Computer aided display of 3D angiograms, using graphics and haptics

Current visualization methods for large volume angiograms share the difficulty of having to display depth information using conventional two-dimensional screens, while static viewing conditions between two consecutive rotations are often required. This thesis presents new directions towards the interactive display of and navigation through cerebral vessel networks.To reduce the computational load and storage requirements; a method is developed to extract a centerline representation of the vessel network from volume images. Shape attributes such as the position of the center point as well as the cross-sectional size, tangent, curvature, torsion and bifurcation of the vessel, are either contained in the representation or can be obtained from it by simple finite differences.A computer agent is introduced to convey depth information. Its first function is to assist a user to trace interactively the vessels without effort. This is accomplished by mapping the user's two dimensional input to three dimensional space, where the vessel centerlines are represented. The agent, programmed to track the centerlines, eliminates the topological ambiguities associated with the projection of three dimensional lines on a two dimensional screen. It also conveys quantitative depth information in the graphic and haptic domains. In the graphic domain, its visual appearance uses shape and color cues to indicate unambiguously its movements in the depth direction. In the haptic domain, the user experiences force cues that also indicate its movements in the depth direction.User performance studies indicate that the graphic and haptic depth cues provide equivalent assistance to a user in coping with the missing depth information. This suggests that in a variety of circumstances, the haptic modality can be used to release the visual modality from the task of depth discrimination, resulting in reduced visual fatigue. It also makes it possible to allocate graphic space to the display of other types of information.The developed user-interactive multimodal display techniques can be integrated in current display platforms for volume angiograms due to the small computational load they require. These techniques can also be applied to the display of more general shapes by replacing the centerline of vessels by the user movement curve that, is constrained on a more general three-dimensional surface