Establishment Of Robotic Catheter System And Study On Its Key Technologies

Endovascular minimally invasive surgery (MIS) has been widely adopted all over the world for its less blood loss, smaller incisions, decreased pain and quicker recovery. The disadvantages existed in three basic links of conventional catheterization, to a great extent, limit the development of endovascular MIS: the maneuverability of the catheter is poor, which leads to many a misoperations and attemptations and hence not only provides the catheterization with low efficiency and success rate but does great harm to vessels; it demands high-level skill for surgeons manually operating the catheter and the intervention process cannot be stable and precise, besides the surgeons suffer from serious radiation on site; conventional 2D x-ray image not only generates much radiation but is difficult to tell the 3D anatomy of vasculature. In order to overcome above limitations, a novel catheter robotic system was presented in this paper, which was composed of the steerable catheter, master-slave intervention mechanism, magnetic tracking sensors and 3D guiding image. Details are as follows:Two kinds of steerable catheters were studied, which were shape-memory-alloy (SMA)-actuated and pull-wire catheters. The SMA actuator characteristic described by Liang's model, the bending mechanics, and a heat transfer model were combined to form the dynamics of the single and multiple SMA actuated catheters. The intrinsic hystersis characteristic was studied by measuring the bending angle and temperature of a prototype, and the dynamic model proposed was verified to be effective.A 7Fr single curve catheter and its special handle were devised. Both ends of the bending segment were integrated with a 5DOF sensor and 2 electrodes and 1 thermal couple were embedded into the distal tip. The distal shape of catheter was correctly displayed when dual 5DOF and single 6DOF magnetic tracking sensors were integrated onto the catheter. The kinematics of pull-wire catheter was analyzed. The flexible catheter was modeled with rigid links and joints, and its kinematic model was built by means of D-H method. The workspace of catheter distal shaft was obtained and inverse kinematic strategy was utilized to control the movement of catheter.Catheterization was performed in a master/slave way. Both insertion mechanism and handle manipulating mechanism were devised to substitute the surgeon on site. The insertion mechanism is able to pull/push and rotate the catheter, thereinto the rotating is the resultant motion of two motors thus avoiding the rotation of motor support. The handle manipulating mechanism is capable of pulling/pushing the slide sleeve of hadle to bend/recover the distal tip, as well as pulling/pushing and rotating the handle. A 3DOF force-feedback handle was used to realize the master/slave operation. Two force sensors were fixed onto the driving rollers to feedback the resistance during intervention, and based on it, the force-feedback handle was set to enhance the emmersion.The 3D image guiding software was developed, which provided four navigation views to facilitate surgeons'determining of the relative position between the catheter tip and surrounding vessels. The generalized potential fied method was utilized to extract the skeleton of 3D vasculature reconstructed with 2D slice images. The navigation path was generated through manually picking the start and target points on the skeleton, and smoothed with the Cardinal cubic spline curve. The virtual camera was set according to the skeleton and hence the roaming was achieved. The realtime collision detection was realized by means of orientation bounding box method and the distance between the catheter tip and vascular wall was provided. The image and sensor coordinate systems corresponded to each other through preregistration and precise registration.A catheter robotic system was constructed with the developed single curve pull-wire catheter, master/slave insertion mechanism and guiding image. The performance of pull-wire catheter and insertion mechanism were tested. The in-vitro catheterization experiments were carried out in a vascular phantom which validated the effectiveness of the system. Quantitative analysis was conducted toward the performance of 3D guiding image and master/slave operation utilizing comparing the duration and success rate of different chatheterization modes. The accuracy of the navigation system was evaluated with the distance between the tip and vascular wall on the guiding image when they actually attached.