Maximum intensity projection at warp speed

Maximum intensity projection (MIP) is a volume rendering technique which is used to extract high-intensity structures from volumetric scalar data. At each pixel the highest data value encountered along the corresponding viewi ng ray is determined. MIP is commonly used to extract vascular structures f rom medical MRI data sets, i.e., angiography. The usual way to compensate f or the loss of spatial and occlusion information in MIP images is to view t he data from different view points by rotating them. As the generation of a MIP is usually non-interactive, this is done by calculating multiple image s offline and playing them back as an animation. In this paper a novel algo rithm is proposed which is capable of interactively generating Maximum Inte nsity Projection images even on low-end hardware using parallel projection. Two methods for preprocessing data and removing voxels which will due to t heir neighborhood never contribute to a MIP are discussed. The remaining vo xels are stored in a way which guarantees optimal cache coherency regardles s of the viewing direction. For use on low-end hardware, a preview-mode is included which renders only the more significant parts of the volume during user interaction. Furthermore, we demonstrate the usability of our data st ructure for extensions of the MIP technique like MIP with depth-shading and local maximum intensity projection (LMIP). (C) 2000 Elsevier Science Ltd. All rights reserved.