Surgical scene visualization

		Cutting of small vessels causes moderate bleeding Heavy bleeding obscure the view Streamlines in the uterine cavity Textured training scene with a myoma A different training scene

In the project we focused on generating realistic visual display of the intra-uterine scene, including interactive processes, for instance bleeding or application of the hydrometra.

The first part of the work was concentrating on the simulation of the distension liquid in the uterine cavity. During hysteroscopy the uterus is distended by irrigation liquid to access the cavity. The flow of the liquid, which can be adjusted by setting the in- and outlet valves on the hysteroscope, is an important aid for the surgeon to obtain a clear view of the operation scene. In the simulator, this has been modeled by using a physically-based fluid solver in 3D, which approximates the flow in real-time. The boundary conditions for the fluid solver are provided by the other modules of the simulator, i.e. the endometrium, pathologies, tool position, in- and outflow intensity. For high intensity flows, the calculated flow field is extended with artificial vortices to better capture the turbulent phase of the flow. The velocity information resulting from the calculated flow field is used to affect the bleeding, move the cut tissue and debris in the virtual scene.

The next part of the project aimed at developing a solution that can produce a visually appealing representation of bleeding for a hysteroscopic simulator. The intra-uterine bleeding is a primary factor in hysteroscopy. The bleeding, which determines the field of view and can cause critical cases, has to be properly handled by the gynecologist, mainly by adjusting the in- and outlet valves on the tool. In the simulator, the bleeding is modeled as a stream of particles which are dynamically textured and alpha-blended. Due to the numerous tuning parameters, versatile bleeding can be configured from focal to diffuse types as well. The movement of the particles is affected by both the blood source and the flow field induced by the distension fluid circulation.

The third part is the coherent texturing of the surgical scene. A basic requirement in the complete texturing solution for the hysteroscopic simulator is the ability to provide realistic texturing on the surfaces and under surfaces of the uterus and pathologies. As the texture can vary substantial over the life cycle of the uterus and with different pathologies, a fully automatic texturing framework that allows for easy user interaction has been developed. The framework makes it possible for a novice user to design their own surgical scenarios with an evolving library of textures. The library of textures consists of in-vivo images forming a ground-truth database. These have then been re-synthesised to produce tileable, variable textures that can be mapped onto arbitrary 3D mesh geometry. The mapping is provided through a mesh parameterization, which takes into account visibility of seams and distortion reduction. Finally, textures are blended across the seams and the junctions between different objects, e.g. pathologies and healthy tissue, to reduce boundary artifacts. The complete framework is automated, allowing for easy user interaction to design and create individual texturing scenarios to meet the needs of the surgical training simulator.