Method and device for monitoring shape of catheter in interventional surgery based on right-angle fiber core triplet

Abstract

The present invention provides a method and device for monitoring the shape of an interventional surgical catheter based on a right-angle configuration fiber core triplet, the device comprising a multi-core optical fiber, an optical frequency domain reflectometer, an interventional surgical catheter, and an acquisition, processing, and display module. A 30-60-90 right-angle configuration fiber core triplet in a multi-core optical fiber is used as a shape sensing unit, and the multi-core optical fiber is attached or embedded in the surface of an interventional surgical catheter. The interventional surgical catheter includes but is not limited to surgical catheters in cardiovascular ablation, tumor interventional therapy, neurointerventional therapy, and interventional radiology. The optical frequency domain reflectometer is used to reconstruct the real-time shape of the optical fiber and catheter during surgery, and realize 3D visual navigation during interventional surgery. Two axially symmetrical outer cores in a new configuration are used to decouple and compensate for torsion, and the cosine similarity algorithm is combined to correct the misalignment of the sensing points between the fiber cores. The intermediate core is used to measure temperature and tensile and compressive strain information to compensate for environmental deviations caused by changes in blood pressure, flow rate, and temperature during surgery. Accurate monitoring of the shape of the interventional surgical catheter is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical devices, and in particular relates to a method and a device for monitoring the shape of an interventional surgery catheter based on a right-angle configuration fiber core triplet. Background Art

[0002] At present, in the field of interventional medicine, the application of interventional treatment methods in liver cancer, hepatic hemangioma, lung cancer, peripheral blood vessels, digestive tract, cardiovascular and other diseases is becoming more and more mature. For example, transarterial chemoembolization (TACE) is the preferred treatment method for advanced liver cancer. As the blood supply artery of the tumor, the hepatic artery first punctures the femoral artery or radial artery to insert a vascular sheath, and then introduces a catheter, guidewire or microcatheter through the vascular sheath and inserts it into the liver cancer blood supply artery. Embolic agents (such as gelatin sponge, polymer organic matter or drug-loaded microspheres) are injected into the liver cancer blood supply artery through the catheter to block the tumor blood supply artery, causing ischemic necrosis, and ultimately achieving the purpose of treatment. At present, most of the catheter insertion operations of interventional surgery are performed under X-ray fluoroscopy. However, X-ray imaging methods carry high doses of radiation, which are harmful to the doctors and patients. Doctors have to wear lead protective clothing weighing dozens of kilograms to perform surgical operations. These are not conducive to the intraoperative diagnosis and treatment of doctors. At the same time, traditional electromagnetic positioning and tracking methods are susceptible to electromagnetic interference in the environment. Therefore, there is an urgent need for a harmless, visual, anti-electromagnetic interference, high-precision shape tracking and navigation method to assist physicians in intraoperative operations. Distributed fiber shape sensing technology has just the above advantages.

[0003] The traditional fiber optic shape sensing technology based on fiber grating array is a point sensing solution with a small number of sensing points and a sensing resolution of centimeters. The engraving of FBG arrays on multi-core optical fibers will also bring about position uncalibration errors. The distributed fiber optic shape sensing technology based on phase demodulation OFDR has the sensing capabilities of anti-electromagnetic interference, distributed, hundreds of microns sensing resolution and millimeter-level shape tracking errors. It is very suitable for accurate tracking of the 3D shape of medical interventional devices during surgery. When doctors manipulate medical catheters into blood vessels or natural cavities and finally reach the target target position, the catheters have complex bending and axial torsion. Then the multi-core optical fiber shape sensor integrated on the catheter will also experience synchronous torsion, and this axial torsion effect has cross-sensitivity with the bending strain. This leads to the inaccuracy of the traditional optical fiber bending-strain model, and the core torsion strain and torsion angle offset make the shape reconstruction algorithm mismatch, which seriously affects the accuracy of shape tracking. At the same time, the existing torsion demodulation method is easily affected by the overall offset and misalignment of the sensing points between the cores, resulting in large torsion measurement errors. Therefore, in the above practical applications, accurate demodulation and effective compensation of the torsion effect are the key to realizing the shape monitoring of interventional surgical catheters. At the same time, accurate demodulation of the torsion effect requires the sensing system to have high strain measurement accuracy. In order to solve the above problems, the present invention proposes a method and device for monitoring the shape of interventional surgical catheters based on phase demodulation OFDR and a multi-core optical fiber right-angle configuration core triplet.

[0004] Traditional fiber core arrangements used for demodulation of torsion and shape sensing mostly adopt an equilateral triangle configuration, that is, the three sensing fiber cores are 120 degrees apart, showing an equilateral triangle arrangement feature. This kind of fiber core triplet needs to use the strain of three outer cores to jointly solve the torsion effect of the optical fiber. In the phase demodulation OFDR system, the sensing spatial resolution can reach tens of microns or even tens of microns. Since the length of each fiber core interrogation optical path is affected by the cumulative influence of the optical switch channel, the fan-in fan-out channel and the fiber core end, the length of each interrogation optical path is not strictly the same (the length difference is several millimeters or even centimeters). This length difference between the fiber core interrogation optical paths will cause the overall offset and misalignment of the sensing points between the fiber cores during torsion demodulation. Under the system sensing resolution of the above order of magnitude, it will cause a large torsion measurement error. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a method and device for monitoring the shape of an interventional surgical catheter based on a right-angle configuration fiber core triplet, using a 30-60-90 right-angle configuration fiber core triplet in a multi-core optical fiber as a shape sensing unit, attaching or embedding the multi-core optical fiber to the surface of a medical catheter, and reconstructing the real-time shape of the optical fiber and the catheter in the human body through an optical frequency domain reflectometer to achieve shape monitoring of the interventional surgical catheter. In order to avoid misalignment of the catheter shape tracking caused by the twisting of the optical fiber in the blood vessel or natural cavity, two axisymmetric outer cores in the new right-angle configuration are used to decouple and compensate for the twisting effect, and the cosine similarity algorithm is combined to correct the misalignment of the sensing points between the fiber cores to accurately measure the twisting amount. The present invention has the characteristics of anti-electromagnetic interference, distributed high-precision shape navigation, etc., and can replace the traditional two-dimensional imaging method of x-rays to avoid exposure of doctors and patients to harmful radiation environments. At the same time, the present invention can be applied to the shape perception of intraoperative interventional instruments such as catheters, cystoscopes, gastroscopes, colonoscopes, and continuum robots to achieve shape monitoring of interventional surgical catheters that are not limited to any human body position organ. After intraoperative matching with magnetic resonance imaging (MRI) image data, it can provide physicians with a new intraoperative instrument visualization solution.

[0006] The technical solution of the present invention is: an interventional surgery catheter shape monitoring device based on a right-angle configuration fiber core triplet, comprising a tunable laser source, a first coupler, a second coupler, an auxiliary interferometer, a main interferometer, a photodetector, a circulator, an optical switch, a fan-in fan-out device, a multi-core optical fiber, a collection processing display module, and an interventional surgery catheter; the photodetector comprises a first photodetector, a second photodetector, and a third photodetector; it is characterized in that: the tunable laser source is respectively connected to the first coupler and the collection processing display module, the first coupler output is connected to the second coupler and the auxiliary interferometer, the second coupler output is connected to the main interferometer and the circulator input port 1, the circulator output ports 3 and 2 are respectively connected to the fifth coupler of the main interferometer and the optical switch, and the optical switch is connected to the multi-core optical fiber through the fan-in fan-out device;

[0007] The auxiliary interferometer includes a third coupler, a delay optical fiber and a fourth coupler, the third coupler and the fourth coupler are connected through the delay optical fiber, and the fourth coupler is connected to the first photodetector;

[0008] The main interferometer comprises a polarization controller, a fifth coupler and a first polarization beam splitter and a second polarization beam splitter, the optical path of the second coupler output 1% is connected to the input polarization controller, the circulator 3 port and the polarization controller output are connected to the fifth coupler input, and the fifth coupler output is respectively connected to the first polarization beam splitter and the second polarization beam splitter; the first polarization beam splitter and the second polarization beam splitter output are connected to the second photodetector and the third photodetector; the first photodetector, the second photodetector and the third photodetector are connected to the acquisition processing display module; the multi-core optical fiber has at least 4 cores forming a right-angled triangle configuration, that is, among the No. 1 core, the No. 2 core, the No. 3 core and the No. 4 core, the distances from the No. 4 core to the No. 1 core, the No. 2 core and the No. 3 core are equal, in the right-angle configuration, the No. 2 core and the No. 3 core have a strictly axially symmetrical structure, the No. 2 core, the No. 3 core and the No. 1 core have a 30-60-90 right-angled triangle configuration, and the multi-core optical fiber is attached or embedded and coupled to the surface of the interventional surgery catheter.

[0009] According to the interventional surgery catheter shape monitoring device based on the right-angle configuration fiber core triplet as described above, it is characterized in that the acquisition processing and display module includes at least a four-channel acquisition card, and the four-channel acquisition card acquires the trigger signal, the auxiliary interferometer and the beat frequency signal of the main interferometer.

[0010] According to the device for monitoring the shape of an interventional surgery catheter based on a right-angle fiber core triplet as described above, the feature of the device is that the process of monitoring the shape of the interventional surgery catheter is as follows:

[0011] (1) Keep the medical catheter straight in a plane and free from external stress, and collect beat frequency information as a reference group signal; then, pass the catheter through the blood vessel or the natural cavity of the human body along the incision during surgery to the target target position, during which the shape of the catheter changes continuously, and collect beat frequency information as a measurement group signal;

[0012] (2) Use the phase demodulation algorithm and the calibration algorithm for the unit misalignment caused by strain to accurately demodulate the strain information of the fiber core triplet: a) Use FFT transformation to convert the reference group and the measurement group signals from the optical frequency domain to the distance domain, and solve the phases of the two groups of optical signals and record them as Φ ref and Φ mea , and the difference between the two is obtained to obtain the differential phase ΔΦ at each position of the fiber core; b) solving the differential phase in segments, and multiplying the optical frequency domain signals of all subsequent segments by a phase shift factor that is linearly related to the differential phase of the current target segment; c) filtering the differential phase to remove the phase jump point, and derivatizing the differential phase after phase unwrapping to obtain the strain value at each position of the fiber core;

[0013] (3) Combining the bending, torsion-total strain decoupling model based on the right-angle configuration fiber core triplet and the sensor point misalignment correction algorithm, the torsion strain and torsion deflection angle are demodulated, and the bending direction angle and bending curvature of each position point of the optical fiber after torsion compensation are solved;

[0014] (4) The shape of the catheter during interventional surgery is reconstructed in real time using a homogeneous transformation matrix framework and position offset correction method.

[0015] The present invention also provides an interventional surgical catheter shape monitoring method based on a right-angle configuration fiber core triplet, characterized in that: it includes a multi-core optical fiber, the multi-core optical fiber has at least 4 fiber cores forming a right-angle triangle configuration, that is, among the No. 1 fiber core, the No. 2 fiber core, the No. 3 fiber core, and the No. 4 fiber core, the distances from the No. 4 fiber core to the No. 1 fiber core, the No. 2 fiber core, and the No. 3 fiber core are equal, and the No. 4 fiber core is used as a compensation fiber core, and the influence of the in vivo environmental deviation is eliminated by subtracting the strain on the No. 4 fiber core from the strain measured by the other fiber cores. In the right-angle configuration, the No. 2 fiber core and the No. 3 fiber core have a strict axially symmetrical structure, and the No. 2 fiber core, the No. 3 fiber core, and the No. 1 fiber core have a 30-60-90 right-angle triangle configuration; the twisted No. 1 fiber core, the No. 2 fiber core, and the No. 3 fiber core are recorded as the No. 1′ fiber core, the No. 2′ fiber core, and the No. 3′ fiber core; the following steps are included:

[0016] Steps to establish bending, torsion-total strain decoupling of the core triplet:

[0017]

[0018] Among them, 2π / 3 and 5π / 3 are the angles between the 2′ core, the 3′ core and the 1′ core respectively, θ is the angle between the 1′ core and the bending direction vector ν after twisting, θ 1 is the angle between the No. 1 fiber core before rotation and the bending direction vector ν, κ is the bending curvature value, Δφ is the torsional deflection angle; ε 1 ′,ε 2 ′ and ε 3 ' is the strain of core 1', core 2', and core 3' after twisting (the strain on core 4 has been subtracted from the strain on core 4). The twisting strains on core 1', core 2', and core 3' are the same and are recorded as ε τ Since the No. 4 fiber core is in the neutral line position, it is not affected by the bending and torsion changes of the optical fiber, and its strain value is zero.

[0019] Find the torsional strain ε τ and the steps of the bending direction angle θ and the bending curvature value κ at each position of the twisted fiber core

[0020]

[0021] Where G is the modulus constant between shear strain and torsion angle; Δz = z1 -z 1 ′,z 1 is the cross-sectional position before torsion, z 1 ′ is the cross-sectional position after twisting; Δz is the axial distance between the two cross-sections before and after twisting. The twisting of the optical fiber causes the core to rotate relative to the cross-sectional angle Δφ;

[0022] Combining equations 1 and 3, we can decouple the steps of the torsional deflection angle Δφ along the multi-core optical fiber. The actual bending direction angle after compensation is θ 1 =θ+Δφ, and θ 1 and κ are used as the transfer quantities after compensating the torsion effect. Spline interpolation is performed to interpolate the discrete transfer parameters along the optical fiber path into a continuous transfer parameter curve. The spatial coordinates of each point are obtained in combination with the homogeneous transformation matrix framework to achieve shape reconstruction of the multi-core optical fiber and catheter.

[0023] According to the above-mentioned method for monitoring the shape of an interventional surgery catheter based on a right-angle configuration fiber core triplet, it is characterized in that: the specific method of obtaining the spatial coordinates of each point in combination with the homogeneous transformation matrix framework is:

[0024] At the sensing point O i and O i+1 The Cartesian coordinate system x is established near the space curve between i -y i -z i , i is the sensor point count, and its value is 1, 2, 3...;

[0025] Establish the coordinate transfer framework:

[0026]

[0027] in, is the arc length tangent rotation angle, P i is the bending direction angle θ of the multi-core optical fiber after compensation twisting 1i , Arc length tangent rotation angle The associated 3x3 rotation matrix, ΔO i is a 3x1 position translation matrix, R i is the bending radius of the optical fiber at this position.

[0028] According to the above-mentioned method for monitoring the shape of an interventional surgery catheter based on a right-angle configuration fiber core triplet, it is characterized by: further comprising the step of using cosine similarity evaluation: the calculation formula is:

[0029]

[0030] Where n is the number of sensing points, x i ,y iThey are the strain values ​​of each sensing point of No. 2 core and No. 3 core respectively.

[0031] The beneficial effects of the present invention are as follows: (1) This patent innovatively proposes a torsional decoupling and compensation scheme based on a right-angle core triplet of a multi-core optical fiber, and establishes a new core triplet bending, torsion-total strain decoupling model. Compared with the traditional equilateral triangle core triplet structure, the new configuration increases the core triplet configuration scheme (new configuration: 12, traditional configuration: 2) while reducing the number of cores used to decouple the torsion effect (new configuration: 2, traditional configuration: 3). The Fresnel reflection peak position at the tail end of the core is used to preliminarily correct the misalignment of the sensing points between the three cores, and the strain relationship of the two axisymmetric outer cores in the new configuration is combined with the cosine similarity evaluation method to further accurately correct the misalignment of the sensing points, so as to accurately decouple the optical fiber torsional strain and torsional deflection angle and compensate for it, effectively reducing the torsional measurement error caused by the overall misalignment of the sensing points between the cores. The shape of the medical catheter is monitored in combination with the homogeneous transformation matrix framework. (2) In this patent, multi-core optical fiber is coupled with a medical catheter as a shape sensor, and the shape monitoring of the catheter during interventional surgery is achieved by reconstructing the posture state of the multi-core optical fiber and the catheter. The interventional surgery catheter shape monitoring device and method in this patent can replace the medical angiography X-ray machine, freeing doctors from the constraints of heavy lead suits and avoiding the risk of radiation exposure to doctors and patients. At the same time, the interventional surgery catheter shape monitoring device is used in conjunction with a nuclear magnetic resonance imaging device (MRI: Nuclear Magnetic Resonance Imaging) to provide doctors with advanced intraoperative visualization navigation technology. (3) Compared with traditional shape measurement methods, the shape sensing technology based on phase demodulation OFDR and multi-core optical fiber has the advantages of anti-electromagnetic interference, small size, distributed, high sensing resolution, high strain measurement accuracy and high shape reconstruction accuracy, which can well meet the clinical surgical application needs in the fields of interventional medicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the catheter shape monitoring device for interventional surgery.

[0033] Figure 2 Schematic diagram of a right-angle core triplet in a multi-core optical fiber.

[0034] Figure 3 Schematic diagram of the positional relationship between two sensing points in a bent segment of a multi-core optical fiber.

[0035] Figure 4 The fiber core bending curvature is 10m -1 The misalignment measurement error under different applied torsion conditions.

[0036] Figure 5Misalignment measurement error for different bending curvatures when the maximum applied torsion is 50με.

[0037] Figure 6 Distance-intensity information for core 3. Zoomed-in image: Fresnel reflection peak at the end of the core.

[0038] Figure 7 Comparison of strain curves when axisymmetric cores 2 and 3 are bent and twisted.

[0039] Figure 8 Schematic diagram of the catheter shape tracking device.

[0040] Fig. 9 Specific process of catheter shape monitoring during interventional surgery.

[0041] Fig.10 for Figure 2 Schematic diagram of the twist in a multi-core optical fiber.

[0042] Fig.11 A schematic diagram of a 3D arterial vascular pathway in a clinical interventional procedure.

[0043] Fig.12 Example: An angiographic catheter used within a blood vessel during interventional surgery. Specific embodiments

[0044] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0045] like Figure 1 As shown, an interventional surgery catheter shape monitoring device based on a right-angle configuration fiber core triplet. The interventional surgery catheter shape monitoring device of the present invention includes a tunable laser source, a first coupler, a second coupler, an auxiliary interferometer, a main interferometer, a photodetector, a circulator, a 1x8 optical switch, a fan-in fan-out device, a multi-core optical fiber (7 cores), an acquisition card, an acquisition processing display module, and an interventional surgery catheter. The photodetector includes a first photodetector, a second photodetector, and a third photodetector.

[0046] The tunable laser source of the present invention is respectively connected to the first coupler and the acquisition processing display module, the first coupler output is connected to the second coupler and the auxiliary interferometer, the second coupler output is connected to the main interferometer and the circulator input port 1, the circulator output ports 3 and 2 are respectively connected to the fifth coupler and the optical switch of the main interferometer, and the optical switch is connected to the multi-core optical fiber through the fan-in fan-out device. The auxiliary interferometer includes a third coupler, a delay optical fiber and a fourth coupler, the third coupler and the fourth coupler are connected through the delay optical fiber, the delay optical fiber can be 60m, and the fourth coupler is connected to the first photodetector. The main interferometer includes a polarization controller, a fifth coupler and the first polarization beam splitter and the second polarization beam splitter, the second coupler output 1% of the optical path is connected to the input polarization controller, the circulator 3 port and the polarization controller output are connected to the fifth coupler input, and the fifth coupler output is respectively connected to the first polarization beam splitter and the second polarization beam splitter. The outputs of the first polarization beam splitter and the second polarization beam splitter are connected to the second photodetector and the third photodetector. The first photodetector, the second photodetector and the third photodetector are connected to the acquisition processing display module.

[0047] The multi-core optical fiber of the present invention can be composed of an intermediate fiber core and six peripheral fiber cores, the distances from the six peripheral fiber cores to the center are equal, and the angle between adjacent fiber cores is 60°. The multi-core optical fiber can also be a spiral seven-core optical fiber (the six peripheral fiber cores are spiral, and there are also three peripheral fiber cores arranged at right angles, but the corresponding strain torsion solution model and shape reconstruction algorithm are different from those of the seven-core straight-core optical fiber in this patent). The multi-core optical fiber can also be arranged in a right-angled triangle by three single-mode optical fibers (achieved by designing corresponding packaging fixtures), and then cured and packaged with glue to form a fiber bundle shape sensor, which can also be used for interventional surgical catheter shape monitoring. The multi-core optical fiber of the present invention is attached or embedded in the surface of the interventional surgical catheter for coupling.

[0048] Functions of each device and module:

[0049] a) Tunable laser, providing intrinsic reference light and detection signal light for the system.

[0050] b) Auxiliary interferometer, used to obtain the instantaneous optical frequency information of the laser and resample the beat frequency signal of the main interferometer at equal frequency intervals to compensate for the nonlinear tuning effect of the light source.

[0051] c) Main interferometer, which obtains the beat signal containing Rayleigh backscattering information (shape change information).

[0052] d) Photoelectric detectors (first photoelectric detector, second photoelectric detector and third photoelectric detector) perform photoelectric conversion on the optical signal to achieve coherent detection of the intrinsic reference light and the detection signal light.

[0053] e) Mechanical optical switch, switching each core channel in the multi-core optical fiber in sequence for inquiry.

[0054] f) Multi-core optical fiber, used as sensing fiber, shape sensor.

[0055] g) Fan-in and fan-out devices to achieve the connection between single-core fiber and multi-core fiber.

[0056] h) Circulator, which feeds the backscattered Rayleigh signal back to the main interferometer.

[0057] g) An acquisition, processing and display module is used to acquire data and display the reconstructed shape after data processing.

[0058] The working process of the catheter shape monitoring device for interventional surgery of the present invention is as follows: after the linear frequency sweep light output by the tunable laser passes through the first coupler, 1% of the light enters the auxiliary interferometer, and after passing through the third coupler, the delay fiber (60m) and the fourth coupler, the beat frequency signal is detected by the first photodetector. 99% of the light output by the first coupler enters the second coupler downward, and after passing through the second coupler, 1% of the light enters the reference arm of the main interferometer, and its polarization state is regulated by the polarization controller to form a reference light. 99% of the light of the second coupler enters the measuring arm, enters through the circulator port 1, and outputs through the port 2, and then passes through the optical switch, the fan-in and fan-out device in turn to reach the multi-core optical fiber to be measured, and the back Rayleigh scattered light of the multi-core optical fiber to be measured is output from the circulator port 3 as the detection light. The detection light and the reference light enter the fifth coupler together, and the two-way light output of the fifth coupler is 50:50 respectively. The two-way light output of the fifth coupler enters the first polarization beam splitter and the second polarization beam splitter respectively, and the P light and S light output by the first polarization beam splitter and the second polarization beam splitter are detected in the second photodetector and the third photodetector respectively. The acquisition, processing and display module includes at least a four-channel acquisition card, which acquires the trigger signal, the beat frequency signal of the auxiliary interferometer and the main interferometer, and finally the measured signal is sent to the processing and display module for phase, strain demodulation and shape reconstruction. During the signal acquisition process, the linear sweep light sends a high-level trigger signal to the acquisition card at the beginning of scanning to control it to collect data, ensuring that the light source scanning and data acquisition are carried out synchronously. The acquisition, processing and display module parses the strain distribution of each sensing core in the multi-core optical fiber through the phase demodulation algorithm. Since the length of the interrogation optical path of each core in the interventional surgery catheter shape monitoring device is not strictly the same, the sensing points between the sensing cores are misaligned, which seriously reduces the measurement accuracy of the optical fiber torsion. Therefore, before solving the torsion and torsion deflection angle Δφ by the core total strain-bending and torsion decoupling model, an effective method is needed to accurately correct the misalignment of the sensing points between the cores.

[0059] 2. Sensing point misalignment correction, torsion decoupling, compensation and shape reconstruction based on multi-core optical fiber right-angle configuration core triplet:

[0060] like Figures 2 to 7 As shown, the present invention also discloses a method for correcting the misalignment of sensing points, which is based on the torsion decoupling, compensation and shape reconstruction method of the right-angle configuration core triplet of a multi-core optical fiber. The method adopts a new core triplet sensing configuration, and can accurately demodulate the torsion of the multi-core optical fiber using only the strain of two cores. At the same time, the tail end alignment correction (rough correction) and cosine similarity correction (precise correction) methods are used to effectively reduce the torsion measurement error caused by the overall offset misalignment of the sensing points between the cores. Figure 2 It is a schematic cross-sectional diagram of a right-angle core triplet and its twisting in a multi-core optical fiber. Figure 2 The figure is a schematic diagram of the cross section of a seven-core optical fiber without external torsion, and r = 42 μm is the distance from the outer core to the geometric center of the optical fiber. Cores 1, 2, and 3 are selected as the core triplet. The geometric position of the cores in the seven-core optical fiber determines that cores 2 and 3 are axially symmetrical, and are arranged together with core 1 to form a special 30-60-90 right triangle. There are 12 such combinations in the cross section. Core 4 is on the bending neutral line of the multi-core optical fiber, so it is insensitive to stress and is not affected by bending and torsion. It is only affected by external temperature changes. The distances from core 4 to cores 1, 2, and 3 are equal. Core 4 is used as a compensation core. The strain measured on other cores minus the strain on core 4 eliminates the influence of the internal environment deviation. In the right-angle configuration, core No. 2 and core No. 3 have a strict axially symmetrical structure, and core No. 2, core No. 3, and core No. 1 have a 30-60-90 right-angle triangle configuration. Fig.10 It is shown in the figure that when core 1, core 2, and core 3 are subjected to external twisting, they are deflected in the same direction by an angle Δφ. The deflected cores are recorded as core 1′, core 2′, and core 3′, and the three also maintain a 30-60-90 right triangle configuration. It should be noted that core 1, core 2, core 3 and core 1′, core 2′, and core 3′ are in different fiber cross sections, and the cross-sectional positions before and after twisting can be recorded as z 1 and z 1 ′. The angle between the No. 1 core and the bending direction vector ν before twisting (i.e. the bending direction angle of the multi-core optical fiber) is θ 1 , the angle between the 1′ core and the bending direction vector ν after twisting is θ, then the actual bending direction angle of the multi-core optical fiber before twisting is θ 1 =θ+Δφ, Δφ is the torsion deflection angle. Therefore, it is necessary to accurately demodulate the torsion amount and torsion deflection angle Δφ of each sensing point along the optical fiber path to compensate for the bending direction angle after torsion, so as to achieve high-precision shape sensing.

[0061] According to the angle and axisymmetric relationship between the fiber cores, a bending, torsion-total strain decoupling model based on the right-angle core triplet of multi-core optical fiber is established.

[0062] The strains of the 1′ core, 2′ core, and 3′ core obtained after twisting (the strain on the 4th core has been subtracted) are denoted as ε 1 ′,ε 2 ′ and ε 3 ′, the torsional strains of cores 1′, 2′, and 3′ are the same and are denoted by ε τ When a multi-core optical fiber is bent, since the 2′ and 3′ cores have an axially symmetrical relationship, their bending strains are always the same in magnitude, opposite in positive and negative, and the sum of the two is always zero. At the same time, the bending, torsion-total strain decoupling equations of the core triplet are established based on the 30-60-90 right-angle triangle position arrangement relationship of the cores 1′ to 3′:

[0063]

[0064] Among them, 2π / 3 and 5π / 3 are the angles between the 2′ and 3′ cores and the 1′ core respectively. The torsional strain ε can be obtained through this coupling model. τ And the bending direction angle θ and bending curvature value κ at each position of the fiber core after twisting.

[0065]

[0066] From the knowledge of material mechanics, we know that the torsion angle at a certain position of the fiber core and the shear strain in its cross section have the following relationship:

[0067]

[0068] Where G is the modulus constant between shear strain and torsion angle. Δz = z 1 -z 1 ′,z 1 is the cross-sectional position before torsion, z 1 ′ is the cross-sectional position after twisting; Δz is the axial distance between the two cross-sections before and after twisting. The twisting of the optical fiber causes the fiber core to rotate relative to the cross-section by an angle Δφ. Combining equations 1 and 3, the twisting deflection angle Δφ along the multi-core optical fiber is decoupled, and the actual bending direction angle after compensation is θ 1 =θ+Δφ, and θ 1 The bending direction angle and curvature value at each sensing point along the optical fiber path are interpolated by spline, and these discrete values ​​are interpolated into a continuous transfer parameter curve. The spatial coordinates of each point are obtained by combining the homogeneous transformation matrix framework to realize the shape reconstruction of the multi-core optical fiber.

[0069] Figure 3It is the position transformation relationship between two sensing points in the bending section of multi-core optical fiber.

[0070] At the sensing point O i and O i+1 The Cartesian coordinate system x is established near the space curve between i -y i -z i , i is the number of sensing points, and its value is 1, 2, 3, etc.; when there are enough sensing points on the optical fiber, the arc segment Oi-Oi+1 is extremely small, and the arc segment Δz can be regarded as a continuous curve on the osculating plane, and its value is the axial distance between two adjacent sensing points, which is the sensing spatial resolution of the system. 1 / κ is the bending radius of the multi-core optical fiber, is the arc length tangent rotation angle, Figure 3 The i-th sensor point in can be transformed to the i+1-th sensor point position by the homogeneous transformation matrix framework. Its coordinate transmission framework is as follows:

[0071]

[0072] Among them, P i is the bending direction angle θ of the multi-core optical fiber after compensation twisting 1i , Arc length tangent rotation angle The associated 3x3 rotation matrix, ΔO i is a 3x1 position translation matrix, R i is the bending radius of the optical fiber at this position. The entire transformation process can be described as: first, around z i The x axis i -y i Plane rotation angle θ 1i Get the new coordinate system x i ′-y i ′-z i ′, and then rotate around the y i ′ axis will be x i ′-z i ′The plane rotates along the arc length direction Get the new coordinate system x i ″-y i ″-z i ″, after the above two rotations, the unit direction of each axis in the coordinate system is the same as the coordinate system x of the sensing point i+1 i+1 -y i+1 -z i+1 The unit direction is exactly the same. Finally, the coordinate axis after the two translations is translated by ΔO i Coordinates can realize the conversion from the sensing point i to the sensing point i+1 spatial coordinates. 1The position can be given by actual measurement or as a reference point, from which all subsequent points can be formed into a spatial position curve based on the first point.

[0073] Among them, it can be known from formula 4 that M i+1 is the transformation matrix of the i+1th sensor point, that is, the 4x4 homogeneous transformation matrix. Then the coordinates of the i-th sensor point are multiplied by M i+1 M i+2 That is, the coordinates of the i+2th sensing point. The spatial coordinates of each optical fiber sensing point can be obtained in turn by formula 4, thereby realizing the distributed shape reconstruction of the multi-core optical fiber.

[0074] Method for correcting the overall offset misalignment of the sensing points between fiber cores:

[0075] As mentioned above, for a phase demodulation OFDR system with a sensing resolution of tens of microns, the length difference caused by the non-strictly identical interrogation optical path lengths of each core will cause an overall offset misalignment of the sensing points between the cores, which will undoubtedly cause a large torsion measurement error. In response to this problem, this patent combines a new right-angle configuration core triplet to develop a tail-end alignment sensing point misalignment correction and a sensing point misalignment correction algorithm based on cosine similarity evaluation to reduce the torsion measurement error caused by the misalignment between the cores. First, based on the core total strain decoupling model (Formula 1), the torsion measurement error caused by the misalignment is simulated to observe the torsion measurement error under different misalignment conditions. Condition setting: The sensing core length is 0.5m, the system sensing resolution is 100μm, and the third core in the model is offset by 1-10 sensing points relative to the first two cores in sequence (corresponding to a position offset misalignment between the cores of 0.1 to 1mm). In the simulation model, the amount of external torsion increases linearly with the fiber distance.

[0076] like Figure 4 As shown, the fiber bending curvature is 10m -1 When the number of misaligned sensing points between the fiber cores increases, the maximum torsion error increases continuously. At the same time, the maximum torsion error increases with the increase of the applied maximum torsion. When the misalignment is 10 sensing points (1 mm), the maximum torsion error reaches about 6.7 με.

[0077] like Figure 5 As shown in the figure, when the maximum applied torsion is 50με, the maximum torsion error increases with the increase of the number of misaligned sensing points between the fiber cores. At the same time, the maximum torsion error increases with the increase of the curvature of the optical fiber. When the misalignment is 10 sensing points (1mm), the maximum torsion error reaches about 27με.

[0078] From the above results, we can see that even a small distance (0.1-1 mm) of misalignment between the fiber cores can cause a relatively large torsion measurement error. Therefore, it is necessary to use an effective misalignment correction method.

[0079] (1) Fiber core tail end alignment correction method (rough correction): For new right-angle configuration or traditional equilateral triangle configuration fiber core triplet, the approximate end length of each fiber core is initially obtained through the Fresnel reflection peak at the fiber core tail end in its distance domain-intensity information, so as to perform preliminary misalignment correction between the fiber cores. Figure 6 is the distance-strength information of fiber core 3.

[0080] from Figure 6 As can be seen in the figure, the Fresnel reflection peak at the tail end can locate the end of the fiber core with mm accuracy, so as to preliminarily align the ends of the three fiber cores. However, due to the inevitable interference of stray peaks or pseudo peaks, the position correction of the sensing points between the fiber cores cannot be more accurate. However, the axial symmetry of the fiber cores 2 and 3 in the new right-angle configuration can be used to further accurately correct the misalignment of the sensing points.

[0081] (2) Sensing point misalignment correction method based on cosine similarity evaluation (precise correction):

[0082] Since the fiber cores 2 and 3 in the new right-angle configuration have a strict axial symmetric structure, the strain values ​​caused by bending on the two fiber cores are always the same in magnitude and opposite in sign. At the same time, the strain values ​​caused by torsion on the two fiber cores are always the same in magnitude. As shown in the experimental results Figure 7 As shown. Therefore, when there is no overall sensing point misalignment between the fiber cores, the strain curve of core 2 is kept unchanged, and after the strain curve of core 3 is taken as a negative value, although the amplitudes of the two strain curves are different, the direction vectors of each position of the two should be exactly the same. When there is a sensing point misalignment, the direction vectors of each position of the two will also shift. Based on this characteristic, the use of cosine similarity can effectively and accurately evaluate and correct the sensing point misalignment. .

[0083] The cosine similarity method ignores the amplitude difference between the two curves and only focuses on the directional characteristics of each position. Its calculation formula is:

[0084]

[0085] Where n is the number of sensing points, x i ,y i are the strain values ​​at the i-th sensing point of fiber core 2 and fiber core 3, that is, x i is the strain value at the ith sensing point of fiber core 2, y iis the strain value at the i-th sensing point of core 3. CS is the cosine similarity result, ranging from 0 to 1. The larger the value and the closer it is to 1, the better the similarity of the two curves, that is, the fewer the number of misaligned sensing points. By moving the strain curve of one of the cores point by point, when CS is the largest, it means that the misalignment of the sensing points between the two cores has been accurately corrected. In this patent, a new right-angle configuration and cosine similarity sensing point misalignment correction method are used to minimize the torsion measurement error caused by misalignment. In the traditional equilateral triangle configuration, the cores do not have the above-mentioned special structural relationship, so the overall sensing point misalignment between the cores cannot be accurately corrected, and the torsion measurement error is large.

[0086] At present, the method in this patent is used to carry out the fiber shape tracking experiment. From the experimental results, it can be seen that the average Euclidean distance between the real coordinates and the reconstructed coordinates of the 3D torus helix shape of a 1m long multi-core optical fiber is ≤1cm.

[0087] like Figure 1 As shown in the figure, since the internal channel of the medical catheter is used to deliver drugs or other medical devices, the multi-core optical fiber is attached or embedded on the outside of the catheter in this patent, and the position state of the catheter is tracked by reconstructing the 3D shape of the multi-core optical fiber to achieve shape monitoring of the catheter for interventional surgery. And the coordinate translation matrix Δd=[Δrcos(θ 1 ) Δrsin(θ 1 ) 0] Calibrate the position offset between the multi-core optical fiber and the catheter centerline (the bending directions of the multi-core optical fiber and the catheter are consistent), where Δr is the geometric center distance between the two. In clinical medical interventional surgery, the medical catheter integrated with the multi-core optical fiber is inserted through the intraoperative incision or natural cavity to reach the target target position. During the operation, the shape of the interventional catheter can be monitored in real time. Fig.11 , Fig.12 They are respectively a schematic diagram of a 3D arterial vascular pathway in an interventional surgery and a schematic diagram of an angiography catheter.

[0088] The process of catheter shape monitoring in clinical interventional surgery is as follows Fig. 9 shown.

[0089] (1) First, the medical catheter is kept straight in a plane and free from external stress, and the beat frequency information is collected as the reference group signal; then the catheter is passed through the blood vessel or the natural cavity of the human body along the intraoperative incision to the target target position. During this period, the shape of the catheter changes continuously, and the beat frequency information is collected as the measurement group signal.

[0090] (2) Use the phase demodulation algorithm and the calibration algorithm for the unit misalignment caused by strain to accurately demodulate the strain information of the fiber core triplet. a) Use FFT transformation to convert the reference group and the measurement group signals from the optical frequency domain to the distance domain, and solve the phase of the two groups of optical signals and record them as Φ ref and Φmea , the difference between the two is obtained to obtain the differential phase ΔΦ at each position of the fiber core; b) The change in the fiber core length caused by strain will cause the sensor units of the measurement group and the reference group to be misaligned. Therefore, the differential phase is solved in segments, and the optical frequency domain signals of all subsequent segments are multiplied by a phase shift factor that is linearly related to the differential phase of the current target segment in turn to compensate for the misalignment scaling in the distance domain; c) The differential phase is filtered to remove the phase jump point, and the differential phase after phase unwinding is derived to obtain the strain curve of each fiber core (i.e., ε 1 ′,ε 2 ′ and ε 3 ′).

[0091] (3) Combining the bending, torsion-total strain decoupling model based on the right-angle core triplet and the sensor point misalignment correction algorithm, the torsional strain and torsional deflection angle are demodulated, and the bending direction angle and bending curvature of each position point of the optical fiber after torsion compensation are solved.

[0092] (4) The homogeneous transformation matrix framework and position offset correction method are used to reconstruct the shape of the catheter in interventional surgery in real time and display it in the processing module interface to achieve 3D visual navigation of blood vessels or natural cavities in interventional surgery.

Claims

1. An interventional surgery catheter shape monitoring device based on a right-angle configuration fiber core triplet, comprising a tunable laser source, a first coupler, a second coupler, an auxiliary interferometer, a main interferometer, a photodetector, a circulator, an optical switch, a fan-in fan-out device, a multi-core optical fiber, an acquisition processing display module, and an interventional surgery catheter; the photodetector comprises a first photodetector, a second photodetector, and a third photodetector; characterized in that: The tunable laser source is connected to the first coupler and the acquisition processing and display module respectively, the output of the first coupler is connected to the second coupler and the auxiliary interferometer, the output of the second coupler is connected to the main interferometer and the circulator input port 1, the circulator output ports 3 and 2 are connected to the fifth coupler of the main interferometer and the optical switch respectively, and the optical switch is connected to the multi-core optical fiber through the fan-in fan-out device; The auxiliary interferometer includes a third coupler, a delay optical fiber and a fourth coupler, the third coupler and the fourth coupler are connected through the delay optical fiber, and the fourth coupler is connected to the first photodetector; The main interferometer comprises a polarization controller, a fifth coupler and a first polarization beam splitter and a second polarization beam splitter, the optical path of the second coupler output 1% is connected to the input polarization controller, the circulator 3 port and the polarization controller output are connected to the fifth coupler input, and the fifth coupler output is respectively connected to the first polarization beam splitter and the second polarization beam splitter; the first polarization beam splitter and the second polarization beam splitter output are connected to the second photodetector and the third photodetector; the first photodetector, the second photodetector and the third photodetector are connected to the acquisition processing display module; the multi-core optical fiber has at least 4 cores forming a right-angled triangle configuration, that is, among the No. 1 core, the No. 2 core, the No. 3 core and the No. 4 core, the distances from the No. 4 core to the No. 1 core, the No. 2 core and the No. 3 core are equal, in the right-angle configuration, the No. 2 core and the No. 3 core have a strictly axially symmetrical structure, the No. 2 core, the No. 3 core and the No. 1 core have a 30-60-90 right-angled triangle configuration, and the multi-core optical fiber is attached or embedded and coupled to the surface of the interventional surgery catheter.

2. The device for monitoring the shape of an interventional surgical catheter based on a right-angle fiber core triplet according to claim 1, characterized in that: The acquisition processing and display module at least includes a four-channel acquisition card, which acquires the trigger signal, the beat frequency signal of the auxiliary interferometer and the main interferometer.

3. The device for monitoring the shape of an interventional surgical catheter based on a right-angle fiber core triplet according to claim 2, characterized in that: The process of monitoring the shape of the interventional catheter is as follows: (1) Keep the medical catheter straight in a plane and free from external stress, and collect beat frequency information as a reference group signal; then, pass the catheter through a surgical incision through a blood vessel or through a natural cavity of the human body to a target location, during which the shape of the catheter changes continuously, and collect beat frequency information as a measurement group signal; (2) Use the phase demodulation algorithm and the calibration algorithm for the unit misalignment caused by strain to accurately demodulate the strain information of the fiber core triplet: a) Use FFT transformation to convert the reference group and the measurement group signals from the optical frequency domain to the distance domain, and solve the phases of the two groups of optical signals and record them as Φ ref and Φ mea , and the difference between the two is obtained to obtain the differential phase ΔΦ at each position of the fiber core; b) solving the differential phase in segments, and multiplying the optical frequency domain signals of all subsequent segments by a phase shift factor that is linearly related to the differential phase of the current target segment; c) filtering the differential phase to remove the phase jump point, and derivatizing the differential phase after phase unwrapping to obtain the strain value at each position of the fiber core; (3) Combining the bending, torsion-total strain decoupling model based on the right-angle configuration fiber core triplet and the sensor point misalignment correction algorithm, the torsion strain and torsion deflection angle are demodulated, and the bending direction angle and bending curvature of each position point of the optical fiber after torsion compensation are solved; (4) The shape of the catheter during interventional surgery is reconstructed in real time using a homogeneous transformation matrix framework and position offset correction method.

4. A method for monitoring the shape of an interventional surgical catheter based on a right-angle fiber core triplet, using the device for monitoring the shape of an interventional surgical catheter based on a right-angle fiber core triplet as claimed in claim 1, characterized in that: The method comprises a multi-core optical fiber, wherein the multi-core optical fiber has at least four cores forming a right-angled triangle configuration, that is, among the No. 1 core, the No. 2 core, the No. 3 core, and the No. 4 core, the distances from the No. 4 core to the No. 1 core, the No. 2 core, and the No. 3 core are equal, and the No. 4 core is used as a compensation core, and the influence of the internal environment deviation is eliminated by subtracting the strain on the No. 4 core from the strain measured by the other cores; in the right-angle configuration, the No. 2 core and the No. 3 core have a strict axially symmetrical structure, and the No. 2 core, the No. 3 core, and the No. 1 core have a 30-60-90 right-angled triangle configuration; the twisted No. 1 core, the No. 2 core, and the No. 3 core are recorded as the No. 1′ core, the No. 2′ core, and the No. 3′ core; and the method comprises the following steps: Steps to establish bending, torsion-total strain decoupling of the core triplet: Wherein, 2π / 3 and 5π / 3 are the angles between core 2′, core 3′ and core 1′ respectively, θ is the angle between core 1′ and the bending direction vector ν after twisting, θ1 is the angle between core 1 and the bending direction vector ν before twisting, κ is the bending curvature value, Δφ is the twisting deflection angle; ε1′, ε2′ and ε3′ are the strains of core 1′, core 2′ and core 3′ obtained after twisting, from which the strain on core 4 has been subtracted; the torsional strains on core 1′, core 2′ and core 3′ are the same and are recorded as ε τ ; Find the torsional strain ε τ And the steps of calculating the bending direction angle θ and bending curvature value κ of each position of the fiber core after twisting: Where G is the modulus constant between shear strain and torsion angle; Δz = z1-z1′, z1 is the cross-sectional position before torsion, z1′ is the cross-sectional position after torsion; Δz is the axial distance between the two cross-sections before and after torsion, and the torsion of the optical fiber causes the core to rotate relative to the cross-section by an angle Δφ, and r is the distance between core No. 1 and core No. 4; The steps of torsional deflection angle Δφ along the multi-core optical fiber are decoupled by combining equations 1 and 3. The actual bending direction angle after compensation is θ1=θ+Δφ. θ1 and κ are used as transfer parameters after compensating for the torsion effect. Spline interpolation is performed to interpolate the discrete transfer parameters along the optical fiber path into a continuous transfer parameter curve. The spatial coordinates of each point are obtained by combining the homogeneous transformation matrix framework to realize the shape reconstruction of the multi-core optical fiber and the catheter.

5. The method for monitoring the shape of an interventional surgery catheter based on a right-angle fiber core triplet according to claim 4, characterized in that: The specific method of obtaining the spatial coordinates of each point in combination with the homogeneous transformation matrix framework is: At the sensing point O i and O i+1 The Cartesian coordinate system x is established near the space curve between i -y i -z i , i is the sensor point count, and its value is 1, 2, 3...; Establish the coordinate transfer framework: in, is the arc length tangent rotation angle, P i is the bending direction angle θ of the multi-core optical fiber after compensation twisting 1i , arc length tangent rotation angle The associated 3x3 rotation matrix, ΔO i is a 3x1 position translation matrix, R i is the bending radius of the optical fiber at this position.

6. The method for monitoring the shape of an interventional surgery catheter based on a right-angle core triplet according to claim 4, characterized in that: It also includes the step of using cosine similarity evaluation: the calculation formula is: Where n is the number of sensing points, x i ,y i They are the strain values ​​of each sensing point of No. 2 core and No. 3 core respectively.

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