Problematic zone for automatic segmentation. Complementary information is found in different imaging planes. (a) Axial view of vertebra showing orientations of sagittal and coronal planes. The shaded ellipses show the regions for which intervertebral disks are hard to segment in sagittal images. (b) Segmented sagittal image corresponding to the plane showed in (a). None of the intervertebral disks are properly segmented in this sagittal image. (c) Segmented coronal image corresponding to the plane showed in (a). Several disk contours that the automatic segmentation algorithm is not able to detect in the sagittal plane, are on the other hand, well detected by algorithm in the coronal plane.