Modeling Spectral Changes to Visualize Embedded Volume Structures for Medical Image Data H.J. Noordmans 1 , H.T.M. van der Voort 2 , and M.A. Viergever 1 1 Image Sciences Institute E.01.334, P.O. Box 85500 University Hospital Utrecht, 3508 GA Utrecht, The Netherlands herke@isi.uu.nl http://www.isi.uu.nl/People/Herke/herke.html 2 Scientific Volume Imaging BV Alexanderlaan 14, 1213 XS Hilversum, The Netherlands info@svi.nl http://www.svi.nl/ Abstract. When a volume structure is embedded in another volume structure, it is difficult to see the inner structure without destroying the view on the outer structure. We present a solution by letting the volume structures scatter light with a different wavelengths. The outer volume structure only absorbs light scattered by the structure itself and does not absorb the light scattered by the inner structure, by which the inner structure is visible without destroying the view on the outer structure. Examples are shown of vascular imaging and CT imaging. 1 Introduction The increasing number of image modalities, their increasing quality and the progressinimagesegmentationalgorithmsincreasethenumberofvolumestruc- tures one wants to combine in a volume rendering. This can be done by giving each structure a distinct color and opacity. However it becomes more compli- cated to show a structure which is embedded in another volume structure. One can think of seeing the organs inside the skin of the surrounding abdomen for laprascopy or to see the veins surrounding the brain in order to avoid them in neurosurgery. It is possible to cut a virtual hole in the outer structure[1] or to decrease its opacity, but a disadvantage is loosing surface information of a part or the total outer structure. If one still wants to see surface detail, for example for navigation, the visualization problem is more difficult. A simple option is to render the two structures separately and combine them at display. Possibilities aretakingthesquarerootoftheirsquaredintensities[2],puttingtheminasepa- rateRGBchannel[2],oraveragingtheRGBcolors.Theresultmaybesatisfying, but the question remains whether there exists a less ambiguous and less ad-hoc way of visualizing an embedded volume structure. C. Taylor, A. Colchester (Eds.): MICCAI’99, LNCS 1679, pp. 706–716, 1999. c  Springer-Verlag Berlin Heidelberg 1999