Torsten W. Kuhlen

Probabilistic fibre tract analysis of cytoarchitectonically defined human inferior parietal lobule areas reveals similarities to macaques

The human inferior parietal lobule (IPL) is a multimodal brain region, subdivided in several cytoarchitectonic areas which are involved in neural networks related to spatial attention, language, and higher motor processing. Tracer studies in macaques revealed differential connectivity patterns of IPL areas as the respective structural basis. Evidence for comparable differential fibre tracts of human IPL is lacking. Here, anatomical connectivity of five cytoarchitectonic human IPL areas to 64 cortical targets was investigated using probabilistic tractography. Connection likelihood was assessed by evaluating the number of traces between seed and target against the distribution of traces from that seed to voxels in the same distance as the target. The main fibre tract pattern shifted gradually from rostral to caudal IPL: Rostral areas were predominantly connected to somatosensory and superior parietal areas while caudal areas more strongly connected with auditory, anterior temporal and higher visual cortices. All IPL areas were strongly connected with inferior frontal, insular and posterior temporal areas. These results showed striking similarities with connectivity patterns in macaques, providing further evidence for possible homologies between these two species. This shift in fibre tract pattern supports a differential functional involvement of rostral (higher motor functions) and caudal IPL (spatial attention), with probable overlapping language involvement. The differential functional involvement of IPL areas was further supported by hemispheric asymmetries of connection patterns which showed left-right differences especially with regard to connections to sensorimotor, inferior frontal and temporal areas.

Comparative analysis of fuzzy ART and ART-2A network clustering performance

Adaptive resonance theory (ART) describes a family of self-organizing neural networks, capable of clustering arbitrary sequences of input patterns into stable recognition codes. Many different types of ART-networks have been developed to improve clustering capabilities. In this paper we compare clustering performance of different types of ART-networks: Fuzzy ART, ART 2A with and without complement encoded input patterns, and an Euclidean ART 2A-variation. All types are tested with two- and high-dimensional input patterns in order to illustrate general capabilities and characteristics in different system environments. Based on our simulation results, Fuzzy ART seems to be less appropriate whenever input signals are corrupted by additional noise, while ART 2A-type networks keep stable in all inspected environments. Together with other examined features, ART-architectures suited for particular applications can be selected.

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.

Depth Perception in Virtual Reality: Distance Estimations in Peri- and Extrapersonal Space

The present study investigated depth perception in virtual environments. Twenty-three participants verbally estimated ten distances between 40 cm and 500 cm in three different virtual environments in two conditions: (1) only one target was presented or (2) ten targets were presented at the same time. Additionally, the presence of a metric aid was varied. A questionnaire assessed subjective ratings about physical complaints (e.g., headache), the experience in the virtual world (e.g., presence), and the experiment itself (self-evaluation of the estimations). Results show that participants underestimate the virtual distances but are able to perceive the distances in the right metric order even when only very simple virtual environments are presented. Furthermore, interindividual differences and intraindividual stabilities can be found among participants, and neither the three different virtual environments nor the metric aid improved depth estimations. Estimation performance is better in peripersonal than in extrapersonal space. In contrast, subjective ratings provide a preferred space: a closed room with visible floor, ceiling, and walls.

Stable Cutting of Deformable Objects in Virtual Environments Using XFEM

Most deformable object simulators suffer from stability problems caused by material slivers in the cut vicinity. The extended finite element method (XFEM) is a novel approach that uses element enrichment to effectively model discontinuities. In combination with an appropriate mass-lumping technique, XFEM provides a stable simulation regardless of cut location.

Virtual reality for physically disabled people

This paper demonstrates how physically disabled people can benefit from the innovative virtual reality techniques. Several specific examples show the applicability of virtual reality to the therapy and rehabilitation of people with various disabilities. In addition, the paper describes how physicians can use virtual reality as an advanced visualization tool for the diagnosis of physical disabilities. Finally, possible display techniques and input devices for diagnosis and rehabilitation purposes are discussed briefly.

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.

VIRACOCHA: An Efficient Parallelization Framework for Large-Scale CFD Post-Processing in Virtual Environments

One recommended strategy for the analysis of CFD-data is the interactive exploration within virtual environments. Common visualization systems are unable to process large data sets while carrying out real-time interaction and visualization at the same time. The obvious idea is to decouple flow feature extraction from visualization. This paper covers the functionality of the parallel CFD post-processing toolkit Viracocha. Two aspects are discussed in more detail. The first approach covers strategies to reduce the loading time. Data caching and prefetching are employed to reduce access time. The second aspect concerns an approach called streaming that minimizes the time a user has to wait for first results. Viracocha already sends coarse intermediate data back to the virtual environment before the final result is available. Different streaming and data handling strategies are described. In order to emphasize the benefit of our implementation efforts, some strategies are applied to multi-block CFD data sets.

ViSTA FlowLib - framework for interactive visualization and exploration of unsteady flows in virtual environments

In the past a lot of work has been invested in various aspects of an interactive visualization of CFD simulation data. This includes e.g. increasing the rendering speed and responsiveness of complex visualizations, using and enhancing multimodal user interfaces, and incorporating parallel approaches for an ef cient extraction of ow properties and their respective visual representation. Still, only few projects combine the signi cant advances in these areas. In this paper, we describe our software framework ViSTA FlowLib, which facilitates merging current research results of various related areas. This is done by connecting dedicated sub-modules with clearly defined responsibilities through appropriate interfaces, whilst implementing sensible default behavior. ViSTA FlowLib combines efficient rendering techniques and a parallel computation of the visualization with intuitive multimodal user interfaces to allow for an interactive exploration of unsteady fluid flows in a virtual environment. Special care has been taken to achieve a high scalability in respect to computing power, projection technology, and input-output device availability.

Horizontal and vertical pseudoneglect in peri- and extrapersonal space

The present study investigates the influence of depth on pseudoneglect in healthy young participants (n=18) within three-dimensional virtual space, by presenting a variation of the greyscales task and a landmark task, which were specifically matched for stimulus-response compatibility, as well as perceptual factors within and across the tasks. Tasks were presented in different depth locations (peripersonal, extrapersonal) and different orientations (horizontal, vertical) within three-dimensional virtual space, using virtual reality technique. A horizontal leftward bias (pseudoneglect) for both tasks was found, which was stronger in peripersonal than in extrapersonal space. For the vertical condition, an upward bias was observed in the greyscales task, but not in the landmark task. These results support the hypotheses of right hemispheric dominance for visual spatial attention and our study is the first to examine horizontal and vertical orienting biases with the greyscales task in peri- and extrapersonal space. Furthermore, the differences in attentional asymmetries with respect to depth suggest dissociable neural mechanisms for visual attentional processing in near and far space and the lack of significant correlations implies independence of horizontal and vertical stimulus processing.