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Abstract—Force feedback plays a significant role in robot-assisted catheter system. How to realize the force feedback? How to transmit the force feedback to the experiences of skilled surgeons? Certainly, it is the force sensing system. In this paper, two kinds of force sensing systems for the robotic catheter system have been proposed�and developed, we did the experiments to evaluate the performances of the developed force sensing systems, the experimental results indicated that the developed force sensing systems for the robotic catheter training system are effective, they are suitable for the robotic catheter system. They can be used to realize the force feedback during endovascular neurosurgery, furthermore, they can be used to extract the operating skills of experienced neurosurgeons to train unskilled neurosurgeons and medical students by using the robotic catheter system.

I. INTRODUCTION

In recent years, minimally invasive surgery (MIS) has been�popular for the diagnosis and surgery of endovascular disease, such as aneurysm, infarction, embolization and so on. Because it has a lot of advantages, less incision, short hospital stay, less recovery time and so on. A lot of diagnosis and medical surgery with an endoscope or a catheter are performed for minimum invasive surgery recently, the neurosurgeon inserts the catheter from femoral artery of human, and Fig.1 shows the conceptual diagram of the catheterization for cerebral aneurysm. However, it requires a great deal of skills and experiences to operate inside the body where direct observation is not possible. Especially cerebral aneurysm surgery, the blood vessels of brain are fragile and narrow, it is difficult for unskilled surgeons to insert the catheter to the position of cerebral aneurysm safely.

Based on the above background, the robot-assisted catheter system for endovascular neurosurgery has been grown, it can solve the problem that the skilled neurosurgeons lack. There are many researches on robot-assisted catheter system. A prototype model of micro catheter with active guide wire that has two bending degrees of freedom using ICPF (Ionic

Jian Guo is with the School of Electrical Engineering, TianJin University of Technology, TianJin, China (corresponding author to provide phone: 15102231710; e-mail: guojianjp@gmail.com).

Shuxiang Guo is with the Intelligent Mechanical Systems Engineering Department, Kagawa University, Takamatsu, Kagawa, Japan. He is also with the School of Electrical Engineering, TianJin University of Technology, TianJin, China (e-mail: guo@eng.kagawa-u.ac.jp).

Nan Xiao is with the Intelligent Mechanical Systems Engineering Department, Kagawa University, Takamatsu, Kagawa, Japan (e-mail: xiao@eng.kagawa-u.ac.jp).

Yunliang Wang is with the School of Electrical Engineering, TianJin University of Technology, TianJin, China (e-mail: wangyl@tjut.edu.cn).

Conducting Polymer Film) and SMA actuator fixed on its front end as the servo actuators have been reported[1][2]. Anew catheter driving method using linear stepping mechanism for intravascular neurosurgery has reported [3].The master-slave catheterization system for positioning the steerable catheter was reported [4]. A Novel Catheter Operating System with Force Feedback for Medical Applications was reported [5]. Tele-Operation Master-Slave System for Minimal Invasive Brain Surgery has been reported [6]. A Novel Robotic Catheter System with Force and Visual Feedback for Vascular Interventional Surgery has been reported [7]. In order to solve the problem which the skilled surgeons lack somewhere, many tele-surgery systems have been developed [8]-[11]. They could not extract the operating skills of experienced surgeons in these robotic catheter systems.

Fig.1 Conceptual diagram of the catheterization for cerebral aneurysm

The force feedback plays a significant role in robot-assisted catheter system [12]. In order to detect the force between catheter and blood vessel, many force sensing systems were developed [13]-[21]. However, it is difficult for them to measure the contact force information between catheter tip and catheter sidewall at the same time.

In order to solve the aforementioned problems, this paper proposed two kinds of force sensing systems for the robotic catheter system, they can be used to enhance the safety during endovascular neurosurgery, in addition, they also can be used to extract the operating skills of experienced surgeons to train unskilled surgeons and medical students to do the operation on endovascular neurosurgery.

This paper is organized as following: part two introduced the robotic catheter operating system, it presents the significance of force feedback during endovascular neurosurgery by using the robotic catheter operating system, part three is the developed two kinds of force sensing systems, in this part, two kinds of force sensing systems are presented, we did experiments to evaluate the performances of two kinds of force sensing systems. Part four is conclusions.

Development of Force Sensing Systems for a Novel Robotic Catheter System

Jian Guo, Shuxiang Guo, Nan Xiao and Yunliang Wang

978-1-4673-2126-6/12/$31.00 © 2012 IEEE

Fig.2 Conceptual diagram of the novel robotic catheter operating system

Fig.3 Master manipulator

Fig.4 Slave manipulator

II. THE ROBOTIC CATHETER OPERATING SYSTEM

The conceptual diagram of the novel robotic catheter operating system with a master-slave structure is shown in Fig.2. On the master side, surgeon operates the master manipulator which is shown in Fig.3 to move along the axial direction and radial direction on the slide stage, as if surgeon operates a catheter directly beside the patient, at the same time, the control commands of the master manipulator were transmitted to the slave side, on the slave side, after receiving the control commands from the master side, the slave manipulator which is shown in Fig.4 drives the catheter to insert and rotate inside the blood vessel, which can simulate surgeon’s operative technique. The force sensing system was fixed on the catheter, if the catheter contact to the blood vessel, the force feedback could be transmitted to the surgeon’s hand by internet communication, the IP camera is

used to monitor the situation of the operation, and the monitoring image can be transmitted to the surgeon. Surgeon can decide whether inserting or rotating the catheter depending on the force feedback and visual feedback, the developed robotic catheter operating system can prevent blood vessel from damaging during endovascular neurosurgery, the operative safety can be enhanced. Because the time delay of monitoring image is longer than the force feedback signals during the telesurgery, so the force feedback is significant during the telesurgery by using robotic catheter system.

. FORCE SENSING SYSTEMS

A. The importance of force sensing system

In endovascular neurosurgery, it is most important issue to enhance the safety of the operation, it is the best way to use the force feedback at present. How to realize the force feedback? How to measure the contact force between catheter and blood vessel wall? It is the issues we focus on in this paper. The conceptual scheme of comparison of safety between two situations (without force sensor and with force sensors) is shown in Fig.5. If the catheter is without force sensors during insertion, the blood vessel will be broken easily during operation, however, when the catheter is with force sensors during insertion, the contact force can be measured and transmitted to the surgeon, the surgeon will decide whether to insert the catheter continuously based on the reminding, the safety of the operation can be enhanced. In this research, we developed two kinds of force sensing systems to solve the aforementioned issues.

Fig.5 Comparison of safety between two situations

(Without force sensor and with force sensors)

B. The first kind of force sensing system

1) The structure and principle of the force sensing system

The Fig.6 shows the structure of the force sensing system, we used the catheter which is with the length of 1.0�103mm and with the external diameter of 1.7mm in this research, an electrode of copperplate is fixed on the front end of catheter by linking shape, and the pressure sensitive rubber is fixed on the electrode of copperplate by linking shape, three wires with the diameter of 0.3mm are putted on the pressure sensitive rubber interval of 120 degrees, in order to enlarge the contact area between lead wire and pressure sensitive

rubber, we put electro conductive paste on the pressure sensitive rubber interval of 60 degrees, the Fig.6 shows the structure of the developed force sensing system.

(a) Front view

(b) Side view

Fig.6 Structure of the force sensing system

Fig.7 The prototype of the force sensing system

2) The characteristics evaluation of the force sensing system

In order to detect the contact force between catheter and blood vessel, we developed the force sensing system with the pressure sensitive rubber, the Fig.7 shows the prototype of the force sensing system. The pressure sensitive rubber is material of insulative silicon high polymer which have conductive particles inside it, if we apply the force on it, the resistance will be changed because the contact of conductive particles. We did the experiments to detect the precision of the force sensing system, the Fig.8 shows the measurement system, we used low pass filter circuit and amplifier to enlarge the outputs of force sensors, we used AD board to receive the detected signal voltage, the sampling frequency is set to 1000Hz, the sampling time is set to 10s, we used the electronic balance to measure the applied force. We applied

force from 10mN to 100nN to the force sensors for five times respectively, the position of input force is shown in Fig.9, the Fig.10 shows the experimental results, it shows the relationship between applied force and output voltage, in order to use the relationship to the robotic catheter system, and we did the linear approximation for the results.

Fig.8 Measurement system for the force sensing system

(a) Side view (b) Front view

Fig.9 Position of the input force

Fig.10 Sensor outputs with input force

Fig.11 Dynamic characteristics (sensor 3)

(a) In the case of input force (0.3mN)

(b)In the case of input force (0.6mN)

(c) In the case of input force (0.9mN)

Fig.12 Sensor outputs with input force position

The Fig.11 shows the dynamic characteristics for sensor 3, it takes about 7s from output of peak value to 0v. Because we used one pressure sensitive rubber to do the force sensing system, so when we applied force on one force sensor, it has the possibility of the outputs of the two other force sensors, we did the experiments to verify it. We applied 30mN, 60mNand 90mN to the force sensors respectively, the experimental results are shown in Fig.12. From the experimental results we can know that the three force sensors are independent when we applied different forces on them.

C. The second kind of force sensing system

In order to detect the contact force�both catheter tip and catheter sidewall, we developed the second force sensing system. The Fig. 13 shows the prototype of the developed

force sensing system, which is composed three pressure sensitive rubber�force sensors and one optical fiber force sensor, The three pressure sensitive rubber�force sensors are fixed on the side wall of front end catheter by linking shape, they are used to measure the contact force between catheter sidewall and blood vessel, their sizes are 4.0 4.0 0.5 mm,a micro optical force sensor was used to measure front end force of the catheter, meanwhile, the optical fiber force sensor was served as guide wire to lead the catheter for inserting and rotating. The FOP-M optical fiber force sensor of FISO Technologies Inc. was used this time in this research.�Fig.14 shows the prototype of the force sensing system.

Fig.13 Structure of force sensing system�

Fig.14 The prototype of the force sensing system

The calibration of the developed tactile force sensors was done, the calibration system is shown in Fig.15, which consists of an electronic balance, a serial electric circuit, an oscilloscope, a power supply and a force load, we adjust the force load to different scale, the electronic balance will become different value, the force sensor is loaded different value with force load, the force sensor output is different, the calibration results are shown in Fig.16, they indicated the relationship between load force and output�voltage, based on the calibration results, we can obtain the concrete force output information of force sensors during the operation.

Fig.15 Calibration system for the first sensing system

Fig.16 Calibration results for the force sensing system

Based on the calibration results, we establish an equation between output�voltages and load force using Matlab curve fitting tool and least squares method, it is shown in equation (1), and we can also obtain the coefficient of equation for sensor1, sensor2 and sensor3.

According to this equation, we can get the detail force output value of developed force sensors if the force sensors touch the blood vessel wall. Through the concrete force output value, surgeon can monitor the situation which catheter contact with the blood vessel sidewall.

3 23 2 1 0 ( 1, 2,3)i i i if c v c v c v c i� � � � ��� � ��������������(1)

In order to verify the validity of the developed force sensing system, we did the catheter inserting experiment in the simulator of blood vessel with aneurysm, the simulator is made of silicon glass, in this experiment we only detect the outputs of force sensors at a corner of blood vessel, the experimental results are shown in Fig.18, from the experimental results we can know that the developed force sensing system is effective, it can detect the contact force between catheter and blood vessel easily.

Fig.17 The environment of experiment

Fig.18 Outputs of the force sensors

. CONCLUSIONS

In this paper, two kinds of force sensing systems for the robotic catheter system have been developed. We did the experiments to evaluate the performances of the developed force sensing systems, the experimental results indicated that the developed two kinds of force sensing systems for the robotic catheter system are effective, they are suitable for the robotic catheter system. In the future, we will�combine the two kinds of force sensing systems to extract the skills of experienced neurosurgeons to train unskilled neurosurgeons and medical students by using the robotic catheter training system, in addition, they also can be used to realize the force feedback in the robotic catheter system to enhance the safety during endovascular neurosurgery. �

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