Abstract— Minimally invasive surgery (MIS) is an emerging technique, which is widely used and studied for computer-assisted training. The cooperation of the catheter and the guidewire is an essential part during the MIS procedure, which is not fully paid attention to but anatomic vascular deformation simulation. In this paper, a novel simulator integrated with a complete strategy for the cooperation of the catheter and the guidewire is proposed. A composite model of the physically based catheter and the guidewire, which are mapped to distinguished visual model and collision model of these two devices, is constructed at the initial point in the aorta vessels. Once it comes into the neurovascular cavity, the composite model is decomposed to two physically based model corresponding to the catheter and the guidewire respectively. Thereafter, the guidewire is operated and propelled through the catheter, which is fixed in position. The results show that the composite model exhibits equivalent efficiency and effectiveness as well as the separate catheter model, especially at the bifurcation of the vessels. The simulator proposed herein provides a fundamental module meeting the real-time and realistic requirements of our endovascular interventional surgery training system.

I. INTRODUCTION

Interventional operation, such as stenting and angioplasty have been widely applied to patients with cardiovascular or neurovascular disease. Minimally Invasive Surgery (MIS) is an emerging medical technique for diagnosis and treatment that uses interventional catheter and guide wire to reach the lesion of the blood vessels. During a MIS procedure, through a small incision on the femoral artery, a catheter together with a guidewire enclosed in it is propelled along the vessel network under the guidance of fluoroscopic imaging (sequence of X-ray images) from the iliac arteries and aorta then into the aortic arch just above the heart. Then the catheter and guidewire are pushed into the neurovascular network or the coronary arteries. Once it comes to the bifurcation of the vessel to the brain, the catheter is too thick for the brain vessels where the guidewire has to be separately push forward without the catheter to the target location.

There have been researches devoted to many types of robotic-assisted interventional surgery operating system have been developed. However, this is a kind of intricate operation requiring the dexterous skill of hand-eye coordination and experience of operating the catheter/guidewire in the catheterization surgery, which demands the surgeons to be massively trained until the formal and standardized procedure is mastered. Traditionally, the widely used approaches to grasp

* This research is partly supported by the National High Tech. Research

and Development Program of China (No.2015AA043202), and National Key Research and Development Program of China (2017YFB1304401).

Shuxiang Guo, Xiaojuan Cai, Yan Zhao, Baofeng Gao are with the Key Laboratory of Convergence Medical Engineering System and Healthcare Technology, the Ministry of Industry and Information Technology, School of Life Science, Beijing Institute of Technology, No.5, Zhongguancun South Street, Haidian District, 100081 Beijing, China (corresponding author to provide phone: 86-010-68912977; e-mail: caixiaojuan@bit.edu.cn).

Shuxiang Guo is also with Faculty of Engineering, Kagawa University, 2217-20 Hayashi-cho, Takamatsu, Japan (e-mail: guo@eng.kagawa-u.ac.jp).

the knowledge of anatomic-pathologic and therapeutic techniques are animals and cadavers, which demands large amount of consumption of training period and other resources. VR (virtual reality) based surgery training system could be an indispensable and promising approach to overcome these problems [1–4].

The catheter operation is an essential part of the MIS surgery operation, which should be definitely simulated to fabricate the whole VR based MIS training system. Many current developed MIS training systems has focused on the vascular modelling [5-11] and some studies on visual rendering, interactive communication, tactile simulation and feedback response [12 -15], as well as the separately single catheter or the guidewire modelling. As for catheter/guidewire modelling, many researches focus on the single model of the catheter or the guidewire instead of the integral operational model of the catheter/guidewire and the interaction effect of the two essential devices in the interventional catheterization technique. A study of guidewires and catheters being visualized as 1D elastic rods were proposed by Tang et al., and they also presented a resolution on forces computation between the guidewire and the vascular model [16]. Mi et al. proposed to use the multi-body mass-spring method to model the catheter or guidewire in their 3D virtual minimally invasive surgery simulator [15]. Guo et al. proposed a new approach to treat arterial aneurysm using finite element method to model the aneurysm [17]. In this paper, we present a complete simulator for interventional catheterization, for which we propose a strategy for cooperation of the catheter and guidewire with considering the integral model comprised of the two devices and interactive effects between them according to the real surgical catheterization procedure. The physics-based composite model includes a catheter part and a guidewire part, which are both based on the finite element method, consisting of a set of connected beam elements that can model bending, twist and other deformations in real-time.

This paper is organized as follows: the proposed strategy for cooperation of catheter and guidewire and the physics-based model for the catheter are formulated in Section II, experimental setup for the simulation and results analysis are presented in Section III. Section IV describes the conclusions and future work.

II. THE PROPOSED CATHETERIZATION SIMULATOR

There have been researches devoted to many types of robotic-assisted interventional surgery operating system have been developed according to a conceptual master-slave system as illustrated in Fig. 1. Many of them are devoted to study the simulator of the interventional endovascular surgery [18-21]. The whole VR (virtual reality) based catheterization simulator for interventional surgery includes the master side and the virtual environment. And the master side could be a haptic device with the embedded haptic rendering. And the virtual environment includes the vascular model, the catheter and the guidewire, which should interactively communicate with the

A novel VR-based simulator for the interventional surgical catheter and guidewire cooperation*

Shuxiang Guo, Xiaojuan Cai, Yan Zhao, Baofeng Gao

978-1-5386-7345-4/18/$31.00 © 2018 IEEE

master side for tactile feedback and force input data transmission. The catheter and the guidewire cooperation is also studied by some researchers integrated in the vascular interventional robot, such as Wang et al. developed a new catheter/guidewire manipulator that allows the catheter/guidewire’s movements and resistance measurements [22]. Bao et al. introduce a novel method that allows catheters and guidewires to be operated simultaneously in complex surgery [23].

Fig.1 A conceptual master-slave system

A. The master side The widely used haptic device include the Geomagic Touch

X (3D Systems, USA) [24], Virtuose (HAPTION, France) [25] and Force dimension (Switzerland) [26]. The master side in this paper is PHANTOM Omni, The Phantom Omni system’s high fidelity force feedback senses motion in 6 degrees of freedom providing the best, most realistic 3D Touch sensation for any application. This device could help us to feel the point of the stylus in all axes, and track its orientation (pitch, roll and yaw).

For the synchronous processing of the position, direction and the force information, a ghost point for the master side is assigned in the virtual environment, and the coordinate system of the virtual and the real world space should be identically mapped as show in Fig. 2. The three axis should be interconnected with the local coordinate space of the Touch X stylus.

Fig. 2 Communication between the master side and the virtual environment

The basic operation in the surgery include pushing forward, pull backward and rotation. The catheter and guidewire will be

synchronously mapped in behavior, such as position and velocity. When the collision between catheter or guidewire and vessel wall occurs, the ghost point on the catheter or the guidewire will transmitted to the master side which will calculate the force feedback using the haptic rendering algorithm. For instance, the resistant force could be calculated form the formula as:

resistantF u λ= Δ ⋅ (1) where uΔ is the displacement of the ghost point, and λ is the multiplying factor, which could be adjusted for different sense of habit of the operators.

B. The physical model Many researchers have been devoted to study the physical

behavior and interactive response of the rod-like or wire-like medical devices, such as mass-spring model, elastic rod model, dynamic spline model and finite element model and etc. In this paper, we adopted the discrete finite element method to physically compute the deformation simulation of the catheter and guidewire respectively. The physically modelling of the catheter is shown in Fig. 3. This method is based on the proposal by Cotin et al. for real-time deformation of devices such as catheters and guidewires using a real-time incremental Finite Element Model [27].This physics-based model is based on a static finite element formulation, consisting of a set of connected beam elements, each of whom has 6 degrees of freedom, modelling bending, torque, twist and other deformations in real time.

Since the material of the catheter and guidewire is locally homogeneous, we assume that the model could be formulized as linear elastic. As the one dimensional model such as catheter or guidewire, is discrete to finite element beams, each of whom could be analyzed as an element with a local stiffness matrix, leading to the whole model with a global matrix K , which is computed from the linear combination of the contribution of elements. The derivation of the force could be computed from the governing equation:

F K u= Δ (2) where K is a band matrix due to the serial structure of the model (one node is only shared by one or two elements) and

uΔ represents a column matrix of displacements corresponding to external forces F .

Fig. 3 Physically modelling of the catheter

The simulation could be solved using an incremental approach [27], which exhibits faster computational efficiency rather than most techniques. Additionally, once the collision between the device and the vessel wall occurs, the contact force will be transmitted to the physical model. Then the contact force will be the external force to the deformable model as illustrated in (1), after which a global equations system is generated to be solved. Meanwhile, an iterative integration scheme will be demanded to solve the whole system to get the state of physical model at a given time step. For the stability with large time steps, we adopted the implicit solver to approximate the representation of the motion system, the system will change to another state (a change on the velocity and position) with an increment of time step, which could be formulized as:

2

2( ) ( ) ( )

( ) ( ) ( )

i i i

i i i

d d dU t h U t h U t hdt dt dt

dU t h U t h U t hdt

+ = + +

+ = + +

(3)

This integration scheme could be expressed as a linear solution expressed in [28]:

2 2( ) ( ) ( )( ) ( ) ( ) ( )( ) ( ) ( )

F t F t F tM h h V t hF t h V tV t U t U t

∂ ∂ ∂− − Δ = +∂ ∂ ∂

(4)

where M is the mass matrix, ( )F t and its derivative is available. By using this equation, the increment on velocity ( )V tΔ will be obtained, from which the velocity and

position at next time ( )id U t hdt

+ ( )iU t h+ will be calculated

by introducing the velocity ( )V tΔ to (3). (4) could be regarded as a linear system of equations, as Ax b= , and the system could be solved by the conjugate gradient method.

C. The proposed strategy for cooperation simulation of catheter and guidewire In a real procedure, surgeons operate the catheter and the

guidewire simultaneously, after puncturing the femoral artery, a guidewire–catheter combination is advanced under fluoroscopic guidance (sequence of X-ray images) through the iliac arteries and aorta then into the aortic arch just above the heart. Then the catheter or guidewire is advanced into the neurovascular network or the coronary arteries [29]. Once the catheter is guided to the neurovascular position, the catheter is stopped to go ahead, yet the guidewire continues to go ahead. However, recent researches focus on the simulation of anatomical deformation simulation or the separate catheter/guidewire simulation as discussed in Section I. To solve this problem and fabricate a complete catheterization simulator, a novel and complete co-operational strategy is proposed for the catheterization simulator based on the real operational procedure, which is illustrated in Fig. 4.

The procedural step could be executed as follows:

1) Construct the visual and collision model for catheter and guidewire as a hollow cylinder and a solid rod, respectively.

2) Construct the physically based model as linked beam elements, both of which are co-axial and at the same initial position.

3) Deactivate the physical model of the guidewire, and combine the catheter and the guidewire as composite model.

4) Once in place, the guidewire is ready to be departed from the catheter, the physical model of the guidewire is activated, then the guidewire is pushed forward through the catheter in to the neurovascular network separately.

Fig. 4 Conceptual procedure of the strategy

As described in paper [30, 31], we adopted the multi-model representation, including visual model, collision model and the visual model. The visual topology of the catheter and the guidewire are built in the 3D modelling software 3D max, as shown in Fig. 5. Also, the visual model and the collision model rendered in the virtual environment is shown in Fig. 6. The physically based model is constructed in Fig. 7.

Fig. 5 The catheter and guidewire model constructed in 3D Max

(a) The visual model

(b) The collision model

Fig. 6 The visual and collision model in the virtual environment

Fig. 7 The physical model in the virtual environment

The physical model of finite element method is discretized to 30 nodes which could simulate the catheter and the guidewire with efficiency of bending and twisting in the operation.

III. SIMULATION AND CHARACTERISTIC EVALUATION

The composite model of the catheter and the guidewire is controlled by the surgeons from the initial point to the target point through the vascular cavity along the center line. Once it comes to the bifurcation of the vessel, the device will correspondingly bend and twist to change the direction forward to one sub-branch of the vessel.

To validate the characteristic and efficiency of the catheter/guidewire model, a traversal of the device model in the vessel. The picture shown in Fig. 8 is the trajectory of the device model in the vessel from the main branch of the vessel to one sub-branch. This simulation exhibits the realistic behavior characteristics of the device model, especially in the bifurcation position of the vascular network.

Fig. 8 The trajectory of the device model in the vascular bifurcation

Fig. 9 Pushing, pulling and twisting of catheter/guidewire in the vessel

To test the interactive adaptability of the two tested devices (catheter/guidewire), the pushing, pulling and rotating operations are conducted in the simulation, as shown in Fig. 9,

the bending and twisting deformation of the composite model is simulated in Fig. 10. Once in place, a button on the stylus of the haptic device is pressed and the guidewire is extracted from the catheter, which is then fixed in position. In the Fig. 11, the guidewire is enclosed in the catheter cavity, a long distance from the tip of the catheter, as shown in Fig. 11(a). Next, the guidewire id pushed forward to get out of the catheter. Finally, the tip of guidewire is propelled out of the cavity of the catheter in Fig. 11(b), and the guidewire is the current device to traverse through the vascular cavity, which will bend to the corresponding interactions between the guidewire and the vessel wall, as shown in Fig.11(c).

Fig. 10 Bending and twisting simulation of the composite model

(a) First step of the guidewire

(b) Second step of the guidewire

(c) Pushing guidewire tip out of catheter into the vessel

Fig. 11 Process of the guidewire moving forward out of the catheter

IV. CONCLUSIONS The catheterization operation is an essential technique in the

process of the interventional vascular surgery, which is a complex procedure demanding the surgeons very dexterous skill in the surgical operation. Recent researches are mostly devoted to the simulation of the vascular deformation and the improvements of the methods to the efficiency and effectiveness. There are also some studies focusing on the wire-like and rod-like medical devices, such as catheter or guidewire. However, nearly researchers give consideration to the cooperation of the catheter and the guidewire, which is an essential issue in the real surgery. In this context, a novel and a complete strategy for the cooperation of the catheter and the guidewire is proposed with consideration to the interaction between the medical device and the vascular wall. The effectiveness was tested by traversing the device through the vascular cavity, especially in the bifurcation of the vascular network. The interaction simulation was performed between the catheter and the guidewire, using the composite model of them and decomposition of the assembly of the two nested devices when it comes to the neurovascular network.

In the future, there still exist more aspects of VR-based simulator to be solved, such as interaction, real time rendering, safety operation, stability and so on. Besides, more precise force feedback and haptic rendering method should be studied for more realistic tactile simulation.

ACKNOWLEDGMENT This research is partly supported by the National High Tech.

Research and Development Program of China (No.2015AA043202), and National Key Research and Development Program of China (2017YFB1304401).

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