Three-dimensional image display in medicine

This article is a tutorial on the methods used to create three-dimensional (3-D) images for use in displaying patient anatomy. This new view into anatomy has developed over the last 10 years from the need of surgeons, radiation therapists, and radiologists to integrate the many images resulting from the recent growth in tomographic imaging including computed tomography (CT) and magnetic resonance imaging (MRI). CT and MRI studies result in 30 to 100 images. 3-D imaging processes and integrates this image data volume and extracts more meaningful, derivative images via multiplanar reconstruction (MPR), shaded surface processing, or volumetric processing. MPR reslices the image volume to produce novel views of patient anatomy while retaining the image voxel intensities. Realistic shaded surface display of 3-D objects can involve extensive processing of the images to create computer representations of objects rendered into a displayable 3-D scene. Volumetric imaging combines the voxel processing of MPR with the techniques of tissue classification and surface shading to produce novel projections of the image data volume that allow automated creation of 3-D scenes without recourse to the complexities of object delineation. As the ultimate 3-D display, recent advances in computer-aided design (CAD) and computer-aided manufacturing (CAM) allow the fabrication of physical models of anatomy using computer-controlled milling machines. New technology that actually builds the model layer by layer from a liquid plastic offers the possibility of complete models with intact internal anatomy. The growth in 3-D is certain as hardware and software costs decrease and medical professionals find further applications for this technology.