Departments of Radiology B, University Hospital of Strasbourg, NHC, 1 Place de l'Hôpital, 67091 Strasbourg, France.
Radiographics. 2012 Sep-Oct;32(5):1381-98. doi: 10.1148/rg.325115098.
Magnetic resonance tagging is used to evaluate the dynamic deformation of lines or grids superimposed on the myocardium during the cardiac cycle. From these data, a specific postprocessing procedure provides two kinds of metrics: (a) three orthogonal components of myocardial motion (longitudinal, circumferential, and radial), and (b) rotation and torsion. Strain expresses the local myocardial deformation and is prone to important physiologic heterogeneities. Peak systolic strain is in the range of -15% to -20% for the longitudinal and circumferential components (fiber shortening) and 30%-40% for the radial component (wall thickening). The helical arrangement of myofibers that run in opposite directions at the epicardium and endocardium explains systolic twist (~15°). This torsion may be enhanced during the early stage of several diseases (eg, hypertrophic cardiomyopathy) or in heart failure with a normal left ventricular ejection fraction. Strain is generally impaired in ischemic heart disease and cardiomyopathy, but the most diagnostically significant finding is the early identification of contractile dysfunction on the basis of longitudinal and circumferential strain reduction in patients with apparently preserved systolic function. Thus, strain impairment appears to be a sensitive and promising marker of subclinical disease, with the potential for improving patient management.
磁共振标记用于评估心脏周期期间叠加在心肌上的线或网格的动态变形。通过这些数据，特定的后处理过程提供了两种度量标准：(a)心肌运动的三个正交分量（纵向、圆周和径向），以及(b)旋转和扭转。应变表示局部心肌变形，容易发生重要的生理异质性。收缩期峰值应变在纵向和圆周分量（纤维缩短）范围为-15%至-20%，在径向分量（壁增厚）范围为 30%-40%。心肌纤维呈螺旋状排列，在心外膜和心内膜处向相反方向运行，解释了收缩期扭转（约 15°）。在几种疾病（例如肥厚型心肌病）的早期或射血分数正常的心衰中，这种扭转可能会增强。应变通常在缺血性心脏病和心肌病中受损，但最具诊断意义的发现是基于纵向和圆周应变降低，在收缩功能似乎正常的患者中早期识别收缩功能障碍。因此，应变损伤似乎是亚临床疾病的敏感且有前途的标志物，有可能改善患者管理。
