Stereo Display of Nested 3d Volume Data Using Automatic Tunnelling

We describe a new technique for visualizing complex, nested features in multivariate volume data sets, such as those commonly found in medical imaging applications. Our work focuses on radiation therapy planning, where the problem is to locate ‘hot’ and ‘cold’ spots in a radiation dose field, inside a target tumour and surrounding organs. It is essential to visualize these different features simultaneously in order to understand their spatial relationships. To guarantee that certain key features inside a volume are visible, we dynamically create a series of circular tunnels through the enclosing volumes. As the viewpoint is rotated, the tunnel orientations remain aligned with the viewing direction. This guarantees visibility, while ensuring that a minimal amount of the enclosing volumes is removed, so retaining important, contextual, spatial cues. However, the changing tunnel orientations do not accord with our normal, everyday experience, leading to problems of interpretation. When viewing monoscopic images users have reported a variety of effects, such as difficulty in perceiving correct depths, as well as features which seem to swim independently during rotation. In this paper we report visualising these volumes on a high-quality headtracked, autostereoscopic display. Subjects in our tests demonstrated a clear preference for stereoscopic viewing, as a way to resolve ambiguities.