Myofiber orientation in the normal and infarcted heart, assessed with MR-diffusion tensor imaging

Cardiac fiber orientation is one of the main determinants of fiber stress and strain during ejection. We measured fiber orientation using magnetic resonance diffusion tensor imaging (MR-DTI). Traditional methods to quantify the cardiac fiber field rely on the definition of the coordinate system. We propose to use the entity 'divergence' for characterization of the continuity of the myocardial fiber structure. The divergence is a scalar quantity with a value that is independent of the actual choice of the coordinate system. Moreover, the divergence value of the fiber field expresses the degree of uniformity of stress along the fiber direction. The divergence of the myofiber field appeared to be <0.08 mm/sup -1/ in the mid-wall for all normal hearts. At the insertion sites of the papillary muscles and the anterior RV (right ventricle) fusion site, the divergence of the fiber field is elevated to values above 0.3 mm/sup -1/. In the infarcted hearts, divergence values in the unaffected tissue are similar to the values observed in healthy hearts. In and adjacent to the infarcted region, no significant differences in the divergence values were observed. This indicates that continuity of the fiber structure remains preserved in the presence of a transmural myocardial infarction.