The rapid motion of the heart presents a significant challenge to the surgeon during intracardiac beating heart procedures. We present a 3D ultrasound-guided motion compensation system that assists the surgeon by synchronizing instrument motion with the heart. The system utilizes the fact that certain intracardiac structures, like the mitral valve annulus, have trajectories that are largely constrained to translation along one axis. This allows the development of a real-time 3D ultrasound tissue tracker that we integrate with a 1 degree-of-freedom (DOF) actuated surgical instrument and predictive filter to devise a motion tracking system adapted to mitral valve annuloplasty. In vivo experiments demonstrate that the system provides highly accurate tracking (1.0 mm error) with 70% less error than manual tracking attempts.

This paper presents a novel miniature uniaxial force sensor for use within a beating heart during mitral valve annuloplasty. The sensor measures 5.5 mm in diameter and 12 mm in length and provides a hollow core to pass instrumentation. A soft elastomer flexure design maintains a waterproof seal. Fiber optic transduction eliminates electrical circuitry within the heart, and acetal components minimize ultrasound-imaging artifacts. Calibration uses a nonlinear viscoelastic method, and in vitro tests demonstrate a 0-4-N force range with rms errors of 0.13 N (< 3.2%). In vivo tests provide the first endocardial measurements of tissue-minimally invasive surgery instrument interaction forces in a beating heart.

Material indentation studies, in which a probe is brought into controlled physical contact with an experimental sample, have long been a primary means by which scientists characterize the mechanical properties of materials. More recently, the advent of atomic force microscopy, which operates on the same fundamental principle, has in turn revolutionized the nanoscale analysis of soft biomaterials such as cells and tissues. This paper addresses the inferential problems associated with material indentation and atomic force microscopy, through a framework for the changepoint analysis of pre- and post-contact data that is applicable to experiments across a variety of physical scales. A hierarchical Bayesian model is proposed to account for experimentally observed changepoint smoothness constraints and measurement error variability, with efficient Monte Carlo methods developed and employed to realize inference via posterior sampling for parameters such as Young's modulus, a key quantifier of material stiffness. These results are the first to provide the materials science community with rigorous inference procedures and uncertainty quantification, via optimized and fully automated high-throughput algorithms, implemented as the publicly available software package BayesCP. To demonstrate the consistent accuracy and wide applicability of this approach, results are shown for a variety of data sets from both macro- and micro-materials experiments--including silicone, neurons, and red blood cells--conducted by the authors and others.

The manipulation of fast-moving, delicate tissues in beating heart procedures presents a considerable challenge to the surgeon. A robotic force tracking system can assist the surgeon by applying precise contact forces to the beating heart during surgical manipulation. Standard force control approaches cannot safely attain the required bandwidth for this application due to vibratory modes within the robot structure. These vibrations are a limitation even for single degree-of-freedom systems that drive long surgical instruments. These bandwidth limitations can be overcome by the incorporation of feed-forward motion terms in the control law. For intracardiac procedures, the required motion estimates can be derived from 3-D ultrasound imaging. Dynamic analysis shows that a force controller with feed-forward motion terms can provide safe and accurate force tracking for contact with structures within the beating heart. In vivo validation confirms that this approach confers a 50% reduction in force fluctuations when compared with a standard force controller and a 75% reduction in fluctuations when compared with manual attempts to maintain the same force.

Robotic cardiac catheters have the potential to revolutionize heart surgery by extending minimally invasive techniques to complex surgical repairs inside the heart. However, catheter technologies are currently unable to track fast tissue motion, which is required to perform delicate procedures inside a beating heart. This paper presents an actuated catheter tool that compensates for the motion of heart structures like the mitral valve apparatus by servoing a catheter guidewire inside a flexible sheath. We examine design and operation parameters and establish that friction and backlash limit the tracking performance of the catheter system. Based on the results of these experiments, we implement compensation methods to improve trajectory tracking. The catheter system is then integrated with an ultrasound-based visual servoing system to enable fast tissue tracking. In vivo tests show RMS tracking errors of 0.77 mm for following the porcine mitral valve annulus trajectory. The results demonstrate that an ultrasound-guided robotic catheter system can accurately track the fast motion of the mitral valve.

Beating heart surgical methods have the potential to remove the need for the heart-lung machine and its attendant side effects, but must contend with the motion of the heart. Recent research in robotically-assisted surgery has produced a handheld, actuated instrument that can track and compensate for heart motion; however, the reaction forces caused by the actuation mechanism make it difficult for the surgeon to feel the heart during the operation, which can lead to unsafe tissue manipulation. This paper investigates an instrument design that negates reaction forces to the user by moving a counterweight out of phase with the moving mass of the actuator. The resulting instrument retains the tracking and motion compensation abilities of the current instrument, but reduces reaction forces felt by the user by over 80%. Subjects used the new instrument in an in vitro beating heart surgical contact task and performance was compared to the previously existing instrument. The new instrument provided a 28% increase in user force sensitivity and improved user reaction times by 51%, indicating that the new instrument greatly enhances force perception in beating heart tasks.

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.

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.

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.

A robotic system is presented that uses threedimensional ultrasound to visually servo a surgical instrument. Tracking of both the surgical instrument and a target was done using image based algorithms on the real-time 3D ultrasound data. The tracking techniques are shown to be especially amenable for execution on powerful graphics processor units. By harnessing a graphics card, it was possible to detect both a surgical instrument and a surgical target at a rate of 25 Hz. The high update rate permits the use of tracked instrument and target locations for controlling a robot. Validation of the system was done in a water tank. The robot successfully tracked a target moving at speeds mimicking a mitral valve within a beating heart. During the trials the robot accurately moved the surgical instrument with maximum errors of 3.9 mm and RMS error of 1.2 mm.