This paper presents in vivo mechanical characterization of the muscularis, submucosa, and mucosa of the porcine stomach wall under large deformation loading. This is particularly important for the development of gastrointestinal pathology-specific surgical intervention techniques. The study is based on testing the cardiac and fundic glandular stomach regions using a custom-developed compression ultrasound elastography system. Particular attention has been paid to elucidate the heterogeneity and anisotropy of tissue response. A Fung hyperelastic material model has been used to model the mechanical response of each tissue layer. A univariate analysis comparing the initial shear moduli of the three layers indicates that the muscularis (5.69 ± 4.06 kPa) is the stiffest followed by the submucosa (3.04 ± 3.32 kPa) and the mucosa (0.56 ± 0.28 kPa). The muscularis is found to be strongly distinguishable from the mucosa tissue in the cardiac and fundic regions based on a multivariate discriminant analysis. The cardiac muscularis is observed to be stiffer than the fundic muscularis tissue (shear moduli of 7.96 ± 3.82 kPa versus 3.42 ± 2.96 kPa), more anisotropic (anisotropic parameter of 2.21 ± 0.77 versus 1.41 ± 0.38), and strongly distinguishable from its fundic counterpart. The results are consistent with the tissue morphology and are in accordance with our previous ex vivo tissue study. Finally, a univariate comparison of the in vivo and ex vivo initial shear moduli for each layer shows that the muscularis and submucosa tissues are softer while in vivo, but the mucosa tissue is stiffer while in vivo. The results concerning the mechanical properties highlight the inhomogeneity and anisotropy of multilayer stomach tissue.
Surgery is characterized by complex tasks performed in stressful environments. To enhance patient safety and reduce errors, surgeons must be trained in environments that mimic the actual clinical setting. Rasmussen’s model of human behavior indicates that errors in surgical procedures may be skill-, rule-, or knowledge-based. While skill-based behavior and some rule-based behavior may be taught using box trainers and ex vivo or in vivo animal models, we posit that multimodal immersive virtual reality (iVR) that includes high-fidelity visual as well as other sensory feedback in a seamless fashion provides the only means of achieving true surgical expertise by addressing all three levels of human behavior. While the field of virtual reality is not new, realization of the goals of complete immersion is challenging and has been recognized as a Grand Challenge by the National Academy of Engineering. Recent technological advances in both interface and computational hardware have generated significant enthusiasm in this field. In this paper, we discuss convergence of some of these technologies and possible evolution of the field in the near term.
In this paper we report the development of a technique to characterize layer-specific nonlinear material properties of soft tissue in situ with the potential for in vivo testing. A Soft Tissue Elastography Robotic Ann (STiERA) system comprising of a robotically manipulated 30 MHz high-resolution ultrasound probe, a custom designed compression head and load cells has been developed to perform compression ultrasound imaging on the target tissue and measure reaction forces. A multi-layer finite element model is iteratively optimized to identify the material coefficients of each layer. Validation has been performed using tissue mimicking agar-based phantoms with a low relative error of ~7% for two--layer phantoms and ~10% error for three layer phantoms when compared to known ground-truth values obtained using a commercial material testing system. The technique has then been used to successfully determine the in situ layer-specific mechanical properties of intact porcine stomach. The mean C10 and C20 for a second order reduced polynomial material model were determined for the muscularis (6.41±0.60, 4.29±1.87 kPa), submucosal (5.21±0.57, 3.68±3.01 kPa) and mucosal layers (0.06±0.02, 0.09±0.24 kPa). Such a system can be utilized to perform in vivo mechanical characterization, which is left as future work.
Natural orifice translumenal endoscopic surgery (NOTES) is viewed as an emerging surgical technique with significant potential to perform surgical interventions with minimal external scarring and reduced patient trauma. However, this technique uses an endoscope to perform surgical operations which require application of substantial forces and torques for insertion and maneuvering. We have, for the first time, developed an instrumented tool handle with a 6 axis load cell to measure the forces and torques applied during NOTES procedures and used it to make actual measurements during the performance of NOTES techniques by surgeons using an ex-vivo simulator. Data were collected for 10 subjects with varying experience levels at the annual SAGES meeting. We observed that the typical forces were about 10 N with peaks up to 25 N in the push/pull direction. A nominal torque of 50 N-mm with peaks up to 200 N-mm in the clockwise and counter-clockwise directions was observed about the push/pull axis. In comparison, the interaction forces in traditional laparoscopic surgery are in the range of 0-10 N. The data are useful not only in understanding the level of force and torque applied during actual NOTES procedures, but also in developing specifications for a custom haptic feedback system for a virtual reality-based NOTES simulator designed to train the next generation of NOTES surgeons.
Natural orifice translumenal endoscopic surgery (NOTES) is a minimally invasive procedure, which utilizes the body’s natural orifices to gain access to the peritoneal cavity. The NOTES procedure is designed to minimize external scarring and patient trauma, however flexible endoscopy based pure NOTES procedures require critical scope handling skills. The delicate nature of the NOTES procedure requires extensive training, thus to improve access to training while reducing risk to patients we have designed and developed the VTEST©, a virtual reality NOTES simulator. As part of the simulator, a novel decoupled 2-DOF haptic device was developed to provide realistic force feedback to the user in training. A series of experiments were performed to determine the behavioral characteristics of the device. The device was found capable of rendering up to 5.62N and 0.190Nm of continuous force and torque in the translational and rotational DOF, respectively. The device possesses 18.1Hz and 5.7Hz of force bandwidth in the translational and rotational DOF, respectively. A feedforward friction compensator was also successfully implemented to minimize the negative impact of friction during the interaction with the device. In this work we have presented the detailed development and evaluation of the haptic device for the VTEST©.
We have developed an instrumented endoscope grip handle equipped with a 6-axis load cell and measured forces and torques during a simulated transgastric NOTES appendectomy procedure performed in an EASIE-R© ex vivo simulator. The data were collected from 10 participating surgeons of varying degrees of expertise which was analyzed to compute a set of 6 force and torque parameters for each coordinate axis for each of the nine tasks of the appendectomy procedure. The mean push/pull force was found to be 3.64 N (σ=3.54 N) in the push direction and the mean torque was 3.3 N-mm (σ=38.6 N-mm) in the counter-clockwise direction about the push/pull axis. Most interestingly, the force and torque data about the non-dominant×and z axes showed a statistically significant difference (p<0.05) between the expert and novice groups for five of the nine tasks. This data may be useful in developing surgical platforms especially new haptic devices and simulation systems for emerging natural orifice procedures.
Background Natural Orifice Translumenal Endoscopic Surgery (NOTES) is an emerging surgical paradigm, where peritoneal access is achieved through one of the natural orifices of the body. It is being reported as a safe and feasible surgical technique with significantly reduced external scarring. Virtual Translumenal Endoscopic Surgical Trainer (VTEST™) is the first virtual reality simulator for the NOTES. The VTEST™ simulator was developed to train surgeons in the hybrid transvaginal NOTES cholecystectomy procedure. The initial version of the VTEST™ simulator underwent face validation at the 2013 Natural Orifice Surgery Consortium for Assessment and Research (NOSCAR) summit. Several areas of improvement were identified as a result, and the corresponding modifications were implemented in the simulator. This manuscript outlines the results of the subsequent evaluation study, performed in order to assess the face and content validity of the latest VTEST™ simulator. Methods Twelve subjects participated in an Institutional Review Board (IRB) approved study that took place at the 2014 NOSCAR summit. Six of the twelve subjects, that are experts with NOTES experience, were used for face and content validation. The subjects performed the hybrid transvaginal NOTES cholecystectomy procedure on VTEST™ that included identification of the Calot’s triangle, clipping and cutting the cystic duct/artery, and detaching the gallbladder. The subjects then answered 5-point Likert scale feedback questionnaires for face and content validity. Results Overall, subjects rated 12/15 questions as 3.0 or greater (60%), for face validity questions regarding the realism of the anatomical features, interface and the tasks. Subjects also highly rated the usefulness of the simulator in learning the fundamental NOTES technical skills (3.50 ± 0.84). Content validity results indicate a high level of usefulness of the VTEST™ for training prior to operating room experience (4.17 ± 0.75).
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