Adaptation of marching cubes for the simulation of material removal from segmented volume data

Virtual reality surgical simulators contain anatomical models constructed from 3D medical image data such as CT or MRI scans. Typically, data is segmented to identify anatomical structures of interest and visualised using a rendering algorithm. Rendered surfaces in surgical simulators must be updated in real time to reflect user interaction within the virtual environment, such as cutting or drilling. Since its introduction in 1987, marching cubes has become a popular rendering algorithm for use in medical image visualisation, due to its simplicity and speed. However, the algorithm is designed for use with continuous data rather than discrete data, as is the case with segmented data. Applying marching cubes to segmented data results in blocky surfaces that require smoothing. In addition, marching cubes uses a single threshold (iso-value) to define the rendered surface and does not provide a means of rendering surfaces based on an upper and lower threshold (iso-interval). This ability is necessary if we wish to render individual segments within a segmented data volume. We introduce modifications to the marching cubes algorithm to enable the use of iso-intervals to construct smooth surfaces representing different segments from segmented volume data. We also discuss a way to render real-time material removal from the constructed surfaces. Our evaluation shows that the performance of this method compares favourably to an existing method, with decreased memory requirements and shorter start-up times.