Extraction of isosurfaces from multi-material CT volumetric data of mechanical parts

We introduce a method for extracting boundary surfaces from volumetric models of mechanical parts by X-ray CT scanning. When the volumetric model is composed of two materials, one for the object and the other for the background (Air), these boundary surfaces can be extracted as isosurfaces using a contouring method such as Marching Cubes [Lorensen and Cline 1987]. For a volumetric model composed of more than two materials, we need to classify the voxel types into segments by material and use a generalized Marching Cubes algorithm that can deal with both CT values and material types. Here we propose a method for precisely classifying the volumetric model into its component materials using a modified and combined method of two well-known algorithms in image segmentation, region growing and Graph-cut. We then apply the generalized Marching Cubes algorithm to generate triangulated mesh surfaces. In addition, we demonstrate the effectiveness of our method by constructing high-quality triangular mesh models of the segmented parts.