Evaluation of methods for shaded surface display of CT-volumes

Twelve methods are evaluated to analyze an ideal sphere and a real human skull. They are different combinations of principles for detection of the surface to be displayed (gray-value threshold, gradient threshold, and zero-crossing of the second derivative), localizing this surface in space (including both grid-point accuracy and subvoxel accuracy), and finally estimating the direction of the surface normal (from the gradient in the 2-D depth image and from the gradient in the 3-D volume). The best quality is obtained by zero-crossing detection, subvoxel localization, and 3-D gradient orientation