"A multi-core CPU pipeline architecture for virtual environments"

Acosta E, Liu A, Sieck J, Muniz G, Bowyer MW, Armonda R. Stud Health Technol Inform, 2009, vol. 142, pp. 10-12.

Abstract: 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 standards. 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 the 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.

"Far Forward Feasibility: Testing a Cricothyroidotomy Simulator in Iraq"

Bowyer MW, Manahl M, Acosta E, Stutzmen J, Liu A. Stud Health Technol Inform, 2008, vol. 132, pp. 37-41.

Abstract: 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 x10-17). 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.

Real-time interactions and synchronization of voxel-based collaborative virtual environments"

Eric Acosta, Alan Liu. IEEE Symposium on 3D User Interfaces, 2007, pp. 131-137.

Abstract: Collaborative virtual environments (C-VE) facilitate team-oriented training on Virtual Reality-based surgical simulators. Many C-VEs replicate the VE on each user's machine to allow for real-time interactions. However, this solution does not work well when modifying voxel-based C-VEs because large and frequent volumetric updates make it difficult to synchronize the C-VE. This paper describes a hybrid depth-buffered image (DBI) and geometry-based rendering method created to simulate visual interactions between local virtual bone cutting tools and remotely maintained volumetric bone material for a craniotomy simulator. For real-time interactions, users only store a DBI of the volumetric C-VE and composite it with rendered images of surgical tools. Additionally, we describe methods to combat network bandwidth/latency to remotely simulate haptic and bone drilling interactions between users' tools and the volumetric VE. For haptic feedback, a multi-rate solution allows users to construct a local approximation of the volumetric C-VE to compute new forces. Only 2D DBI updates are required to synchronize different users when the bone changes due to drilling. Our approach provides an improved performance over a replicated VE that uses 3D model-based updates.

"Real-time volumetric haptic and visual burrhole simulation"

Eric Acosta, Alan Liu. IEEE Virtual Reality 2007, pp. 247-250.

Abstract: This paper describes real-time volumetric haptic and visual algorithms developed to simulate burrhole creation for a Virtual Reality based craniotomy surgical simulator. A modified Voxmap pointshell algorithm is created to simulate haptic interactions between bone cutting tools and voxel-based bone. New surface boundary detection and force feedback calculation methods help reduce “force discontinuities” of the original Voxmap point-shell algorithm. To maintain stable haptic update rates, new forces are calculated outside the haptics rendering loop. A multi-rate haptic solution is used to introduce calculated forces into the haptics loop and to interpolate forces between updates. A bone erosion method is also created to simulate bone drilling capabilities of different tools. 3D texture-based volume rendering is used to display the bone and to visually remove bone material due to drilling in real-time. Volumetric shading is computed by the GPU of the video card. The algorithms described make it possible to simulate several tools typically used for a craniotomy. Realistic 3D models are also created from real surgical tools and controlled by the haptic device.

"Burrhole Simulation for an Intracranial Hematoma Simulator"

Eric Acosta, Alan Liu, Rocco Armonda, Michael J. Fiorill, Randy Haluck, Carol Lake, Gilbert Muniz, and Mark Bowyer. Studies in Health Technology and Informatics, 2007, vol. 125, pp. 1-6.

Abstract: 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.

"Towards an Immersive Virtual Environment for Medical Team Training"

Chang Ha Lee, Alan Liu, Sofia del Castillo, Mark Bowyer, Dale Alverson, Gilbert Muniz, Thomas P. Caudell. Studies in Health Technology and Informatics, 2007, vol. 125, pp. 274-9.

Abstract: Many computer based medical simulators focus on individual skills training. However, medical care is frequently rendered by teams. In addition, the conditions under which care is provided can be a crucial factor in training. For example, mass-casualty events can involve the management and triage of large numbers of victims under austere environments. Learning to care for the injured warfighter during combat requires realistic simulation of battlefield conditions. Current simulation systems do not adequately address team training requirements within lifelike environments. This paper describes our work toward the development of an immersive virtual environment that meets these needs.

"The Design and Implementation of a Pulmonary Artery Catheterization Simulator"

Alan Liu, Yogendra Bhasin, Michael Fiorill, Mark Bower, Randy Haluck. Studies in Health Technology and Informatics, vol. 119, pp. 334-9, IOS Press 2006.

Abstract: Pulmonary Artery Catheterization (PAC) is a commonly performed procedure. It is used when hemodynamic and other cardiac measures must be accurately monitored in seriously ill patients. A flow-directed, balloon-tipped (Swan-Ganz) catheter is typically inserted into a major vein, passed through the heart, and into the pulmonary artery. This procedure is normally not performed under fluoroscopy. Instead, transducer readings from the catheter tip provide a continuous report of local blood pressure. An experienced practitioner can infer the catheter's location from this information, yet several studies have found that physicians and critical care nurses have a wide variability in competency. A simulator for this procedure can address some of the educational and training issues highlighted. This paper describes our ongoing progress in developing a PAC trainer.

"Bounds for Damping that Guarantee Stability in Mass-Spring Systems"

Yogendra Bhasin, Alan Liu. Studies in Health Technology and Informatics, vol. 119, pp. 55-60, IOS Press 2006.

Abstract: Mass-spring systems are often used to model anatomical structures in medical simulation. They can produce plausible deformations in soft tissue, and are computationally efficient. Determining damping values for a stable mass-spring system can be difficult. Previously stable models can become unstable with topology changes, such as during cutting. In this paper, we derive bounds for the damping coefficient in a mass-spring system. Our formulation can be used to evaluate the stability for user specified damping values, or to compute values that are unconditionally stable.

"A Haptic-Enabled Simulator for Cricothyroidotomy"

Alan Liu, Yogendra Bhasin, Mark Bower. Studies in Health Technology and Informatics, vol. 111., pp. 308-313. IOS Press, 2005.

Abstract: Cricothyroidotomy is an emergency procedure that is performed when the patient's airway is blocked, and less invasive attempts to clear it have failed. Cricothyroidotomy has been identified as an essential skill for military readiness. This training is relevant to more than 40,000 U.S. military medics, and thousands of civilian health care providers. Current training methods use animals, cadavers and plastic mannequins. Animal models do not have the correct anatomy. Cadavers do not have the correct physiology. Mannequins do not adequately cover the full range of anatomical variations. In this paper, we describe our effort to build a computer-based cricothyroidotomy simulator to address these problems.

"Simulating Surgical Incisions Without Polygon Subdivision"

Yogendra Bhasin, Alan Liu, Mark Bowyer. Studies in Health Technology and Informatics, vol. 111., pp. 43-49, IOS Press, 2005.

Abstract: Modeling cuts, bleeding and the insertion of surgical instruments are essential in surgical simulation. Both visual and haptic cues are important. Current methods to simulate cuts change the topology of the model, invalidating pre-processing schemes or increasing the model's complexity. Bleeding is frequently modeled by particle systems or computational fluid dynamics. Both can be computationally expensive. Surgical instrument insertion, such as intubation, can require complex haptic models. In this paper, we describe methods for simulating surgical incisions that do not require such computational complexity, yet preserve the visual and tactile appearance necessary for realistic simulation.

"A Study on the Perception of Haptics in Surgical Simulation"

Lukas Batteau, Alan Liu, J.B. Antoine Maintz, Yogendra Bhasin, Mark Bowyer. Lecture Notes in Computer Science vol. 3078, pp. 185-192, 2004.

Abstract: Physically accurate modeling of human soft-tissue is an active research area in surgical simulation. The challenge is compounded by the need for real-time feedback. A good understanding of human haptic interaction can facilitate tissue modeling research, as achieving accuracy beyond perception may be counterproductive. This paper studies the human sensitivity to haptic feedback. Specifically, the ability of individuals to consistently recall specific haptic experience, and their ability to perceive latency in haptic feedback. Results suggest that individual performance varies widely, and that this ability is not correlated with clinical experience. A surprising result was the insensitivity of test subjects to significant latency in haptic feedback. The implications of our findings to the design and development of surgical simulators are discussed.

"A Survey of Surgical Simulation: Applications, Technology, and Education"

Alan Liu, Frank Tendick, Kevin Cleary, Christoph Kaufmann. The final version of this article will be published in Presence , Vol. 12, Issue 6, (December 2003), published by The MIT Press.

Abstract: Surgical simulation for medical education is increasingly perceived as a valuable addition to traditional teaching methods. Simulators provide a structured learning experience, permitting practice without danger to patients. Simulators facilitate the teaching of rare or unusual cases. Simulators can also be used to provide an objective assessment of skills. This paper is a survey of current surgical simulator systems. The components of a simulator are described, current research directions are discussed, and key research questions are identified.

"A computer-based simulator for diagnostic peritoneal lavage"

Alan Liu, Christoph Kaufmann, Thomas Ritchie. Published in Medicine Meets Virtual-Reality, 2001.

Abstract: Diagnostic peritoneal lavage (DPL) is an emergency diagnostic procedure performed when intra-abdominal bleeding secondary to trauma is suspected. This procedure is part of the surgical skills section of the Advanced Trauma Life Support course. DPL is traditionally taught using anesthetized animals or cadavers. For reasons described below, these alternatives are not ideal. We have developed a computer-based diagnostic peritoneal lavage simulator. Our system addresses the shortcomings of the traditional method. We have used our system to teach ATLS®. Preliminary results suggests that our system is effective.

The Presentation


"An architecture for simulating needle-based surgical procedures"

Alan Liu, Christoph Kaufmann, Daigo Tanaka. Medical Image Computing and Computer-Assisted Intervention (MICCAI), Lecture Notes in Computer Science 2208 Springer 2001, ISBN 3-540-42697-3, pp. 1137-11144, 2001.

Abstract: Many surgical procedures use cannulas, guidewires, and catheters in the treatment of life threatening conditions (e.g. cardiac tamponade and tension pneumothorax), or for diagnosis (e.g. diagnostic peritoneal lavage). Simulator development is costly in time and resources. Most computer-based trainers are procedure-specific. Each trainer uses a different hardware configuration. The cost of using multiple simulators for teaching is prohibitive. A result is decreased acceptance of simulation for teaching. A generalized software architecture has been developed that simplifies the process of constructing trainers for needle-based surgical procedures. Different procedures use the same hardware platform. The architecture has been used to develop two trauma simulators. A third simulator is currently being developed using this architecture.

"The Evaluation of the Color Blending Function for the Texture Generation from Photographs"

Daigo Tanaka, Alan Liu, Christoph Kaufmann. Medical Image Computing and Computer-Assisted Intervention (MICCAI), Lecture Notes in Computer Science 2208 Springer 2001, ISBN 3-540-42697-3, pp. 1199-1200, 2001.

Abstract: Mass-casualty triage simulation requires the realistic depiction of wounds and other signs of external injury on victims. Texture maps permit images of actual wounds to be rendered over computer models. Several images may be required to depict extensive injuries. Seamlessly combining these images requires an appropriate blending function. This paper compares two functions for their ability to create visually appealing integrations.

"First Steps in Eliminating the Need for Animals and Cadavers in Advanced Trauma Life Support®"

Christoph Kaufmann, Scott Zakaluzny, Alan Liu. Published in Medical Image Computing and Computer-Assisted Intervention (MICCAI), Lecture Notes in Computer Science 1935 Springer 2000 ISBN 3-540-41189-5, pp. 618-623, 2000.

Abstract: The Advanced Trauma Life Support® course is designed to provide for optimal initial resuscitation of the seriously injured patient. The surgical skills component of this course requires the use of cadavers or anesthetized animals. Significant anatomical differences and ethical issues limit the utility of animals. The cost and difficulty in procuring cadavers makes widespread use of this option impractical. A combination of mannequin and computer-based surgical simulators is being developed to replace these animals and cadavers. The first of these simulators, a pericardiocentesis trainer, is complete.