Particle-based Visualization of Soft-Tissue Deformation in the Human Orbit

Orbital fat is the soft tissue inside the eye socket, or orbit, that surrounds the eye muscles, eyeball, optic nerve and blood vessels. It plays an important role in the mechanical operation of the eye during eyeball rotation. Knowledge of how this orbital fat behaves is limited. It is important for surgeons to improve this knowledge to make better informed decisions before and during eye surgery. Visualization of the deformation of orbital fat can improve this knowledge. Herein lie two problems. First, we do not have accurate and detailed information on how the orbital fat deforms. Second, we do not have a visualization method that provides the necessary insight into orbital fat deformation data. We obtain deformation data by deriving it from a sequence of MRI volumes that represent the rotating eyeball. We do this by using a method from the optic flow family, which uses the changing tissue boundaries in the MRI data to locally extract deformation data. We visualize this deformation data using a particle-based method. In particle-based visualization, a large number of tiny, point-like particles are placed inside part of the volume. The positions of individual particles are affected by the deformation data. We smoothly animate the particles as they move through the orbit while the eyeball rotates, giving a detailed impression of the deformation of a subvolume of orbital fat. Demarcation of where inside the volume to place the particles is called region of interest (ROI) specification. We developed a method that uses anatomical information from the MRI volumes to specify sensible ROIs. We implemented our solutions in two software tools that work together to allow quick exploration of deformation from a sequence of MRI volumes. Experts in the fields of ophthalmology and biomechanics have expressed that our visualization software is a significant improvement over previous techniques and that the software should continue to be developed.