A direct multi-volume rendering method aiming at comparisons of 3-D images and models

The authors present a new method for direct volume rendering of multiple three-dimensional (3-D) functions using a density emitter model. The work is aimed at obtaining visual assessment of the results of a 3-D image registration algorithm which operates on anisotropic and non-segmented medical data. They first discuss the fundamentals associated with direct, simultaneous rendering of such datasets. Then, they recall the fuzzy classification and fuzzy surface rendering theory within the density emitter model terminology, and propose an extension of standard direct volume rendering that can handle the rendering of two or more 3-D functions; this consists of the definition of merging rules that are applied on emitter clouds. The included rendering applications are related on one hand, to volume-to-volume registration, and on the other hand, to surface-to-volume registration: the first case is concerned with global elastic registration of CT data, and the second one presents fitting of an implicit surface over a CT data subset. In these two medical imaging application cases, the rendering scheme offers a comprehensive appreciation of the relative position of structural information.