Matthias Harders

Evaluation of a virtual-reality-based simulator using passive haptic feedback for knee arthroscopy.

AbstractPurposenThe aim of this work is to determine face validity and construct validity of a new virtual-reality-based simulator for diagnostic and therapeutic knee arthroscopy.MethodsThe study tests a novel arthroscopic simulator based on passive haptics. Sixty-eight participants were grouped into novices, intermediates, and experts. All participants completed two exercises. In order to establish face validity, all participants filled out a questionnaire concerning different aspects of simulator realism, training capacity, and different statements using a seven-point Likert scale (range 1–7). Construct validity was tested by comparing various simulator metric values between novices and experts.ResultsFace validity could be established: overall realism was rated with a mean value of 5.5 points. Global training capacity scored a mean value of 5.9. Participants considered the simulator as useful for procedural training of diagnostic and therapeutic arthroscopy. In the foreign body removal exercise, experts were overall significantly faster in the whole procedure (6xa0min 24xa0s vs. 8xa0min 24xa0s, pxa0<xa00.001), took less time to complete the diagnostic tour (2xa0min 49xa0s vs. 3xa0min 32xa0s, pxa0=xa00.027), and had a shorter camera path length (186 vs. 246xa0cm, pxa0=xa00.006).ConclusionThe simulator achieved high scores in terms of realism. It was regarded as a useful training tool, which is also capable of differentiating between varying levels of arthroscopic experience. Nevertheless, further improvements of the simulator especially in the field of therapeutic arthroscopy are desirable. In general, the findings support that virtual-reality-based simulation using passive haptics has the potential to complement conventional training of knee arthroscopy skills.nLevel of evidenceII.

Identification of Vibrotactile Patterns Encoding Obstacle Distance Information

Delivering distance information of nearby obstacles from sensors embedded in a white cane - in addition to the intrinsic mechanical feedback from the cane - can aid the visually impaired in ambulating independently. Haptics is a common modality for conveying such information to cane users, typically in the form of vibrotactile signals. In this context, we investigated the effect of tactile rendering methods, tactile feedback configurations and directions of tactile flow on the identification of obstacle distance. Three tactile rendering methods with temporal variation only, spatio-temporal variation and spatial/temporal/intensity variation were investigated for two vibration feedback configurations. Results showed a significant interaction between tactile rendering method and feedback configuration. Spatio-temporal variation generally resulted in high correct identification rates for both feedback configurations. In the case of the four-finger vibration, tactile rendering with spatial/temporal/intensity variation also resulted in high distance identification rate. Further, participants expressed their preference for the four-finger vibration over the single-finger vibration in a survey. Both preferred rendering methods with spatio-temporal variation and spatial/temporal/intensity variation for the four-finger vibration could convey obstacle distance information with low workload. Overall, the presented findings provide valuable insights and guidance for the design of haptic displays for electronic travel aids for the visually impaired.

Data-Driven Simulation of Detailed Surface Deformations for Surgery Training Simulators.

Data-driven methods have received increasing attention in recent years in order to meet real-time requirements in computationally intensive tasks. In our current work we examine the application of such approaches in soft-tissue simulation. The core idea is to split deformations into a coarse approximation and a differential part that contains the details. We employ the data-driven stamping approach to enrich a fast simulation surface with details that have been extracted from a set of example deformations obtained in offline computations. In this paper we detail our technique, and suggest further extensions over our previous work. First, we propose an improved method for correlating the current coarse approximation to the examples in the database. The new correlation metric combines Euclidean distances with cosine similarity. It allows for better example discrimination, resulting in a well-conditioned linear system. This also enables us to use a non-negative least squares solver that leads to a better regression and guarantees positive stamp blending weights. Second, we suggest a frequency-space stamp compression scheme that saves memory and, in most instances, is faster, since many operations can be done in the compressed space. Third, cutting is included by employing a physically-inspired influence map that allows for proper handling of material discontinuities that were not present in the original examples. We thoroughly evaluate our method and demonstrate its practical application in a surgical simulator prototype.

Haptic Tumor Augmentation: Exploring Multi-Point Interaction

We currently explore the application of haptic augmentation in the context of palpation training systems. The key idea is to modify real touch sensations with computed haptic feedback. In earlier work, we have introduced an algorithmic framework for determining appropriate augmentation forces during interaction at one contact point. In this paper, we present an extension of the approach to deal with manipulations at more than one contact location. At the heart of our method is the data-driven estimation of Hunt-Crossley model parameters in a pre-computation step. Feeding the parameters into a contact dynamics model allows us to approximate the feedback behavior of various physical tissue mock-ups. Further, we combine the parameter estimation with the tracking of the position of a stiffer inclusion in the mock-up. These data are employed to create a model of movement due to external forces. The combination of these models then allows us to represent and render the mutual effects at multiple contact points. Several experiments have been carried out on a setup with two haptic devices. Comparisons of recorded with simulated interaction data demonstrate the performance and potential of our method.

Augmenting contact stiffness in passive haptics — Preliminary results with twisted string actuation

Haptic feedback is often employed in medical simulators, with the goal to improve user interaction and the training outcome. One option for providing touch sensations is using passive haptics, by including actual physical mock-ups of the anatomical objects in the simulated scene. While this approach has advantages, the usual one-to-one mapping between virtual and physical objects is a fundamental drawback, especially when invasive scene alterations are to be performed, such as cutting or drilling. In this work we propose to alleviate this situation by modifying the mock surgical instruments used for interaction. Twisted string actuation is employed to display variable stiffness while indenting an anatomical model. Quantitative experiments characterizing the performance of a testbed are reported and a prototype system for a surgical bone drill is introduced. Results show that the setup is capable of providing different stiffness augmentations, representing varying bone densities.

Improved Control Methods for Vibrotactile Rendering

Many applications in the domain of haptics make use of vibrotactile rendering. One means for the delivery of the signals is employing voice coil actuators. However, existing control strategies for these exhibit limitations, for instance their dynamic characteristic is often not taken into account leading to output distortion. We propose two new control methods to improve vibrotactile rendering --- once based on data-driven spline interpolation and once on following power spectral density. Both approaches rely on the idea of first decomposing a desired signal into a combination of harmonic components of different frequencies. For these, separate optimal gains are then employed to achieve a flat frequency response. The behavior of these controllers is examined in experiments and compared to a constant gain strategy. Both proposed methods result in improvements, such as lower spectral dissimilarity scores.

Motion-Based Augmented Broadcasting System with Haptic Feedback

This paper introduces a motion-based augmented broadcasting system enabling haptic, auditory, and visual augmentation of conventional television content. An entertainment use case scenario of the proposed system is presented that comprises haptic feedback for playing along with a TV show using virtual musical instruments. In a preliminary study, the influence of providing haptic feedback as well as visual body skeleton augmentation on the performance in selecting an interactive virtual object in the augmented broadcasting system is examined. While the methods of presentation did not show significant improvements, users clearly favored haptic feedback for interaction.

Comparison of Tactile Signals for Collision Avoidance on Unmanned Aerial Vehicles

Our recent work focused on the development of intuitive user interfaces for the control of unmanned aerial vehicles, such as quadcopters. Next to intuitive gesture control, a key challenge with remotely operated quadcopters is the display of information about the aircraft surroundings. To this end, we examined the use of rendering tactile stimuli to warn about nearby obstacles. Directional information and distance is encoded via vibrotactile signals from rotating mass motors. Three different methods of delivering the tactile feedback were tested in a user study. Results show that even though participants guided the quadcopter through a maze by tactile stimuli alone, they were, on average, able to avoid full crashes. Further, we found that using sequential signals to indicate obstacles lead to significantly increased numbers of wall contacts.

Haptic Augmentation in Soft Tissue Interaction

Haptic augmented reality is a new paradigm in human—computer interaction. Akin to traditional visual augmented reality, the technique strives to combine real and virtual sensory stimuli to alter perception during object manipulation. In the context of soft tissue interaction the stimuli felt during contact and indentation of a deformable object are overlaid with forces generated with a haptic device. Such a combined rendering can provide a user with an altered percept of object properties and/or shape. This chapter first outlines the general concept of integrating haptics into augmented reality. Thereafter, we will introduce two heuristic algorithms for haptic augmentation—covering stiffness modulation at either one or two contact points. This will address topics of parameter estimation, contact detection and augmentation computation. Finally, an application example is given in the context of tissue palpation. A method for augmenting virtual stiffer inclusions in physical soft tissue samples is presented.