Evaluation of 3D Voxel Rendering Algorithms for Real-Time Interaction on a SIMD Graphics Processor

The display of three-dimensional medical data is becoming more common, but current hardware and image rendering algorithms do not generally allow real-time interaction with the image by the user. Real-time interactions, such as image rotation, utilize the motion processing capabilities of the human visual system, allowing a better understanding of the structures being imaged. Recent advances in general purpose graphics display equipment could make real-time interaction feasible in clinical setting. We have evaluated the capabilities of one type of advanced display architecture, the PIXAR Imaging Computer, for real-time interaction while displaying three-dimensional medical data as two-dimensional projections. It was discovered during this investigation that most suitable algorithms for implementation were based on the rendering of voxel rather than surface data. Two voxel-based techniques, back-to-front and front-to-back rendering produced acceptable, but not real-time performance. The quality of the images produced was not high, but allowed the determination of an image orientation which could then be used by a later high-quality rendering technique. Two conclusions were reached: first, the current performance of display hardware may allow acceptable interactive performance and produce high-quality images if a scheme of adaptive refinement is used wherein successively higher quality images are generated for the user. Second, the correct algorithm to use for fast rendering of volume data is highly dependent upon the architecture of the display processor, and in particular upon the ability of the processor to randomly access image data. If the processor is constrained to sequential or near sequential access to the voxel data, the choice of algorithms and the utilization of parallel processing is severely limited