First-class patterns

Pure pattern calculus supports pattern-matching functions in which patterns are first-class citizens that can be passed as parameters, evaluated and returned as results. This new expressive power supports two new forms of polymorphism. Path polymorphism allows recursive functions to traverse arbitrary data structures. Pattern polymorphism allows patterns to be treated as parameters which may be collected from various sources or generated from training data. A general framework for pattern calculi is developed. It supports a proof of confluence that is parameterised by the nature of the matching algorithm, suitable for the pure pattern calculus and all other known pattern calculi. © 2009 Copyright Cambridge University Press

Design and Control of Motion Compensation Cardiac Catheters

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 proposes an actuated catheter tool that compensated 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 that affect performance and establish that friction and backlash limit the tracking performance of the catheter system. Based on the results of these experiments and a model of the backlash behavior, we propose and implement compensation methods to improve trajectory tracking performance. The catheter system is evaluated with 3D ultrasound guidance in simulate in vivo conditions. the results demonstrate that with mechanical and control system design improvements, a robotic catheter system can accurately track the fast motion of the human mitral valve.Engineering and Applied Science

Ultrasound Servoing of Catheters for Beating Heart Valve Repair

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.Engineering and Applied Science

Position Control of Motion Compensation Cardiac Catheters

Robotic catheters have the potential to revolutionize cardiac surgery by enabling minimally invasive structural repairs within the beating heart. This paper presents an actuated catheter system that compensates for the fast motion of cardiac tissue using 3-D ultrasound image guidance. We describe the design and operation of the mechanical drive system and catheter module and analyze the catheter performance limitations of friction and backlash in detail. To mitigate these limitations, we propose and evaluate mechanical and control-system compensation methods, which include inverse and model-based backlash compensation, to improve the system performance. Finally, in vivo results are presented, which demonstrate that the catheter can track the cardiac tissue motion with less than 1-mm rms error. The ultimate goal of this research is to create a fast and dexterous robotic catheter system that can perform surgery on the delicate structures inside of the beating heart.Engineering and Applied Science

Discriminating tissue stiffness with a haptic catheter: Feeling the inside of the beating heart

Catheter devices allow physicians to access the inside of the human body easily and painlessly through natural orifices and vessels. Although catheters allow for the delivery of fluids and drugs, the deployment of devices, and the acquisition of the measurements, they do not allow clinicians to assess the physical properties of tissue inside the body due to the tissue motion and transmission limitations of the catheter devices, including compliance, friction, and backlash. The goal of this research is to increase the tactile information available to physicians during catheter procedures by providing haptic feedback during palpation procedures. To accomplish this goal, we have developed the first motion compensated actuated catheter system that enables haptic perception of fast moving tissue structures. The actuated catheter is instrumented with a distal tip force sensor and a force feedback interface that allows users to adjust the position of the catheter while experiencing the forces on the catheter tip. The efficacy of this device and interface is evaluated through a psychophyisical study comparing how accurately users can differentiate various materials attached to a cardiac motion simulator using the haptic device and a conventional manual catheter. The results demonstrate that haptics improves a user's ability to differentiate material properties and decreases the total number of errors by 50% over the manual catheter system.Engineering and Applied Science

Robotic catheter cardiac ablation combining ultrasound guidance and force control

Cardiac catheters allow physicians to access the inside of the heart and perform therapeutic interventions without stopping the heart or opening the chest. However, conventional manual and actuated cardiac catheters are currently unable to precisely track and manipulate the intracardiac tissue structures because of the fast tissue motion and potential for applying damaging forces. This paper addresses these challenges by proposing and implementing a robotic catheter system that uses 3D ultrasound image guidance and force control to enable constant contact with a moving target surface in order to perform interventional procedures, such as intracardiac tissue ablation. The robotic catheter system, consisting of a catheter module, ablation and force sensing end effector, drive system, and image-guidance and control system, was commanded to apply a constant force against a moving target using a position-modulated force control method. The control system uses a combination of position tracking, force feedback, and friction and backlash compensation to achieve accurate and safe catheter–tissue interactions. The catheter was able to maintain a 1 N force on a moving motion simulator target under ultrasound guidance with 0.08 N RMS error. In a simulated ablation experiment, the robotic catheter was also able to apply a consistent force on the target while maintaining ablation electrode contact with 97% less RMS contact resistance variation than a passive mechanical equivalent. In addition, the use of force control improved catheter motion tracking by approximately 20%. These results demonstrate that 3D ultrasound guidance and force tracking allow the robotic system to maintain improved contact with a moving tissue structure, thus allowing for more accurate and repeatable cardiac procedures.Engineering and Applied Science

Force control of flexible catheter robots for beating heart surgery

Recent developments in cardiac catheter technology promise to allow physicians to perform most cardiac interventions without stopping the heart or opening the chest. However, current cardiac devices, including newly developed catheter robots, are unable to accurately track and interact with the fast moving cardiac tissue without applying potentially damaging forces. This paper examines the challenges of implementing force control on a flexible robotic catheter. In particular, catheter friction and backlash must be compensated when controlling tissue interaction forces. Force controller designs are introduced and evaluated experimentally in a number of configurations. The controllers are based on the inner position loop force control approach where the position trajectory is adjusted to achieve a desired force on the target. Friction and backlash compensation improved force tracking up to 86% with residual RMS errors of 0.11 N while following a prerecorded cardiac tissue trajectory with accelerations of up to 3800 mm/s$^2$. This performance provides sufficient accuracy to enable a wide range of beating heart surgical procedures.Engineering and Applied Science