Kinematic analysis of left ventricular deformation in myocardial infarction using magnetic resonance cardiac tagging

The Magnetic Resonance (MR) tagging technique provides detailed information about 2D motion in the plane of observation. Interpretation of this inform ation as a reflection of the 3D motion of the entire cardiac wall is a majo r problem. In finite element models of the mechanics of the infarcted heart , an infarcted region causes motional asymmetry, extending far beyond the i nfarct boundary. Here we present a method to quantify such asymmetry in amp litude and orientation. For this purpose images of a short-axis cross-secti on of the ejecting left ventricle were acquired from 9 healthy volunteers a nd 5 patients with myocardial infarction. MR-tags were applied in a 5 mm gr id at end-diastole. The tags were tracked by video-image analysis. Tag moti on was fitted to a kinematic model of cardiac motion. For the volunteers an d the patients the center of the cavity displaced by about the same amount (p=0.11) during the ejection phase: 3.8 +/- 1.4 and 3.0 +/- 0.9 mm (mean +/ - sd), respectively. Cross-sectional rotation and the decrease in cross-sec tional area of the cavity were both greater in the volunteers than in the p atients: 6.4 +/- 1.5 vs. 3.0 +/- 0.8 degrees (p < 0.001), and 945 +/- 71 vs . 700 +/- 176 mm(2) (p=0.02), respectively. In the patients, asymmetry of w all motion, as expressed by a sine wave dependency of contraction around th e circumference, was significantly enlarged (p=0.02). The proposed method o f kinematic analysis can be used to assess cardiac deformation in humans. W e expect that by analyzing images of more cross-sections simultaneously, th e 3D location and the degree of infarction can be assessed efficiently.