Continuum robots provide inherent structural compliance with high dexterity to access the surgical target sites along tortuous anatomical paths under constrained environments and enable to perform complex and delicate operations through small incisions in minimally invasive surgery These advantages enable their broad applications with minimal trauma and make challenging clinical procedures possible with miniaturized instrumentation and high curvilinear access capabilities However, their inherent deformable designs make it difficult to realize 3-D intraoperative real-time shape sensing to accurately model their shape Solutions to this limitation can lead themselves to further develop closely associated techniques of closed-loop control, path planning, human–robot interaction, and surgical manipulation safety concerns in minimally invasive surgery Although extensive model-based research that relies on kinematics and mechanics has been performed, accurate shape sensing of continuum robots remains challenging, particularly in cases of unknown and dynamic payloads This survey investigates the recent advances in alternative emerging techniques for 3-D shape sensing in this field and focuses on the following categories: fiber-optic-sensor-based, electromagnetic-tracking-based, and intraoperative imaging modality-based shape-reconstruction methods The limitations of existing technologies and prospects of new technologies are also discussed

Shape Sensing Techniques for Continuum Robots in Minimally Invasive Surgery: A Survey

Background

Remote-controlled catheter navigation systems have recently been introduced into minimally invasive vascular surgery and some of them have already been applied in clinical practice. Steerable catheters with improved manoeuvrability play an important role in these innovations for conventional catheterization.



Methods

This review details the development of various steerable catheters, both in use clinically and under investigation. Comprehensive comparison and analysis in several key aspects are followed to reveal both the advantages and limitations of these catheters, as well as the requirements for relevant techniques.



Results

Steerable catheters are able to select direction in the distal end, and superior to conventional counterparts in many aspects. Differences between magnetic and active catheters mainly lie in function, safety, configuration of operating room and cost. They have similar requirements for miniaturization and slave insertion mechanisms.



Conclusions

Steerable catheters are rapidly evolving and still require technological refinements to extend current capabilities. Copyright © 2009 John Wiley & Sons, Ltd.

Steerable catheters in minimally invasive vascular surgery.

Abstract We have developed a new batch fabrication process of a shape memory alloy (SMA) sheet based on electrochemical pulse etching with a sacrificial dummy metal layer. The method has realized a throughout micromachining of the SMA sheet. Using the new batch fabrication process, flat meandering S-shape SMA actuators of 38 μm in thickness have been developed. The actuators whose widths were narrower than 290 μm could generate the forces over 75 mN. The batch fabrication process was also applied to a micromachining of NiTi super elastic alloy (SEA) helical coils. A small outer diameter active catheter was developed by using the flat meandering SMA actuators of 290 μm in width and the SEA helical coil of about 460 μm in outer diameter. The outer diameter of the catheter without an outer tube was 0.8 mm. A silicon rubber outer tube of 75 μm in wall thickness was put on the catheter, nevertheless, the outer diameter was smaller than 1 mm. The bending angle of the developed active catheter without the outer tube was about 50°at heating current of 60 mA. The bending angle tended to be lower after the outer tube was put on, however, the catheter with outer tube could be bent to the angle of 35°.

Batch fabrication flat meandering shape memory ally actuator for active catheter

Remote-controlled vascular interventional robots (RVIRs) are being developed to increase the overall accuracy of surgical operations and reduce the occupational risks of intervening physicians, such as radiation exposure and chronic neck/back pain. Several RVIRs have been used to operate catheters or guidewires accurately. However, a lack of cooperation between the catheters and guidewires results in the surgeon being unable to complete complex surgery by propelling the catheter/guidewire to the target position. Furthermore, it is a significant challenge to operate the catheter/guidewire accurately and detect their proximal force without damaging their surfaces. In this study, we introduce a novel method that allows catheters and guidewires to be operated simultaneously in complex surgery. Our method accurately captures force measurements and enables precisely controlled catheter and guidewire operation. A prototype is validated through various experiments. The results demonstrate the feasibility of the proposed RVIR to operate a catheter and guidewire accurately, detect the resistance forces, and complete complex surgical operations in a cooperative manner.

A cooperation of catheters and guidewires-based novel remote-controlled vascular interventional robot

This paper proposes a master-slave catheterisation system including a steerable catheter with positioning function and an insertion mechanism with force feedback. The steerable catheter is integrated with two magnetic tracking sensors for positioning. The distal shape of catheter is displayed with virtual vascular model to generate 3D guiding image to provide the relative relationship between the catheter and its surrounding vessels. The master-slave insertion mechanism with differential gear structure is designed with force feedback to assist surgeons to manipulate the catheter. It can implement pulling/pushing, rotating and bending/recovering the catheter. Based on this system, surgeons in the control room can utilise the master handle to operate the insertion mechanism for positioning the distal end of catheter with the assistance of 3D guiding image. The stability and accuracy of the system is validated in-vitro.

The master-slave catheterisation system for positioning the steerable catheter

Background

The emergence of the active catheter has prompted the development of catheterization in minimally invasive surgery. However, it is still operated using only the physician's vision; information supplied by the guiding image and tracking sensors has not been fully utilized.



Methods

In order to supply the active catheter with more useful information for automatic navigation, we extract the skeleton of blood vessels by means of an improved distance transform method, and then present the crucial geometric information determining navigation. With the help of tracking sensors' position and pose information, two operations, advancement in the proximal end and direction selection in the distal end, are alternately implemented to insert the active catheter into a target blood vessel.



Results

The skeleton of the aortic arch reconstructed from slice images is extracted fast and automatically. A navigation path is generated on the skeleton by manually selecting the start and target points, and smoothed with the cubic cardinal spline curve. Crucial geometric information determining navigation is presented, as well as requirements for the catheter entering the target blood vessel. Using a shape memory alloy active catheter integrated with magnetic sensors, an experiment is carried out in a vascular model, in which the catheter is successfully inserted from the ascending aorta, via the aortic arch, into the brachiocephalic trunk.



Conclusions

The navigation strategy proposed in this paper is feasible and has the advantage of increasing the automation of catheterization, enhancing the manoeuvrability of the active catheter and providing the guiding image with desirable interactivity. Copyright © 2009 John Wiley & Sons, Ltd.

Skeleton-based active catheter navigation.

Background

An active catheter is a minimally invasive surgery catheter that can perform deflectable motions. The active catheter can be controlled from outside the body and moves like a snake, utilizing a multi-joint mechanism with distributed shape memory alloy (SMA) actuators.



Methods

It was considered that the deflection curve of the axis of the catheter is determined by the output force of the SMA actuators. Based on the large deflection theory, the deflection curve equation of the axis of the catheter was derived, using the precise form of the curvature.



Results

Through experimentation, the axial bending curve shape of the blended active catheter was measured precisely, and the experimental results were compared with the calculation results obtained from the large deflection theory and the circular arc hypothesis. The experimental results show that the curves calculated by large deflection theory are very close to the actual axis curves.



Conclusions

An active catheter prototype has been designed using the theory presented in this paper. Utilizing a vascular model, the active catheter-based invasive surgery was simulated. The experiment confirmed that the large deflection theory calculation method can be used to guide the design of the active catheter. Copyright © 2008 John Wiley & Sons, Ltd.

Research on the axis shape of an active catheter

In this paper, a micro bending robot (MBR) for an active catheter which allows any bending direction and bending angle and has a simple structure for miniaturization was developed. The MBR is 1.25 mm in outer diameter. In order to achieve a large bending angle meanwhile not to increase the outer diameter of the MBR too much, the MBR consists of 3 bending units. A bending unit consists of a bias spring and 3 incorporating shape memory alloy (SMA) coil actuators. The bending model of a bending unit was established based on a design chart and equation. Kinematics of a bending unit was analysed, and the position and orientation of the tip center and the displacements of all 3 SMA coil actuators of the bending unit in any bending direction and bending angle were obtained. Finally, the position and orientation of the tip center of the MBR and its bending angle in any bending direction were deduced. The works of this paper help to consummate the design theory of active catheter and has important theoretic significance and practical applied value.

Xianling Li

Papers

Skeleton-based active catheter navigation.

Research on the axis shape of an active catheter

Kinematics of Micro Bending Robot Using Shape Memory Alloy for Active Catheter