A novel high-precision and robust method for capsule endoscope localization

Abstract

The present invention discloses a novel high-precision and robust capsule endoscope positioning method, which includes the following steps: S1, initial calibration of magnetometer parameters; S2, preprocessing of magnetometer data during the positioning process; S3, positioning and calculating the position p and direction n of the capsule in the body. By simultaneously optimizing the poses of the capsule in the body and the magnetometer device outside the body, the present invention solves the defect that the external device of the current magnetic positioning system needs to be rigidly fixed, and improves the positioning accuracy and robustness. Moreover, a new mathematical model and solution method are designed to eliminate the interference of the geomagnetic field and the locally varying magnetic environment in the magnetometer observation model, ensuring that millimeter-level positioning accuracy of the capsule endoscope can be achieved even when the human body moves freely.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and particularly to a novel high-precision and robust capsule endoscope positioning method. Background Art

[0002] The capsule endoscope system is an intelligent system with a capsule shape, which is internally equipped with sensors such as a camera and a wireless signal transmission device. By orally taking the intelligent capsule and relying on the peristalsis of the digestive tract, the capsule endoscope system can move completely in the digestive tract and capture images; medical staff can diagnose digestive tract diseases through the images obtained by an external receiver. The capsule endoscope system is an effective supplement to the traditional electronic gastroscope examination system, especially in the small intestine area where the traditional electronic gastroscope cannot directly examine; and the capsule endoscope system also has the advantages of being painless, non-invasive, convenient for examination, and not affecting the patient's activities.

[0003] Doctors need to infer the position of the lesion by estimating the position of the capsule endoscope in the digestive tract. Therefore, the positioning problem of the capsule endoscope in the digestive tract is a key technical problem that the capsule endoscope system needs to solve. The existing capsule endoscope positioning technologies, including magnetic positioning technology, visual positioning technology, etc., can achieve high positioning accuracy under ideal laboratory conditions. However, in actual use, on the one hand, the current magnetic positioning system requires a rigid connection of the magnetic sensor device worn outside the body to ensure the positioning accuracy, which affects the free movement of the human body, and the rigid connection makes the signal receiving device worn outside the body prone to deformation, resulting in a decrease in the positioning accuracy. On the other hand, the current magnetic positioning system needs to accurately calibrate and calculate various inherent parameters related to the earth environment and magnetometer equipment such as the geomagnetic field and zero bias in advance, and needs to keep the local magnetic field environment stable. However, in actual use scenarios, accurate calibration may not be possible to achieve, and the local magnetic field environment is complex and variable, resulting in low positioning accuracy and non-robust positioning results. Summary of the Invention

[0004] In view of the above problems, the present invention provides a novel high-precision and robust capsule endoscope positioning method to solve the problems of low positioning accuracy and non-robust positioning results of the current capsule endoscope positioning system.

[0005] The present invention adopts the following technical solutions:

[0006] A novel high-precision and robust capsule endoscope positioning method, characterized by comprising the following steps:

[0007] S1. Initial calibration of magnetometer parameters:

[0008] S101. Power on the external magnetometer array and make an 8-shaped movement, record the magnetometer readings, and by minimizing ∑ i ||m i -b m ||, where mi is the observed value of the i-th dynamometer, and the zero bias b of the magnetometer is calculated m ;

[0009] S102. Place the external magnetometer array statically and power it on. The in-vivo capsule contains a permanent magnet. Record the magnetometer readings at different positions of the permanent magnet, construct a non-linear least squares problem, and use the Levenberg-Marquardt iterative method to solve it to calculate the relative positions and direction parameters between different magnetometers.

[0010] S2. During the positioning process, preprocess the magnetometer data: unify the magnetometer data to the same time system, the same sampling frequency, and align the timestamps through interpolation.

[0011] S3. Calculate the position p and direction n of the in-vivo capsule during positioning solution:

[0012] S301. Model the magnetic field of the permanent magnet based on the magnetic dipole model. Magnetic dipole model:

[0013]

[0014] Δp = p s - p m

[0015] ρ = ||Δp||

[0016]

[0017] In the formula, m is a constant depending on the magnet material; B is the magnetic field generated by the magnetic rod located in the reference coordinate system {n m , p m} at p s ; n m is the direction of the permanent magnet; p m is the position of the permanent magnet;

[0018] Obtain the perturbation model by perturbing the direction vector n m :

[0019] n m + ∈ 3×1 = exp so3 (T 3×2 δ 2×1 )n m

[0020] In the formula, T 3×2 is the orthogonal basis of the orthogonal plane of n m ; ∈ 3×1 is the perturbation term corresponding to the direction vector in the Lie group, exp so3 is the exponential transformation of the SO3 group, and δ 2×1 is the perturbation term corresponding to the direction vector in the Lie algebra;

[0021] S302. Establish a magnetometer measurement model:

[0022]

[0023] Wherein, is the rotation from the magnetometer coordinate system s to the positioning reference coordinate system w; m s is the magnetometer measurement; b s is the magnetometer zero bias; is the value of the geomagnetic field in the reference coordinate system w; is the value of the locally slowly changing magnetic interference in the reference coordinate system w; noise is the white noise of the magnetometer observation;

[0024] S303. Eliminate the interference of the geomagnetic field and the local magnetic field environment through the differential technology of the magnetometer observation model, and the magnetic observation single-difference equation:

[0025]

[0026] Wherein, are the rotation matrices of the magnetometers s i and s j in the reference coordinate system w respectively; are the corresponding magnetometer measurement values respectively; are the zero biases of the corresponding magnetometers respectively; B i , B j are the theoretical values of the magnetic fields generated by the permanent magnets at the magnetometers s i and s j respectively; noise is the white noise;

[0027] S304. Calculate the 3-degree-of-freedom position and 2-degree-of-freedom orientation of the capsule with relatively low precision through the CoordinateDescent method as the initial values for subsequent joint optimization;

[0028] S305. Use the nonlinear optimization technology to jointly optimize the position and orientation of the capsule, as well as the relative position and orientation of the external magnetometer device to obtain a robust and high-precision capsule endoscope positioning result.

[0029] The beneficial effects of the present invention are:

[0030] 1. By simultaneously optimizing the poses of the in-vivo capsule and the external magnetometer device, the defect that the external device of the current magnetic positioning system needs to be rigidly fixed is solved, and the positioning accuracy and robustness are improved;

[0031] 2. A new mathematical model and solution method are designed to eliminate the interference of the geomagnetic field and the locally changing magnetic environment in the magnetometer observation model, ensuring that the millimeter-level positioning accuracy of the capsule endoscope can be achieved even when the human body moves freely. Description of the Drawings

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present invention and do not limit the present invention.

[0033] Figure 1 It is a schematic flow chart of the present invention;

[0034] Figure 2 It is a schematic diagram of the device of the present invention. Detailed Description of the Invention

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Unless otherwise defined, the technical terms or scientific terms used in this disclosure shall have the ordinary meanings understood by those of ordinary skill in the art to which this disclosure belongs. The terms "including" or "comprising" and the like used in this disclosure mean that the elements or items appearing before the term cover the elements or items listed after the term and their equivalents, without excluding other elements or items. "Upper", "lower", "left", "right", etc. are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0038] As Figure 1 shown, a new type of high-precision and robust capsule endoscope positioning method is characterized by including the following steps:

[0039] S1. Initial calibration of magnetometer parameters:

[0040] S101. Power on the external magnetometer array and make an eight-shaped movement, record the magnetometer readings, and calculate the magnetometer zero bias b i by minimizing ∑ i ||m m -b i ||, where m m is the observation value of the i-th dynamometer;

[0041] S102. Place the extracorporeal magnetometer array still and power it on. The intracorporeal capsule contains a permanent magnet. Record the magnetometer readings at different positions of the permanent magnet. Construct a nonlinear least squares problem and solve it using the Levenberg-Marquardt iterative method to calculate the relative position and orientation parameters between different magnetometers.

[0042] S2. During the positioning process, magnetometer data preprocessing: the magnetometer data are unified into the same time system, the same sampling frequency and the timestamps are aligned by interpolation;

[0043] S3. Position and calculate the position p and direction n of the capsule in the body:

[0044] S301. Modeling the permanent magnet magnetic field based on the magnetic dipole model. Magnetic dipole model:

[0045]

[0046] Δp=p s -p m

[0047] ρ=||Δp||

[0048]

[0049] Where m is a constant that depends on the magnetic material; B is the reference coordinate system {n m ,p m}The magnetic bar is at p s The magnetic field generated at n m is the direction of the permanent magnet; p m is the position of the permanent magnet;

[0050] The direction vector n is perturbed by the Lie group m Get the perturbation model:

[0051] n m +∈ 3×1 =exp so3 (T 3×2 δ 2×1 )n m

[0052] Where, T 3×2 n m The orthogonal basis of the orthogonal plane; ∈ 3×1 is the perturbation term of the Lie group corresponding to the direction vector, exp so3 is the exponential transformation of the SO3 group, δ 2×1 is the perturbation term of the Lie algebra corresponding to the direction vector;

[0053] S302, establish a magnetometer measurement model:

[0054]

[0055] In the formula, is the rotation from the magnetometer coordinate system s to the positioning reference coordinate system w; m s is the force measurement of the force sensor; b s is the zero bias of the magnetometer; is the value of the geomagnetic field in the reference coordinate system w; is the value of the locally slowly changing magnetic interference in the reference coordinate system w; noise is the white noise observed by the magnetometer;

[0056] S303. By using the magnetometer observation model differential technology to eliminate the interference of the geomagnetic field and the local magnetic field environment, the magnetic observation single-difference equation:

[0057]

[0058] In the formula, are respectively the rotation matrices of the magnetometers s i and s j in the reference coordinate system w; are respectively the corresponding magnetometer measurement values; are respectively the zero biases of the corresponding magnetometers; B i , B j are respectively the theoretical values of the magnetic fields generated by the permanent magnets at the magnetometers s i and s j ; noise is the white noise;

[0059] S304. By using the Coordinate Descent method, arbitrarily select a point inside the magnetometer array as the initial value of the permanent magnet position, fix the position and use the nonlinear least squares method to calculate the orientation of the permanent magnet, then fix the orientation and use the nonlinear least squares method to calculate the position of the permanent magnet, and iterate repeatedly until convergence; obtain the 3-degree-of-freedom position and 2-degree-of-freedom direction of the capsule with low precision as the initial values for subsequent joint optimization;

[0060] S305. Use the nonlinear least squares method and solve it through the Levenberg-Marquardt iteration technology to jointly optimize the position and orientation of the capsule, as well as the relative position and orientation of the external magnetometer device, and obtain the robust and high-precision capsule endoscope positioning result.

[0061] Figure 2 This is a schematic diagram of the positional relationship between the capsule of the present invention and the magnetometer array.

[0062] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A novel high-precision and robust capsule endoscope positioning method, characterized in that, It includes the following steps: S1. Initial calibration of magnetometer parameters: S101. Power on the external magnetometer array and make an 8-shaped movement, record the magnetometer readings, and calculate the magnetometer zero bias by minimizing , where is the observed value of the i-th dynamometer ; S102. Place the external magnetometer array statically and power it on. The in-vivo capsule contains a permanent magnet. Record the magnetometer readings at different positions of the permanent magnet, construct a non-linear least squares problem, and solve it using the Levenberg-Marquardt iterative method to calculate the relative positions and direction parameters between different magnetometers; S2. During the positioning process, preprocess the magnetometer data: Unify the magnetometer data to the same time system, the same sampling frequency and align the timestamps through interpolation; S3. Locate and calculate the position p and orientation n of the in-vivo capsule: S301. Model the magnetic field of the permanent magnet based on the magnetic dipole model. Magnetic dipole model: Wherein, is a constant depending on the magnetic material; is the magnetic field generated by the magnetic rod located in the reference coordinate system at ; is the direction of the permanent magnet; is the position of the permanent magnet; Perturb the direction vector through the Lie group to obtain the perturbation model: In the formula, is the orthogonal basis of the orthogonal plane of the perturbation term of the Lie group corresponding to the direction vector, is the exponential transformation of the SO3 group, the perturbation term of the Lie algebra corresponding to the direction vector; S302. Establish the magnetometer measurement model: In the formula, is the rotation from the magnetometer coordinate system to the positioning reference coordinate system ; is the force measurement is the zero offset of the magnetometer is the value of the geomagnetic field in the reference coordinate system ; is the value of the locally slowly varying magnetic interference in the reference coordinate system ; is the white noise observed by the magnetometer S303. Eliminate the interference of the geomagnetic field and the local magnetic field environment through the magnetometer observation model difference technique. Magnetic observation single difference equation: Wherein, , are the rotation matrices of the magnetometers and in the reference coordinate system respectively; are the measured values of the corresponding magnetometers respectively; are the zero biases of the corresponding magnetometers respectively; are the theoretical values of the magnetic fields generated by the permanent magnets at the magnetometers and respectively; is white noise; S304. Calculate the relatively low-precision 3-degree-of-freedom position and 2-degree-of-freedom direction of the capsule through the Coordinate Descent method as the initial values for subsequent joint optimization; S305. Use non-linear optimization techniques to jointly optimize the position and direction of the capsule, as well as the relative positions and directions of the external magnetometer devices to obtain a robust and high-precision capsule endoscope positioning result.

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