Projects

Real Time Blood Flow Simulation

One of the challenges in the management of cardiovascular disease (coronary artery disease and peripheral vascular disease) is dealing with many different complex scenarios. The decision on whether or how to intervene is based on separate pieces of information from different sources that need to be integrated to enable a successful outcome for the patient. These include coronary anatomy, results from physiological and imaging tests and the patient’s history and condition. Increasingly patients are being treated who have had previous surgery, coronary angioplasty and who have suffered previous myocardial infarction and have multiple coronary lesions. Any modelling tool incorporating these patient specific characteristics must be highly robust and applicable to a wide range of scenarios. Moreover, in cases where there has been previous myocardial infarction or other damage to the muscle wall, there are a number of additional variables that can affect how the heart responds to treatment. These include the extent of the damage and scarring, presence of collateral vessels, the efficiency of blood flow remodelling of the heart, and any associated valve disease. Nevertheless, due to their limitations, the current diagnostic imaging and procedures may not provide the complete necessary information about the geometry or the dynamics of the vascular system (e.g. some stenosis may be “hidden” further along the vessel), hence subsequent decisions may be prone to error.

An important component of any modern surgical planning tool is an accurate modelling system that simulates realistically any complex mechanical interaction and physiological behaviour of the human body with respect to the surgeon’s actions. Realistic blood flow simulation and its interaction with the vessel walls is one such component. However, the blood flow in complex networks such as collateral coronary circulation received little attention with respect to the interaction between blood flow and vessel walls or blockages, an aspect which can influence the quality of the simulator. Such knowledge of a blockage or aneurysm, it’s spatial or stress distribution, and subsequently the flow structure around it, can provide sensible information about rupture risk or the existence of other similar aneurysms further down the vessel. It is also essential for systems that describe surgical procedures where the view is periodically obscured by additional bleeding or floating tissue fragments. Blood flow patterns play a major role in these events and the body’s response such as collateralization, which is the growth of one or several blood vessels to serve a part of the vascular network that could not function adequately. Coronary collateralization is considered a protective and normal response to hypoxia (a pathological condition in which a region of the body is deprived of an adequate oxygen supply) and can also exist even when blood supply is adequate to an area. To build a very reliable simulator of cardiac events, the blood circulation through a large and complex network of collateral arteries must therefore be based on patient specific data. The virtual blood flow model should respond realistically to dynamic changes in structure, and so illustrate accurately the usage of collateral vessels in a specific predesigned scenario.

(A) Pre-computed domain highlighting the centrifugal forces (Network simplified for clarity). (B) Plane-slice of an artery illustrating the velocity distribution affected by the corresponding centrifugal forces.
Figure 1: (A) Pre-computed domain highlighting the centrifugal forces (Network simplified for clarity). (B) Plane-slice of an artery illustrating the velocity distribution affected by the corresponding centrifugal forces. [PNG]

Our group is actively developing new blood flow models, designed by combining novel concepts from mathematical and computer modelling into efficient, highly adaptive and robust systems which can later on be integrated into any interactive decision support tool for the management of patients with cardiovascular disease. One of these models (Directed Particle System - DPS) uses artificially intelligent virtual blood particles to visualize in real-time the blood flow through complex geometries. Based on the computer graphics concept of flocking agents, DPS approximates flow phenomena accurately through massive networks of vessels (reconstructed as 3D geometry) in real-time, responding to blockages and dynamic changes to the myocardial wall. The model is built respecting the structural format of existing particle dynamics systems for fluids such as Smoothed Particle Hydrodynamics, however significant computational requirements are reduced by optimizing the search for nearby DPS particles. The number of DPS particles inside the domain during the entire simulation is kept statistically constant so that the system’s mass is conserved. As in the SPH method, each DPS particle carries its own physical quantities such as mass, speed and position, which enable control over the main physical parameters of the fluid and ensures the accuracy of the model. The computational resources required to run the system in real-time on a standard PC desktop configuration are drastically reduced by applying several novel techniques and modelling considerations. Currently, DPS requires low computational time and so simulations can be performed on large domains such as complex real patient arterial networks.

The same domain is flooded with DPS particles in real-time. (A) Global view of the network; (B) Cut-away centreline view of the network.
Figure 2: The same domain is flooded with DPS particles in real-time. (A) Global view of the network; (B) Cut-away centreline view of the network. [PNG]

Related Publications

  1. Pop, S. R., Hughes, C. J., Ap Cenydd, L., John, N. W., & others. (2012). A directed particle system for optimised visualization of blood flow in complex networks. Studies In Health Technology and Informatics, 184, 330–336. [bib]
  2. John, N. W., Hughes, C., Pop, S., Vidal, F. P., & Buckley, O. (2009). Computational Requirements of the Virtual Patient. In First International Conference on Computational and Mathematical Biomedical Engineering (CMBE09), Swansea June 2009. [bib]

Transperineal Ultrasound-Guided Biopsy Simulator

Health care professionals can use high-fidelity virtual training simulation (VTS) so that necessary procedures may be practised and refreshed before operating on a real person. Advantages of relying on such controlled learning environments includes; zero patient risk, development of psychomotor skills for the medical tools and the opportunity to experience challenging ‘what if’ scenarios. In this theme we explore the use of haptics in a series of haptic-enabled biopsy simulators, such as Transperineal Prostate and Kidney biopsies. We couple haptic devices, such as Phantom Omnis with novel interfaces such as zSpace and Oculus Rift.

During a transperineal prostate biopsy, the needle is injected through the grid, which is placed against the perineum, into the prostate and a sample is selected. Our prototype uses physical props for the body with a grid attached, a Geomagic Touch and a G-Coder Simball 4D. The main guiding visualization for the process is the ultrasound display mock-up.
Figure 1: During a transperineal prostate biopsy, the needle is injected through the grid, which is placed against the perineum, into the prostate and a sample is selected. Our prototype uses physical props for the body with a grid attached, a Geomagic Touch and a G-Coder Simball 4D. The main guiding visualization for the process is the ultrasound display mock-up. [JPG]

Related Publications

  1. Ritsos, P. D., Edwards, M. R., Shergill, I. S., & John, N. W. (2015). A Haptics-enabled Simulator for Transperineal Ultrasound-Guided Biopsy. In K. Bühler, L. Linsen, & N. W. John (Eds.), Eurographics Workshop on Visual Computing for Biology and Medicine. The Eurographics Association. [bib]

Low-Cost Wheelchair Simulation

Our simulator, called wheelchair-rift, consists of a controllable virtual wheelchair and a series of different navigation tasks that replicate issues faced by wheelchair users in the real world. Wheelchair-rift has been created using a game development platform, called Unity3D, and is able to run on standard Windows and Mac computers. Currently it supports a generic rear drive wheelchair with the correct physics to model realistic motion. However, other wheelchair types can easily be included. To view and interact with the virtual environment, a combination of the Oculus Rift Head Mounted Display (HMD), a Leap Motion hand tracking device, and a Microsoft XBox controller are used. The HMD supports head tracking and allows the users to look around the environment and feel completely immersed in the virtual world. The Leap Motion allows the users to interact with objects in the virtual world using their own hands. The joystick on the Xbox controller is the main navigation interface, representing the joystick on a real wheelchair.

Several scenarios have been designed to simulate the skills of real life usage. They include: a maze of corridors with tight turns to practice manoeuvrability in indoor spaces; another maze filled with a complex arrangement of doorways; a room of moving objects that simulates crossing a crowed room of people; and a task containing a series of ramps to be traversed. The Unity3D software provides extensive support for creating any indoor or outdoor environment and so the inclusion of additional scenarios in the future will be straightforward. Metrics such as the time taken to travel a room, number of collisions, or navigation paths can be automatically recorded and used in various assessments.

Different views of the wheelchair trainer prototype environment. The images depict the obstacle course where users train on spatial awareness and movement, the instruction cues (teal text) which provide the user with information on how to complete the level, and third-person views of the wheelchair itself. The user
Figure 1: Different views of the wheelchair trainer prototype environment. The images depict the obstacle course where users train on spatial awareness and movement, the instruction cues (teal text) which provide the user with information on how to complete the level, and third-person views of the wheelchair itself. The user's view is rendered through the Oculus Rift head-mounted display. Using the Leap Motion hand tracking the users natural gestures are captured and rendered into the virtual world. [PNG]

Wheelchair-rift has been demonstrated to professionals from four Posture and Mobility units in the UK to provide initial face validation. In particular, we needed to assess the fidelity of the wheelchairs functionality. Each test subject used the simulator for up to 15 minutes and attempted the different navigation scenarios. Overall, a positive response was given about the potential of the simulator. Some improvements were identified, such as being able to adjust the wheelchairs settings to suit the user, and the inclusion of more manoeuvrability and navigation tasks. Cyber-sickness whilst using the HMD was identified as an issue for some users, with every individual affected in a different way and degree. The panel also discussed other assessments that a wheelchair user would have to complete, including spatial perception, reaction time and visual tests.

Related Publications

  1. Headleand, C. J., Day, T., Pop, S. R., Ritsos, P. D., & John, N. W. (2016). A Cost-Effective Virtual Environment for Simulating and Training Powered Wheelchairs Manoeuvres. In Proceedings of NextMed/MMVR22 (pp. 134–141). IOS Press. [bib]
  2. Headleand, C. J., Day, T., Pop, S. R., Ritsos, P. D., & John, N. W. (2015). Challenges and Technologies for Low Cost Wheelchair Simulation. In K. Bühler, L. Linsen, & N. W. John (Eds.), Eurographics Workshop on Visual Computing for Biology and Medicine. The Eurographics Association. [bib]