The Virtual Magic Lantern: An Interaction Metaphor for Enhanced Medical Data Inspection Eva Moncl´ us, Jos´ e D´ıaz, Isabel Navazo and Pere-Pau V´ azquez * MOVING Group, Universitat Polit` ecnica de Catalunya (a) Original model (b) Virtual Magic (c) Zoom-in of the VML (d) Virtual Magic (e) Zoom-in of the VMW Lantern (VML) region of interest Window (VMW) region of interest Figure 1: Advanced inspection of a medical dataset using the Virtual Magic Lantern (b and c) and the Virtual Magic Window metaphors (d and e). Note how the first metaphor produces higher amount of contextual information because it displays the boundary of the two differently visualized regions. Abstract In Volume Rendering, it is difficult to simultaneously visualize in- terior and exterior structures. Several approaches have been devel- oped to solve this problem, such as cut-away or exploded views. Nevertheless, in most cases, those algorithms usually require either a preprocess of the data, or an accurate determination of the region of interest, previous to data inspection. In this paper we present the Virtual Magic Lantern (VML), an in- teraction tool tailored to facilitate volumetric data inspection. It behaves like a lantern whose virtual illumination cone provides the focal region which is visualized using a secondary transfer func- tion or different rendering style. This may be used for simple vi- sual inspection, surgery planning, or injure diagnosis. The VML is a particularly friendly and intuitive interaction tool suitable for an immersive Virtual Reality setup with a large screen, where the user moves a Wanda device, like a lantern pointing to the model. We show that this inspection metaphor can be efficiently and easily adapted to a GPU ray casting volume visualization algorithm. We also present the Virtual Magic Window (VMW) metaphor as an ef- ficient collateral implementation of the VML, that can be seen as a restricted case where the lantern illuminates following the viewing direction, through a virtual window created as the intersection of the virtual lantern (guided by the Wanda device) and the bounding box of the volume. CR Categories: I.3.6 [Computer Graphics]: Methodology and Techniques—Interaction Techniques; J.3 [Life and Medical Sci- ences]: Medical Information Systems Keywords: Virtual Reality, Medical Models, Interaction * {emonclus,jdiriberri,isabel,pere.pau}@lsi.upc.edu. This work has been partially funded by the Spanish Ministry of Science and Technology under grant TIN2007-67982-C02-01. J. D´ıaz also is supported by MCI-FPI Grant of the same Ministry. 1 Introduction The recent advances in Medical Imaging, Direct Volume Render- ing, graphics hardware, and Virtual Reality technologies at afford- able prices have empowered the development of Virtual Reality applications tailored to the real time medical data manipulation. Therefore, applications such as interactive inspection, surgery plan- ning and surgeon training have become a reality [Robb 2008]. Clin- ical use of such applications requires reduced data preprocess times, efficient rendering algorithms, and friendly and intuitive user inter- faces. Direct Volume Rendering (DVR) allows spacial interpretation of medical images but this causes that values from different images are rendered onto a single pixel. This poses problems for the si- multaneous visualization of the whole information captured by the volumetric dataset. Recently, different techniques and strategies have been proposed with the objective of facilitating the identifica- tion and exploration of features or regions of interest (for space rea- sons, we only mention some papers): Cut-away views([McInerney and Broughton 2006]), focus+context visualization ([Bruckner and Gr¨ oller 2006]), Lens and Distortion ( [Wang et al. 2005]) and ad- vanced Transfer Functions (TF) ([Kniss et al. 2001] and [Bruckner and Gr¨ oller 2007]). Most of them have been proposed for 2D dis- plays (although some of them could be adapted to stereo), and their focus is to provide the specialist with a view of the feature of inter- est without occlusions of other neighbor structures. Complementary to these advanced visualization techniques, some medical applications can benefit from the anatomy’s knowledge the specialist has, in order to facilitate the localization and identifica-