Tracing Tubular Objects in 3D Confocal Images Using Haptic Device

Blood capillaries in brain [5] and skeletal muscle [1] can be visualized and studied in 3D by confocal microscopy. 3D data enable direct analysis of the geometric properties of complex networks by image analysis techniques. The graphs of capillaries that cannot be detected automatically due to low contrast, high noise or complicated background but are clearly visible can still be digitized manually using a 3D editing program. We use a custom made program for PC with 3D interface. The interface consists of stereoscopic volume rendering of images with 3D cursor with 6 degrees of freedom (DOF) controlled by a haptic device (SensableOmni, SenseGraphics AB, Sweden) with 3 DOF force proportional to the gradient of the image intensity. The haptic feedback serves as a cue for depth perception and allows better placement of cursor in the capillaries. The program enables 3D drawing of capillaries as chains of line segments, moving individual points, connecting the chains together or splitting them and deleting the vertices or whole chains. All operations are stored in a queue and can be reversed by undo/redo commands. The virtual camera position is controlled interactively by mouse or by 6 DOF device (Space Navigator, 3dconnexion, USA).