Real-Time Maximum Intensity Projection

Maximum Intensity Projection (MIP) is a volume rendering technique which is used to extract high-intensity structures from volumetric data. At each pixel the highest data value encountered along the corresponding viewing ray is determined. MIP is commonly used to extract vascular structures from medical MRI data sets (angiography). The usual way to compensate for the loss of spatial and occlusion information in MIP images is to view the data from different view points by rotating them. As the generation of MIP is usually non-interactive, this is done by calculating multiple images offline and playing them back as an animation. In this paper a new algorithm is proposed which is capable of interactively generating Maximum Intensity Projection images using parallel projection and templates. Voxels of the data set which will never contribute to a MIP due to their neighborhood are removed during a preprocessing step. The remaining voxels are stored in a way which guarantees optimal cache coherency regardless of the viewing direction. For use on low-end hardware, a preview-mode is included which renders only more significant parts of the volume during user interaction. Furthermore we demonstrate the usability of our data structure for extensions of the MIP technique like MIP with depth-shading and Local Maximum Intensity Projection (LMIP). keywords: Volume Visualization, Maximum Intensity Projection, angiography