Person:

Howe, Robert

Beating heart intracardiac procedures promise significant benefits for patients, however, the fast motion of the heart poses serious challenges to surgeons. We present a new 3D ultrasound-guided motion (3DUS) compensation system that synchronizes instrument motion with the heart. The system utilizes the fact that the motion of some intracardiac structures, including the mitral valve annulus, is largely constrained to translation along one axis. This allows the development of a real-time 3DUS tissue tracker which we integrate with a 1 degree-of-freedom actuated surgical instrument, real-time 3DUS instrument tracker, and predictive filter to devise a system with synchronization accuracy of 1.8 mm RMSE. User studies involving the deployment of surgical anchors in a simulated mitral annuloplasty procedure demonstrate that the system increases success rates by over 100%. Furthermore, it enables more careful anchor deployment by reducing forces to the tissue by 50% while allowing instruments to remain in contact with the tissue for longer periods.

Beating heart procedures promise significant health benefits to patients but the fast motion of the heart poses a serious challenge to the surgeon. Robotic motion synchronization to heart movements could facilitate these surgeries, although for intracardiac procedures this requires the development of a predictive filter to compensate for the measurement noise and time delay present in 3D ultrasound imaging. In this paper, we present a quasiperiodic cardiac motion model and apply the extended Kalman filter to estimation of its parameters in real-time. We experimentally demonstrate high accuracy robot tracking to heart motion using this filter.

Minimally invasive surgery systems typically involve thin and cable-driven surgical instruments. This introduces link and joint flexibility in the slave robot of a master-slave teleoperation system, reducing the effective stiffness of the slave and the transparency of teleoperation. In this paper, we analyze transparency under slave link and joint flexibility (tool flexibility). We also evaluate the added benefits of using extra sensors at the tip of the flexible robot. It is shown that tip velocity (or position) feedback improves free-space position tracking performance in the presence of robot flexibility. Also, when the interaction forces with an environment are measured by a force sensor and fed back to the user’s hand, tip velocity feedback improves hard-contact force tracking performance. During a hard contact task, tip velocity feedback can also eliminate the transmission of robot flexibility to the user’s hand. Parts of this research have previously been published as M. Tavakoli, R.D. Howe, The Effect of Joint Elasticity on Bilateral Teleoperation, In Proceedings of the 2007 IEEE/RSJ International Conference on Intelligent Robots & Systems, pp. 1618-1623, San Diego, CA, 2007, and as M. Tavakoli, R.D. Howe, Haptic Implications of Tool Flexibility in Surgical Teleoperation, In Proceedings of the 16th Symposium on Haptic Interfaces for Virtual Environments & Teleoperator Systems, pp. 377-378, Reno, NV, March 2008.

3D ultrasound imaging has enabled minimally invasive, beating heart intracardiac procedures. However, rapid heart motion poses a serious challenge to the surgeon that is compounded by significant time delays and noise in 3D ultrasound. This paper investigates the concept of using a one-degree-of-freedom motion compensation system to synchronize with tissue motions that may be approximated by 1D motion models. We characterize the motion of the mitral valve annulus and show that it is well approximated by a 1D model. The subsequent development of a motion compensation instrument (MCI) is described, as well as an extended Kalman filter (EKF) that compensates for system delays. The benefits and robustness of motion compensation are tested in user trials under a series of non-ideal tracking conditions. Results indicate that the MCI provides an approximately 50% increase in dexterity and 50% decrease in force when compared with a solid tool, but is sensitive to time delays. We demonstrate that the use of the EKF for delay compensation restores performance, even in situations of high heart rate variability. The resulting system is tested in an in vitro 3D ultrasound-guided servoing task, yielding accurate tracking (1.15 mm root mean square) in the presence of noisy, time-delayed 3D ultrasound measurements.

The manipulation of fast moving, delicate tissues in beating heart procedures presents a considerable challenge to surgeons. We present a new robotic force stabilization system that assists surgeons by maintaining a constant contact force with the beating heart. The system incorporates a novel, miniature uniaxial force sensor that is mounted to surgical instrumentation to measure contact forces during surgical manipulation. Using this sensor in conjunction with real-time tissue motion information derived from 3D ultrasound, we show that a force controller with feed-forward motion terms can provide safe and accurate force stabilization in an in vivo contact task against the beating mitral valve annulus. This confers a 50% reduction in force fluctuations when compared to a standard force controller and a 75% reduction in fluctuations when compared to manual attempts to maintain the same force.

Surgical repair of the mitral valve results in better outcomes than valve replacement, yet diseased valves are often replaced due to the technical difficulty of the repair process. A surgical planning system based on patient-specific medical images that allows surgeons to simulate and compare potential repair strategies could greatly improve surgical outcomes. The system must simulate valve closure quickly and handle the complex boundary conditions imposed by the chords that tether the valve leaflets. We have developed a process for generating a triangulated mesh of the valve surface from volumetric image data of the opened valve. The closed position of the mesh is then computed using a mass-spring model of dynamics. In the mass-spring model, triangle sides are treated as linear springs supporting only tension. Chords are also treated as linear springs, and self-collisions are detected and handled inelastically. The equations of motion are solved using implicit numerical integration. The simulated closed state is compared with an image of the same valve taken in the closed state to assess accuracy of the model. The model exhibits rapid valve closure and is able to predict the closed state of the valve with reasonable accuracy.

Limitations in modern sensing technologies result in large errors in sensed target object geometry and location in unstructured environments. As a result, positioning a robotic end-effector includes inherent error that will often lead to unsuccessful grasps. In previous work, we demonstrated that optimized configuration, compliance, viscosity, and adaptability in the mechanical structure of a robot hand facilitates reliable grasping in unstructured environments, even with purely feedforward control of the hand. In this paper we describe the addition of a simple contact sensor to the fingerpads of the SDM Hand (Shape Deposition Manufactured Hand), which, along with a basic control algorithm, significantly expands the grasp space of the hand and reduces contact forces during the acquisition phase of the grasp. The combination of the passive mechanics of the SDM Hand along with this basic sensor suite enables positioning errors of over 5 cm in any direction. In the context of mobile manipulation, the performance demonstrated here may reduce the need for much of the complex array of sensing currently utilized on mobile platforms, greatly increase reliability, and speed task execution, which can often be prohibitively slow.

Material indentation is a popular method for determining the mechanical properties of biomaterials. The basic premise of an indentation experiment is to physically displace the sample using an indenter that measures resistive force, in order to formulate a force-displacement curve. However, doing so requires estimating the initial contact event between the indenter and the sample-a statistical changepoint detection problem that has not been rigorously addressed in the biomaterials literature to date. Here we adopt a hierarchical Bayesian approach to contact point determination based on switching regressions, which generalizes an algorithm popular with practitioners and enables both hyperparameter estimation as well as uncertainty quantification. Results using several experimentally obtained silicone indentation data sets indicate that our approach outperforms existing techniques.

Properly selected port sites for robot-assisted coronary artery bypass graft (CABG) improve the efficiency and quality of these procedures. In clinical practice, surgeons select port locations using external anatomic landmarks to estimate a patient’s internal anatomy. This paper proposes an automated approach to port selection based on a preoperative image of the patient, thus avoiding the need to estimate internal anatomy. Using this image as input, port sites are chosen from a grid of surgeon-approved options by defining a performance measure for each possible port triad. This measure seeks to minimize the weighted squared deviation of the instrument and endoscope angles from their optimal orientations at each internal surgical site. This performance measure proves insensitive to perturbations in both its weighting factors and moderate intraoperative displacements of the patient’s internal anatomy. A validation study of this port site selection was performed. cardiac algorithm also Six surgeons dissected model vessels using the port triad selected by this algorithm with performance compared to dissection using a surgeon-selected port triad and a port triad template described by Tabaie et al., 1999. With the algorithm-selected ports, dissection speed increased by up to 43% (p = 0.046) with less overall vessel trauma. Thus, this algorithmic approach to port site selection has important clinical implications for robot-assisted CABG which warrant further investigation.

This paper presents the design and testing of a multi-channel vibrotactile display composed of cylindrical handle with four embedded vibrating elements driven by piezoelectric beams. The experimental goal of the paper is to analyze the performance of the device during a teleoperated force controlled task. As a test bed, a teleoperator system composed of two PHANToM haptic devices is used to trace a rectangular path while the operator attempts to maintain a constant force at the remote manipulator's tip. Four sensory modalities are compared. The first is visual feedback alone. Then, visual feedback is combined with vibration, force feedback, and force feedback plus vibration. Comparisons among these four modes are presented in terms of mean force error. Results show that force feedback combined with vibration provide the best feedback for the task. They also indicate that the vibrotactile device provides a clear benefit in the intended application, by reducing the mean force errors by 35 percent when compared to visual feedback alone.