Registration and displacement field. Axial plane through non-rigid registration of the anal canal: Original data are shown in (a) and (d) – US and MR image, respectively. For simplification of visualization only the difference components in x-direction (b left) and in y-direction (b right) are shown. The difference in z-direction is ommited. (e) shows the difference image of (a) and (d) together with the difference components in x direction (e left) and in y direction (e right). (c) shows the registered image after the application of the displacement field.