CN104224089B - A kind of endoscopic system with surgical navigational function for possessing antijamming capability - Google Patents

Abstract

The invention provides an endoscope system with an anti-jamming capability and a surgical navigation function. The surgical navigation subsystem of the present invention is realized by an inertial navigation module, which includes three sensors: a three-axis accelerometer, a three-axis gyroscope and a three-axis magnetometer. Relying on micro-electro-mechanical technology, the navigation subsystem can be integrated into the handle of the endoscope, so that the endoscope itself has the positioning function. In the positioning algorithm, through appropriate anti-interference processing, the positioning error caused by the external magnetic field and the movement of the endoscope is reduced, and the stability and accuracy of positioning are improved.

Description

An endoscope system with anti-interference ability and surgical navigation function

technical field

The invention belongs to the technical field of computer-aided endoscopic surgery navigation.

Background technique

With the development of modern medicine, minimally invasive surgery with endoscopic system as the main implementation tool has been widely recognized and rapidly popularized. In order to better achieve the purpose of minimally invasive, doctors must accurately obtain the current posture and position of the endoscope, so surgical positioning and navigation technology is often needed. Therefore, modern endoscopic technology and medical navigation technology complement each other, and it is often necessary to cooperate with each other at the same time during surgery.

Chinese patent CN200910198524 discloses a "device combining surgical navigation system with endoscope system and its application", which provides a method for combining optical positioning system with endoscope: through special mechanical The structure fixes the optical positioning ball on the handle of the endoscope. During use, it is necessary to track the optical positioning ball through the camera group, so as to position the endoscope.

The above-mentioned patents have the following problems in practical application: 1. The introduction of the mechanical structure leads to a large increase in the volume of the handle of the endoscope, which may affect the normal operation of the endoscope. 2. In principle, optical positioning needs to ensure that there is an unobstructed line of sight between the camera and the positioning ball. This condition will limit the positioning range of the system and may result in multiple unlocatable areas. 3. In principle, optical positioning requires multiple cameras to complete the positioning task, which will bring unnecessary space pressure to the operating room.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned problems existing in the prior art, and to provide an endoscope system with an anti-interference capability and a surgical navigation function.

First of all, the system integrates the positioning subsystem composed of the inertial navigation module into the endoscopic system, which overcomes the influence of the positioning subsystem on the operation of the endoscope, and eliminates the unlocatable area in the optical positioning. space pressure. On the other hand, for inertial navigation itself, the non-inertial motion of electronic equipment, iron instruments and endoscopes in the working space will directly affect the accuracy and stability of positioning. Therefore, in the algorithm implementation part of the present invention, a corresponding Anti-interference design to improve the robustness of positioning.

The endoscope system with anti-interference ability and surgical navigation function provided by the present invention includes an endoscope and a host computer responsible for control and positioning calculation, and a navigation module installation platform is reserved in the handle of the endoscope , with the help of the inertial navigation module installed on the internal mounting platform of the endoscope handle after the microcomputer electrode is miniaturized, the inertial navigation module includes three sensors: a three-axis accelerometer, a three-axis gyroscope and a three-axis magnetometer, and a sensor with wireless communication Functional system on a chip and a micro-antenna, the system-on-chip collects the sensing data output by the three sensors, and sends the sensing data to the host computer by means of the micro-antenna; the host computer includes a computer, a system-on-chip with a wireless communication function, As well as the antenna, the system-on-a-chip with wireless communication function receives the sensing data output by the inertial navigation module through the antenna, and packs and transmits the sensing data to the computer, which performs positioning calculation through the designed positioning algorithm.

The positioning algorithm in the computer has anti-interference ability, and can suppress the sensor output noise caused by magnetic field distortion and non-inertial motion of the endoscope; when the attitude of the endoscope is converged through the geomagnetic vector and the force vector, the geomagnetic The relative error of the vector output and the relative error of the specific force vector output are used as the weight of the convergence observation function to adjust the convergence direction and adaptively obtain the attitude convergence results; the specific force vector is decomposed into linear acceleration, Gravitational acceleration and centripetal acceleration are three items, and the position result is obtained by performing quadratic integration on the linear acceleration.

Specifically, the method applies the traditional inertial navigation system used for carrier navigation to the field of surgical positioning. A MEMS inertial sensing unit consisting of a three-axis gyroscope, a three-axis accelerometer and a three-axis magnetometer is fixed inside the endoscope handle to obtain sensing data. The sensing data is then transmitted to the host computer through wireless communication, and the host computer realizes full-dimensional positioning through algorithms. The positioning algorithm can be roughly divided into two steps. In the first step, the attitude is updated through the output of the gyroscope, and the attitude quaternion is converged through the output of the accelerometer and the output of the magnetometer. During the convergence process, by measuring the relative error of the accelerometer output and the magnetometer output, the weight of the acceleration vector and the geomagnetic vector in the convergence process is controlled to obtain an adaptive attitude result with anti-noise characteristics. In the second step, based on the obtained attitude results and the output of the accelerometer and gyroscope, the three-dimensional position is calculated by constructing the equation of motion of the rigid body. This part does not directly use the geomagnetic measurement results, so it can further avoid possible magnetic interference.

Advantage and positive effect of the present invention:

Aiming at the bottlenecks in the published patents, the present invention introduces inertial sensing into the field of medical navigation, and installs a miniaturized inertial sensing module inside the endoscope handle with the help of micro-electromechanical technology. The specific force, angular velocity and geomagnetic vector are measured in real time through acceleration, gyroscope and magnetometer; the collected sensor data is sent to the host computer through wireless communication, and the real-time attitude and position of the endoscope are obtained through algorithm calculation.

The invention embeds the navigation system inside the endoscope system without changing the shape of the endoscope, thus preventing the influence of the navigation system on the endoscope system. At the same time, inertial navigation does not have the line-of-sight requirement in optical positioning, and there is no need to arrange peripheral equipment (such as the camera group in the optical positioning system, etc.), which reduces the space pressure in the operating room.

(1) Overcoming the clinical difficulties of traditional surgical navigation methods. Traditional surgical navigation methods include optical positioning and electromagnetic positioning. The former has strict line of sight requirements, while the latter requires strict control of electromagnetic interference sources in the workspace. These two points are difficult to achieve in the actual surgical environment. However, inertial navigation can effectively avoid these problems: on the one hand, the inertial system is not limited by line-of-sight conditions in use; on the other hand, the fusion of multi-sensor information can reduce the system’s dependence on magnetic sensing. Algorithm design, the system's response to noise can be further weakened. Finally, a set of stable surgical positioning system that can be used in the whole spatial range can be constructed.

(2) The endoscopic system and the navigation system do not interfere with each other. In the present device, the navigation system is installed inside the endoscope system, which does not change the shape of the endoscope, thus causing no inconvenience to the doctor's operation. At the same time, the endoscope system can move arbitrarily in the whole space, and there is no problem of blocking the observation line of sight in the optical positioning system.

(3) Strong anti-interference ability and high robustness. The system introduces inertial sensing, and improves the stability of the system through information fusion technology. In the fusion process, the credibility of the information source is examined by observing the relative error output by the magnetometer and accelerometer. According to the size of the relative error, the direction and degree of convergence are controlled, and the optimal attitude solution adaptive to noise is obtained. To sum up, through the method of hardware and software level, the overall robustness of the system can be improved as much as possible.

(4) Good real-time performance and strong adaptability. Compared with the disclosed inertial positioning method with anti-noise characteristics, the method avoids complicated filtering process, reduces algorithm complexity, and obtains better real-time performance. At the same time, the method does not require a prior calibration process, thus avoiding the problem of repeated calibration when changing the use environment, and improving the adaptability of the system to different environments.

Description of drawings

Figure 1 is a system composition frame diagram of the surgical positioning system.

Fig. 2 is a schematic diagram of the installation method of the navigation unit. In the figure, 1 is an endoscope (partial), and 2 is an inertial sensing unit installed on the handle of the endoscope.

Fig. 3 is an overall flowchart of the adaptive tracking method based on sensor fusion.

detailed description

Example 1:

As shown in Figure 1 and Figure 2, the endoscope system with anti-interference capability and surgical navigation function provided by the present invention includes an endoscope and a host computer responsible for control and positioning calculation. A navigation module installation platform is reserved in the handle, and the inertial navigation module is installed on the installation platform inside the endoscope handle after miniaturization of the microcomputer electrodes. The inertial navigation module includes a three-axis accelerometer, a three-axis gyroscope and a three-axis magnetometer Three kinds of sensors, as well as a system-on-a-chip with a wireless communication function and a micro-antenna, the system-on-a-chip collects the sensing data output by the three sensors, and sends the sensing data to the host computer by means of the micro-antenna; the host computer includes a computer, System-on-a-chip with wireless communication function and antenna. The system-on-chip with wireless communication function receives the sensing data output by the inertial navigation module through the antenna, and packs and transmits the sensing data to the computer. The computer passes the designed positioning algorithm Perform positioning calculations.

Before the endoscope handle is assembled, a rectangular groove with the same size as the inertial navigation module is processed inside the handle, and the two sides are respectively parallel or perpendicular to the endoscope tube, as the installation platform of the rectangular inertial navigation module. .

The invention fixes the inertial sensor unit inside the handle of the endoscope in a specific manner, adopts an on-chip system to collect sensing data and transmits it to a host computer through wireless communication. The host computer uses the algorithm proposed by the invention to calculate the position of 6 degrees of freedom, so as to realize the real-time positioning and navigation of the endoscope. In the algorithm part, the attitude is initially estimated through the output of the three-axis gyroscope, and the attitude is measured respectively through the output of the three-axis magnetometer and the three-axis accelerometer, and the estimated value is converged to obtain the attitude measurement value. During the convergence process, the relative error between the magnetometer output and the geomagnetic field and the relative error between the accelerometer output and the acceleration of gravity are used as adaptive factors to judge the size of the noise, adjust the convergence weight, and obtain the adaptive convergence result. After obtaining the real-time attitude results, separate the output components of the accelerometer to construct the kinematic differential equation. Furthermore, the linear acceleration component is solved and numerically integrated with respect to time to obtain the current position.

1. System hardware composition

As shown in Figure 1, the system is divided into two parts in hardware. The first part is the sensor unit installed inside the handle of the endoscope; it consists of a sensor module, a wireless transmitter module and a miniature antenna. The sensor module contains three MEMS sensors, namely accelerometer, gyroscope and magnetometer. The wireless transmitting module is mainly a system-on-chip with wireless transmitting function. The second part is the upper computer responsible for data calculation and display; it consists of a communication control center, a wireless transmitting module and an antenna. The communication control center is the center of the system, responsible for system control and data processing. The wireless receiving module is also mainly composed of a system-on-chip with a wireless transmitting function.

As shown in Figure 2, when the navigation system is installed inside the endoscopy system, the coordinate axes of the two systems need to be strictly aligned. The principle of alignment is: the X-axis of the sensor unit is parallel to the working mirror tube of the endoscope, and the Z-axis is perpendicular to the working mirror tube of the endoscope and faces away from the handle. In order to achieve the purpose of alignment, a rectangular groove is processed inside the handle of the endoscope. The length of the two sides is the same as that of the rectangular inertial navigation module. As the installation platform for the inertial navigation module, one side of the installation platform is parallel to the working mirror of the endoscope. tube, one side is perpendicular to the working mirror tube. The rectangular sensor unit circuit board is fixed on the installation platform by screws, and its sides are respectively aligned with the sides of the installation platform. In order to ensure that the sensor unit circuit board is completely attached to the installation platform, all electronic components of the circuit board are placed on one side of the circuit board.

2. System workflow

When the system is working, the wireless transmitter module collects the output of the sensor module through a specific communication method, and transmits it to the host computer through a miniature antenna. After the wireless receiving module of the upper computer receives the data through the antenna, it sends it to the communication control center, which performs calculations and obtains the positioning result. For example, a system-on-a-chip that supports the ZigBee protocol can be used as the wireless transmitter module and the wireless receiver module, and the ZigBee protocol can be used as the communication method between the two parts of the system; the desktop computer is used as the communication control center; the wireless transmitter module and the sensor module The group communicates with I2C or SPI protocol; the wireless receiving module communicates with the communication control center with USB protocol.

3. Adaptive attitude positioning method

The overall positioning process is shown in Figure 3. The present invention uses the gravity vector and the geomagnetic vector to converge the attitude quaternion of the sensor. During the convergence process, weighting factors are assigned based on the difference between the accelerometer output and the acceleration of gravity and the difference between the magnetometer output and the magnetic intensity of the earth.

set up, is the output of the accelerometer in the carrier coordinate system, is the output of the magnetometer in the carrier coordinate system; g ⁿ is the output of the accelerometer in the reference coordinate system, and m ⁿ is the output of the magnetometer in the reference coordinate system.

For accelerometer measurements, linear and centripetal accelerations are small quantities relative to the acceleration due to gravity. The introduction of linear acceleration and centripetal acceleration will not obviously affect the direction of specific force, and the direction of specific force can basically be regarded as the direction of gravitational acceleration. Therefore, only scalar values are used to construct relative errors. which is:

For magnetic strength measurements. It is entirely possible that the magnetic distortion is in the same order of magnitude as the Earth's magnetic strength. The introduction of magnetic distortion can significantly affect the direction of the total magnetic intensity. Therefore, the relative error is jointly constructed by the two factors of size and direction.

Similar to the magnitude error of acceleration, the magnitude error of magnetic intensity can be expressed as:

Magnetic intensity direction error: Considering that the linear acceleration and centripetal acceleration basically do not affect the direction of the specific force, the angle between the magnetic intensity and the specific force is selected to describe the direction of the magnetic intensity in the reference coordinate system and the carrier coordinate system. In the reference coordinate system, this angle is recorded as β ⁿ ; in the carrier coordinate system, considering the existence of distortion, this angle is recorded as but,

So, the magnetic intensity direction error:

The total magnetic strength error is:

f _adm =k ₁ f _adm1 +k ₂ f _adm2 (6)

In the formula, k ₁ and k ₂ are two constant weight factors. Both numbers are empirical values, and satisfy:

k ₁ +k ₂ =1 (7)

In summary, the adaptive error observation function is shown in (8). When the gravity measurement error is large, f _adg increases accordingly, making the geomagnetic measurement item dominates the convergence process; similarly, when the geomagnetic measurement error is large, f _adm increases accordingly, making the gravity measurement item dominate the convergence process.

In the formula, is an estimate of the rotation matrix. It can be seen that for gravity measurement and geomagnetic measurement, the side with larger noise will take a secondary position in the convergence process, and the larger the error, the lower its relative weight. Therefore, this method can be adjusted adaptively according to the degree of sensor interference, so that the result is closer to the optimal solution.

The convergence objective matrix corresponding to (8) is:

According to the two formulas (10) and (11), perform Gauss-Newton descent on the formula (9), and converge to estimate the quaternion The adaptive pose result can be obtained.

Among them, (10) is the relational expression updated from the mth iteration to the m+1th iteration, and α is the iteration step size.

4. Positioning method

The specific force output of the accelerometer consists of three components: linear acceleration, centripetal acceleration and gravitational acceleration. Therefore, in the carrier coordinate system, there is the following relationship:

Among them, a ^b is the linear acceleration of the front end of the endoscope in the carrier coordinate system. ω ^b is the output of the gyroscope in the carrier coordinate system, and the three-axis components are ω _x , ω _y and ω _z ; ω ^b ×v ^b is the centripetal acceleration of the endoscope in the carrier coordinate system. g ^b is the gravitational acceleration in the carrier coordinate system.

In the attitude tracking stage, the real-time rotation matrix has been obtained as So g ^b can be obtained by the following relationship:

Linear acceleration is the differential of velocity with respect to time, that is:

Substituting (13) and (14) into (12), the first-order differential equation of velocity with respect to time in the carrier coordinate system can be obtained, as follows.

Express the velocity vector in the reference coordinate system by formula (16),

Substitute Equation (16) into Equation (15) to obtain the mathematical relationship between the velocity vector and sensor output in the reference coordinate system.

Also, in the reference coordinate system, the position vector is the first-order integral of the velocity with respect to time, namely

p ⁿ =∫v ⁿ dt (18)

The formula (17) is numerically solved in one positioning period, and the result is discretely integrated with the speed in one positioning period through formula (18), so that the position vector can be updated in real time. To sum up, according to the above two sub-steps, the positioning information of 6 degrees of freedom can be obtained.

Practice has proved that when the magnitude of the magnetic distortion is within ±25% of the geomagnetic field and the specific force is within ±25% of the acceleration of gravity, the angle tracking error can be controlled within 3.5°, and the position positioning error can be controlled within 3.5mm. Both of them meet the requirements of clinical application and have ideal anti-interference ability and stability.

Claims (1)

1. An endoscope system with a surgical navigation function with anti-interference ability, comprising an endoscope and a host computer responsible for control and positioning calculation, characterized in that a navigation system is reserved inside the handle of the endoscope Module installation platform, the inertial navigation module installed on the internal installation platform of the endoscope handle after miniaturization of microcomputer electrodes, the inertial navigation module includes three sensors: three-axis accelerometer, three-axis gyroscope and three-axis magnetometer, and An on-chip system with wireless communication function and a micro-antenna. The system-on-chip collects the sensing data output by three sensors, and sends the sensing data to the host computer by relying on the micro-antenna; the host computer includes a computer, a computer with a wireless communication function On-chip system and antenna, the on-chip system with wireless communication function receives the sensing data output by the inertial navigation module through the antenna, and packs and transmits the sensing data to the computer. The positioning algorithm performs positioning calculation; the positioning algorithm has anti-interference ability, and can suppress the sensor output noise caused by magnetic field distortion and non-inertial motion of the endoscope; when the posture of the endoscope is converged through the geomagnetic vector and the specific force vector When , the relative error of the geomagnetic vector output and the relative error of the specific force vector output are used as the weight of the convergence observation function to adjust the convergence direction and adaptively obtain the attitude convergence result; the specific force vector is decomposed by the output of the gyroscope and the accelerometer These are three items of linear acceleration, gravitational acceleration and centripetal acceleration, and the position result is obtained by performing quadratic integration on the linear acceleration.