Stefan Tuchschmid

Evaluation of a new virtual-reality training simulator for hysteroscopy

BackgroundTo determine realism and training capacity of HystSim, a new virtual-reality simulator for the training of hysteroscopic interventions.MethodsSixty-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.ResultsTwenty-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.ConclusionFace 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.

Adaptive Space Warping to Enhance Passive Haptics in an Arthroscopy Surgical Simulator

Passive haptics, also known as tactile augmentation, denotes the use of a physical counterpart to a virtual environment to provide tactile feedback. Employing passive haptics can result in more realistic touch sensations than those from active force feedback, especially for rigid contacts. However, changes in the virtual environment would necessitate modifications of the physical counterparts. In recent work space warping has been proposed as one solution to overcome this limitation. In this technique virtual space is distorted such that a variety of virtual models can be mapped onto one single physical object. In this paper, we propose as an extension adaptive space warping; we show how this technique can be employed in a mixed-reality surgical training simulator in order to map different virtual patients onto one physical anatomical model. We developed methods to warp different organ geometries onto one physical mock-up, to handle different mechanical behaviors of the virtual patients, and to allow interactive modifications of the virtual structures, while the physical counterparts remain unchanged. Various practical examples underline the wide applicability of our approach. To the best of our knowledge this is the first practical usage of such a technique in the specific context of interactive medical training.

Virtual reality based simulation of hysteroscopic interventions

Virtual reality based simulation is an appealing option to supplement traditional clinical education. However, the formal integration of training simulators into the medical curriculum is still lacking. Especially, the lack of a reasonable level of realism supposedly hinders the widespread use of this technology. Therefore, we try to tackle this situation with a reference surgical simulator of the highest possible fidelity for procedural training. This overview describes all elements that have been combined into our training system as well as first results of simulator validation. Our framework allows the rehearsal of several aspects of hysteroscopyfor instance, correct fluid management, handling of excessive bleeding, appropriate removal of intra-uterine tumors, or the use of the surgical instrument.

Modeling intravasation of liquid distension media in surgical simulators

During therapeutic hysteroscopy and transurethral resection of the prostate, intravasation of the liquid distension media into the vascular system of the patient occurs. We present a model which allows the integration of the intravasation process into surgical simulator systems. A linear network flow model is extended with a correction for non-Newtonian blood behavior in small vessels and an appropriate handling of vessel compliance. We employ a fast lookup scheme in order to allow for real-time simulation. Cutting of tissue is accounted for by adjusting pressure boundary conditions for all cut vessels. We investigate the influence of changing distention fluid pressure settings and of the position of tissue cuts. In addition, we quantify the intravasation occurring with different approaches of fluid control, and we compare the performance of direct and iterative solvers applied to the non-linear system of the compliant model. Our simulation predicts significant intravasation only on the venous side, and just in cases when larger veins are cut. The implemented methods allow the realistic control of bleeding for short-term and of the total resulting intravasation volume for long-term complication scenarios. While the simulation is fast enough to support real-time training, it is also adequate for explaining intravasation effects which were previously observed on a phenomenological level only.

A flexible framework for highly-modular surgical simulation systems

We present a modular software framework which is currently used for high-fidelity surgical simulation of hysteroscopic interventions. Main design criteria was to meet various real-time requirements without losing maintainability or extensibility of the overall system. Moreover, communication and synchronization tools were developed for the multi-threaded environment. The efficiency and scalability of a convenient thread-based parallelization scheme is demonstrated for the distension fluid computation, as well as the collision detection algorithm. Performance measurements on a four processor system show an almost perfect scalability for larger problems

Modelling intravasation of liquid distension media in surgical simulators

We simulate the intravasation of liquid distention media into the systemic circulation as it occurs during hysteroscopy and transurethral resection of the prostate. A linear network flow model is extended with a correction for non-newtonian blood behaviour in small vessels and an appropriate handling of vessel compliance. We then integrate a fast lookup scheme in order to allow for real-time simulation. Cutting of tissue is accounted for by adjusting pressure boundary conditions for all cut vessels. We investigate the influence of changing distention fluid pressure settings and of the position of tissue cuts. Our simulation predicts significant intravasation only on the venous side, and just in cases when larger veins are cut. The implemented methods allow the realistic control of bleeding for short-term and the total resulting intravasation volume for long-term complication scenarios. While the simulation is fast enough to support real-time training, it is also adequate for explaining intravasation effects which were previously observed on a phenomenological level only.

Comparing automatic simulator assessment with expert assessment of virtual surgical procedures

This study focuses on the comparison of expert assessment of virtual surgical procedures through Objective Structured Assessment of Technical Skills (OSATS) with the automatic assessment and feedback provided by a surgical simulator for hysteroscopic procedures. The existing multi-metric scoring system of the simulator was extended to include hysteroscopic myomectomy. The original OSATS was also modified for the examined surgical procedure. OSATS reliability, expert coherence, and interrater agreement with simulator feedback were investigated in a study with eight experts. The same selection of six movies showing virtual procedures performed at a hysteroscopy training course was rated by each expert. For the task-specific checklist, the reliability of the simulator was significantly higher than that of the individual human raters (p=0.006). In addition, the ranked order of the overall scores of all movies was the same for both simulator and expert consensus opinion. This is a first step to providing simulator feedback with the same reliability as an expert panel, thus facilitating competency-based surgical education and assessment in the near future.