Organ-mounted robot localization via function approximation.

BACKGROUND: Organ-mounted robots adhere to the surface of a mobile organ as a platform for minimally invasive interventions, providing passive compensation of physiological motion. This approach is beneficial during surgery on the beating heart. Accurate localization in such applications requires accounting for the heartbeat and respiratory motion. Previous work has described methods for modeling quasi-periodic motion of a point and registering to a static preoperative map. The existing techniques, while accurate, require several respiratory cycles to converge. METHODS: This paper presents a general localization technique for this application, involving function approximation using radial basis function (RBF) interpolation. RESULTS: In an experiment in the porcine model in vivo, the technique yields mean localization accuracy of 1.25 mm with a 95% confidence interval of 0.22 mm. CONCLUSIONS: The RBF approximation provides accurate estimates of robot location instantaneously.

Beating-heart registration for organ-mounted robots.

BACKGROUND: Organ-mounted robots address the problem of beating-heart surgery by adhering to the heart, passively providing a platform that approaches zero relative motion. Because of the quasi-periodic deformation of the heart due to heartbeat and respiration, registration must address not only spatial registration but also temporal registration. METHODS: Motion data were collected in the porcine model in vivo (N = 6). Fourier series models of heart motion were developed. By comparing registrations generated using an iterative closest-point approach at different phases of respiration, the phase corresponding to minimum registration distance is identified. RESULTS: The spatiotemporal registration technique presented here reduces registration error by an average of 4.2 mm over the 6 trials, in comparison with a more simplistic static registration that merely averages out the physiological motion. CONCLUSIONS: An empirical metric for spatiotemporal registration of organ-mounted robots is defined and demonstrated using data from animal models in vivo.

Physiological motion modeling for organ-mounted robots.

BACKGROUND: Organ-mounted robots passively compensate heartbeat and respiratory motion. In model-guided procedures, this motion can be a significant source of information that can be used to aid in localization or to add dynamic information to static preoperative maps. METHODS: Models for estimating periodic motion are proposed for both position and orientation. These models are then tested on animal data and optimal orders are identified. Finally, methods for online identification are demonstrated. RESULTS: Models using exponential coordinates and Euler-angle parameterizations are as accurate as models using quaternion representations, yet require a quarter fewer parameters. Models which incorporate more than four cardiac or three respiration harmonics are no more accurate. Finally, online methods estimate model parameters as accurately as offline methods within three respiration cycles. CONCLUSIONS: These methods provide a complete framework for accurately modelling the periodic deformation of points anywhere on the surface of the heart in a closed chest.

Parallel Force/Position Control of an Epicardial Parallel Wire Robot.

Gene therapies for heart failure have emerged in recent years, yet they lack an effective method for minimally invasive, uniform delivery. To address this need we developed a minimally invasive parallel wire robot for epicardial interventions. Accurate and safe interventions using this device require control of force in addition to injector position. Accounting for the nonidealities of the device design, however, yields nonlinear and underconstrained statics. This work solves these equations and demonstrates the efficacy of using this information in a parallel control scheme, which is shown to provide superior positioning compared to a position-only controller.

Design of a Coupled Thermoresponsive Hydrogel and Robotic System for Postinfarct Biomaterial Injection Therapy.

BACKGROUND: In preclinical testing, ventricular wall injection of hydrogels has been shown to be effective in modulating ventricular remodeling and preserving cardiac function. For some approaches, early-stage clinical trials are under way. The hydrogel delivery method varies, with minimally invasive approaches being preferred. Endocardial injections carry a risk of hydrogel regurgitation into the circulation, and precise injection patterning is a challenge. An epicardial approach with a thermally gelling hydrogel through the subxiphoid pathway overcomes these disadvantages. METHODS: A relatively stiff, thermally responsive, injectable hydrogel based on N-isopropylacrylamide and N-vinylpyrrolidone (VP gel) was synthesized and characterized. VP gel thermal behavior was tuned to couple with a transepicardial injection robot, incorporating a cooling feature to achieve injectability. Ventricular wall injections of the optimized VP gel have been performed ex vivo and on beating porcine hearts. RESULTS: Thermal transition temperature, viscosity, and gelling time for the VP gel were manipulated by altering N-vinylpyrrolidone content. The target parameters for cooling in the robotic system were chosen by thermal modeling to support smooth, repeated injections on an ex vivo heart. Injections at predefined locations and depth were confirmed in an infarcted porcine model. CONCLUSIONS: A coupled thermoresponsive hydrogel and robotic injection system incorporating a temperature-controlled injectate line was capable of targeted injections and amenable to use with a subxiphoid transepicardial approach for hydrogel injection after myocardial infarction. The confirmation of precise location and depth injections would facilitate a patient-specific planning strategy to optimize injection patterning to maximize the mechanical benefits of hydrogel placement.

Toward hybrid force/position control for the Cerberus epicardial robot.

Gene therapies have emerged as a promising treatment for congestive heart failure, yet they lack a method for minimally invasive, uniform delivery. To address this need we developed Cerberus, a minimally invasive parallel wire robot for cardiac interventions. Prior work on Cerberus was limited to controlling the device using only position feedback. In order to ensure safety for both the patient and the device, as well as to improve the performance of the device, this paper presents work on enhancing the existing system with force feedback capabilities. By modeling the statics of the system and developing a tension distribution optimization technique, existing position control schemes were modified to a hybrid force/position controller. Experimental results show that using a hybrid force-position control scheme as opposed to position decreases positioning error by 38%.

Auto-Calibration for a Planar Epicardial Wire Robot.

Gene therapies have emerged as a promising treatment for congestive heart failure, yet they lack a method for minimally invasive, uniform delivery. To address this need we developed Cerberus, a minimally invasive parallel wire robot for cardiac interventions. Prior work on controlling the movement of Cerberus required accurate knowledge of device geometry. In order to determine the geometry of the device in vivo, this paper presents work on developing an auto-calibration procedure to measure the geometry of the robot using force sensors to move injector. The presented auto-calibration routine is able to identify the shape of the device to within 0.5 mm and 0.9°.

A parallel wire robot for epicardial interventions.

This paper describes the design and preliminary testing of a planar parallel wire robot that adheres to the surface of the beating heart and provides a stable platform for minimally invasive epicardial therapies. The device is deployed through a small subxiphoid skin incision and attaches to the heart using suction. This methodology obviates mechanical stabilization and lung deflation, which are typically required during minimally invasive beating-heart surgery. The prototype design involves three vacuum chambers connected by two flexible arms. The chambers adhere to the epicardium, forming the vertices of a triangular base structure. Three cables connect a movable end-effector head to the three bases; the cables then pass out of the body to external actuators. The surgical tool moves within the triangular workspace to perform injections, ablation, or other tasks on the beating heart. Tests in vitro and in vivo were conducted to demonstrate the capabilities of the system. Tests in vivo successfully demonstrated the ability to deploy through a subxiphoid incision, adhere to the surface of the beating heart, move the surgical tool head within the robot's workspace, and perform injections into the myocardium.

Space-Time Localization and Registration on the Beating Heart.

This paper presents a framework for localizing a miniature epicardial crawling robot, HeartLander, on the beating heart using only 6-degree-of-freedom position measurements from an electromagnetic position tracker and a dynamic surface model of the heart. Using only this information, motion and observation models of the system are developed such that a particle filter can accurately estimate not only the location of the robot on the surface of the heart, but also the pose of the heart in the world coordinate frame as well as the current physiological phase of the heart. The presented framework is then demonstrated in simulation on a dynamic 3-D model of the human heart and a robot motion model which accurately mimics the behavior of the HeartLander robot.

Towards localizing on the surface of the beating heart.

This paper presents preliminary work toward localizing on a surface which undergoes periodic deformation, as an aspect of research on HeartLander, a miniature epicardial crawling robot. Using only position measurements from the robot, the aim of this work is to use the nonuniform movements of the heart as features to aid in localization. Using a particle filter, with motion and observation models which accurately model the robotic system, registration and localization parameters can be quickly and accurately identified. The presented framework is demonstrated in simulation on dynamic 2-D models which approximate the deformation of the surface of the heart.

Toward Onboard Estimation of Physiological Phase for an Epicardial Crawling Robot.

HeartLander is a miniature mobile robot which adheres to and crawls over the surface of the beating heart to provide therapies in a minimally invasive manner. Although HeartLander inherently provides a stable operating platform, the motion of the surface of the heart remains an important factor in the operation of the robot. The quasi-periodic motion of the heart due to physiological cycles, respiration and the heartbeat, affects the ability of the robot to move, as well as localize accurately. In order to improve locomotion efficiency, as well as register different locations on the heart in physiological phase, two methods of identifying physiological phases are presented: sliding-window-based and model-based. In the sliding-window-based approach a vector of previous measurements is compared to previously learned motion templates to determine the current physiological phases, while the model-based approach learns a Fourier series model of the motion, and uses this model to estimate the current physiological phases using an Extended Kalman Filter (EKF). The two methods, while differing in approach, produce similarly accurate results on data recorded from animal experiments in vivo.

Dexterous miniature robot for advanced minimally invasive surgery.

This study demonstrates the feasibility of using a miniature robot to perform complex, single-incision, minimal access surgery. Instrument positioning and lack of triangulation complicate single-incision laparoscopic surgery, and open surgical procedures are highly invasive. Using minimally invasive techniques with miniature robotic platforms potentially offers significant clinical benefits. A miniature robot platform has been designed to perform advanced laparoscopic surgery with speed, dexterity, and tissue-handling capabilities comparable to standard laparoscopic instruments working through trocars. The robotic platform includes a dexterous in vivo robot and a remote surgeon interface console. For this study, a standard laparoscope was mounted to the robot to provide vision and lighting capabilities. In addition, multiple robots could be inserted through a single incision rather than the traditional use of four or five different ports. These additional robots could provide capabilities such as tissue retraction and supplementary visualization or lighting. The efficacy of this robot has been demonstrated in a nonsurvival cholecystectomy in a porcine model. The procedure was performed through a single large transabdominal incision, with supplementary retraction being provided by standard laparoscopic tools. This study demonstrates the feasibility of using a dexterous robot platform for performing single-incision, advanced laparoscopic surgery.

Position Estimation of an Epicardial Crawling Robot on the Beating Heart by Modeling of Physiological Motion.

HeartLander, a small mobile robot designed to provide treatments to the surface of the beating heart, overcomes a major difficulty of minimally invasive cardiac surgery, providing a stable operating platform. This is achieved inherently in the way the robot adheres to and crawls over the surface of the heart. This mode of operation does not require physiological motion compensation to provide this stable environment; however, modeling of physiological motion is advantageous in providing more accurate position estimation as well as synchronization of motion to the physiological cycles. The work presented uses an Extended Kalman Filter framework to estimate parameters of non-stationary Fourier series models of the motion of the heart due to the respiratory and cardiac cycles as well as the position of the robot as it moves over the surface of the heart. The proposed method is demonstrated in the laboratory with HeartLander operating on a physiological motion simulator. Improved performance is demonstrated in comparison to the filtering methods previously used with HeartLander. The use of detected physiological cycle phases to synchronize locomotion of HeartLander is also described.

Fourier modeling of porcine heartbeat and respiration in vivo for synchronization of HeartLander robot locomotion.

HeartLander is a small mobile robot which adheres to and navigates over the surface of the heart to provide therapies in a minimally invasive manner. HeartLander's ability to efficiently operate in this dynamic environment is greatly affected by physiological motion, namely the cardiac and respiration cycles. Synchronization of robot motion with minimal intrapericardial pressure results in safer and more efficient travel. The work presented models the physiological components of motion using Fourier series and estimates their parameters using an Extended Kalman Filter. Using the Fourier series parameters, estimates of physiological phase values are calculated to be used for step synchronization. The proposed methods are demonstrated on data from a HeartLander animal study for four locations on the heart. Mean respiration phase estimates are shown to be within 5% of the true respiration phases, while mean cardiac phase estimates are shown to have a minimum error of 11%.

Needle steering system using duty-cycled rotation for percutaneous kidney access.

The authors present ongoing work on the use of a variable curvature flexible needle steering system to gain percutaneous access to the kidney for medical interventions. A nonlinear control law is introduced which drives the needle to track a predetermined planar path using a steering approach based on duty-cycled rotation during insertion. Renal access is performed in simulation and tested in vitro in a tissue phantom to validate the proposed control method.

Semi-autonomous surgical tasks using a miniature in vivo surgical robot.

Natural Orifice Translumenal Endoscopic Surgery (NOTES) is potentially the next step in minimally invasive surgery. This type of procedure could reduce patient trauma through eliminating external incisions, but poses many surgical challenges that are not sufficiently overcome with current flexible endoscopy tools. A robotic platform that attempts to emulate a laparoscopic interface for performing NOTES procedures is being developed to address these challenges. These robots are capable of entering the peritoneal cavity through the upper gastrointestinal tract, and once inserted are not constrained by incisions, allowing for visualization and manipulations throughout the cavity. In addition to using these miniature in vivo robots for NOTES procedures, these devices can also be used to perform semi-autonomous surgical tasks. Such tasks could be useful in situations where the patient is in a location far from a trained surgeon. A surgeon at a remote location could control the robot even if the communication link between surgeon and patient has low bandwidth or very high latency. This paper details work towards using the miniature robot to perform simple surgical tasks autonomously.

Video. Natural Orifice Translumenal Endoscopic Surgery with a miniature in vivo surgical robot.

BACKGROUND: The application of flexible endoscopy tools for Natural Orifice Translumenal Endoscopic Surgery (NOTES) is constrained due to limitations in dexterity, instrument insertion, navigation, visualization, and retraction. Miniature endolumenal robots can mitigate these constraints by providing a stable platform for visualization and dexterous manipulation. This video demonstrates the feasibility of using an endolumenal miniature robot to improve vision and to apply off-axis forces for task assistance in NOTES procedures. METHODS: A two-armed miniature in vivo robot has been developed for NOTES. The robot is remotely controlled, has on-board cameras for guidance, and grasper and cautery end effectors for manipulation. Two basic configurations of the robot allow for flexibility during insertion and rigidity for visualization and tissue manipulation. Embedded magnets in the body of the robot and in an exterior surgical console are used for attaching the robot to the interior abdominal wall. This enables the surgeon to arbitrarily position the robot throughout a procedure. RESULTS: The visualization and task assistance capabilities of the miniature robot were demonstrated in a nonsurvivable NOTES procedure in a porcine model. An endoscope was used to create a transgastric incision and advance an overtube into the peritoneal cavity. The robot was then inserted through the overtube and into the peritoneal cavity using an endoscope. The surgeon successfully used the robot to explore the peritoneum and perform small-bowel dissection. CONCLUSION: This study has demonstrated the feasibility of inserting an endolumenal robot per os. Once deployed, the robot provided visualization and dexterous capabilities from multiple orientations. Further miniaturization and increased dexterity will enhance future capabilities.

Natural orifice cholecystectomy using a miniature robot.

BACKGROUND: Natural orifice translumenal endoscopic surgery (NOTES) is surgically challenging. Current endoscopic tools provide an insufficient platform for visualization and manipulation of the surgical target. This study demonstrates the feasibility of using a miniature in vivo robot to enhance visualization and provide off-axis dexterous manipulation capabilities for NOTES. METHODS: The authors developed a dexterous, miniature robot with six degrees of freedom capable of applying significant force throughout its workspace. The robot, introduced through the esophagus, completely enters the peritoneal cavity through a transgastric insertion. The robot design consists of a central "body" and two "arms" fitted respectively with cautery and forceps end-effectors. The arms of the robot unfold, allowing the robot to flex freely for entry through the esophagus. Once in the peritoneal cavity, the arms refold, and the robot is attached to the abdominal wall using the interaction of magnets housed in the robot body with magnets in an external magnetic handle. Video feedback from the on-board cameras is provided to the surgeon throughout a procedure. RESULTS: The efficacy of this robot was demonstrated in three nonsurvivable procedures in a porcine model, namely, abdominal exploration, bowel manipulation, and cholecystectomy. After insertion, the robot was attached to the interior abdominal wall. The robot was repositioned throughout the procedure to provide optimal orientations for visualization and tissue manipulation. The surgeon remotely controlled the actuation of the robot using an external console to assist in the procedures. CONCLUSION: This study has shown that a dexterous miniature in vivo robot can apply significant forces in arbitrary directions and improve visualization to overcome many of the limitations of current endoscopic tools for performing NOTES procedures.

In vivo robotics for natural orifice transgastric peritoneoscopy.

Natural Orifice Translumenal Endoscopic Surgery (NOTES) is potentially the next paradigm shift in minimally invasive surgery. Currently, NOTES procedures are performed using modified endoscopic tools with significant constraints. New tools are necessary that allow the surgeon to better visualize and dexterously manipulate within the surgical environment. In this study, a two-armed dexterous miniature in vivo robot with stereoscopic vision capabilities has been developed that addresses many of these constraints. The design and kinematic configuration of the robot allows for its complete insertion into the peritoneal cavity, and provides intuitive visualization and sufficient force application for tissue manipulation within the dexterous workspace. The NOTES robot successfully demonstrated various capabilities in a non-survival natural orifice surgical procedure in a porcine model suggesting the feasibility of using miniature in vivo robots for performing natural orifice procedures within the peritoneal cavity.

Surgery with cooperative robots.

Advances in endoscopic techniques for abdominal procedures continue to reduce the invasiveness of surgery. Gaining access to the peritoneal cavity through small incisions prompted the first significant shift in general surgery. The complete elimination of external incisions through natural orifice access is potentially the next step in reducing patient trauma. While minimally invasive techniques offer significant patient advantages, the procedures are surgically challenging. Robotic surgical systems are being developed that address the visualization and manipulation limitations, but many of these systems remain constrained by the entry incisions. Alternatively, miniature in vivo robots are being developed that are completely inserted into the peritoneal cavity for laparoscopic and natural orifice procedures. These robots can provide vision and task assistance without the constraints of the entry incision, and can reduce the number of incisions required for laparoscopic procedures. In this study, a series of minimally invasive animal-model surgeries were performed using multiple miniature in vivo robots in cooperation with existing laparoscopy and endoscopy tools as well as the da Vinci Surgical System. These procedures demonstrate that miniature in vivo robots can address the visualization constraints of minimally invasive surgery by providing video feedback and task assistance from arbitrary orientations within the peritoneal cavity.