Figure 1.

Coordinate and angle system used to describe fibre and sheet orientations in the heart. (a) A base–apex axis is fitted to the centre of the left ventricle. This axis is normal to the transverse plane, shown in grey. The centroid for each slice is the location where the apex–base axis intersects the transverse plane, and is shown as a filled circle. (b) For each voxel (shown here as an open circle), three orthogonal reference axes are defined. The base–apex axis is parallel to that defined previously, the radial axis passes through the centroid and the voxel, and the tangential axis lies in the transverse plane perpendicular to the other two axes. (c) The fibre helix (inclination) angle αH and the fibre transverse angle αT. (d) The sheet angle αS. In (c,d), the DT-MRI eigenvector is shown in bold; projections of this eigenvector are in grey.