A multi-core CPU pipeline architecture for virtual environments.

Physically-based virtual environments (VEs) provide realistic interactions and behaviors for computer-based medical simulations. Limited CPU resources have traditionally forced VEs to be simplified for real-time performance. Multi-core processors greatly increase the computational capacity of computers and are quickly becoming standard. However, developing non-application specific methods to fully utilize all available CPU cores for processing VEs is difficult. The paper describes a pipeline VE architecture designed for multi-core CPU systems. The architecture enables development of VEs that leverage the computational resources of all CPU cores for VE simulation. A VE's workload is dynamically distributed across the available CPU cores. A VE can be developed once and scale efficiently with the number of cores. The described pipeline architecture makes it possible to develop complex physically-based VEs for medical simulations. Initial results for a craniotomy simulator being developed have shown super-linear and near-linear speedups when tested with up to four cores.

Collaborative voxel-based surgical virtual environments.

Virtual Reality-based surgical simulators can utilize Collaborative Virtual Environments (C-VEs) to provide team-based training. To support real-time interactions, C-VEs are typically replicated on each user's local computer and a synchronization method helps keep all local copies consistent. This approach does not work well for voxel-based C-VEs since large and frequent volumetric updates make synchronization difficult. This paper describes a method that allows multiple users to interact within a voxel-based C-VE for a craniotomy simulator being developed. Our C-VE method requires smaller update sizes and provides faster synchronization update rates than volumetric-based methods. Additionally, we address network bandwidth/latency issues to simulate networked haptic and bone drilling tool interactions with a voxel-based skull C-VE.

Far forward feasibility: testing a cricothyroidotmy simulator in Iraq.

This study describes our experience with using a virtual reality simulator, CricSim, to enhance the training of combat medics to perform a cricothyroidotomy (surgical airway) while in Iraq. Over a six month period, 65 medics used the simulator as part of a Combat Medic Advanced Skills Training class while in Iraq and were asked to evaluate it. Students self-assessed comfort level with the procedure improved dramatically from baseline (p<5.6 x 10(-17)). The CricSim was rated highly on realism but only moderately on ease of use. The use of this simulator in a far forward setting was feasible, enhanced training, and provided necessary end-user feedback for future development of this training platform.

Burrhole simulation for an intracranial hematoma simulator.

Traumatic head injuries can cause internal bleeding within the brain. The resulting hematoma can elevate intracranial pressure, leading to complications and death if left untreated. A craniotomy may be required when conservative measures are ineffective. To augment conventional surgical training, a Virtual Reality-based intracranial hematoma simulator is being developed. A critical step in performing a craniotomy involves cutting burrholes in the skull. This paper describes volumetric-based haptic and visual algorithms developed to simulate burrhole creation for the simulator. The described algorithms make it possible to simulate several surgical tools typically used for a craniotomy.

An interactive three-dimensional virtual body structures system for anatomical training over the internet.

The Visible Human digital datasets make it possible to develop computer-based anatomical training systems that use virtual anatomical models (virtual body structures-VBS). Medical schools are combining these virtual training systems and classical anatomy teaching methods that use labeled images and cadaver dissection. In this paper we present a customizable web-based three-dimensional anatomy training system, W3D-VBS. W3D-VBS uses National Library of Medicine's (NLM) Visible Human Male datasets to interactively locate, explore, select, extract, highlight, label, and visualize, realistic 2D (using axial, coronal, and sagittal views) and 3D virtual structures. A real-time self-guided virtual tour of the entire body is designed to provide detailed anatomical information about structures, substructures, and proximal structures. The system thus facilitates learning of visuospatial relationships at a level of detail that may not be possible by any other means. The use of volumetric structures allows for repeated real-time virtual dissections, from any angle, at the convenience of the user. Volumetric (3D) virtual dissections are performed by adding, removing, highlighting, and labeling individual structures (and/or entire anatomical systems). The resultant virtual explorations (consisting of anatomical 2D/3D illustrations and animations), with user selected highlighting colors and label positions, can be saved and used for generating lesson plans and evaluation systems. Tracking users' progress using the evaluation system helps customize the curriculum, making W3D-VBS a powerful learning tool. Our plan is to incorporate other Visible Human segmented datasets, especially datasets with higher resolutions, that make it possible to include finer anatomical structures such as nerves and small vessels.

Haptic laparoscopic skills trainer with practical user evaluation metrics.

Limited sense of touch and vision are some of the difficulties encountered in performing laparoscopic procedures. Haptic simulators can help minimize these difficulties; however, the simulators must be validated prior to actual use. Their effectiveness as a training tool needs to be measured in terms of improvement in surgical skills. LapSkills, a haptic skill-based laparoscopic simulator, that aims to provide a quantitative measure of the surgeon's skill level and to help improve their efficiency and precision, has been developed. Explicitly defined performance metrics for several surgical skills are presented in this paper. These metrics allow performance data to be collected to quantify improvement within the same skill over time. After statistically significant performance data is collected for expert and novice surgeons, these metrics can be used not only to validate LapSkills, but to also generate a performance scale to measure laparoscopic skills.

Dynamic generation of surgery specific simulators -- a feasibility study.

Most of the current surgical simulators rely on preset anatomical virtual environments (VE). The functionality of a simulator is typically fixed to anatomy-based specific tasks. This rigid design principle makes it difficult to reuse an existing simulator for different surgeries. It also makes it difficult to simulate procedures for specific patients, since their anatomical features or anomalies cannot be easily replaced in the VE. In this paper, we demonstrate the reusability of a modular skill-based simulator, LapSkills, which allows dynamic generation of surgery-specific simulations. Task and instrument modules are easily reused from LapSkills and the three-dimensional VE can be replaced with other anatomical models. We build a nephrectomy simulation by reusing the simulated vessels and the clipping and cutting task modules from LapSkills. The VE of the kidney is generated with our anatomical model generation tools and then inserted into the simulation (while preserving the established tasks and evaluation metrics). An important benefit for the created surgery and patient-specific simulations is that reused components remain validated. We plan to use this faster development process to generate a simulation library containing a wide variety of laparoscopic surgical simulations. Incorporating the simulations into surgical training programs will help collect data for validating them.

Web-based three-dimensional Virtual Body Structures: W3D-VBS.

Major efforts are being made to improve the teaching of human anatomy to foster cognition of visuospatial relationships. The Visible Human Project of the National Library of Medicine makes it possible to create virtual reality-based applications for teaching anatomy. Integration of traditional cadaver and illustration-based methods with Internet-based simulations brings us closer to this goal. Web-based three-dimensional Virtual Body Structures (W3D-VBS) is a next-generation immersive anatomical training system for teaching human anatomy over the Internet. It uses Visible Human data to dynamically explore, select, extract, visualize, manipulate, and stereoscopically palpate realistic virtual body structures with a haptic device. Tracking user's progress through evaluation tools helps customize lesson plans. A self-guided "virtual tour" of the whole body allows investigation of labeled virtual dissections repetitively, at any time and place a user requires it.

Heuristic haptic texture for surgical simulations.

Generation of credible force feedback renderings adds the sense of touch crucial for the development of a realistic virtual surgical environment. However, a number of difficulties must be overcome before this can be achieved. One of the problems is the paucity of data on the in-vivo tissue compliance properties needed to generate acceptable output forces. Without this "haptic texture," the sense of touch component remains relatively primitive and unrealistic. Current research in the quantitative analysis of biomechanics of living tissue, including collection of in-vivo tissue compliance data using specialized sensors, has made tremendous progress. However, integration of all facets of biomechanical data in order to transfer them into haptic texture remains a very difficult problem. For this reason, we are attempting to create a library of heuristic haptic textures of anatomical structures. The library of heuristic haptic textures will capture the expert's sense of feel for selected anatomical structures and will be used to convey the sense of touch for surgical training simulations. Once the techniques for converting biomechanical data into haptic texture become more robust, this library can be used as a benchmark to verify theoretical computational models used for generating output forces in haptic devices.