Intercentre reproducibility of second eigenvector orientation in cardiac diffusion tensor imaging

Background Diffusion tensor imaging enables the study of cardiac microstructure in vivo, including its changes through the cardiac cycle. The left ventricle consists of myocytes with opposing helical arrangements in the epiand endocardium. Histology shows that these myocytes are arranged into small laminar “sheetlet” structures, separated by shear layers which allow the sheetlets to move and reorient relative to each other during myocardial contraction. While the direction of the first eigenvector of the cardiac diffusion tensor indicates the average direction of the myocytes in a voxel, the second eigenvector appears to indicate the mean orientation of the sheetlets (1). Recent work has demonstrated that there are differences between the motion of these sheetlets between healthy volunteers and patients with hypertrophic cardiomyopathy (2). In order to facilitate comparison of sheetlet orientations in disease between different centres, the aim of this study was to test the intercentre reproducibility of the second eigenvector orientation.