Sebastian Ullrich

Haptic Palpation for Medical Simulation in Virtual Environments

Palpation is a physical examination technique where objects, e.g., organs or body parts, are touched with fingers to determine their size, shape, consistency and location. Many medical procedures utilize palpation as a supplementary interaction technique and it can be therefore considered as an essential basic method. However, palpation is mostly neglected in medical training simulators, with the exception of very specialized simulators that solely focus on palpation, e.g., for manual cancer detection. In this article we propose a novel approach to enable haptic palpation interaction for virtual reality-based medical simulators. The main contribution is an extensive user study conducted with a large group of medical experts. To provide a plausible simulation framework for this user study, we contribute a novel and detailed interaction algorithm for palpation with tissue dragging, which utilizes a multi-object force algorithm to support multiple layers of anatomy and a pulse force algorithm for simulation of an arterial pulse. Furthermore, we propose a modification for an off-the-shelf haptic device by adding a lightweight palpation pad to support a more realistic finger grip configuration for palpation tasks. The user study itself has been conducted on a medical training simulator prototype with a specific procedure from regional anesthesia, which strongly depends on palpation. The prototype utilizes a co-rotational finite-element approach for soft tissue simulation and provides bimanual interaction by combining the aforementioned techniques with needle insertion for the other hand. The results of the user study suggest reasonable face validity of the simulator prototype and in particular validate medical plausibility of the proposed palpation interaction algorithm.

Virtual reality-based simulator for training in regional anaesthesia

BACKGROUND The safe performance of regional anaesthesia (RA) requires theoretical knowledge and good manual skills. Virtual reality (VR)-based simulators may offer trainees a safe environment to learn and practice different techniques. However, currently available VR simulators do not consider individual anatomy, which limits their use for realistic training. We have developed a VR-based simulator that can be used for individual anatomy and for different anatomical regions. METHODS Individual data were obtained from magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) without contrast agent to represent morphology and the vascular system, respectively. For data handling, registration, and segmentation, an application based on the Medical Imaging Interaction Toolkit was developed. Suitable segmentation algorithms such as the fuzzy c-means clustering approach were integrated, and a hierarchical tree data structure was created to model the flexible anatomical structures of peripheral nerve cords. The simulator was implemented in the VR toolkit ViSTA using modules for collision detection, virtual humanoids, interaction, and visualization. A novel algorithm for electric impulse transmission is the core of the simulation. RESULTS In a feasibility study, MRI morphology and MRA were acquired from five subjects for the inguinal region. From these sources, three-dimensional anatomical data sets were created and nerves modelled. The resolution obtained from both MRI and MRA was sufficient for realistic simulations. Our high-fidelity simulator application allows trainees to perform virtual peripheral nerve blocks based on these data sets and models. CONCLUSIONS Subject-specific training of RA is supported in a virtual environment. We have adapted segmentation algorithms and developed a VR-based simulator for the inguinal region for use in training for different peripheral nerve blocks. In contrast to available VR-based simulators, our simulation offers anatomical variety.

A simulation framework for sensor-based systems in second life

This paper describes a simulation framework for sensor-based systems based on Second Life, a popular virtual 3D multi-user online world. With this platform, the components of sensor-based systems can be mapped to, or represented by, virtual devices and objects. The intuitive user interface of Second Life (SL) and its comprehensive visualization capability support evaluation tasks of ubiquitous computing applications. Developers, as avatars, can directly control and manipulate virtual devices. In this way, different settings of sensor-based systems can be tested, and interactively improved. A bidirectional interface between sensor-based systems and Second Life has been implemented to demonstrate Second Life as a testbed for an RFID-based positioning system.

An intersubject variable regional anesthesia simulator with a virtual patient architecture

PurposeThe main purpose is to provide an intuitive VR-based training environment for regional anesthesia (RA). The research question is how to process subject-specific datasets, organize them in a meaningful way and how to perform the simulation for peripheral regions.MethodsWe propose a flexible virtual patient architecture and methods to process datasets. Image acquisition, image processing (especially segmentation), interactive nerve modeling and permutations (nerve instantiation) are described in detail. The simulation of electric impulse stimulation and according responses are essential for the training of peripheral RA and solved by an approach based on the electric distance.ResultsWe have created an XML-based virtual patient database with several subjects. Prototypes of the simulation are implemented and run on multimodal VR hardware (e.g., stereoscopic display and haptic device). A first user pilot study has confirmed our approach.ConclusionThe virtual patient architecture enables support for arbitrary scenarios on different subjects. This concept can also be used for other simulators. In future work, we plan to extend the simulation and conduct further evaluations in order to provide a tool for routine training for RA.

Haptic Pulse Simulation for Virtual Palpation

In this paper we propose a software-based approach to simulate the haptics of the human pulse. This effect can then be interactively explored by virtual palpation. The algorithm features a flexible, user-defined setup. In addition the simulation takes dynamic parameters into account and allows for many different use cases.

Influence of the bimanual frame of reference with haptics for unimanual interaction tasks in virtual environments

In this paper, we present the results of a user study with a bimanual haptic setup. The goal of the experiment was to evaluate if Guiards theory of the bimanual frame of reference can be applied to interaction tasks in virtual environments (VE) with haptic rendering. This theory proposes an influence of the non-dominant hand (NDH) on the dominant hand (DH). The experiment was conducted with multiple trials under two different conditions: bimanual and unimanual. The interaction task in this scenario was a sequence of pointing, alignment and docking sub-tasks for the dominant hand. In the bimanual condition, an asynchronous pointing task was added for the non-dominant hand. This additional task was primarily designed to bring the non-dominant hand closer to the other hand and thus enable the creation of a frame of reference. Our results show the potential of this task design extension (with NDH utilization). Task completion times are significantly lower in the bimanual condition compared to the unimanual case, without significant impact on overall precision. Furthermore, the bimanual condition shows better mean accuracy over several measures, e.g., lateral displacement and penetration depth. Additionally, subject performance was not only compared for all participants, but also between subgroups: medical vs. non-medical and gamer vs. non-gamer. User preference for a bimanual system over a unimanual system has been indicated with a post-test questionnaire.

Bimanual haptic simulator for medical training: system architecture and performance measurements

In this paper we present a simulator for two-handed haptic interaction. As an application example, we chose a medical scenario that requires simultaneous interaction with a hand and a needle on a simulated patient. The system combines bimanual haptic interaction with a physics-based soft tissue simulation. To our knowledge the combination of finite element methods for the simulation of deformable objects with haptic rendering is seldom addressed, especially with two haptic devices in a non-trivial scenario. Challenges are to find a balance between real-time constraints and high computational demands for fidelity in simulation and to synchronize data between system components. The system has been successfully implemented and tested on two different hardware platforms: one mobile on a laptop and another stationary on a semi-immersive VR system. These two platforms have been chosen to demonstrate scaleability in terms of fidelity and costs. To compare performance and estimate latency, we measured timings of update loops and logged event-based timings of several components in the software.

Subject-Based Regional Anaesthesia Simulator Combining Image Processing and Virtual Reality

In this paper, a novel virtual reality-based simulator for regional anaesthesia is presented. Individual datasets of patients with nerve cords are created from medical scans with the help of advanced segmentation and registration algorithms. Techniques for interaction and immersive visualization are utilized by the simulator to improve training of medical residents.

Comprehensive Architecture for Simulation of the Human Body Based on Functional Anatomy

In this paper we propose a structured approach for the simulation of the human body which is comprehensive and extendable. Our architecture resembles the human organism as defined by the systematic and functional anatomy to integrate a broad range of simulation algorithms. To share common data and to create interlinks between algorithms without modifying the algorithms themselves we introduce abstract control entities that mimic the basic setup of physiological systems. We utilize the model-view-controller pattern to establish a separation of algorithms and data. The structure was designed for the purpose of interactive simulation of the human body in virtual environments.

MITK-based segmentation of co-registered MRI for subject-related regional anesthesia simulation

With a steadily increasing indication, regional anesthesia is still trained directly on the patient. To develop a virtual reality (VR)-based simulation, a patient model is needed containing several tissues, which have to be extracted from individual magnet resonance imaging (MRI) volume datasets. Due to the given modality and the different characteristics of the single tissues, an adequate segmentation can only be achieved by using a combination of segmentation algorithms. In this paper, we present a framework for creating an individual model from MRI scans of the patient. Our work splits in two parts. At first, an easy-to-use and extensible tool for handling the segmentation task on arbitrary datasets is provided. The key idea is to let the user create a segmentation for the given subject by running different processing steps in a purposive order and store them in a segmentation script for reuse on new datasets. For data handling and visualization, we utilize the Medical Imaging Interaction Toolkit (MITK), which is based on the Visualization Toolkit (VTK) and the Insight Segmentation and Registration Toolkit (ITK). The second part is to find suitable segmentation algorithms and respectively parameters for differentiating the tissues required by the RA simulation. For this purpose, a fuzzy c-means clustering algorithm combined with mathematical morphology operators and a geometric active contour-based approach is chosen. The segmentation process itself aims at operating with minimal user interaction, and the gained model fits the requirements of the simulation. First results are shown for both, male and female MRI of the pelvis.