Quantifying perception of nonlinear elastic tissue models using multidimensional scaling

Simplified soft tissue models used in surgical simulations cannot perfectly reproduce all material behaviors. In particular, many tissues exhibit the Poynting effect, which results in normal forces during shearing of tissue and is only observed in nonlinear elastic material models. In order to investigate and quantify the role of the Poynting effect on material discrimination, we performed a multidimensional scaling (MDS) study. Participants were presented with several pairs of shear and normal forces generated by a haptic device during interaction with virtual soft objects. Participants were asked to rate the similarity between the forces felt. The selection of the material parameters – and thus the magnitude of the shear\ud and normal forces – was based on a pre-study prior to the MDS experiment. It was observed that for nonlinear elastic tissue models exhibiting the Poynting effect, MDS analysis indicated that both shear and normal forces affect user perception

Robust interactive cutting based on an adaptive octree simulation mesh

We present an adaptive octree based approach for interactive cutting of deformable objects. Our technique relies on efficient refine- and node split-operations. These are sufficient to robustly represent cuts in the mechanical simulation mesh. A high-resolution surface embedded into the octree is employed to represent a cut visually. Model modification is performed in the rest state of the object, which is accomplished by back-transformation of the blade geometry. This results in an improved robustness of our approach. Further, an efficient update of the correspondences between simulation elements and surface vertices is proposed. The robustness and efficiency of our approach is underlined in test examples as well as by integrating it into a prototype surgical simulato

Evaluation of a new virtual-reality training simulator for hysteroscopy

Background: To determine realism and training capacity of HystSim, a new virtual-reality simulator for the training of hysteroscopic interventions. Methods: Sixty-two gynaecological surgeons with various levels of expertise were interviewed at the 13th Practical Course in Gynaecologic Endoscopy in Davos, Switzerland. All participants received a 20-min hands-on training on the simulator and filled out a four-page questionnaire. Twenty-three questions with respect to the realism of the simulation and the training capacity were answered on a seven-point Likert scale along with 11 agree-disagree statements concerning the HystSim training in general. Results: Twenty-six participants had performed more than 50 hysteroscopies ("experts”) and 36 equal to or fewer than 50 ("novices”). Four of 60 (6.6%) responding participants judged the overall impression as "7 - absolutely realistic”, 40 (66.6%) as "6 - realistic”, and 16 (26.6%) as "5 - somewhat realistic”. Novices (6.48; 95% confidence interval [CI] 6.28-6.7) rated the overall training capacity significantly higher than experts (6.08; 95% CI 5.85-6.3), however, high-grade acceptance was found in both groups. In response to the statements, 95.2% believe that HystSim allows procedural training of diagnostic and therapeutic hysteroscopy, and 85.5% suggest that HystSim training should be offered to all novices before performing surgery on real patients. Conclusion: Face validity has been established for a new hysteroscopic surgery simulator. Potential trainees and trainers assess it to be a realistic and useful tool for the training of hysteroscopy. Further systematic validation studies are needed to clarify how this system can be optimally integrated into the gynaecological curriculu

Establishing construct validity of a virtual-reality training simulator for hysteroscopy via a multimetric scoring system

Background: The aims of this study are to determine construct validity for the HystSim virtual-reality (VR) training simulator for hysteroscopy via a new multimetric scoring system (MMSS) and to explore learning curves for both novices and experienced surgeons. Methods: Fifteen relevant metrics had been identified for diagnostic hysteroscopy by means of hierarchical task decomposition. They were grouped into four modules (visualization, ergonomics, safety, and fluid handling) and individually weighted, building the MMSS for this study. In a first step, 24 novice medical students and 12 experienced gynecologists went through a self-paced teaching tutorial, in which all participants received clearly stated goals and instructions on how to carry out hysteroscopic procedures properly for this study. All subjects performed five repeated trials on two different exercises on HystSim (exploration and diagnosis exercises). After each trial the results were presented to the participants in the form of an automated objective feedback report (AOFR). Construct validity for the MMSS and learning curves were investigated by comparing the performance between novices and experienced surgeons and in between the repeated trials. To study the effect of repeated practice, 23 of the novices returned 2weeks later for a second training session. Results: Comparing novices with the experienced group, the ergonomics and fluid handling modules resulted in construct validity, while the visualization module did not, and for the safety module the experienced group even scored significantly lower than novices in both exercises. The overall score showed only construct validity when the safety module was excluded. Concerning learning curves, all subjects improved significantly during the training on HystSim, with clear indication that the second training session was beneficial for novice surgeons. Conclusions: Construct validity for HystSim has been established for different modules of VR metrics on a new MMSS developed for diagnostic hysteroscopy. Careful refinement and further testing of metrics and scores is required before using them as assessment tools for operative skill

Haptic Simulation of Breast Cancer Palpation: A Case Study of Haptic Augmented Reality

ABSTRACT Haptic augmented reality (AR) allows to modulate the haptic properties of a real object by providing virtual haptic feedback. We previously developed a haptic AR system wherein the stiffness of a real object can be augmented with the aid of a haptic interface. To demonstrate its potential, this paper presents a case study for medical training of breast cancer palpation. A real breast model made of soft silicone is augmented with a virtual tumor rendered inside. Haptic stimuli for the virtual tumor are generated based on a contact dynamics model identified via real measurements, without the need of geometric information on the breast. A subjective evaluation confirmed the realism and fidelity of our palpation system

Evaluation of a new virtual-reality training simulator for hysteroscopy

BACKGROUND: To determine realism and training capacity of HystSim, a new virtual-reality simulator for the training of hysteroscopic interventions. METHODS: Sixty-two gynaecological surgeons with various levels of expertise were interviewed at the 13(th) Practical Course in Gynaecologic Endoscopy in Davos, Switzerland. All participants received a 20-min hands-on training on the simulator and filled out a four-page questionnaire. Twenty-three questions with respect to the realism of the simulation and the training capacity were answered on a seven-point Likert scale along with 11 agree-disagree statements concerning the HystSim training in general. RESULTS: Twenty-six participants had performed more than 50 hysteroscopies ("experts") and 36 equal to or fewer than 50 ("novices"). Four of 60 (6.6%) responding participants judged the overall impression as "7 - absolutely realistic", 40 (66.6%) as "6 - realistic", and 16 (26.6%) as "5 - somewhat realistic". Novices (6.48; 95% confidence interval [CI] 6.28-6.7) rated the overall training capacity significantly higher than experts (6.08; 95% CI 5.85-6.3), however, high-grade acceptance was found in both groups. In response to the statements, 95.2% believe that HystSim allows procedural training of diagnostic and therapeutic hysteroscopy, and 85.5% suggest that HystSim training should be offered to all novices before performing surgery on real patients. CONCLUSION: Face validity has been established for a new hysteroscopic surgery simulator. Potential trainees and trainers assess it to be a realistic and useful tool for the training of hysteroscopy. Further systematic validation studies are needed to clarify how this system can be optimally integrated into the gynaecological curriculum

Einleitung

Harders A-C. Einleitung. In: Haake M, Harders A-C, eds. Politische Kultur und soziale Struktur der Römischen Republik. Bilanzen und Perspektiven. Akten der internationalen Tagung anlässlich des 70. Todestages von Friedrich Münzer (Münster, 18.-20. Oktober 2012). Stuttgart: Steiner; 2017: 13-26