7.0 T MR扩散张量成像技术对大鼠肥厚心肌纤维特性的研究

The study of characteristic of hypertrophy myocardial fibers in rat by using 7.0 T diffusion tensor magnetic resonance imaging

目的采用7.0 T MR扩散张量成像(DT-MRI)技术从心肌纤维水分子扩散、心肌纤维微结构及心肌力学单元角度综合定量研究心肌肥厚模型大鼠的心肌纤维特性。材料与方法 20只健康雄性SD大鼠随机分为正常组(n=10)与心肌肥厚组(n=10),正常组大鼠离体心脏并固定,心肌肥厚组大鼠行胸主动脉缩窄手术12周后离体心脏并固定,采用扩散张量成像技术获取图像,并使用Diffusion Toolkit、Trackvis及Matlab软件进行图像后处理。观察两组大鼠心脏三维整体观、乳头肌层面心肌纤维和张量图以及心肌组织HE染色的特点,使用独立样本t检验统计分析两组大鼠左心室心肌纤维平均ADC值、FA值及螺旋角的差异。结果心脏三维整体观显示,两组大鼠心肌纤维由心外膜向心内膜均呈致密、规则的螺旋排布。乳头肌层面心肌纤维示踪图以及张量图显示正常组心肌纤维走行规则、排布均匀,心肌肥厚组左心室壁较正常组增厚,像素内的张量显示较正常组增加,心外膜向心内膜过渡的三层结构较正常组更明显;心肌肥厚组大鼠较正常组大鼠左心室心肌纤维平均ADC值下降(P<0.01),FA值上升(P<0.05),两组间均有统计学差异。心肌肥厚组大鼠左心室由心外膜至心内膜的平均螺旋角透壁范围较正常组增大(P<0.01),两组间均具有统计学差异。结论扩散张量成像及图像后处理技术可三维可视化定量综合评价大鼠心肌肥厚模型心肌纤维特性较正常大鼠的变化,为将来实现心肌纤维结构、力学、电生理特性的在体研究奠定基础。

Objective： To quantitatively evaluate the characteristic of myocardial ifbers in myocardial hypertrophy rats from the viewpoint of water molecular diffusion, microstructure and mechanical unit by using 7.0 T diffusion tensor magnetic resonance imaging （DT-MRI）.Materials and Methods：A total of 20 fixed rat hearts [control groupn=10, transverse aortic constriction （TAC） groupn=10] underwent DT-MRI and the myocardial structures were quantitatively measured by Diffusion Toolkit, Trackvis and Matlab. The characteristic of global 3D tractography of myocardium, tractography of myocardium and tensor in papillary muscle plane and HE stained section were discussed between the two groups. Mean ADC value, FA value and helix angle of left ventricular between the two groups were analyzed by using Independent-Samplet test.Results：Control group and TAC group showed that myocardial ifbers arranged orderly and densely from epicardium to endocardium at global 3D tractography of myocardium. Regular direction and arrangement were presented at tractography of myocardium and tensor in papillary muscle plane. Left ventricular wall thickness in TAC group was thicker than control group. The number of tensor had been increasingly recognized in TAC group compared with control group. There were signiifcant differences in ADC value （P〈0.01） and FA value （P〈0.05） between TAC group and control group. Left ventricular mean helix angle from epicardium to endocardium in TAC group were larger than control group （P〈0.01）.Conclusions： DT-MRI and imaging post-processing technique can quantitatively measure the variation of myocardial ifbers in myocardial hypertrophy compared with normal rat hearts and visualize the character of myocardial ifbers in multiple parameters. This promising approach also lay the foundation for further study of myocardial ifbers in vivo.