Person:

Howe, Robert

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 in- strument that can track and compensate for heart motion; however, the reaction forces caused by the actuation mechanism make it dif- ficult 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 compensa- tion 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 in- strument provided a 28% increase in user force sensitivity and im- proved user reaction times by 51%, indicating that the new instru- ment greatly enhances force perception in beating heart tasks.

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 driving long surgical instruments. These bandwidth limitations can be overcome by incorporating feed-forward motion terms in the control law. For intracardiac procedures, the required motion estimates can be derived from 3D 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 to a standard force controller and a 75% reduction in fluctuations when compared to manual attempts to maintain the same force.

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 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 (1.0mm error) with 70%less error than manual tracking attempts.