A Hydraulic Haptic Actuator for Simulation of Cardiac Catheters.

This article presents a haptic actuator made of silicone rubber to provide both passive and active haptic forces for catheter simulations. The haptic actuator has a torus outer shape with an ellipse-shaped inside chamber which is actuated by hydraulic pressure. Expansion of the chamber by providing positive pressure can squeeze the inside passage to resist the catheter traveling through. Further expansion can hold and push back the catheter in the axial direction to render active haptic forces. The size of the catheter passage is increased by providing negative pressure to the chamber, allowing various diameters of the actual medical catheters to be used and exchanged during the simulation. The diameter of the catheter passage can be enlarged up to 1.6 times to allow 5 to 7 Fr (1 Fr = 1/3 mm) medical catheters to pass through. Experiment results show that the proposed haptic actuator can render 0 to 2.0 N passive feedback force, and a maximum of 2.0 N active feedback force, sufficient for the cardiac catheter simulation. The haptic actuator can render the commanded force profile with 0.10 N RMS (root-mean-squares) and 10.51% L2-norm relative errors.

Scaling behavior and text cohesion in Korean texts.

This study examines whether different types of texts, particularly in Korean, can be distinguished by the scaling exponent and degree of text cohesion. We use the controlled growth process model to incorporate the interaction effect into a power-law distribution and estimate the implied parameter explaining the degree of text cohesiveness in a word distribution. We find that the word distributions of Korean languages differ from English regarding the range of scaling exponents. Additionally, different types of Korean texts display similar scaling exponents regardless of their genre. However, the interaction effect is higher for expert reports than for the benchmark novels. The findings suggest a valid framework for explaining the scaling phenomena of word distribution based on microscale interactions. It also suggests that a viable method exists for inferring text genres based on text cohesion.

Effects of a Fluoroscopy Agent on Radio Opacity and Steering Performance of Pressure-Driven Steerable Micro Guidewire.

This paper presents experimental results of effects of a fluoroscopy agent on the radio opacity and steering performance of the steerable micro guidewire. The guidewire is driven by internal pressure, and made of the silicone polymer mixed with the barium sulfate, BaSO4, masterbatch. Steerable distal tips with different BaSO4 densities up to 30 % are fabricated. The radio opacity is measured by comparing CT (computed tomography) numbers of the steerable distal tips. The steering performance is measured by the bending angle at particular internal pressures while being bent up to 180 0. Experiment results show that the radio opacity improves while the bending stiffness decreases as the concentration of the barium sulfate increases.

Hydraulically Steerable Micro Guidewire Capable of Distal Sharp Steering.

Current steerable catheters or guidewires often cannot advance into small diameter vessels due to their large diameters or lack of sharp steering capacity. This paper proposes a hydraulically steerable guidewire with 400 µm diameter, which can access 1 mm diameter vessels whose branching angle is larger than 90 degrees. The designed steering mechanism consists of a flexible eccentric tube with inner micro patterns, which can bend in two different curvatures when pressurized. Its distal sharp curve of the 2 mm segment allows access to small diameter vessels because it provides a large steering angle even in confinement inside the narrow vessels. Its proximal gradual curve of the 9 mm segment allows access to relatively large diameter vessels because of its large steering distance. Fabrication of the steering mechanism uses a template and does not use adhesion or division. A 3D printed cylindrical template is patterned by stamping and chemically removed after silicone coating. The performance of selective insertion of the proposed guidewire is evaluated in a blood circulatory system specially developed to mimic human arterial environment. It emulates viscosity, pressure, and flow velocity inside the blood vessels as well as bifurcation geometry. Experiment result shows that the proposed guidewire can access 1 mm diameter vessels with 128 degrees of bifurcation angle. The developed guidewire uses only biocompatible materials including driving fluid.

Adaptive surface representation based on homogeneous hexahedrons for interactive simulation of soft tissue cutting.

BACKGROUND AND OBJECTIVE: Interactive simulation of cutting soft tissues is essential in simulation of surgery and medical procedures. Cutting simulation involves topological and geometrical changes of the finite elements, and requires significant additional computational burden. This problem is handled, in this paper, by approximating a small gap between the model boundaries and the volumetric finite elements. METHOD: Deformations are computed using only the regular hexahedrons, and the surface structure is embedded in the hexahedrons for visualizing the objects and detecting the collisions. Cutting is handled separately for the hexahedrons and the surface structure. The intersected hexahedrons are duplicated in the cutting without geometrical changes, and the surface structure is conformed to the cutting path to represent the cut surfaces faithfully. A method of using partial elements is introduced to compensate for inaccuracies due to the gap between the cut surface and the hexahedron. RESULT: Simulation results show that the additional computation burden of the proposed method is reduced to 34% and 37.12% of the previous method in the literature. The theoretical range of additional arithmetic operations for each method is derived, showing the superiority of the proposed method. CONCLUSION: The proposed method improves the real-time performance of the simulation through an adaptive approximation of the cut surface.

Deformable objects modeling with iterative updates of local positions.

BACKGROUND AND OBJECTIVE: Deformation of elastic material such as soft tissues of human body in the virtual environment is computed based on actual material properties. But this often leads to computational overhead hindering real-time simulation. This paper proposes a new modeling method of deformable objects for real-time simulation, using iterative updates of local positions, and control of the desired behavior by material properties. METHOD: The Saint Venant-Kirchhoff model is used to form the governing equation to express and control the nonlinear behavior and properties of the material. This governing equation is combined with a local iterative solver using position-based dynamics framework. The proposed method updates the local positions iteratively by finding the solution to minimize the energy of related elements surrounding the target nodes. A grouping method is devised to determine the optimal order of computation. RESULT: Various dynamic behaviors can be simulated using the proposed method corresponding to different Young's modulus. Maximum deformations simulated by the proposed method are compared with those results from commercial ANSYS. Relative errors of the real-time simulation results are less than 15% when Young's modulus ranges from 4 kPa to 10 kPa. Real-time performance is evaluated using a liver model composed of 596 tetrahedral elements. CONCLUSION: Simulation results show that the proposed method can simulate, in real-time, the stiffness of the model faithfully according to their material properties.

Investigation on energy bandgap states of amorphous SiZnSnO thin films.

The variation in energy bandgaps of amorphous oxide semiconducting SiZnSnO (a-SZTO) has been investigated by controlling the oxygen partial pressure (Op). The systematic change in Op during deposition has been used to control the electrical characteristics and energy bandgap of a-SZTO. As Op increased, the electrical properties degraded, while the energy bandgap increased systematically. This is mainly due to the change in the oxygen vacancy inside the a-SZTO thin film by controlling Op. Changes in oxygen vacancies have been observed by using X-ray photoelectron spectroscopy (XPS) and investigated by analyzing the variation in density of states (DOS) inside the energy bandgaps. In addition, energy bandgap parameters, such as valence band level, Fermi level, and energy bandgap, were extracted by using ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and high-resolution electron energy loss spectroscopy. As a result, it was confirmed that the difference between the conduction band minimum and the Fermi level in the energy bandgap increased systematically as Op increases. This shows good agreement with the measured results of XPS and DOS analyses.

Grid Generation for Rendering Realistic X-ray Images of Narrow Blood Vessels in Real-time Angiography Simulation.

This paper proposes a method to generate grids to render realistic X-ray images of the narrow blood vessels in real-time angiography simulation. The vertexes of the narrow blood vessels are projected onto the image-rendering plane. The grids aligned in the vessel direction are generated using the projected boundary vertexes on the image-rendering plane. The average computation time of the entire simulation is reduced by 80.17% compared to the simulation using the uniform grids. The results of the questionnaire survey show that the rendered X-ray images are realistic and useful to be applied to the angiography simulation.

A hybrid contact model for cannulation simulation of ERCP.

This paper proposes a hybrid contact model, which enables an efficient simulation of cannulation procedure of ERCP. Meshless model and mass-spring model are employed together to construct the major papilla model. This method divides contact cases into visible and invisible contacts. We employ Signorini's contact model for visible contacts and develop the centerline-based contact model for invisible contacts. The comparison in computation time verifies that our proposed model reduces computation time up to eighty percent.

Markerless tracking for augmented reality for image-guided Endoscopic Retrograde Cholangiopancreatography.

This paper proposes a markerless tracking method with adaptive pose estimation for augmenting 3D organ models on top of the endoscopic image for Endoscopic Retrograde Cholangiopancreatography (ERCP). While many applications of augmented reality (AR) to surgeries need special markers to track the camera's position and orientation in the live video, our method employs the feature detection techniques to track the endoscopic camera. One of the most difficult problems when applying feature-based method to AR for ERCP is the lack of texture & highly specular reflection surface of duodenum in the endoscopic images, which does not provide a stable number of keypoints to track in the endoscopic video sequence. By introducing an adaptive weight function in the combination of reference-current frame tracking with previous-current frame tracking, we enhance the tracking performance remarkably. The proposed method is evaluated using an endoscopic video of a real ERCP and 3D duodenum model reconstructed from CT data of the patient. The result shows real-time performance and robustness of the method.

Dynamic cylindrical free-form deformation for interactive simulation of tool-tissue interaction.

BACKGROUND: Dynamic lattice-based free-form deformation (FFD) allows efficient simulation of global deformation of complex geometric objects. However, directly imposing a number of position constraints due to contact with a tool is non-trivial since it is an over-determined problem. METHOD: This paper extends the FFD to directly impose a number of position constraints for the objects to be embedded in (rounded) cylindrical lattice structures. The position constraints are applied by enabling each surface point to locally deform along the near-normal direction to the surface. RESULT: The computational time of the local deformation is independent of the number of constrained points other than finite element method. As a real-time application, the proposed method is applied to colonoscopic polypectomy simulation running at over 60 Hz. CONCLUSION: The proposed method allows efficient simulation of the global and local deformations of complex geometric objects while achieving accurate tool-tissue interaction in a realistic and robust manner.

Real-time simulation of interaction between colon and endoscope for the colonoscopy simulation.

This paper proposes a novel simulation framework for the real-time deformation of the colon and endoscope using a skeleton-driven deformation method. Cylindrical lattices and a centerline are employed as the skeletons, and a mass-spring model is applied to the skeletons for the mechanics-based simulation. The centerline-based collision detection and resolution algorithm is applied to simulate the interaction between the colon and endoscope. The proposed simulation framework is integrated with a colonoscopy simulation. Simulation results show that the proposed method allows real-time simulation (28 Hz) using the colon model composed of up to 241,440 meshes.

Real-time deformation of colon and endoscope for colonoscopy simulation.

BACKGROUND: Colonoscopy simulation has been increasingly applied as a method of training, which can supplement the traditional patient-based training in recent years. However, the current level of realism of the simulation is insufficient. One of the main difficulties degrading the realism is real-time simulation of colon deformation involving multi-contact interaction with the endoscope. METHODS: This paper proposes a novel simulation framework for real-time deformation of the colon and endoscope, using a skeleton-driven deformation method. Cylindrical lattices and a centre-line are employed as the skeletons, and a mass-spring model is applied to the skeletons for the mechanics-based simulation. The centre-line-based collision detection and resolution algorithm is proposed to simulate the interaction between the colon and endoscope. A haptic rendering algorithm using the energy method is proposed to produce feedback force, based on physical interaction between the colon and endoscope. RESULTS: The proposed simulation framework has been implemented and evaluated in colonoscopy simulation. The simulation results show that the proposed method allows real-time simulation (28 Hz) using a colon model composed of up to 241,440 meshes. CONCLUSIONS: The proposed method allows real-time simulation of colon and endoscope deformation while maintaining a visually plausible result and realistic haptic sensation.

A design of hardware haptic interface for gastrointestinal endoscopy simulation.

Gastrointestinal endoscopy simulations have been developed to train endoscopic procedures which require hundreds of practices to be competent in the skills. Even though realistic haptic feedback is important to provide realistic sensation to the user, most of previous simulations including commercialized simulation have mainly focused on providing realistic visual feedback. In this paper, we propose a novel design of portable haptic interface, which provides 2DOF force feedback, for the gastrointestinal endoscopy simulation. The haptic interface consists of translational and rotational force feedback mechanism which are completely decoupled, and gripping mechanism for controlling connection between the endoscope and the force feedback mechanism.

Real-time resolution of self-intersection in dynamic cylindrical free-form deformation.

This paper presents a method of self-intersection detection and resolution for dynamic cylindrical-lattice-based free-form deformation (FFD). The lattice-based approach allows efficient computation of deformation of complex geometries. But excessive deformation can cause visual anomalies such as surface infiltration and distortion. This paper derives a geometrically intuitive sufficient condition to guarantee that the FFD function is a homeomorphism and there is no self-intersection. The FFD function is defined by linear and quadratic B-Spline functions with the control points of the cylindrical lattice cell. The sufficient condition is satisfied if each trilinear function of the nine prism-shaped pentahedrons derived from the cell has a positive Jacobian determinant. The positivity is satisfied if the 12 tetrahedrons derived from the pentahedron have positive volumes. Based on the sufficient condition, the proposed method converts the self-intersection problem into a point-face collision detection and response problem suitable for dynamic simulation. The efficiency and accuracy of the self-intersection detection algorithm is analyzed and compared with a previous method. The results show that the proposed technique allows simulation of excessive deformation of tubular objects in an efficient and realistic manner.

GPU-based real-time soft tissue deformation with cutting and haptic feedback.

This article describes a series of contributions in the field of real-time simulation of soft tissue biomechanics. These contributions address various requirements for interactive simulation of complex surgical procedures. In particular, this article presents results in the areas of soft tissue deformation, contact modelling, simulation of cutting, and haptic rendering, which are all relevant to a variety of medical interventions. The contributions described in this article share a common underlying model of deformation and rely on GPU implementations to significantly improve computation times. This consistency in the modelling technique and computational approach ensures coherent results as well as efficient, robust and flexible solutions.

Estimation of environmental force for the haptic interface of robotic surgery.

BACKGROUND: The success of a telerobotic surgery system with haptic feedback requires accurate force-tracking and position-tracking capacity of the slave robot. The two-channel force-position control architecture is widely used in teleoperation systems with haptic feedback for its better force-tracking characteristics and superior position-tracking capacity for the maximum stability margin. This control architecture, however, requires force sensors at the end-effector of the slave robot to measure the environment force. However, it is difficult to attach force sensors to slave robots, mainly due to their large size, insulation issues and also large currents often flowing through the end-effector for incision or cautery of tissues. METHODS: This paper provides a method to estimate the environment force, using a function parameter matrix and a recursive least-squares method. The estimated force is used to feed back the force information to the surgeon through the control architecture without involving the force sensors. RESULTS: The simulation and experimental results verify the efficacy of the proposed method. The force estimation error is negligible and the slave device successfully tracks the position of the master device while the stability of the teleoperation system is maintained. CONCLUSIONS: The developed method allows practical haptic feedback for telerobotic surgery systems in the two-channel force-position control scheme without the direct employment of force sensors at the end-effector of the slave robot.

Sectional Analysis of Learning on the KAIST-Ewha Colonoscopy Simulation II.

The goal of this study is to validate the KAIST-Ewha Colonoscopy Simulation II as a training tool by examining the sectional learning curve of the trainees' performance on the simulation. Nine subjects including three fellows and six residents in the internal medicine participated in this study. All the subjects practiced the colonoscopy on the simulation until their performance surpasses the criteria preset by colonoscopy experts. Performance of the subjects during all the trials was measured in terms of eight performance indices and analyzed according to the colon segments. The results show that the trainees' skills significantly improved through training on the KAIST-Ewha Colonoscopy Simulation II. Particularly, most of the improvement appeared in the sigmoid and descending colon. On the other hand, there was little improvement in the ascending colon.

Haptic interface of the KAIST-Ewha colonoscopy simulator II.

This paper presents an improved haptic interface for the Korea Advanced Institute of Science and Technology Ewha Colonoscopy Simulator II. The haptic interface enables the distal portion of the colonoscope to be freely bent while guaranteeing sufficient workspace and reflective forces for colonoscopy simulation. Its force-torque sensor measures the profiles of the user. Manipulation of the colonoscope tip is monitored by four deflection sensors and triggers computations to render accurate graphic images corresponding to the rotation of the angle knob. Tack sensors are attached to the valve-actuation buttons of the colonoscope to simulate air injection or suction as well as the corresponding deformation of the colon. A survey study for face validation was conducted, and the result shows that the developed haptic interface provides realistic haptic feedback for colonoscopy simulations.

Improvement of colonoscopy skills through simulation-based training.

The objective of this study is to determine whether targeted colonoscopy skills are acquired through simulation-based training using the KAIST-Ewha Colonoscopy Simulator II, and the acquired skills can be transferred to colonoscopy to actual patients. Eleven subjects consisting of six fellows and five residents participated in the study. The fellows and residents were divided into two groups, simulation-trained group and control group. Simulation-based training included practicing the targeted skills of colonoscopy using two training scenarios with different colon flexures and degrees of difficulty. The trainees were requested to practice until they reach all the established training goals. The both groups were evaluated during their colonoscopies to actual patients, which were performed under close supervision of colonoscopy experts. The results of this study show that the developed colonoscopy simulator is effective in teaching the targeted colonoscopy skills, and transferring those skills to actual colonoscopy.