Calibration method and calibration system for an ultrasound probe comprising a magnetic sensor array

Abstract

The disclosure provides a kind of calibration method and calibration system of ultrasonic probe comprising magnetic sensor array, both involve a calibration device, in the calibration device, calibration support body is used to place ultrasonic probe, electromagnet is fixed on calibration support body and is evenly distributed around magnetic sensor array, N type line and acoustic medium are installed in the imaging range of ultrasonic probe.In the method, first, the correction coefficient of each magnetic sensor is calculated based on the ellipsoid fitting method, then each electromagnet is turned on one by one and the magnetic field vector is obtained, the relative pose relationship of each magnetic sensor in the magnetic sensor array is calculated based on the least square method, finally, the coordinates of the center of N type line section in different coordinate systems are registered, and the relative pose relationship of ultrasonic probe and magnetic sensor array is calculated.The disclosure effectively improves the convenience of calibrating ultrasonic probe comprising magnetic sensor array, and reduces the cumulative error of calculation, so that the positioning accuracy of magnetic navigation system can be improved.

Description

Technical Field

[0001] This disclosure relates to the field of medical imaging technology, specifically to a calibration method and calibration system for an ultrasound probe comprising a magnetic sensor array. Background Technology

[0002] Interventional therapy is a common clinical diagnostic and treatment method that requires doctors to accurately insert instruments such as needles and catheters into the patient's target tissue, such as peripheral nerve blocks for surgical anesthesia or postoperative analgesia. Currently, ultrasound imaging technology is commonly used to guide interventional procedures. During guidance, the ultrasound image simultaneously displays images of the patient's body and the interventional device, allowing doctors to determine the relative position of the device and the target site. However, because interventional devices are elongated and the ultrasound imaging range is limited to a single plane, the device can easily deviate from the ultrasound imaging plane, making it difficult for doctors to accurately determine its position. To address this issue, various navigation methods have been developed. By installing sensors on the ultrasound probe and the interventional device, the positional information of both the probe and the device can be simultaneously acquired and provided to the doctor through a graphical interface, enabling the doctor to consistently and accurately determine the relative position of the device and the target site.

[0003] In recent years, magnetic navigation technology has gradually gained attention, as exemplified by patents CN103945772A and CN113473916A. Its principle involves installing a magnetic sensor array inside an ultrasound probe. This array contains multiple triaxial magnetic sensors that can acquire three-dimensional magnetic field vectors in real time. The interventional device is magnetized in a certain way, generating a stable and unchanging magnetic field, causing magnetic anomalies in the surrounding magnetic field. The magnetic sensor array in the ultrasound probe analyzes these anomalies to calculate the relative position and orientation of the interventional device and the ultrasound probe. Compared to other navigation methods, this magnetic navigation method offers better portability and flexibility. The magnetic sensor array is very small and can be integrated into the ultrasound probe while maintaining its overall shape. Furthermore, no sensors need to be installed on the interventional device; only magnetization is required, eliminating the need for a specific interventional device.

[0004] Calculating the relative pose of interventional devices and ultrasound probes using magnetic navigation technology requires accurately acquiring the parameters and pose relationships of each magnetic sensor in the magnetic sensor array, as well as the relative pose relationship between the magnetic sensor array and the ultrasound probe. The process of acquiring the pose and parameters of the magnetic sensor array and the ultrasound probe is called calibration, and the accuracy of calibration directly affects the accuracy of positioning. Currently, commonly used calibration methods consist of two steps. The first step is to calibrate the magnetic sensor array separately, calculating the parameters of each magnetic sensor in the array and their relative pose relationships, as disclosed in Chinese invention patent applications CN113514789A and CN114859280A. The second step is to calculate the relative pose relationship between the magnetic sensor array and the ultrasound probe. A common method is to use the ultrasound probe to image a phantom of known size, and then calculate the pose of the ultrasound probe and the magnetic sensor array based on the phantom's characteristics, as disclosed in Chinese invention patent application CN115005864A. However, the two-step calibration method not only requires two sets of equipment for each step, making the operation cumbersome, but also the numerous calculation steps increase the cumulative error, reducing the accuracy of the calibration.

[0005] In conclusion, it is essential to design a calibration method and system for an ultrasonic probe containing a magnetic sensor array that offers high positioning accuracy and is simple and quick to operate. Summary of the Invention

[0006] In view of this, it is necessary to provide a calibration method and calibration system for an ultrasonic probe containing a magnetic sensor array, so as to overcome the problems of cumbersome calibration process and low calibration accuracy in the prior art.

[0007] To address the aforementioned technical problems, the first aspect of this disclosure provides a calibration method for an ultrasonic probe comprising a magnetic sensor array, wherein the magnetic sensor array is fixed to the ultrasonic probe and contains a plurality of magnetic sensors for acquiring magnetic field vectors. The calibration method includes the following steps:

[0008] Step 1: Allow the ultrasonic probe containing the magnetic sensor array to move randomly in an open environment and obtain the magnetic field vector during the movement;

[0009] Step 2: Based on the ellipsoid fitting method, calculate the correction coefficient of each magnetic sensor in the magnetic sensor array, and calculate the corrected magnetic field vector based on the correction coefficient of the magnetic sensor in the subsequent magnetic field vector measurement;

[0010] Step 3: Place the ultrasonic probe containing the magnetic sensor array into the calibration device. The calibration device includes a calibration support, several electromagnets mounted on the calibration support and evenly distributed around the magnetic sensor array, an N-shaped line mounted on the calibration support and intersecting the imaging plane of the ultrasonic probe, and a sound-conducting medium filling the calibration support and including the imaging range of the ultrasonic probe.

[0011] Step 4: Control all electromagnets to be turned on and off one by one, turning on only one electromagnet at a time, and record the magnetic field vector acquired by the magnetic sensor array each time;

[0012] Step 5: Based on the magnetic field vector, calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array and the calibration support body using the least squares method, and calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array.

[0013] Step 6: Acquire an ultrasound image using the ultrasound probe, the ultrasound image including the acoustic medium and the N-shaped cross-section;

[0014] Step 7: Select the center position of the N-shaped line section from the ultrasound image;

[0015] Step 8: Based on the center position of the N-shaped cross section and the relative pose relationship between the magnetic sensor array and the calibration support body, calculate the relative pose relationship between the ultrasonic probe and the calibration support body, and calculate the relative pose relationship between the ultrasonic probe and the magnetic sensor array.

[0016] In some embodiments, the correction coefficients include a bias vector V and a scaling matrix W. The magnetic field vector measurements of each magnetic sensor are treated as three-dimensional coordinates and fitted to an ellipsoid. The center coordinates of the fitted ellipsoid are the bias vector V of the magnetic sensor, and the coefficient matrix for transforming the ellipsoid into a sphere is the scaling matrix W of the magnetic sensor. Therefore, for each magnetic field vector measurement... Based on the correction coefficients, the corrected magnetic field vectors B are as follows:

[0017] In some embodiments, the number of electromagnets should be no less than four, and the electromagnets should be able to generate the same or approximately the same magnetic field.

[0018] In some embodiments, the N-type line includes multiple N-type structures, in which two straight lines are parallel, and at least one straight line is perpendicular to the imaging plane of the ultrasound probe.

[0019] In some embodiments, step 5 specifically includes:

[0020] Let i be a positive integer not greater than the number of magnetic sensors in the magnetic sensor array, and j be a positive integer not greater than the number of electromagnets. When the j-th electromagnet is activated, the corrected magnetic field vector acquired by the i-th magnetic sensor in the magnetic sensor array is: Ti B ij The superscript Ti denotes the coordinate system of the i-th magnetic sensor, and the coordinates of the j-th electromagnet center in the coordinate system of the calibration support are denoted as . w P j The direction of the magnetic field vector at the center of the j-th electromagnet is given by the coordinate system of the calibration support. w H j The superscript w denotes the coordinate system of the calibration support; when all electromagnets are in the off state, let the corrected magnetic field vector acquired by the i-th magnetic sensor in the magnetic sensor array be . Ti B i0 In the coordinate system of the calibrated support, the coordinates of the measuring components for the i-th magnetic sensor measuring the X-axis and Y-axis magnetic field components replaced by the Z-axis are respectively... w P ix , w P iy and w P iz The rotation matrix of the i-th magnetic sensor coordinate system relative to the calibration support body coordinate system is... Then the i-th magnetic sensor measures the theoretical value of the magnetic field vector generated by the j-th electromagnet. The following formula is used to calculate:

[0021]

[0022] Among them, M e Let be the coercivity coefficient of the electromagnet, (·) x Represents the X-axis component of the vector, (·) y Represents the Y-axis component of the vector, (·) z Let ||·|| represent the Z-axis component of the vector, and ||·|| represent the L2 norm of the vector.

[0023] The coercivity coefficient M of the electromagnet was calculated using the least squares method. e The pose parameters of the i-th magnetic sensor w P ix , w P iy , w P iz , The calculation formula is:

[0024]

[0025] Based on the pose parameters of the i-th magnetic sensor w P ix , w P iy , w P iz , The relative pose relationships between the magnetic sensors in the magnetic sensor array are obtained.

[0026] In some embodiments, step 8 specifically includes:

[0027] Assuming the ultrasound probe coordinate system and the ultrasound image coordinate system {I} coincide, and based on the imaging parameters of the ultrasound probe, let the actual length of the pixel side length for acquiring the ultrasound image be s. Then, the coordinates of the kth selected pixel in the ultrasound probe coordinate system are... I P pk =[sx k sy k 0] T , (x k ,y k Let be the pixel coordinates of the kth selected pixel; calculate the coordinates of the center of the N-shaped line section corresponding to the kth selected pixel in the coordinate system of the calibration support based on the geometric relationship of the N-shaped line in the ultrasound image. w P pk The coordinates of the origin of the ultrasonic probe coordinate system under the main coordinate system of the calibration support were calculated using the point cloud fine registration method. w P I And the transformation and rotation matrix between the coordinate system of the calibration support body and the coordinate system of the ultrasonic probe. The calculation formula is:

[0028]

[0029] in, For rotation matrix, I t T It is a translation vector. w P 1x Let the coordinates of the measuring element in the first magnetic sensor in the magnetic sensor array be the X-axis magnetic field component. Assume that the origin of the magnetic sensor array coordinate system coincides with the bridge of the first magnetic sensor measuring the X-axis magnetic field component, and the direction is the same as the direction of the first magnetic sensor coordinate system.

[0030] The relative pose relationship between the ultrasonic probe and the magnetic sensor array is obtained according to the above formula.

[0031] The second aspect of this disclosure provides a calibration system for an ultrasonic probe comprising a magnetic sensor array, the magnetic sensor array being fixed to the ultrasonic probe, the magnetic sensor array containing a plurality of magnetic sensors for acquiring magnetic field vectors, and the calibration system comprising a calibration device and a calculation module.

[0032] The calibration device includes:

[0033] The calibration support includes a calibration support body and an ultrasonic probe placement hole, multiple electromagnet mounting holes, an N-type wire mounting hole, and a sound-conducting medium receiving cavity formed in the calibration support body. The ultrasonic probe containing a magnetic sensor array is placed in the ultrasonic probe placement hole.

[0034] Multiple electromagnets are installed in corresponding electromagnet mounting holes and are evenly distributed around the magnetic sensor array. The magnetic field generated by the electromagnets can be acquired by the magnetic sensor array.

[0035] An N-shaped wire is installed in the N-shaped wire mounting hole and intersects with the imaging plane of the ultrasonic probe;

[0036] A sound-conducting medium is filled in the cavity of the sound-conducting medium so that the sound-conducting medium exists throughout the imaging range of the ultrasonic probe, and the N-shaped line completely passes through the sound-conducting medium.

[0037] The calculation module is used to calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array and the relative pose relationship between the magnetic sensor array and the ultrasonic probe.

[0038] In some embodiments, the number of electromagnets should be no less than four, and the electromagnets should be able to generate the same or approximately the same magnetic field. During the calibration process, all electromagnets are controlled to be turned on and off one by one, with only one electromagnet turned on at a time, and the magnetic field vector is recorded each time.

[0039] In some embodiments, the N-type line includes multiple N-type structures, in which two straight lines are parallel, and at least one straight line is perpendicular to the imaging plane of the ultrasound probe.

[0040] In some embodiments, the calculation process of the calculation module includes:

[0041] After the ultrasonic probe containing the magnetic sensor array is placed in the ultrasonic probe placement hole, all electromagnets are turned on and off one by one, with only one electromagnet turned on at a time, and the magnetic field vector is recorded each time.

[0042] Based on the magnetic field vector each time, the relative pose relationship between each magnetic sensor in the magnetic sensor array and the calibration support body is calculated using the least squares method, and the relative pose relationship between each magnetic sensor in the magnetic sensor array is also calculated.

[0043] An ultrasonic image is acquired using the ultrasonic probe, and the ultrasonic image includes the acoustic guiding medium and the N-shaped cross-section;

[0044] Select the center position of the N-shaped line section from the ultrasound image;

[0045] Based on the center position of the N-shaped cross section and the relative pose relationship between each magnetic sensor in the magnetic sensor array and the calibration support body, the relative pose relationship between the ultrasonic probe and the calibration support body is calculated, and the relative pose relationship between the ultrasonic probe and the magnetic sensor array is also calculated.

[0046] Compared with the prior art, the beneficial effects of this disclosure include:

[0047] The calibration method and system for the ultrasonic probe containing a magnetic sensor array employs a calibration device that integrates a stable magnetic field source and an N-type line ultrasonic imaging structure. This device can be used simultaneously to calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array, as well as the relative pose relationship between the ultrasonic probe and the magnetic sensor array. Compared with traditional technologies, this device effectively simplifies the complexity of calibration equipment and reduces the cost required for calibrating ultrasonic probes containing magnetic sensor arrays.

[0048] The calibration method and system for the ultrasonic probe containing a magnetic sensor array utilizes the dimensional characteristics of the calibration support body of the calibration device as a reference to achieve rapid registration of the magnetic sensor array pose and the ultrasonic probe pose. Specifically, only one calibration device is needed to complete the two calibration steps: calculating the pose of the magnetic sensors in the magnetic sensor array and calculating the relative pose relationship between the ultrasonic probe and the magnetic sensor array, greatly improving the convenience of calibration. In traditional technologies, due to the lack of a unified reference, an additional positioning step is required for the magnetic sensor array. The method provided by this invention eliminates this additional positioning step. Furthermore, since the electromagnet and the N-shaped wire are both fixed on the calibration support body, the relative pose relationship between the ultrasonic probe and the magnetic sensor array can be directly calculated based on the coordinate system of the calibration support body, reducing accumulated errors and improving calibration accuracy. In addition, this method automates the calculation of the relative pose relationships of each magnetic sensor in the magnetic sensor array and the calculation of the relative pose relationship between the ultrasonic probe and the magnetic sensor array. Attached Figure Description

[0049] Figure 1This is a schematic flowchart of an embodiment of the calibration method for an ultrasonic probe including a magnetic sensor array provided in this disclosure;

[0050] Figure 2 This is a schematic diagram of the structure of an embodiment of the calibration device provided in this disclosure;

[0051] Figure 3 This is a front cross-sectional view of an embodiment of the calibration device provided in this disclosure.

[0052] Figure 4 This is a side cross-sectional structural schematic diagram of an embodiment of the calibration device provided in this disclosure;

[0053] Figure 5 A schematic cross-sectional view of the plane containing the N-shaped line of an embodiment of the calibration device provided in this disclosure;

[0054] Figure 6 A schematic diagram of the dimensional parameters of an embodiment of the N-type line of the calibration device provided in this disclosure. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this application clearer, the application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application.

[0056] Conversely, this application covers any alternatives, modifications, equivalent methods, and schemes made within the spirit and scope of this application as defined by the claims. Furthermore, to provide the public with a better understanding of this application, certain specific details are described in detail below. However, this application can be fully understood by those skilled in the art even without these detailed descriptions.

[0057] The structures, proportions, and sizes illustrated in the accompanying drawings are solely for illustrative purposes to aid those skilled in the art and to facilitate understanding. They are not intended to limit the scope of this application and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, provided they do not affect the effectiveness or purpose of this application, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of this application. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of this application's implementation.

[0058] The first aspect of this disclosure provides a calibration method for an ultrasonic probe including a magnetic sensor array. This method requires the use of a calibration device to calibrate the ultrasonic probe. A magnetic sensor array is fixedly installed in the ultrasonic probe. The relative pose of the ultrasonic probe 1 and the magnetic sensor array 12 remains constant. The magnetic sensor array is installed close to the head of the ultrasonic probe, i.e., close to the location of the ultrasonic image. The magnetic sensor array contains multiple magnetic sensors for acquiring magnetic field vectors. Combined with... Figure 1 Let's take a look. Figure 1 A schematic flowchart of an embodiment of the calibration method for an ultrasonic probe including a magnetic sensor array provided in the first aspect of this disclosure includes steps S101 to S108, wherein:

[0059] In steps S101 and S102, individual magnetic sensors in the magnetic sensor array are calibrated. This is because errors in the manufacturing process of the magnetic sensors and electromagnetic interference in the surrounding circuits cause a difference between the magnetic field vector directly measured by the magnetic sensors and the actual magnetic field vector. A calibration coefficient is needed to obtain the calibration coefficient, and the calibrated magnetic field vector, i.e., the true magnetic field vector, is calculated using the calibration coefficient and the measured value of the magnetic sensors. According to the description in patent US7275008B2, when the magnetic sensor array rotates in an open environment, the collected magnetic field vector is recorded in three-dimensional coordinates. The recorded result should present a tilted ellipsoidal distribution deviating from the origin. Since the magnitude of the magnetic field remains constant in an open environment, the actual magnetic field vector distribution should be a sphere centered at the origin.

[0060] In step S101, the magnetic sensor array moves randomly in an open environment, and the magnetic sensor array should be oriented in as many directions as possible, and the magnetic field vector measurement value of each magnetic sensor in the magnetic sensor array is recorded during the movement.

[0061] In step S102, the correction coefficients of each magnetic sensor are calculated based on the measured magnetic field vector values. The correction coefficients of the magnetic sensors include a bias vector V and a scaling matrix W. The measured magnetic field vector values ​​are treated as three-dimensional coordinates and fitted to an ellipsoid. The center coordinates of the fitted ellipsoid are the bias vector V of the magnetic sensor, and the coefficient matrix for transforming the ellipsoid into a sphere is the scaling matrix W of the magnetic sensor. Therefore, for each magnetic sensor's measured magnetic field vector value... The true magnetic field vector B of each can be calculated using the following formula:

[0062]

[0063] In step S103, the ultrasonic probe containing the magnetic sensor array is placed in the calibration device, combined with... Figures 2 to 5 Let's take a look. Figure 2This is a schematic diagram of an embodiment of the calibration apparatus used in the calibration method provided in the first aspect of this disclosure. Figure 3 This is a front cross-sectional view of an embodiment of the calibration apparatus used in the calibration method provided in the first aspect of this disclosure. Figure 4 This is a side cross-sectional view of an embodiment of the calibration device used in the calibration method provided in the first aspect of this disclosure. Figure 5 This is a schematic cross-sectional view of the N-shaped wire in an embodiment of the calibration device used in the calibration method provided in the first aspect of this disclosure. The calibration device 1 includes a calibration support, several electromagnets 12, an N-shaped wire 13, and a sound-conducting medium 14. Wherein:

[0064] The calibration support includes a calibration support body 11 and an ultrasonic probe placement hole 111, multiple electromagnet mounting holes, N-type wire mounting holes, and a sound-conducting medium receiving cavity formed within the calibration support body 11. The calibration support body 11 is made of non-ferromagnetic materials, such as aluminum or acrylic, to avoid interference with the magnetic field. An ultrasonic probe placement hole 111 is formed in the center of the upper half of the calibration support body 11 for placing an ultrasonic probe 2 containing a magnetic sensor array 21.

[0065] All electromagnets 12 are installed in corresponding electromagnet mounting holes on the calibration support body 11 and are evenly distributed around the ultrasonic probe 2 containing the magnetic sensor array 21. The magnetic field generated by the electromagnets 12 can be acquired by the magnetic sensor array 21. There should be no fewer than four electromagnets 12, and they should all be of the same model or have the same structure and size. Therefore, when the same current is input, all electromagnets 12 will have the same or approximately the same magnetic coercivity and generate the same or approximately the same magnetic field.

[0066] The N-type wire 13 is installed in the N-type wire mounting hole on the main body 11 of the calibration device, and intersects with the imaging plane of the ultrasonic probe 2, such as... Figure 5 As shown, an N-shaped line 13, after multiple direction changes, forms multiple "N-shaped structures." The starting point, ending point, and direction change point of an N-shaped line 13 are called "inflection points." Adjacent inflection points are connected by straight lines. Four consecutive inflection points, consisting of three straight lines, form an N-shaped structure. Within an N-shaped structure, two straight lines are parallel; these two lines are called "edge lines," and the other straight line is called the "diagonal line." Each N-shaped structure contains a straight line perpendicular to the imaging plane of the ultrasound probe 2. The material used for the N-shaped line 13 should have a significantly different density from human muscle, such as nylon, to ensure good ultrasound imaging performance.

[0067] The acoustic medium 14 is filled in the acoustic medium receiving cavity located directly below the ultrasonic probe 2 within the calibration support body 11, ensuring that the acoustic medium 14 is present throughout the imaging range of the ultrasonic probe 2. The N-shaped line 13 completely passes through the acoustic medium 14, enabling the ultrasonic probe 2 to image the cross-section of the N-shaped line 13. The density of the material used for the acoustic medium 14 should be similar to that of human muscle, such as water or agar.

[0068] During the calibration process, both calibration device 1 and ultrasonic probe 2 should remain stationary.

[0069] In step S104, all electromagnets 12 are turned on and off one by one. When an electromagnet 12 is turned on, at most one electromagnet 12 should be turned on at any given time, and every electromagnet 12 should have been turned on at least once. Furthermore, the current applied to each electromagnet 12 when it is turned on should be consistent, and when an electromagnet 12 is turned off, a reverse current should be applied to eliminate residual magnetism. Let i be a positive integer not greater than the number of magnetic sensors, and j be a positive integer not greater than the number of electromagnets. When the j-th electromagnet 12 is turned on, the corrected magnetic field vector obtained by the i-th magnetic sensor in the magnetic sensor array 21 is... Ti B ij And let the coordinates of the center of the j-th electromagnet 12 in the coordinate system of the calibration support body 11 be denoted as . w P j The direction of the central magnetic field vector of the j-th electromagnet 12 is given by the coordinate system of the calibration support body 11. w H j When all electromagnets 12 are in the off state, the magnetic field vector obtained by the i-th magnetic sensor in the magnetic sensor array 21 after correction is: Ti B i0 The coordinate system of the calibration support body 11 is {w}, and the coordinate system of the i-th magnetic sensor is {T}. i}

[0070] In step S105, the pose of each magnetic sensor in the magnetic sensor array 21 is calculated based on the data obtained in step S104. The magnetic sensors on the magnetic sensor array 21 are triaxial magnetic sensors. Triaxial magnetic sensors typically use three measuring elements to measure the magnetic field magnitude in three directions respectively. For example, a magnetoresistive sensor uses three magnetic bridges for measurement, and a Hall sensor uses three Hall elements for measurement. Therefore, the pose of the magnetic sensor should include the coordinates of the three measuring elements and the orientation of the magnetic sensor coordinates. For the i-th magnetic sensor, in the coordinate system of the calibration support body 11, the coordinates of the measuring element measuring the X-axis magnetic field component are: w P ix The coordinates of the measuring element for measuring the Y-axis magnetic field component are as follows: w P iyThe coordinates of the measuring components for measuring the Z-axis magnetic field component are as follows: w P iz And the rotation matrix of the i-th magnetic sensor coordinate system relative to the calibration support body 11 coordinate system. In calculating the pose of the magnetic sensor, an electromagnet magnetic field model is required. This model is simplified to a current-loop magnetic dipole model, where the theoretical value of the magnetic field vector generated by the j-th electromagnet is obtained from the measurement of the i-th magnetic sensor. The calculation formula is:

[0071]

[0072] Among them, M e Let be the coercivity coefficient of electromagnet 12, (·) x Represents the X-axis component of the vector, (·) y Represents the Y-axis component of the vector, (·) z Let ||·|| represent the Z-axis component of the vector, and let ||·|| represent the L2 norm of the vector.

[0073] The coercivity coefficient M of an electromagnet can be calculated using least squares methods, such as the Quantum Particle Swarm Optimization (QPSO) algorithm. e The pose parameters of the i-th magnetic sensor w P ix , w P iy , w P iz , The specific calculation formula is as follows:

[0074]

[0075] Since the above calculation results represent the pose of the magnetic sensor in the coordinate system of the calibration support body 11, it needs to be converted to the pose in the coordinate system of the magnetic sensor array 21. Assume that the origin of the coordinate system of the magnetic sensor array 21 coincides with the bridge used by the first magnetic sensor to measure the X-axis magnetic field component, and its direction is the same as that of the first magnetic sensor coordinate system. Let the coordinate system of the magnetic sensor array 21 be {T}, and the bridge used by the i-th magnetic sensor in the coordinate system of the magnetic sensor array 21 to measure the X-axis magnetic field component be {T}. T P ix The bridge used to measure the Y-axis magnetic field component is a coordinate system. T P iy The bridge used to measure the Z-axis magnetic field component is a coordinate system. T P iz And the rotation matrix of the i-th magnetic sensor coordinate system relative to the magnetic sensor array 2 coordinate system. The calculation formula is:

[0076]

[0077] After obtaining the pose of each magnetic sensor in the magnetic sensor array 21, it is also necessary to obtain the relative pose relationship between the magnetic sensor array 21 and the ultrasonic probe 2, which will be described in step S108.

[0078] In step S106, an ultrasonic image is acquired using the ultrasonic probe 2. The ultrasonic image includes the acoustic medium 14 and the cross section of the N-shaped line 13.

[0079] In step S107, the center position of the N-shaped line 13 cross-section is selected from the ultrasound image obtained in step S106. In the ultrasound image, the N-shaped line 13 cross-section is displayed as a white dot. The pixel located at the center of the white dot is determined by manual or automatic selection. Let k be a positive integer not greater than the number of selected pixels, and the pixel coordinates of the kth selected pixel be (x... k ,y k ).

[0080] In step S108, the relative pose relationship between the magnetic sensor array 21 and the ultrasonic probe 2 is calculated, where the coordinate system of the ultrasonic probe 2 and the ultrasonic image coordinate system {I} are assumed to coincide. Based on the imaging parameters of the ultrasonic probe 2, the actual length of the side length of the ultrasonic image pixel can be obtained as s. Then, the coordinates of the k-th selected pixel in the coordinate system of the ultrasonic probe 2 are... I P pk =[sx k sy k 0] T Combining Figure 6 In an N-shaped structure of N-shaped line 13, the intersection of the ultrasound image and the edge of the N-shaped structure is called the "edge point," and the intersection of the ultrasound image and the oblique line of the N-shaped structure is called the "oblique point." Let the distances between the oblique point and the two edge points be d1 and d2, respectively. The two edge lines and the oblique point divide the oblique line into two segments with lengths l1 and l2, respectively. The edge point and the oblique line segment with the same index are located on the same side of the oblique point. Therefore, according to the parallel relationship of the edge lines, l1 / l2 = d1 / d2. The values ​​of d1 and d2 can be calculated from the coordinates of the pixel in the coordinate system of ultrasound probe 2. Since the dimensions of the calibration support body 11 and N-shaped line 13 are known, the values ​​of l1 and l2 can be calculated based on the above dimensional relationship. Thus, the coordinates of the center of the N-shaped line 13 section corresponding to the k-th selected pixel in the coordinate system of the calibration support body 11 can be calculated. w P pk The coordinates of the origin of the ultrasonic probe in the coordinate system 2 under the coordinate system of the calibration support body 11 were calculated using the Iterative Closest Point (ICP) method. w P IAnd the transformation rotation matrix of the coordinate system of the calibrated support body 11 and the coordinate system of the ultrasonic probe 2. The calculation formula is:

[0081]

[0082] The relative pose relationship between the ultrasonic probe 2 and the magnetic sensor array 21 can be calculated, and the rotation matrix can be obtained. Translation vector At this point, the calibration of ultrasonic probe 2 is complete.

[0083] A calibration system for an ultrasonic probe including a magnetic sensor array is provided in a second aspect embodiment of this disclosure, comprising:

[0084] The calibration device, wherein the calibration device is adopted in the calibration method provided in the first aspect of this disclosure, the specific structure of which has been described above and will not be repeated here; and

[0085] The calculation module is used to calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array 21 and the relative pose relationship between the magnetic sensor array 21 and the ultrasonic probe 2.

[0086] Furthermore, the calculation process of the calculation module includes:

[0087] After the ultrasonic probe 2 containing the magnetic sensor array 21 is placed in the ultrasonic probe placement hole, all electromagnets 12 are turned on and off one by one, with only one electromagnet 12 turned on at a time, and the magnetic field vector is recorded each time.

[0088] Based on the magnetic field vector each time, the relative pose relationship between each magnetic sensor in the magnetic sensor array 12 and the calibration support body 11 is calculated using the least squares method, and the relative pose relationship between each magnetic sensor in the magnetic sensor array 21 is also calculated.

[0089] An ultrasonic image is acquired using ultrasonic probe 2, which includes the cross-section of acoustic medium 14 and N-shaped line 13.

[0090] Select the center position of section 13 of the N-type line from the acquired ultrasound images;

[0091] Based on the center position of the selected N-type line 13 section and the relative pose relationship between each magnetic sensor in the magnetic sensor array 21 and the calibration support body 11, the relative pose relationship between the ultrasonic probe 2 and the calibration support body 11 is calculated, and the relative pose relationship between the ultrasonic probe 2 and the magnetic sensor array 21 is also calculated.

[0092] It should be noted that the foregoing explanation of the embodiment of the calibration method for an ultrasonic probe containing a magnetic sensor array also applies to the calibration device for the ultrasonic probe containing a magnetic sensor array in this embodiment, and will not be repeated here.

[0093] This disclosure provides a calibration method and system for an ultrasonic probe comprising a magnetic sensor array. In the calibration system, a calibration support body is used to hold the ultrasonic probe. Electromagnets are fixed to the calibration support body and uniformly distributed around the magnetic sensor array. An N-shaped wire and a sound-conducting medium are installed within the imaging range of the ultrasonic probe. In the calibration method, firstly, the correction coefficients of each magnetic sensor are calculated based on an ellipsoid fitting method. Then, each electromagnet is activated individually to obtain the magnetic field vector. The relative pose relationship between each magnetic sensor in the magnetic sensor array is calculated based on the least squares method. Finally, the coordinates of the center of the N-shaped wire section in different coordinate systems are registered to calculate the relative pose relationship between the ultrasonic probe and the magnetic sensor array.

[0094] The technical solution provided in this disclosure can complete two calibration steps—calculation of the magnetic sensor pose and calculation of the relative pose relationship between the ultrasonic probe and the magnetic sensor array—using only one calibration device, greatly improving the convenience of calibration. Simultaneously, the provided calibration method achieves accurate calculation of the positions of the three measuring elements of the magnetic sensor, enabling the magnetic navigation system to have higher positioning accuracy. Furthermore, since the electromagnet and N-shaped wire are both fixed on the calibration support body, the calculation of the relative pose relationship between the ultrasonic probe and the magnetic sensor array can be directly calculated based on the coordinate system of the calibration support body, avoiding repeated calculations and accumulated errors.

[0095] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0096] Although examples of the invention have been shown and described above, it is understood that the above examples are exemplary and should not be construed as limiting the invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above examples within the scope of the invention.

Claims

1. A calibration method for an ultrasonic probe comprising a magnetic sensor array, characterized in that, The magnetic sensor array is fixed on the ultrasonic probe, and the magnetic sensor array contains multiple magnetic sensors for acquiring magnetic field vectors. The calibration method includes the following steps: Step 1: Allow the ultrasonic probe containing the magnetic sensor array to move randomly in an open environment and obtain the magnetic field vector during the movement; Step 2: Based on the ellipsoid fitting method, calculate the correction coefficients of each magnetic sensor in the magnetic sensor array, and calculate the corrected magnetic field vector based on the correction coefficients in the subsequent magnetic field vector measurement; the correction coefficients include the bias vector. and scaling matrix The magnetic field vector measurements of each magnetic sensor are treated as three-dimensional coordinates, and an ellipsoid is fitted to them. The coordinates of the center of the fitted ellipsoid are the bias vector of the magnetic sensor. The coefficient matrix for transforming an ellipsoid into a sphere is the scaling matrix of the magnetic sensor. Then, for each magnetic sensor, the measured value of the magnetic field vector... The corrected magnetic field vectors are obtained according to the correction coefficients. for: ; Step 3: Place the ultrasonic probe containing the magnetic sensor array into the calibration device. The calibration device includes a calibration support, several electromagnets mounted on the calibration support and evenly distributed around the magnetic sensor array, an N-shaped line mounted on the calibration support and intersecting the imaging plane of the ultrasonic probe, and a sound-conducting medium filling the calibration support and including the imaging range of the ultrasonic probe. Step 4: Control all electromagnets to be turned on and off one by one, turning on only one electromagnet at a time, and record the magnetic field vector acquired by the magnetic sensor array each time; Step 5: Based on the magnetic field vector, calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array and the calibration support body using the least squares method, and calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array. Step 6: Acquire an ultrasound image using the ultrasound probe, the ultrasound image containing a sound-conducting medium and an N-shaped cross-section; Step 7: Select the center position of the N-shaped line section from the ultrasound image; Step 8: Based on the center position of the N-shaped cross section and the relative pose relationship between the magnetic sensor array and the calibration support body, calculate the relative pose relationship between the ultrasonic probe and the calibration support body, and calculate the relative pose relationship between the ultrasonic probe and the magnetic sensor array.

2. The calibration method according to claim 1, characterized in that, The number of electromagnets should be no less than four, and the electromagnets should be able to generate the same magnetic field.

3. The calibration method according to claim 1, characterized in that, The N-type line comprises multiple N-type structures, in which two straight lines are parallel, and at least one straight line is perpendicular to the imaging plane of the ultrasound probe.

4. The calibration method according to claim 1, characterized in that, Step 5 specifically includes: set up It is a positive integer not greater than the number of magnetic sensors in the magnetic sensor array. It is a positive integer not greater than the number of electromagnets, when the... After the electromagnet is turned on, the first one in the magnetic sensor array The corrected magnetic field vector acquired by each magnetic sensor is superscript Indicates the first The coordinate system of the first magnetic sensor is recorded, and the coordinate system of the second magnetic sensor is recorded. The coordinates of the center of the electromagnet in the coordinate system of the calibration support are: , No. The direction of the magnetic field vector at the center of the electromagnet is, in the coordinate system of the calibration support, as follows: superscript This indicates the coordinate system of the calibration support; when all electromagnets are in the off state, let the first electromagnet in the magnetic sensor array be... The corrected magnetic field vector acquired by each magnetic sensor is ; In the coordinate system of the calibrated support body, the first The coordinates of the measuring components for the magnetic sensors that measure the X-axis, Y-axis, and Z-axis magnetic field components are as follows: , and and the The rotation matrix of the magnetic sensor coordinate system relative to the calibration support body coordinate system is: Then the first The magnetic sensor measured the first... The theoretical value of the magnetic field vector generated by the electromagnet. The following formula is used to calculate: in, The coercivity coefficient of the electromagnet is given. Represents the X-axis component of a vector. Represents the Y-axis component of the vector. Represents the Z-axis component of the vector. The second norm of a vector; The coercivity coefficient of the electromagnet was calculated using the least squares method. , No. Pose parameters of a magnetic sensor , , , The calculation formula is: According to the Pose parameters of a magnetic sensor , , , The relative pose relationships between the magnetic sensors in the magnetic sensor array are obtained.

5. The calibration method according to claim 1, characterized in that, Step 8 specifically includes: Let the ultrasound probe coordinate system and the ultrasound image coordinate system be defined. Overlapping, based on the imaging parameters of the ultrasound probe, let the actual length of the pixel side length for acquiring the ultrasound image be... Then the first The coordinates of the selected pixels in the coordinate system of the ultrasonic probe , For the first The pixel coordinates of the selected pixel are calculated based on the geometric relationship of the N-shaped lines in the ultrasound image. The coordinates of the center of the N-shaped cross section corresponding to each selected pixel in the coordinate system of the calibration support The coordinates of the origin of the ultrasonic probe coordinate system under the main coordinate system of the calibration support were calculated using the point cloud fine registration method. And the transformation and rotation matrix between the coordinate system of the calibration support body and the coordinate system of the ultrasonic probe. The calculation formula is: The relative pose relationship between the ultrasonic probe and the magnetic sensor array is obtained according to the calculation formula.

6. A calibration system for an ultrasonic probe comprising a magnetic sensor array based on the calibration method of claim 1, characterized in that, The magnetic sensor array is fixed on the ultrasonic probe. The magnetic sensor array contains multiple magnetic sensors for acquiring magnetic field vectors. The calibration system includes a calibration device and a calculation module. The calibration device includes: The calibration support includes a calibration support body and an ultrasonic probe placement hole, multiple electromagnet mounting holes, an N-type wire mounting hole, and a sound-conducting medium receiving cavity formed in the calibration support body. An ultrasonic probe containing a magnetic sensor array is placed in the ultrasonic probe placement hole. Multiple electromagnets are installed in corresponding electromagnet mounting holes and are evenly distributed around the magnetic sensor array. The magnetic field generated by the electromagnets can be acquired by the magnetic sensor array. An N-shaped wire is installed in the N-shaped wire mounting hole and intersects with the imaging plane of the ultrasonic probe; A sound-conducting medium is filled in the cavity of the sound-conducting medium so that the sound-conducting medium exists throughout the imaging range of the ultrasonic probe, and the N-shaped line completely passes through the sound-conducting medium. The calculation module is used to calculate the relative pose relationship between each magnetic sensor in the magnetic sensor array and the relative pose relationship between the magnetic sensor array and the ultrasonic probe.

7. The calibration system according to claim 6, characterized in that, The number of electromagnets should be no less than 4, and the electromagnets should be able to generate the same magnetic field. During the calibration process, all electromagnets are controlled to be turned on and off one by one, with only one electromagnet turned on at a time, and the magnetic field vector is recorded each time.

8. The calibration system according to claim 6, characterized in that, The N-type line comprises multiple N-type structures, in which two straight lines are parallel, and at least one straight line is perpendicular to the imaging plane of the ultrasound probe.

9. The calibration system according to any one of claims 6 to 8, characterized in that, The calculation process of the calculation module includes: After the ultrasonic probe containing the magnetic sensor array is placed in the ultrasonic probe placement hole, all electromagnets are turned on and off one by one, with only one electromagnet turned on at a time, and the magnetic field vector is recorded each time. Based on the magnetic field vector each time, the relative pose relationship between each magnetic sensor in the magnetic sensor array and the calibration support body is calculated using the least squares method, and the relative pose relationship between each magnetic sensor in the magnetic sensor array is also calculated. An ultrasonic image is acquired using the ultrasonic probe, and the ultrasonic image includes the acoustic guiding medium and the N-shaped cross-section; Select the center position of the N-shaped line section from the ultrasound image; Based on the center position of the N-shaped cross section and the relative pose relationship between each magnetic sensor in the magnetic sensor array and the calibration support body, the relative pose relationship between the ultrasonic probe and the calibration support body is calculated, and the relative pose relationship between the ultrasonic probe and the magnetic sensor array is also calculated.

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