after operation on delayed-enhancement MR imaging.There were a total of 30 hyperenhanced segments in ten MI models.And there was no difference in regions and segments with MI between DE-MRI and TTC staining.③In the judging transmural extent of MI,the results of DE-MRI was correlative with TTC staining(Pearson Chi-Square,P<0.05);and the concordance was good(K>0.75).But the results of two methods was different(McNemar Test,P<0.05). The transmural extent judged by DE-MRI was higher than TTC staining. ④24-hour pathology of high signal area in DE-MRI(myocardial infarction in TTC staining) showed eosinophilic cytoplasm of myocardial cells,homogeneous degeneration,nuclear pyknosis;72-hour pathology showed multifocal myocardial fibers dissoloved irregularly.1-week pathology showed myocardial fibers dissoloved, interstitial fibroblasts and capillary proliferation,small blood vessels congestive.The pathology of slightly higher signal area in DE-MRI(non-infarcion in TTC staining) showed obvious interstitial edema,edema degeneration and balloon-like change of myocardial fibers.Conclusion:DE-MRI is an excellent tool for detecting the myocardial infarction.Especially,it can cleary demonstrate the suberdocardial or transmural myocardial infarction.That is very important for the clinical evaluation and treatment of the ischemic heart disease But in the clinical evaluation we should be noted that the bright areas on DE-MRI will may be "zoom" the real areas of myocardial infarction.And we should observe whether are brightness difference in high-intensity zone. Objectives:Cardiac troponin(cTnT or cTnI) is regarded as a best marker to determine the acute myocardial injury,In addition,the delayed enhancement MR imaging is becoming the new gold standard in the clinical myocardial viability assessment.This study to explore whether the clinic reagent for detection of the serum cardiac troponin I(cTnI) in the human can be applicable to swine model with acute myocardial infarction;And to investigate the relationships between the cTnl peak value and the degree of myocardial infarction quantificated by delayed-enhancment MR imaging(DE-MRI) and pathological findings.Materials and Methods10 successful pig model with acute myocardial infarction were underwent cardiac troponin(cTnI) detection at preoperation,]postoperative 1 h,2 h,after 5 h, 24 h,48 h,72 hours and 1 week;and also were underwent Delayed-Enhancement MR imaging at preoperation,postoperative 24 h,72 h and 1 W,respectively.After MR examination,2,3,5-triphenyltetrazolium chlorid(TTC) staining and immunohistochemistry examination were performed.The degree of myocardial infarction was assessed by DE-MRI and TTC.The cTnI value of 24h after the operation and the degree of myocardial infarction were made correlation analysis.Results①The cardiac troponin can be seen raise at 1h after operation,and reached the peak at 24h arfter aperation,then decrease gradually.1 week later the cTnI value return to preoperative levels. ②The segments of myocardial infarction were found in the all of 10 pigs on the immunohistochemistry examination.It displayed:24h group showed HHF35, Myoglobin,Desmin proteins significantly reduced in the infaction region,and pale staining,surrounded by normal myocardial cells with brown staining;72h group showed HHF35,Myoglobin,Desmin protein reduced than 24h group significantly, showed a large region with dyeing missing in the infarction region,and had the clear boundaries with the normal stained brown myocardium,1w group had no significant change compared with 72h group.③The cTnI peak values of 24h was correlated strongly to the degree of myocardial infarction assessed by TTC(correlation coefficient=0.85,P=0.002) as well as to DE-MRI(correlation coefficient =0.84,P=0.002).The scatter plot shows a clear linear correlation between the cTnI peak values and the degree of myocardial infarction assessed by TTC and DE-MRI.Conclusion:The clinical reagent for detection of the serum cardiac troponin I(cTnI) can be applicable to swine model.The cTnI measurement,specially 24h after the operation, can reflects degree of myocardial injury.DE-MRI is currently a very effective, non-invasive technique,and has high spatial resolution in detection of myocardial viability.The cTnI combined with DE-MRI will be more help for clinical work and research in coronary heart disease.更多还原