Fig. 5

(a) 3d rendering of the ID19 dataset with color shading representing electron density. Values are shown for all voxels within the segmentation mask, excluding the left ventricle, but including the right ventricle which typically collapses in the excised hearts. (b) The corresponding 3D rendering of the structure tensor. The z-component of the eigenvector with the smallest eigenvalue is used for the visualisation. Lighter values represent a larger z-component, i.e. at a higher helical angle. The dark spots are remnants of the original image (isolated tomographic artefacts) which then appear larger after convolution with the local average (\(N_{ROI}\)) used in the eigenvalues analysis. Here, \(N_{ROI}=\)+/-6 voxel was used for the analysis of the orientational vector field. In other words, the local average over which the orientation field is determined corresponds to a cube of 13 pixel side length. (c,d) False-color representation of the quasi-vector field representing the orientation of the myocyte chains in (c) a long axis, and (d) a transverse orientation of the 2d sections. The plots show the (c) y-component, and (d) z-component of the normalized structure tensor eigenvector. In (d) a ring-shaped layer is observed in the middle of the myocardium with the predominant myofiber orientation in plane. (e) The nematic order parameter s, and (f) the anisotropy \(\Omega\), shown in a representative transverse plane. Note that since the computation of s requires a local average, the boundary of the slice shrinks by the cross-section of this region, since values for s are only assigned to as points in the interior.