End sensor and tactile feedback interventional catheter and autonomous navigation method thereof

Abstract

The invention relates to an end sensor, a tactile feedback type interventional catheter and an autonomous navigation method thereof.The end sensor comprises a hemispherical optical waveguide, a compound eye array lens, a multimode optical fiber and an optical fiber image transmitting bundle, the compound eye array lens is arranged at the front end of the optical fiber image transmitting bundle, the hemispherical optical waveguide is arranged in front of the compound eye array lens, and the multimode optical fiber is arranged in front of the hemispherical optical waveguide. Four multimode optical fibers are circumferentially arranged at the bottom of the optical waveguide and couple light into the optical waveguide at a certain incident angle, so that the end surfaces of the optical fibers coincide with the bottom surface of the optical waveguide; the tactile feedback type interventional catheter is internally provided with the end sensor, based on the synergistic effect of a large-angle imaging function provided by a compound eye array lens and a force feedback function provided by light leakage caused by optical waveguide contact, accurate force feedback and contact point positions can be provided through autonomous navigation, a guide wire is not needed to serve as a guide device, and the operation is simple and convenient. The catheter can directly intervene in the blood vessel and feed back mechanical information and position information of contact between the catheter and the blood vessel wall in real time in the interventional process, and the interventional direction of the catheter can be changed according to needs.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to an end sensor and tactile feedback type interventional catheter and an autonomous navigation method thereof. Background Art

[0002] In modern medicine, interventional surgery has become the main means of treating major cardiovascular diseases. Traditional cardiovascular interventional surgery requires doctors to flexibly operate catheters, guidewires and other instruments with the assistance of fluoroscopic imaging equipment such as CT to perform interventional treatment. Among them, the catheter is a necessary pathway for transmitting interventional surgical instruments to the lesion for further interventional treatment, but the current interventional catheter does not have a navigation function, so it is necessary to use a guidewire as a guiding device to guide the catheter to the lesion. However, the guidewire is usually composed of a soft and slender structure, and its distal force transmission loss is large, which makes the doctor lack tactile information about the interventional instrument and cardiovascular tissue, often causing accidents such as vascular perforation and heart wall perforation. To avoid the above problems, doctors usually use fluoroscopic imaging equipment to observe the position and shape of the guidewire to avoid the guidewire from applying excessive contact force to the vascular wall, but the ionizing radiation generated during the use of fluoroscopic imaging equipment will cause certain radiation damage to doctors and patients. Therefore, during interventional surgery, doctors will try to reduce the frequency of fluoroscopic imaging and blindly navigate the interventional instrument based on surgical experience. This operation will greatly increase the probability of vascular damage or perforation.

[0003] At present, the following two methods are mainly used to avoid ionizing radiation exposure to doctors and patients during interventional surgery and ensure the safety of the surgery:

[0004] One method is to use magnetic resonance imaging (MRI) equipment without ionizing radiation to navigate interventional devices. Although this method can avoid radiation risks, most of the current interventional devices and their supporting equipment contain metal materials, and some patients have a history of treatment with metal implants such as vascular stents. The presence of metal materials and devices makes the MRI imaging navigation method extremely risky, which in turn limits the practical application of this method.

[0005] Another method is to embed shape and force sensors at the front end of the interventional device to track the shape of the interventional device during navigation. Although this method can avoid perforation events caused by excessive operating force during blind navigation, it cannot ensure that the interventional device is always in the correct path during blind navigation. In addition, the design of the front-end force sensor may cause the guidewire to be unable to achieve the required plastic deformation in complex blood vessels, thereby greatly limiting its ability to pass through narrow or tortuous blood vessels. Therefore, although the integration of force sensors helps to reduce the risk of perforation, in actual operation, it may face the problem that the guidewire cannot adapt to complex vascular paths, limiting its actual application effect. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an end sensor.

[0007] Another technical problem to be solved by the present invention is to provide a tactile feedback interventional catheter including the above-mentioned end sensor.

[0008] Another technical problem to be solved by the present invention is to provide an autonomous navigation method for the above-mentioned tactile feedback interventional catheter.

[0009] In order to solve the above technical problems, the technical solutions proposed by the present invention are as follows:

[0010] An end sensor comprises a hemispherical optical waveguide 4, a compound eye array lens 5, a multimode optical fiber 6 (used as an optical fiber tendon) and an optical fiber image transmission bundle 7. The front end of the optical fiber image transmission bundle 7 is provided with a compound eye array lens 5, and the front of the compound eye array lens is provided with a hemispherical optical waveguide 4. Four multimode optical fibers 6 are placed along the circumference at the bottom of the hemispherical optical waveguide and light is coupled into the optical waveguide at a certain incident angle so that the end face of the optical fiber coincides with the bottom surface of the optical waveguide.

[0011] The above-mentioned optical fiber image transmission bundle cooperates with the front compound eye array lens device and its optical system to realize contact state imaging and image transmission. The compound eye array lens is designed and optimized using ray tracing software and printed using micro-nano manufacturing technology.

[0012] Preferably, in the above-mentioned end sensor, the four multi-mode optical fibers are arranged in a cross shape.

[0013] Preferably, in the above-mentioned end sensor, the optical waveguide is a PMMA optical waveguide.

[0014] Preferably, in the above-mentioned end sensor, the multimode optical fiber is a multimode optical fiber whose outer circumference (the entire circumference, except for the two end faces for light input and light output) is coated with polyimide.

[0015] Preferably, in the above-mentioned end sensor, the optical fiber imaging bundle is made of quartz glass.

[0016] Preferably, the above-mentioned end sensor is based on large sensing angle tactile feedback, and its dynamic contact force calibration and characterization method starts from the contact force and establishes a theoretical model of visual image and dynamic and static contact force based on spot pattern analysis. The contact force between the catheter and the blood vessel wall during the intervention process is calculated through this model.

[0017] Preferably, for the above-mentioned end sensor, the theoretical model of the static contact force is to calibrate the three-axis contact force of the cardiovascular visual-tactile navigation sensor using a static force calibration device, and to evaluate the isotropy of its force measurement using a sensitivity matrix.

[0018] Preferably, for the above-mentioned end sensor, the theoretical model of the dynamic contact force is that the refractive index distribution of the materials on both sides of the optical waveguide in the non-contact state constitutes a total reflection condition, while the change in the refractive index distribution of the contact part in the contact state destroys the total reflection condition of the area, thereby forming light energy leakage in the contact area; during the dynamic contact process, the contact area of ​​the optical waveguide at the end of the catheter will undergo local deformation, thereby generating bending loss of part of the optical waveguide, causing the contact spot area to present a non-uniform light intensity distribution, and quantitatively characterizing the part of the overflowed loss light energy.

[0019] Preferably, the above-mentioned end sensor adopts a leakage light energy-contact force conversion model. When the end sensor contacts the blood vessel wall, the optical waveguide on the surface is deformed, causing the light inside the optical waveguide to leak. The leaked light is captured by the compound eye array lens in the center and forms a light spot pattern on the end face of the optical fiber image transmission bundle. The magnitude and direction of the contact force can be obtained by analyzing the light spot pattern.

[0020] A tactile feedback interventional catheter comprises a catheter body, the catheter body has the above-mentioned end sensor built in, the compound eye array lens of the end sensor is placed at the end of the catheter body, the compound eye array lens is connected to the optical fiber image transmission bundle of the end sensor and is arranged at the center of the inner cavity of the catheter body, and the compound eye array lens is combined with the hemispherical optical waveguide of the end sensor, the hemispherical optical waveguide is fixedly connected to the end of the catheter body and is used to encapsulate the compound eye array lens 5, multimode optical fiber 6 and optical fiber image transmission bundle 7 of the end sensor in the catheter body, an instrument channel 3 for inserting surgical instruments is provided at an eccentric position of the cross section of the catheter body, and a hole for specially placing the surgical instrument channel is reserved at a corresponding position on the optical waveguide.

[0021] Preferably, in the above-mentioned tactile feedback interventional catheter, a section of the catheter body close to the hemispherical optical waveguide is made of a flexible base material, and a section away from the hemispherical optical waveguide is made of a rigid base material.

[0022] Preferably, in the above-mentioned tactile feedback interventional catheter, the length of the catheter body using the flexible base material segment does not exceed 30% of the total length of the catheter body.

[0023] Preferably, in the above-mentioned tactile feedback interventional catheter, the rigid base material is made of shape memory polymer or other polymers with good biocompatibility, and the flexible base material is made of polymer materials with good biocompatibility and better flexibility such as polytetrafluoroethylene, so as to achieve large curvature deformation of the catheter end. At the same time, due to the shape memory effect of the shape memory polymer, it can be ensured that the catheter can return to its original shape after long-term storage, which is convenient for storage.

[0024] Preferably, in the above-mentioned tactile feedback interventional catheter, the shape memory polymer is a polyurethane (PU)-based shape memory polymer.

[0025] Preferably, in the above-mentioned tactile feedback interventional catheter, the hemispherical optical waveguide of the end sensor is located at the end of the catheter body and its inner diameter and outer diameter are consistent with those of the catheter body.

[0026] In the above-mentioned autonomous navigation method of the tactile feedback interventional catheter, when the catheter enters the blood vessel, the pushing mechanism pushes the catheter forward. If the curvature of the blood vessel changes during the advancement of the catheter, causing the end of the catheter to contact the blood vessel wall, and the contact force shows a significant increase (with a tendency of transitional contact), the sensor feeds back the tiny force change to the PC end, and the PC end outputs instructions to the pushing mechanism to drive the optical fiber tendon in the catheter to make the end of the catheter make a corresponding bending action to reduce it to 0 or a safe contact force range. The navigation process repeatedly cycles the above process to complete the closed-loop control of autonomous navigation.

[0027] Technical Effects

[0028] The above-mentioned end sensor is an end sensor structure of an autonomous navigation catheter based on large sensing angle tactile feedback. The tactile feedback interventional catheter assembled by the end sensor can be used in cardiovascular interventional surgery to achieve the purpose of directly navigating to the lesion and directly treating it without the need for guidewire guidance.

[0029] The tactile feedback interventional catheter can autonomously navigate to provide precise force feedback and contact point location based on the synergistic effect of the large-angle imaging function provided by the compound eye array lens and the force feedback function provided by light leakage caused by the contact of the optical waveguide. The catheter does not require a guide wire as a guiding device, can directly intervene in the blood vessel and provide real-time feedback on the mechanical information and position information of the contact between the catheter and the blood vessel wall during the intervention process, and can change the direction of catheter intervention by driving the four optical fiber tendons on the catheter wall when the doctor needs it. It has extremely high safety, real-time performance, and high precision during the navigation process. The specific advantages are as follows:

[0030] (1) Quantitative observation of contact force at a large sensing angle is achieved. By introducing a compound eye array lens device at the front end of the catheter, the field of view of the sensor is increased, large sensing angle measurement and sensor miniaturization design are achieved, and an optical waveguide is placed in front to achieve quantitative observation of contact force in a cardiovascular visual-tactile catheter.

[0031] (2) A method for calibrating and characterizing dynamic and static contact forces based on large sensing angle tactile feedback was proposed. Based on the optimized design and calibration of the compound eye array lens, a leakage light energy-contact force conversion model was proposed by combining the contact mechanics theoretical model and the waveguide optics theoretical model. The dynamic calibration and characterization of the contact force was realized based on the dynamic force calibration method.

[0032] (3) An autonomous navigation method and its closed-loop control method based on the safe contact force range were designed. Different navigation strategies were proposed in combination with different navigation task characteristics, so that the sensor can adapt to the large curvature changes of the vascular pathway and enhance its adaptability and navigation safety.

[0033] (4) The designed autonomous navigation catheter based on large sensing angle feedback can help doctors and patients avoid the effects of ionizing radiation. While achieving navigation, interventional devices can be directly used for treatment, ensuring safety while improving surgical efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the overall appearance structure of the tactile feedback interventional catheter of the present invention.

[0035] Figure 2 It is a schematic diagram of the enlarged structure of the end sensor described in the present invention.

[0036] Figure 3 It is a schematic diagram of the cross-sectional structure of the end sensor of the present invention.

[0037] Figure 4 It is a schematic diagram of the sensing principle of the sensor in the tactile feedback interventional catheter of the present invention.

[0038] Figure 5 It is a schematic diagram showing that the interventional blood vessel of the present invention does not contact the blood vessel wall.

[0039] Figure 6 It is a schematic diagram of the bending control after the interventional blood vessel contacts the blood vessel wall according to the present invention.

[0040] Figure 7 It is a schematic diagram of the navigation control mechanism of the tactile feedback interventional catheter of the present invention.

[0041] In the figure: 1- Rigid base material section 2- Flexible base material section 3- Instrument channel 4- Optical waveguide

[0042] 5- Compound eye array lens 6- Multimode optical fiber 7- Optical fiber image transmission bundle 8- Catheter pushing mechanism

[0043] 9-Inner wall of blood vessel 10-Outer wall of blood vessel 11-Blood DETAILED DESCRIPTION

[0044] The tactile feedback interventional catheter device of the present invention is described in detail below with reference to the embodiments and drawings.

[0045] Example 1

[0046] like Figure 2 , Figure 3As shown, the end sensor includes a hemispherical optical waveguide 4, a compound eye array lens 5, a multimode optical fiber 6 (used as an optical fiber tendon) and an optical fiber image transmission bundle 7. The optical waveguide is a PMMA optical waveguide, which is manufactured using soft lithography due to its large size. The multimode optical fiber is a multimode optical fiber coated with polyimide on the periphery. The optical fiber image transmission bundle is made of quartz glass, which has good light transmittance, a large light transmittance wavelength range and high resolution. A compound eye array lens 5 is provided at the front end of the optical fiber image transmission bundle 7 to transmit speckle images, realize contact state imaging and image transmission. The compound eye array lens is designed and optimized using ray tracing software and printed using femtosecond laser processing micro-nano manufacturing technology. A hemispherical optical waveguide 4 is provided in front of the compound eye array lens, and four multimode optical fibers 6 are placed along the circumferential direction at the bottom thereof. The four multimode optical fibers are arranged in a cross shape. The multimode optical fiber couples light into the optical waveguide at a certain incident angle, so that the optical fiber end face coincides with the bottom surface of the optical waveguide.

[0047] The above-mentioned end sensor is based on large sensing angle tactile feedback. Its dynamic contact force calibration and characterization method starts from the contact force and establishes a theoretical model of visual image and dynamic and static contact force based on spot diagram analysis. Through this model, the contact force between the catheter and the blood vessel wall during the intervention process can be calculated. While realizing the integrated visual and tactile measurement, interventional treatment can be directly performed, which greatly improves the efficiency of the operation.

[0048] The theoretical model of static contact force is to calibrate the three-axis contact force of the cardiovascular visual-tactile navigation sensor using a static force calibration device, and evaluate the isotropy of its force measurement using a sensitivity matrix.

[0049] The theoretical model of dynamic contact force is that the refractive index distribution of the materials on both sides of the optical waveguide in the non-contact state constitutes the total reflection condition, while the change in the refractive index distribution of the contact part in the contact state destroys the total reflection condition of the area, thereby forming light energy leakage in the contact area; during the dynamic contact process, the contact area of ​​the optical waveguide at the end of the catheter will undergo local deformation, resulting in bending loss of part of the optical waveguide, making the contact spot area present a non-uniform light intensity distribution, and quantitatively characterizing the loss of this part of the overflowing light energy.

[0050] Using the leakage light energy-contact force conversion model, when the end sensor contacts the blood vessel wall, the optical waveguide on the surface is deformed, causing the light inside the optical waveguide to leak. The leaked light is captured by the compound eye array lens in the center and forms a spot pattern on the end face of the optical fiber image transmission bundle. The magnitude and direction of the contact force can be obtained by analyzing the spot pattern.

[0051] The dynamic and static contact force calibration and characterization of the above-mentioned end sensor are as follows:

[0052] The optical waveguide at the catheter end is designed to be hemispherical. Since the radius of curvature of cardiovascular tissue is much larger than that of the catheter end, and the rigidity of the catheter end is much larger than that of cardiovascular tissue, the contact model can be assumed to be the contact between a flexible plane and a rigid hemispherical shape. According to the contact mechanics theory, the contact indentation morphology during the contact process is described as follows:

[0053]

[0054] Where h is the contact indentation shape, V is the Poisson's ratio of biological soft tissue, E is the elastic modulus of biological soft tissue, and R t is the outer diameter of the optical waveguide, x is the lateral displacement value, and P is the normal pressure F N The normal pressure generated. k1, k2, η1 are the spring coefficient and viscosity coefficient, respectively, which are obtained by fitting through relaxation and creep experiments. ε0 is the initial strain, Δγ is the adhesion energy (the work done by the contact body from the equilibrium position to infinity), G is the shear modulus, and F T is the shear force, the pull-off force F o =-3πΔγR t / 2, s is the distance from the point to the shear force, r is the distance from the shear force to the center of the probe contact surface, θ is the angle between the shear force and the x-axis, and a is the contact radius.

[0055] The refractive index distribution of the materials on both sides of the optical waveguide in the non-contact state constitutes the total reflection condition, while the change in the refractive index distribution of the contact part in the contact state destroys the total reflection condition of the area, thereby forming light energy leakage in the contact area. The contact area between the catheter tip and the cardiovascular tissue can be quantitatively described using formula (1), and the functional mapping relationship between the leakage light energy area s1 and the contact area s2 is described using formula (2):

[0056]

[0057] Where s1 is the spot area, s2 is the contact area, n1 is the substrate refractive index of the optical waveguide, n2 is the core refractive index of the optical waveguide, n3 is the refractive index of the contact object, d is the thickness of the optical waveguide, c is the wave speed of light in vacuum, and f′(s) is the fitting curve of the contact area and the spot area, which is obtained through calibration experiments.

[0058] During the dynamic contact process, the contact area of ​​the optical waveguide at the catheter end will be locally deformed, resulting in bending loss of part of the optical waveguide, making the contact spot area present a non-uniform light intensity distribution. The part of the overflow loss light energy can be quantitatively characterized by formula (3):

[0059]

[0060] In the formula, β is the propagation constant, k0 is the wave number of light in vacuum, P1 is the pixel optical power increment in the photosensitive area of ​​the image sensor, P2 is the unit optical power increment in the contact area, and g′(P2) is the fitting curve of the pixel optical power increment and the unit optical power increment, which is obtained through calibration experiments.

[0061] Based on the above light-force conversion model theory, the light energy leakage distribution map of the contact process between the catheter tip and cardiovascular tissue within a large field of view can be obtained based on the compound eye array device. The light energy spatial distribution gradient in the light energy leakage distribution map contains the contact force distribution information in the x-axis and y-axis directions, and by comparing the light energy spatiotemporal distribution gradient of the z-axis, the contact force distribution information in the z-axis direction is included. The light intensity gradient in the three directions of the light energy leakage distribution map is obtained through image processing technology. According to formula (4), the three-axis contact force of the cardiovascular visual tactile navigation sensor is calibrated using a static force calibration device, and the isotropy of its force measurement is evaluated using a sensitivity matrix.

[0062]

[0063] Using a static force calibration device, the sensor is subjected to force in the range of 0 to 2 N with a step size of 0.05 N, and the sensitivity matrix of formula (4) is obtained. The 0 to 2 N sensing range can ensure that the sensor can achieve a wide range of tactile feedback in the blood vessel, and at the same time ensure that the catheter is not damaged when inserted into the sheath. When calculating the contact force later, it is only necessary to calculate the inverse matrix of the sensitivity matrix and multiply it by the contact force distribution information in the light energy leakage distribution map to calculate the actual contact force between the optical waveguide and the blood vessel wall.

[0064] The frequency response method is used to overcome the influence of blood flow on the contact between the catheter and the blood vessel wall. The sinusoidal force is used as the input signal. According to the output frequency response function of the visual-tactile navigation sensor, the dynamic sensitivity and other parameters of the sensor are analyzed according to formula (5).

[0065]

[0066] Where G(jω) is the dynamic sensitivity, e j∠G(jω) It is the phase-frequency characteristic and the output hysteresis of the sensor in steady state.

[0067] In the dynamic contact force calibration and characterization method of the above-mentioned navigation catheter end sensor, starting from the contact force, a theoretical model of visual image and dynamic and static contact force was established based on spot pattern analysis. This model can accurately calculate the contact force between the catheter and the blood vessel wall during the intervention process.

[0068] Example 2

[0069] like Figure 1-4As shown, the tactile feedback interventional catheter includes a catheter body, the catheter body has the end sensor as claimed in claim 1 built in, the compound eye array lens 5 of the end sensor is placed at the end of the catheter body, the compound eye array lens 5 is connected to the optical fiber imaging bundle 7 of the end sensor and is arranged at the center of the inner cavity of the catheter body, and the compound eye array lens 5 is combined with the hemispherical optical waveguide 4 of the end sensor, the hemispherical optical waveguide 4 is located at the end of the catheter body and its inner diameter and outer diameter are consistent with the catheter body, the hemispherical optical waveguide 4 is fixedly connected to the end of the catheter body for encapsulating the compound eye array lens 5, multimode optical fiber 6 and optical fiber imaging bundle 7 of the end sensor in the catheter body, an instrument channel 3 for inserting surgical instruments is provided at an eccentric position of the cross section of the catheter body, and a hole for specially placing the surgical instrument channel is reserved at a corresponding position on the optical waveguide. A section of the catheter body close to the hemispherical optical waveguide adopts a flexible base material, and a section away from the hemispherical optical waveguide adopts a rigid base material. The length of the catheter body using the flexible base material section 2 does not exceed 30% of the total length of the catheter body, and the rest is a rigid base material section 1. The rigid base material section 1 uses a polyurethane (PU)-based shape memory polymer as a base to ensure that the force applied to the catheter to move forward can be effectively transmitted and the catheter will not undergo a large deformation to affect the intervention; the flexible base material section 2 uses polytetrafluoroethylene as a base to achieve a large curvature deformation of the catheter end, and ensure that the catheter end can be well controlled to bend by four optical fiber tendons when encountering complex vascular conditions. At the same time, due to the shape memory effect of the shape memory polymer, it can be ensured that the catheter can return to its original state after long-term storage, which is convenient for storage.

[0070] In this embodiment, the inner diameter of the catheter body is designed to be 2mm, and the outer diameter is designed to be 2.2mm. This diameter is suitable for most interventional surgeries, such as cardiovascular interventional surgeries. The compound eye array lens connected to the optical fiber image transmission bundle is placed at the center of the catheter, and its diameter is designed to be 0.6mm, which can transmit optical signals well; the surgical instrument channel is placed in an eccentric position, and its diameter is designed to be 0.8mm, which can provide interventional treatment for instruments of different diameters. Four identical polyimide-coated multimode optical fibers are evenly placed on the inner wall of the catheter, and their diameter is about 0.2mm. The multimode optical fiber used has good bending resistance, mechanical strength and corrosion resistance. It mainly has the following two functions: one is to illuminate the hemispherical PMMA optical waveguide at the end of the catheter. The four evenly distributed multimode optical fibers can ensure that the light intensity is sufficient and evenly distributed when illuminating the optical waveguide; the second is that due to its good bending resistance and mechanical strength, it can act as an optical fiber tendon rope. When encountering complex vascular conditions, the optical fiber tendon rope is driven to adjust the bending of the flexible part of the catheter to ensure safety while further intervening in the blood vessel.

[0071] One end of the tactile feedback interventional catheter is connected to a catheter pushing mechanism 8, which includes a linear drive module and a torsion drive module (An Enhanced Dual-finger Robotic Hand for Catheter Manipulating in Vascular Intervention: A Preliminary Study*, Proceeding of the IEEE International Conference on Information and Automation Yinchuan, China, August 2013). The linear drive module can use a DC24 V DC motor with a rated power of 70W. The motor has two steel wheels and a regulator. The knob on the regulator can adjust the diameter of the pushing catheter and the opening and closing of the mechanism. The drive module of the motor uses an H-bridge L298 logic driver, which can drive two DC motors at the same time, with a single channel reaching a high power of 7A, and has isolation and undervoltage protection. The microcontroller model used for linear drive control is STM32F103C8T6, which is a 32-bit microcontroller based on the Cortex-M3 core. The internal 8MHz clock HSI can be multiplied to 64MHz, and the external 8MHz clock HSE can be multiplied to 72MHz. It has up to 4 built-in timers, each of which has different modes and frequency counts. In addition, the low-power design technology of this microcontroller is very suitable for the motor, which can reduce power consumption as much as possible while maintaining the high performance of the DC motor. The PWM code for the control of the motor speed is written in C language, with the frequency set to 310Hz and the duty cycle set to 6% to 8%. The catheter torsion module consists of a stepper motor and two rollers, and the torsion of the catheter is achieved by rubbing the rollers up and down. A 42 linear screw stepper motor is used to control the up and down movement of one of the rollers. The stepper motor has a stroke of 50mm, a lead of 2mm, a rated torque of 0.7N·m, and a motor length of 60mm. The motor driver uses the TB6600 driver. The interface of the driver adopts high-speed optical coupling isolation and has strong anti-high-frequency interference ability. It has input voltage reverse connection protection and overheating, overcurrent short circuit protection, and has good performance and safety. The driver can select 7-speed subdivision control (1, 2 / A, 2 / B, 4, 8, 16, 32) through a 3-position dip switch, and select 8-speed current control (0.5A, 1A, 1.5A, 2A, 2.5A, 2.8A, 3.0A, 3.5A) through a 3-position dip switch. The driver pulse signal 3.3V / 5V / 24V is universal and does not require a series resistor. The power supply can be connected to DC9~40V DC. The outer wall of the catheter is evenly coated with a hydrophilic coating to ensure that the catheter can smoothly intervene in complex vascular structures when pushed.

[0072] The fiber-optic imaging bundle is a collection of tiny optical fibers that can transmit imaging information from the end of the catheter to the imaging system at the other end. It can capture image information from the optical waveguide for detecting and analyzing light leakage. The hemispherical PMMA optical waveguide is located at the end of the catheter body and its inner and outer diameters are consistent with those of the catheter. The optical waveguide contacts the blood vessel wall through its surface. When contact occurs, the light in the optical waveguide leaks at the contact point. The compound eye array lens at the end of the catheter is directly connected to the fiber-optic imaging bundle. The compound eye array lens is composed of multiple micro lenses and is responsible for capturing the light leaking inside the optical waveguide to ensure that the imaging bundle can image the leaked light and transmit it to the external imaging system. The four multimode optical fibers on the inner wall of the catheter are arranged in a cross shape, which not only acts as a tendon to control the bending movement of the catheter end, but also provides a light source for the optical waveguide. Multimode optical fibers can transmit light beams of different modes, produce uniform illumination in the optical waveguide, and facilitate the detection of light leakage. During the catheter intervention, the four multimode optical fibers continuously illuminate the hemispherical optical waveguide at the end of the catheter, and parameters such as light intensity remain unchanged. Once the optical waveguide contacts biological tissue and deforms, light leakage will occur immediately, and the leaked light will be captured by the compound eye array lens at the center of the catheter, presenting a light spot diagram at a certain height of the end face of the optical fiber image bundle, and transmitted to the computer through the optical fiber image bundle. Since the optical fiber tendon drive causes the catheter end sensor to bend, and the optical fiber image bundle also bends with it, the transmitted light spot diagram may be distorted, which needs to be repaired. The present invention repairs the distorted image based on the ResNet (Residual Neural Network) model in the neural network. ResNet solves the problem of gradient disappearance caused by the increase in the number of network layers by introducing residual blocks. It allows the input to directly jump (skip connections) when passing through multiple layers of convolution, so that the model can better retain the original image information, thereby avoiding information loss. First, determine the data set. The optical fiber bending angle ranges from 0 degrees to 180 degrees, and each bending of 1 degree corresponds to a distorted sample, which provides a relatively rich supervised learning data for the model. 80% of the samples are used for training, 10% for verification, and 10% for testing.Then, the distorted 224×224×1 spot image is used as the input of the model. The convolution kernel of the first convolution layer is 7×7, the stride is 2, and the number of output channels is 64, followed by a BN (Batch Normalization) layer for stable training and ReLU (Rectified Linear Unit) activation function; the pooling kernel of the maximum pooling layer is 3×3, the stride is 2, and the input is downsampled; residual blocks 1-2, each residual block contains two 3×3 convolutions, and the number of output channels is 64; residual blocks 3-4, each residual block contains two 3×3 convolutions, and the number of output channels is 128; residual blocks 5-6, each residual block contains two 3×3 convolutions, and the number of output channels is 256; residual blocks 7-8, each residual block contains two 3×3 convolutions, and the number of output channels is 512. The global average pooling layer reduces the convolution output to 1 dimension, and the fully connected layer is mapped to the repaired spot image. Next, two loss functions are combined to improve the restoration effect: mean square error (MSE) and structural similarity index (SS iM).

[0073] MSE is used to calculate the pixel difference between the restored image and the original image, which can be expressed as formula (10):

[0074]

[0075] SSIM is used to measure the perceptual similarity between the restored image and the original image, which can be expressed as formula (11):

[0076]

[0077] Where μ x , μ y is the image mean, σ x , σ y is the image variance, σ xy is the covariance.

[0078] The Adam learning rate adaptive optimizer is used, with the initial learning rate set to 0.001, ββ1=0.9, ββ2=0.999, the batch size set to 16~32, the number of training rounds to 50~100, and the adjustment is made according to the performance of the validation set. The learning rate decays by half after every 10 rounds of training. After all the parameters are set, the ResNet model is trained using the training set data, and the changes in MSE and SS IM are monitored on the validation set. The model performance is evaluated on the test set, and MSE, SSIM and PSNR (peak signal-to-noise ratio: an indicator used to measure the quality of image restoration) are calculated.

[0079] According to the repaired spot image output by the neural network, the established "light-force" conversion model is used to calculate the size, direction and other information of the contact force.

[0080] The catheter navigation control mechanism of the above-mentioned tactile feedback interventional catheter is as follows:

[0081] Since cardiovascular tissue is more fragile than myocardial tissue, the feedback of tiny dynamic contact force during catheter navigation is very important for the safety of surgery. Therefore, a biological experiment is first used to determine the safe contact force range suitable for vascular navigation. The designed biological experiment selected rat cardiovascular tissue samples as experimental objects. The catheter was precisely controlled by a force sensor to apply pressure on the inner wall of the vascular sample in the range of 0 to 1N with a step of 0.05N. The vascular damage under different contact forces was evaluated by histological analysis, including intimal damage, inflammatory response, and endothelial cell peeling. The effects of different contact forces on vascular tissue were obtained, and the safe contact force range that would not damage the vascular wall was determined. Before determining the specific control mechanism, it is necessary to determine the location of the optical waveguide leaking light energy, that is, the specific location of the contact point between the vascular wall and the optical waveguide on the optical waveguide. It is advisable to establish a three-dimensional Cartesian coordinate system (x, y, z) with the center of the end face of the image transmission fiber bundle as the origin. The surface of the hemispherical optical waveguide is located at z = 0, and the outer diameter is R t The contact point position on the optical waveguide surface is represented by P(x p ,y p , z p ) indicates that there is the following relationship:

[0082] x p 2 +y p 2 +z p 2 =R t 2 (6)

[0083] Since the optical waveguide is hemispherical and the contact point is at the top of the hemisphere, z p ≥0. When the optical waveguide contacts the blood vessel wall, light leakage occurs. The direction of the leaked light can be expressed by equation (7):

[0084]

[0085] In the formula is the direction of the leaked light, θ p It is the leakage angle when the light enters the external air from the inside (core layer) of the optical waveguide, which is the angle between the light and the normal line. is the azimuth of light leakage, which is the rotation angle of the light relative to the xy plane in the horizontal direction and can be expressed by formula (8):

[0086]

[0087] Where θ2 is the incident angle of light propagating in the waveguide core layer (relative to the normal), n2 is the refractive index of the core layer of the optical waveguide, and n0 is the refractive index of air. The propagation of light in the compound eye array lens follows a simple ray tracing model. After entering the image transmission fiber bundle, a light spot pattern is formed at the end face z=h of the fiber bundle. The center position of the light spot in the end face light spot pattern of the image transmission fiber bundle can be set as C(x c ,y c , z c ), we can reversely deduce the contact point P(x p ,y p , z p ) is as shown in formula (9):

[0088]

[0089] In order to realize autonomous navigation control, an invasive sensor closed-loop control mechanism based on micro-contact force feedback is designed to precisely control the catheter. When the catheter enters the blood vessel, the push mechanism pushes the catheter forward. If the catheter encounters changes in the curvature of the blood vessel during advancement, causing the end of the catheter to contact the blood vessel wall, and the contact force shows a significant increase (with a tendency to transition contact), the sensor will feedback the change in the micro-force to the PC end, and the PC end will output instructions to the push mechanism to drive the optical fiber tendon in the catheter to make the end of the catheter make a corresponding bending action to reduce it to 0 or a safe contact force range. The navigation process repeats the above process to complete the closed-loop control of autonomous navigation. The large deformation controllable ability of the catheter enables it to adapt to the large curvature changes of the vascular pathway, ensuring the safety and effectiveness of the autonomous navigation process.

[0090] Example 3

[0091] The application example of the tactile feedback interventional catheter described in Example 2 is specifically applied as follows:

[0092] like Figure 5 As shown, after the catheter is pushed into the blood vessel by the pushing mechanism, it only contacts the blood 11. However, the force exerted by the blood 11 on the sensor is very small compared to the contact force between the sensor and the inner wall 9 of the blood vessel, and can be ignored. Here we only consider the contact force. Then, when the catheter is just inserted, it is in a non-contact state with the inner wall 9 of the blood vessel. At this time, because the curvature of the blood vessel does not change much, the catheter is likely not to contact the inner wall 9 of the blood vessel, and the optical waveguide does not leak light. The end of the catheter does not need to be bent, and it can continue to be pushed.

[0093] like Figure 6As shown, when encountering a blood vessel bifurcation or a large change in blood vessel curvature, the end of the catheter will contact the inner wall 9 of the blood vessel, and both the inner wall 9 and the outer wall 10 of the blood vessel will produce slight deformations. When the deformation of the outer wall 10 of the blood vessel is too large, the blood vessel will rupture. At this time, light leakage can be generated by the optical waveguide of the end sensor, and the spatial position of the contact point can be calculated according to the established model. Then, the corresponding optical fiber tendon is driven to make the catheter end bend in the opposite direction of the contact point. At this time, the catheter is away from the blood vessel wall or its contact force is in a safe contact range.

[0094] like Figure 7 As shown in the figure, since there is no need for the guidewire to intervene in navigation in advance, the catheter can be directly inserted after the sheath is inserted. When the catheter does not contact the blood vessel wall, no light leakage occurs, and it can continue to advance until the lesion. Once the blood vessel contacts the blood vessel wall, the optical waveguide generates light leakage, and the magnitude of the contact force and the specific position of the contact point are calculated by the spot diagram. Then the drive device drives the fiber optic tendon to bend the catheter end to the safe contact range. After reaching the safe contact range, the catheter continues to be pushed and its curvature and path information are recorded. At the same time, the navigation process is calculated based on the recorded information. The sensor at the end of the catheter further measures the mechanical information. If the contact force is within the safe range, the catheter is driven to continue to move forward. If the contact force exceeds the safe range, the fiber optic tendon is adjusted until the contact force is within the safe range. Then the catheter is driven within the safe contact range until it reaches the navigation end. During this period, if there is a significant increase in contact force but it is still within the safe range, it is necessary to fine-tune the multimode optical fiber to the optimal contact force or avoid contact. This is to ensure that the catheter can move forward safely when it is close to the inner wall of the blood vessel and the navigation path can be clearly calculated. When the catheter safely reaches the navigation endpoint, i.e. the lesion, the required surgical instruments can be inserted through the instrument channel to directly perform treatment, which can greatly improve the efficiency of the operation while ensuring safety.

[0095] The drive control of multimode optical fiber (fiber optic tendon) can be manual or automatic. Take PID autonomous control as an example: Since the vascular intervention process is a real-time dynamic process, a PID controller is used to control the drive of the fiber optic tendon through the PID algorithm. The PID controller can adjust the control output instantly according to the current error. The proportional part can quickly reduce the error, while the differential part can predict the error change, thereby speeding up the response speed of the system. It is suitable for dynamically changing systems. The specific coordinates of the contact point have been obtained by the previous derivation, and P = (x p ,y p , z p ), the tensions of tendon 1 (upper part), tendon 2 (lower part), tendon 3 (left part), and tendon 4 (right part) are T1, T2, T3, and T4 respectively, and the reference value is T0. The target position to be adjusted by the optical fiber is expressed as: SP = (SP x , S.P.y , S.P. z ), then the error vector can be expressed by equation (10):

[0096] e(t)=SP-P=(SP x -x p , S.P. y -y p , S.P. z -z p ) (12)

[0097] Further, according to the PID principle, the control signal of each dimension is obtained:

[0098]

[0099] In the formula, K p is the proportional gain, K i is the differential gain, K d is the integral gain. Further discretizing the above formula, we can get the control signal of each dimension:

[0100]

[0101] Where Δt is the control period. Similarly, the digital control signals of the x, y, and z axes can be expressed as (13):

[0102]

[0103] Combined with the tendon tension, the tendon control logic can be obtained:

[0104] The sizes of T1 and T2 are given by u y [n] Control, from a bird's-eye view, increasing the tension of the upper tendon rope T1 can make the catheter bend upward, and increasing the tension of the lower tendon rope T2 can make the catheter bend downward:

[0105]

[0106] Where K1 and K2 are proportional coefficients, and specific values ​​are set according to actual conditions.

[0107] The sizes of T3 and T4 are determined by u x [n] Control, increasing the tension of the left tendon rope T3 can make the catheter bend to the left, and increasing the tension of the right tendon rope T4 can make the catheter bend to the right:

[0108]

[0109] Where K3 and K4 are proportional coefficients, and specific values ​​are set according to actual conditions.

[0110] After the driving catheter reaches the designated position, the required surgical instruments are inserted through the surgical instrument channel to achieve the goal of efficient and safe treatment.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An end sensor, characterized in that: The optical waveguide comprises a hemispherical optical waveguide, a compound eye array lens, a multimode optical fiber and an optical fiber image transmission bundle. A compound eye array lens is arranged at the front end of the optical fiber image transmission bundle, a hemispherical optical waveguide is arranged in front of the compound eye array lens, four multimode optical fibers are placed circumferentially at the bottom of the hemispherical optical waveguide, and light is coupled into the optical waveguide at a certain incident angle so that the end face of the optical fiber coincides with the bottom face of the optical waveguide.

2. The end sensor according to claim 1, characterized in that: The four multimode optical fibers are arranged in a cross shape.

3. The end sensor according to claim 1, characterized in that: The optical waveguide is a PMMA optical waveguide; the multimode optical fiber is a multimode optical fiber with polyimide coated on the periphery; and the optical fiber image transmission bundle is made of quartz glass.

4. The end sensor according to claim 1, characterized in that: Based on large sensing angle tactile feedback, the dynamic contact force calibration and characterization method starts from the contact force and establishes a theoretical model of visual image and dynamic and static contact force based on spot pattern analysis. The contact force between the catheter and the blood vessel wall during the intervention process is calculated through this model.

5. The end sensor according to claim 4, characterized in that: The theoretical model of static contact force is to calibrate the three-axis contact force of the cardiovascular visual-tactile navigation sensor using a static force calibration device, and to evaluate the isotropy of its force measurement using a sensitivity matrix; the theoretical model of dynamic contact force is that the refractive index distribution of the materials on both sides of the optical waveguide in the non-contact state constitutes a total reflection condition, while the change in the refractive index distribution of the contact part in the contact state destroys the total reflection condition of the area, thereby forming light energy leakage in the contact area; during the dynamic contact process, the contact area of ​​the optical waveguide at the end of the catheter will undergo local deformation, resulting in bending loss of part of the optical waveguide, causing the contact spot area to present a non-uniform light intensity distribution, and quantitatively characterizing the loss of this part of the overflowing light energy.

6. The end sensor according to claim 1, 4 or 5, characterized in that: Using the leakage light energy-contact force conversion model, when the end sensor contacts the blood vessel wall, the optical waveguide on the surface is deformed, causing the light inside the optical waveguide to leak. The leaked light is captured by the compound eye array lens in the center and forms a spot pattern on the end face of the optical fiber image transmission bundle. The magnitude and direction of the contact force can be obtained by analyzing the spot pattern.

7. A tactile feedback interventional catheter, comprising a catheter body, wherein the catheter body has an end sensor as claimed in any one of claims 1 to 6 built in, the compound eye array lens of the end sensor being disposed at the end of the catheter body, the compound eye array lens being connected to the optical fiber imaging bundle of the end sensor being disposed at the center of the inner cavity of the catheter body, the compound eye array lens being combined with the hemispherical optical waveguide of the end sensor, the hemispherical optical waveguide being fixedly connected to the end of the catheter body for encapsulating the compound eye array lens, multimode optical fiber and optical fiber imaging bundle of the end sensor in the catheter body, an instrument channel for inserting surgical instruments being provided at an eccentric position of the cross section of the catheter body, and a hole for specifically placing the surgical instrument channel being reserved at a corresponding position on the optical waveguide.

8. The tactile feedback interventional catheter according to claim 7, characterized in that: The section of the catheter body close to the hemispherical optical waveguide is made of a flexible base material, and the section away from the hemispherical optical waveguide is made of a rigid base material.

9. The tactile feedback interventional catheter according to claim 8, characterized in that: The rigid substrate material is a shape memory polymer, and the flexible substrate material is polytetrafluoroethylene.

10. The autonomous navigation method of the tactile feedback interventional catheter according to any one of claims 7 to 9, characterized in that: When the catheter enters the blood vessel, the pushing mechanism pushes the catheter forward. If the curvature of the blood vessel changes during the advancement of the catheter, causing the end of the catheter to contact the blood vessel wall and the contact force increases significantly, the sensor will feed back the tiny force change to the PC. The PC outputs instructions to the pushing mechanism to drive the optical fiber tendon in the catheter to make the end of the catheter make corresponding bending movements to reduce the contact force to 0 or a safe contact force range. The navigation process repeatedly cycles the above process to complete the closed-loop control of autonomous navigation.

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