CN114699168A - Calibration system and calibration method of biplane ultrasonic probe - Google Patents

Abstract

The invention discloses a calibration system based on a dual-plane ultrasonic probe, comprising an orthogonal dual-plane ultrasonic probe, a magnetic field generator, a magnetic navigation positioning receiver, a calibration phantom and a container. Among them, the calibration phantom is a cuboid, which is fixed at the bottom of the container and is submerged by the ultrasonic imaging medium in the container; the calibration phantom is divided into upper and lower parts, which are respectively interspersed with N-shaped wire groups; the two imaging planes of the dual-plane ultrasonic probe are mutually Vertical, it can intersect with the two sets of wire sets for the calibration phantom; the magnetic navigation positioning receiver is fixed in the middle of the dual-plane ultrasonic probe; the magnetic navigation positioning probe is used to select the surface points of the phantom to locate and calibrate the phantom; the magnetic field generates The device is placed on the side of the container to ensure that its magnetic field range can cover the magnetic navigation positioning receiver and the magnetic navigation positioning probe on the ultrasonic probe. The scheme is beneficial to standardize the calibration data collection and labeling process; it is beneficial to calculate the coordinate transformation matrix from the magnetic navigation positioning receiver to the ultrasound image with high precision.

Description

Calibration system and calibration method for a dual-plane ultrasonic probe

technical field

The invention relates to a calibration system and a calibration method for an orthogonal double plane ultrasonic probe, belonging to the technical fields of medical equipment and computer vision.

Background technique

Prostate biopsy is the gold standard for prostate cancer diagnosis. Ultrasound images are often used to guide prostate puncture because of the convenience of acquisition and the real-time nature of images. At present, the prostate biopsy system that uses preoperative MR and intraoperative ultrasound fusion in clinical practice needs to obtain the spatial position information of two-dimensional ultrasound images. By fixing the electromagnetic positioning sensor on the ultrasonic probe, the spatial pose information of the sensor can be acquired in real time. In addition, the ultrasound probe needs to be calibrated, so as to obtain the conversion relationship between the sensor coordinate system and the ultrasound image coordinate system, and then obtain the spatial position information of the ultrasound image.

At present, the common ultrasonic image calibration method is to scan the N-line body membrane in the water tank to form several bright spots, identify and calculate the spatial position information of the bright spots, and combine the pixel coordinate information in the ultrasonic image to calculate Calibration matrix.

In the prior art, the ultrasonic calibration phantom is mainly designed as a single plane ultrasonic probe. For the dual-plane ultrasound probe, because its two imaging planes are orthogonal to each other, the field of view is limited, and it cannot be fully immersed in the water tank, it is difficult to find a suitable angle and position to scan all the points of the N-line phantom. Because the imaging quality of ultrasound images is poor, there are problems such as reflection and artifacts, and the bright spot area is too large when the ultrasound section is not completely perpendicular to the N line, so the recognition accuracy of feature points is poor. The above reasons lead to the difficulty in the acquisition of calibration images, and the low precision of the calculated calibration matrix.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide a convenient and easy-to-use dual-plane ultrasonic probe calibration system, and a robust and high-precision calibration method.

In order to achieve the above object, the present invention adopts the following technical solutions: a biplane ultrasonic probe calibration system, including an orthogonal biplane ultrasonic probe, which has two ultrasonic imaging sections, and the two sections are orthogonal to each other; It is used to generate the magnetic field for electromagnetic positioning; the magnetic navigation positioning receiver, whose rigid body is fixed on the dual-plane ultrasonic probe, can obtain its own spatial position and attitude parameters in real time in the magnetic field generated by the magnetic field generator, so that after calibration It can be used to obtain the spatial pose parameters of the two ultrasonic sections; the magnetic navigation positioning probe, in the magnetic field generated by the magnetic field generator, can obtain the spatial position parameters of the needle tip in real time for positioning and calibrating the phantom; A rectangular parallelepiped; container and fixture for holding ultrasound imaging media.

Further, the calibration phantom is made of resin material, and the whole is a cuboid, divided into upper and lower regions, each with a square hole, and the side wall of the hole is provided with a number of inverted triangular through holes, interspersed with nylon threads.

Further, in the calibration phantom, the holes in the upper and lower regions are all punched in the side walls, and lines are inserted to form 5 groups of N shapes. And for the upper and lower regions of the phantom, five groups of N-shaped lines interspersed with nylon threads are the same in shape and size, and are perpendicular to each other. The upper half area is used to collect the data required for the sagittal calibration of the ultrasonic probe, and the lower half area is used to collect the data required for the cross-sectional calibration of the ultrasonic probe.

Further, in the calibration phantom, the wire passing through the triangular through holes is made of nylon, and the diameter is similar to the ultrasonic length used by the ultrasonic probe, so that the intersection point with the nylon wire in the ultrasonic image is clearer.

Further, in the container and the fixing device, the height of the container is sufficient to hold the calibration phantom and the fixing device. The fixing device can fix the calibration dummy to the bottom of the container. The container can be used to hold hot water at human body temperature and submerge the calibration phantom. The four walls of the container are provided with absorbing materials to reduce ultrasonic reflection.

A calibration method based on a dual-plane ultrasonic probe calibration system, comprising the following steps:

Step (1) calibration data collection: use the above-mentioned dual-plane ultrasonic probe calibration system to collect the raw data required for calibration;

Step (2) Labeling of calibration data: automatically or non-automatically, for several points formed by the intersection of the ultrasonic section and the N-shaped line of the calibration phantom, automatically or non-automatically, according to a specific geometric relationship, identify and label the points in the image. coordinate;

Step (3) Calibration data preprocessing: According to several points formed by the intersection of the ultrasonic cross-section and the N-shaped line of the calibration phantom, and their distance geometric relationship, calculate several feature points that intersect with the hypotenuse of each group of N-lines, and in the simulation The coordinates in the body coordinate system;

Step (4) iterative optimization of least squares method, removing outliers and calculating calibration matrix: calculating the coordinate transformation matrix from the coordinate system of the magnetic navigation receiver to the ultrasonic image coordinate system;

Step (5) averaging of two-plane calibration matrices: averaging the calibration matrices obtained by the two probes according to the prior information that the two imaging planes of the ultrasonic probe are mutually orthogonal;

Further, the concrete process of described step (1) is:

In step (1.1), the calibration phantom is vertically fixed in the container, and the imaging medium is immersed in the phantom;

Step (1.2) establishes the coordinate system of the magnetic field generator based on the magnetic field generator;

Step (1.3) uses a needle probe to collect phantom positioning data, including the coordinates of several points on the right surface, upper surface and front of the phantom calibrated by a cuboid;

Step (1.4) ensure that the magnetic navigation positioning receiver is fixed in the middle of the ultrasonic probe;

Step (1.5) Collect cross-section calibration data: make the ultrasonic cross-section intersect with the N line of the lower half of the calibration phantom.

Under the premise of ensuring that the ultrasound image intersects with all N-shaped lines and the intersection points are clearly visible, adjust the 3 translational degrees of freedom and 3 rotational degrees of freedom of the ultrasound probe respectively, and collect several images;

Step (1.6) Collect sagittal plane calibration data: make the ultrasound sagittal plane intersect with the N line of the upper half of the calibration phantom.

Under the premise of ensuring that the ultrasound image intersects with all N-shaped lines and the intersection points are clearly visible, adjust the 3 translational degrees of freedom and 3 rotational degrees of freedom of the ultrasound probe respectively, and collect several images;

Further, the specific process of the step (2) is, considering that for the foreground points in a single frame image, some ABC collinear, DEF collinear, GHI collinear, JKL collinear, MNO collinear, ADG collinear, BEH collinear. collinear, CFI is collinear, and there are AC∥DF∥GI, and AG∥BH∥CI, then the interference of other noise points that do not meet the above rules can be excluded when labeling, and according to the collinear and parallel rules, more accurate identification Attractions

Further, the concrete process of described step (4) is:

In step (4.1), the magnetic field generator coordinate system T (transmitter) is established based on the magnetic field transmitter, and the phantom reconstruction coordinate system C (reconstruction) is established based on the calibration phantom as shown in Figure 2, and the receiver is positioned with magnetic navigation. The receiver coordinate system R(receiver) is established as the benchmark, and the image coordinate system I(image) is established based on the cross-sectional and sagittal ultrasound images, then for any feature point, there is a coordinate transformation: p _c =T _ct *T _tr *T _ri * _pi ;

In step (4.2), the parameter information of the calibration phantom is known, and the coordinates of the magnetic field generator coordinate system of 30 points on the right surface, upper surface and front of the cuboid phantom that have been collected are used to calculate the transmitter coordinate system the transformation matrix Tct to the phantom reconstruction coordinate system (reconstruction);

Step (4.3), based on the coplanarity of 5 points, filter out outliers. The five feature points in the above calibration pictures should belong to the same plane. Fit the plane using the magnetic field generator coordinate system coordinates of these 5 points. If the calculated distance between any point and the plane is greater than a certain threshold, discard the frame of picture data;

Step (4.4), use iterative least squares to fit the transformation matrix Tri from the image coordinate system to the sensor/receiver coordinate system;

Step (4.5), use the calibration matrix _Tri obtained in the above-mentioned step 6, carry out coordinate transformation to the existing key points, and reconstruct the coordinates of its imitation body coordinate system;

Step (4.6), for the calculated coordinates of the phantom coordinate system, the points that differ greatly from the real values are screened out as outliers;

Step (4.7), repeat (4.4) to (4.6) until no outliers are screened out, and obtain the calibration matrix _Tri of the transverse or sagittal plane.

Further, the concrete process of described step (5) is

其中

其物理意义分别是超声探头轴线方向、正上方、正右方在接收器坐标系下的方向向量；Step (5.1), for the transverse and sagittal planes, the calibration matrix is in the form of a 4*4 matrix

in

Its physical meaning is the direction vector of the ultrasonic probe axis direction, directly above, and just right in the receiver coordinate system;

构造新的横断面、矢状面标定矩阵

Step (5.2), make

Construct new transverse and sagittal calibration matrices

The present invention has the following advantages due to taking the above technical solutions:

1. The design of the calibration phantom in the present invention is standardized, the production cost is low, and the design of the inverted triangular hole in the side wall ensures the accuracy of the coordinates of the interspersed nylon wire;

2. In the calibration phantom of the present invention, its N-shaped line is divided into upper and lower regions and perpendicular to each other, which is suitable for the situation where the cross-section and sagittal plane of the biplane calibration phantom are perpendicular to each other. After fixing the calibration phantom, insert the ultrasound probe vertically into the imaging medium. You can use the N-shaped lines in the upper and lower regions of the calibration phantom to collect the calibration images required for the two planes, the ultrasound imaging plane and the N-shaped line. Roughly vertical, the feature points in the image are clearer and easier to identify;

3. The calibration image acquisition process proposed by the present invention systematically specifies the movement mode of the probe during the image acquisition process, and adjusts 3 translational degrees of freedom and 3 rotational degrees of freedom respectively, so as to collect a large number of ultrasonic data in different poses, It is beneficial to the accuracy of the calibration matrix solution;

4. The calibration phantom positioning method proposed by the present invention avoids the difficulty of manually locating specific points by using multi-point coordinates to fit the three planes of the rectangular phantom by least squares respectively, and improves the calculation efficiency of the phantom position. stability;

5. The 5 groups of N-shaped line threading methods of the calibration phantom specified in the present invention provide the prior information of the verticality of the N-shaped line, which is helpful for identifying key points when the calibration image is manually annotated;

6. The calibration image preprocessing method proposed by the present invention improves the calculation accuracy of the calibration matrix by screening out outliers;

7. The dual-plane vertical calibration post-processing proposed by the present invention reduces the calculation error of the calibration matrix by introducing the information of the dual-plane perpendicularity of the ultrasonic probe.

Description of drawings

Fig. 1 is the schematic diagram of all hardware placement positions of the calibration system described in the present invention;

Figure 2 shows the use of the N-shaped line in the lower half of the calibration phantom to collect the cross-sectional calibration data of the ultrasound probe (left image); the N-shaped line in the lower half of the calibration phantom is used to collect the sagittal calibration data of the ultrasound probe (right image)

3 is a schematic diagram of several coordinate systems involved in the calibration process;

Fig. 4 is the three-dimensional view of the calibration dummy described in the present invention, does not include the silk thread group interspersed therein;

Fig. 5 is the front view of the calibration phantom described in the present invention;

Fig. 6 is the right side view of the calibration phantom described in the present invention;

Fig. 7 is the schematic diagram of interspersed all silk thread groups in the phantom;

8 is a schematic diagram of a group of N-shaped lines interspersed in the phantom;

FIG. 9 is an example of a single-frame sagittal plane calibration image collected;

Figure 10 is a flow chart of the entire calibration process.

In the figure: 1. Orthogonal biplane ultrasonic probe, 2. Magnetic field generator, 3. Magnetic navigation positioning receiver, 4. Ultrasonic scanning section, 5. Calibration phantom, 6. Container.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings. However, the accompanying drawings are provided only for a better understanding of the present invention, and they should not be construed as limiting the present invention.

Embodiment 1: Referring to Figures 1, 4, 5, 6, and 7, a biplane ultrasonic probe calibration system includes an orthogonal biplane ultrasonic probe 1, which has two ultrasonic imaging sections 4, and the two sections are orthogonal to each other ; Magnetic field generator 2, used to generate a magnetic field for electromagnetic positioning; Magnetic navigation positioning receiver 3, whose rigid body is fixed on the dual-plane ultrasonic probe, in the magnetic field generated by the magnetic field generator, can obtain its own space in real time The position and attitude parameters can be used to obtain the spatial pose parameters of the two ultrasonic sections after calibration; the magnetic navigation positioning probe, in the magnetic field generated by the magnetic field generator, can obtain the spatial position parameters of the needle tip in real time for positioning and calibration The phantom; the calibration phantom 5 is a rectangular parallelepiped; the container 6 and the fixing device are used to hold the ultrasound imaging medium.

The calibration phantom 5 is made of resin material. As shown in Figures 4, 5, 6, and 7, it is a cuboid as a whole, divided into upper and lower regions, each with a square hole, and the side walls of the hole are provided with a number of inverted triangles Through holes can be used to thread wires.

The calibration dummy 5, as shown in FIG. 7 , has holes in the upper and lower regions, and holes are punched in the side walls, and lines are inserted to form 5 groups of N-shaped lines. And for each of the five groups of N-shaped lines formed by interpenetrating nylon threads in the upper and lower regions of the phantom, the shapes and sizes are the same, and they are perpendicular to each other.

The calibration phantom 5, as shown in Figure 7, is formed by interspersed nylon threads to form 5 groups of N-shaped lines, wherein 3 groups of N-shaped lines are parallel to each other, that is, 3 groups of N-shaped lines of C, D, and E in Figure 7; the other 2 groups The direction of the hypotenuse of the N-shaped line is opposite to that of the aforementioned N-shaped line, that is, the two groups of N-shaped lines A and B in FIG. 7 . As shown in Figure 7, from the inside to the outside, there are a total of 5 groups of N-shaped wires A, B, C, D and E.

In the calibration phantom 5, the wire passing between the triangular through holes is made of nylon, and the diameter is similar to the ultrasonic length used by the ultrasonic probe.

For the container 6 and the fixing device, the height of the container is sufficient to hold the calibration dummy and the fixing device. The fixing device can fix the calibration dummy to the bottom of the container. The container can be used to hold hot water at human body temperature and submerge the calibration phantom. The four walls of the container are provided with absorbing materials to reduce ultrasonic reflection.

Embodiment 2: Referring to Figures 2, 3, 8, 9, and 10, based on the above-mentioned dual-plane ultrasonic probe calibration system, the present invention also provides a calibration method based on the dual-plane ultrasonic probe calibration system, comprising the following steps:

(1) Calibration data collection: Use the above-mentioned dual-plane ultrasonic probe calibration system to collect the original data required for calibration, as follows:

(1.1) Fix the calibration phantom vertically in the container, and immerse the phantom in clean water. Heat the water so that it reaches the human body temperature of 37°C;

(1.2) Based on the magnetic field generator, establish the coordinate system of the magnetic field generator;

(1.3) Use a needle probe to collect phantom positioning data. That is, randomly collect the coordinates of the magnetic field generator coordinate system of 30 points on the right surface, upper surface and front of the cuboid phantom;

(1.4) Fix the magnetic navigation positioning receiver in the middle of the ultrasonic probe;

(1.5) Collect cross-sectional calibration data, as shown in Figure 2 (left);

(1.5.1) Insert the ultrasonic probe vertically into the water, and immerse the first half in the water. Adjust the position of the ultrasound probe so that its cross-sectional field of view intersects with the 5 groups of N lines in the lower half of the phantom, and a total of 15 bright spots corresponding to the 5 groups of N lines can be clearly seen on the cross-sectional imaging;

(1.5.2) Collect a total of 360 images at a frequency of 0.3s per frame, and collect the pose data of the magnetic navigation positioning receiver at the same time. During this period, translate the ultrasound probe in the x, y, and N directions of the calibration phantom coordinate system, rotate the ultrasound probe with the axis of the ultrasound probe as the axis, and the imaging plane of the ultrasound probe faces the phantom, and tilt the ultrasound probe and the imaging plane of the ultrasound probe face the phantom , rotate the ultrasound probe left and right, and ensure that 15 bright spots are clearly visible;

(1.6) Collect sagittal plane calibration data, as shown in Figure 2 (right):

(1.6.1) Insert the ultrasonic probe vertically into the water, and immerse the first half in the water. Adjust the position of the ultrasound probe so that its sagittal field of view intersects with the 5 groups of N lines in the lower and upper half of the phantom, and a total of 15 bright spots corresponding to the 5 groups of N lines can be clearly seen on the cross-sectional imaging;

(1.6.2) Collect a total of 360 images at a frequency of 0.3s per frame, and collect the pose data of the magnetic navigation positioning receiver at the same time. During this period, translate the ultrasound probe in the x, y, and N directions of the calibration phantom coordinate system, rotate the ultrasound probe with the axis of the ultrasound probe as the axis, and the imaging plane of the ultrasound probe faces the phantom, and tilt the ultrasound probe and the imaging plane of the ultrasound probe face the phantom , rotate the ultrasound probe left and right, and ensure that 15 bright spots are clearly visible;

(2) Labeling of calibration data: After the collection of calibration data is completed, it is necessary to manually label the images. As shown in Figure 9, taking the cross-sectional ultrasound section calibration image as an example, the ultrasound section intersects with 5 sets of N lines to form a total of 15 bright spots from A to O, and the pixel coordinates of these 15 points in the image coordinate system are manually marked. Further, according to the 5 groups of N-line interspersed methods specified in Figure 7, for the foreground points in the sagittal plane annotation data shown in Figure 9, the points ABC are collinear, DEF collinear, GHI collinear, JKL collinear, MNO collinear Collinear, ADG collinear, BEH collinear, CFI collinear, and there are AC∥DF∥GI, and AG∥BH∥CI. When manually labeling, the interference of other noise points that do not meet the above rules can be excluded, and the foreground points can be more accurately identified according to the collinear and parallel rules;

在标定仿体形状已知的前提下，容易计算点D,H 坐标。则有

(3) Calibration data preprocessing: For the 15 points formed by the intersection of the ultrasonic section and 5 groups of N lines, calculate the 5 points formed by the intersection with the hypotenuse of each group of N lines, and the coordinates in the calibration phantom coordinate system . As shown in Figure 6, taking a group of N lines as an example, it includes three sides, AC, EG, IK, among which, points A, C, E, G, I, K are the distance between the N line and the inner wall of the calibration phantom, respectively. intersection. During the calibration image acquisition process, the ultrasonic cross-section BFJ intersects this group of N lines at three points B, F, and J. In addition, if the extension lines of sides AC and EG intersect at point D, and the extension lines of sides EG and IK intersect at point H, there are △BDF~△JHF, therefore, there are

On the premise that the shape of the calibration phantom is known, it is easy to calculate the coordinates of points D and H. then there are

(4) Iterative optimization of the least squares method, removing outliers and calculating the calibration matrix: calculating the coordinate transformation matrix from the coordinate system of the magnetic navigation receiver to the coordinate system of the ultrasound image;

(4.1) The magnetic field generator coordinate system T (transmitter) is established based on the magnetic field transmitter, and the phantom reconstruction coordinate system C (reconstruction) is established based on the calibration phantom, as shown in Figure 3, and the magnetic navigation positioning receiver is used as the benchmark. The receiver coordinate system R(receiver) is established, and the ultrasound image coordinate system I(image) is established based on the transverse and sagittal ultrasound images, then for any feature point, there is a coordinate transformation: p _c =T _ct *T _tr *T _ri * _pi ;

(4.2) Knowing the parameter information of the calibration phantom, use the coordinates of the magnetic field generator coordinate system of 30 points on the right surface, upper surface and front of the cuboid phantom that have been collected to calculate the transmitter coordinate system to the simulacrum. the transformation matrix T _ct of the volume reconstruction coordinate system (reconstruction);

(4.2.1) For 30 points on the right surface, upper surface and front of the phantom, respectively, the least squares method fits the plane equation A*x+B*y+C*N-1=0, for the three planes respectively Calculate 3 sets of plane parameters A1, B1, C1, A2, B2, C2, A3, B3, C3;

(4.2.2) Using 3 sets of plane parameters, jointly calculate the coordinates of the magnetic field generator coordinate system of the upper right corner of the front of the cuboid calibration phantom;

(4.2.3) Using 3 sets of plane parameters, calculate the coordinates of the magnetic field generator coordinate system in the positive directions of the x, y, and z axes of the cuboid calibration phantom;

(4.2.4) Using 1 point coordinate and 3 direction vectors shown in 2.2 and 2.3, a total of 4 homogeneous coordinates, the least squares method is used to calculate the coordinate system of the magnetic field generator T to the phantom reconstruction coordinate system C transformation matrix Tct;

(4.3) Screen out outliers based on the coplanarity of 5 points. For the 5 points in each of the above pictures, they should belong to the same plane. Fit a plane using 5-point coordinates:

(4.3.1) For each calibration image, the coordinates of the magnetic field generator coordinate system of the intersections of the five N-line hypotenuses calculated, and fit the plane;

(4.3.2) Calculate the distance between 5 points and the plane respectively;

(4.3.3) If the distance between any point and the plane is greater than a certain threshold, discard all the data of the frame calibration image and no longer participate in the calculation;

(4.4) Fit the transformation matrix _Tri from the image coordinate system to the sensor/receiver coordinate system using iterative least squares:

(4.4.1) For all the marked feature points in the calibration data preprocessing step, the coordinates of the magnetic field generator coordinate system _pt =inverse(T _ct )*pc are calculated from the coordinates of the _phantom reconstruction coordinate system;

(4.4.2) For each magnetic field generator coordinate system coordinate in the above steps, calculate its receiver coordinate system coordinate _{pr =inverse(T tr )} * _pt , where T _tr is the magnetic navigation positioning receiver to the transmitter The transformation matrix between them is obtained by the magnetic navigation and positioning device;

(4.4.3) Arbitrarily select a set of 6 parameters to construct the initial rigid body transformation matrix, including rotation along the x axis by γ angle, along the y axis by β angle, along the N axis by α angle, and translation (x, y, z);

(4.4.4), modify the matrix transformation parameters α, β, γ, x, y, N, and reconstruct the transformation matrix;

(4.4.5), calculation

(4.4.6), calculate the difference

(4.4.7), if the difference is smaller, keep the iterative modification of this step;

(4.4.8), repeat steps (4.4.4) to (4.4.7) until the error converges.

(4.5) Using the calibration matrix _Tri obtained in the above-mentioned 6th step, coordinate transformation is carried out on the existing key points, and the coordinates of the imitation body coordinate system are reconstructed;

(4.6) For the coordinates of the reconstructed coordinate system of the phantom obtained by calculation, the points with a large difference from the real values are screened out as outliers;

(4.7) Repeat (4.4) to (4.6) until no outliers are screened out, and obtain the calibration matrix _Tri of the transverse or sagittal plane;

(5) Average dual-plane calibration matrix: According to the prior information that the two imaging planes of the ultrasonic probe are mutually orthogonal, the calibration matrix obtained by the two probes is averaged;

其中

其物理意义分别是超声探头轴线方向、正上方、正右方在接收器坐标系下的方向向量；(5.1) For transverse and sagittal planes, the calibration matrix is in the form of a 4*4 matrix

in

Its physical meaning is the direction vector of the ultrasonic probe axis direction, directly above, and just right in the receiver coordinate system;

构造新的横断面、矢状面标定矩阵

(5.2), order

Construct new transverse and sagittal calibration matrices

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and can also be made within the scope of knowledge possessed by those of ordinary skill in the art without departing from the purpose of the present invention. Various changes.

Claims (10)

1. A biplane ultrasonic probe calibration system is characterized in that the calibration system comprises

The orthogonal biplane ultrasonic probe is provided with two ultrasonic imaging sections which are vertical to each other and can be respectively intersected with the two groups of silk thread groups of the calibration phantom;

the magnetic field generator is used for generating a magnetic field for electromagnetic positioning, is arranged on one side of the container and ensures that the magnetic field range can cover a magnetic navigation positioning receiver and a magnetic navigation positioning probe on the ultrasonic probe;

the magnetic navigation positioning receiver is fixed in the middle of the biplane ultrasonic probe through a rigid body, and can acquire self spatial position and attitude parameters in real time in a magnetic field generated by the magnetic field generator;

the magnetic navigation positioning probe can acquire the space position parameter of the needle tip in real time in a magnetic field generated by the magnetic field generator and is used for positioning and calibrating the phantom;

the calibration imitation body is a cuboid, is fixed at the bottom of the container and is immersed by the ultrasonic imaging medium in the container; the calibration imitation body is divided into an upper part and a lower part, and N-shaped wire groups are respectively inserted in the upper part and the lower part;

and the container and the fixing device are used for containing the ultrasonic imaging medium.

2. The bi-planar ultrasonic probe calibration system of claim 1, wherein the calibration phantom 5 is made of resin, and is a rectangular solid divided into an upper region and a lower region, each region has a square hole, the side wall of each hole has an inverted triangular through hole, and a nylon wire is inserted in the through holes.

3. The biplane ultrasonic probe calibration system according to claim 2, wherein holes in the upper and lower regions of the calibration phantom 5 are perforated in the side wall and inserted with lines to form 5 groups of N-shaped lines, and the 5 groups of N-shaped lines formed by respectively inserting nylon lines in the upper and lower regions of the phantom are identical in shape and size and perpendicular to each other.

4. The system for calibrating a biplane ultrasound probe according to claim 3, wherein the nylon threads are interlaced to form 5 sets of N-shaped threads, wherein 3 sets of N-shaped threads are parallel to each other, and the other 2 sets of N-shaped threads are opposite to the hypotenuse of the N-shaped threads.

5. The bi-planar ultrasound probe calibration system of claim 2, wherein the lines passing through the triangular through holes are made of nylon and have a diameter similar to the ultrasound wavelength used by the ultrasound probe.

6. A calibration method based on any biplane ultrasonic probe calibration system in claims 1-5, characterized by comprising the following steps:

step (1) calibration data acquisition: acquiring original data required by calibration by using a biplane ultrasonic probe calibration system;

marking calibration data: automatically or non-automatically, identifying and marking coordinates of a plurality of points formed by intersecting the ultrasonic cross section and the N-shaped line of the calibration phantom according to a specific geometric relationship;

step (3) calibration data preprocessing: according to the distance geometric relationship of a plurality of points formed by the intersection of the ultrasonic section and the N-shaped line of the calibration phantom, calculating a plurality of characteristic points formed by the intersection of the ultrasonic section and the bevel edge of each group of N lines and the coordinates of the characteristic points in the phantom coordinate system;

and (4) performing iterative optimization by using a least square method, removing outliers and calculating a calibration matrix: calculating a coordinate transformation matrix from a magnetic navigation receiver coordinate system to an ultrasonic image coordinate system;

step (5), averaging a biplane calibration matrix: and averaging the calibration matrixes respectively obtained by the two probes according to the prior information of the mutual orthogonality of the two imaging planes of the ultrasonic probe.

7. The calibration method based on the biplane ultrasonic probe calibration system as claimed in claim 6, wherein the specific process of the step (1) is as follows:

vertically fixing a calibration imitation in a container, and enabling an imaging medium to immerse the imitation;

step (1.2) establishing a magnetic field generator coordinate system by taking the magnetic field generator as a reference;

step (1.3) acquiring the positioning data of the imitation body by using a needle-type probe, wherein the positioning data respectively comprise coordinates of a plurality of points on the right surface, the upper surface and the front surface of the cuboid calibration imitation body;

step (1.4) ensuring that the magnetic navigation positioning receiver is fixed in the middle of the ultrasonic probe;

step (1.5) collecting cross section calibration data: intersecting the ultrasonic cross section with the N line of the lower half part of the calibration phantom; respectively adjusting 3 translational degrees of freedom and 3 rotational degrees of freedom of an ultrasonic probe and collecting a plurality of images on the premise of ensuring that the ultrasonic image is intersected with all the N-shaped lines and the intersection points are clear and visible;

step (1.6) of collecting sagittal plane calibration data: the ultrasonic sagittal plane is intersected with the N lines of the upper half part of the calibration phantom, 3 translational degrees of freedom and 3 rotational degrees of freedom of the ultrasonic probe are respectively adjusted on the premise of ensuring that the ultrasonic image is intersected with all the N lines and the intersection points are clearly visible, and a plurality of images are acquired.

8. The bi-planar ultrasound probe calibration system-based calibration method according to claim 6, wherein the specific process of step (2) is to consider that for foreground points in a single frame image, there are points ABC collinear, DEF collinear, GHI collinear, JKL collinear, MNO collinear, ADG collinear, BEH collinear, CFI collinear, and there are AC | | | DF | | | GI, and AG | | | | BH | | | CI, then eliminate the interference of other noise points that do not meet the above rules during labeling, and identify foreground points more accurately according to the collinear and parallel rules.

9. The calibration method based on the biplane ultrasonic probe calibration system as claimed in claim 6, wherein the specific process of the step (4) is as follows:

step (4.1) establishing a magnetic field generator coordinate system T (transmitter) by taking a magnetic field transmitter as a reference, establishing a simulated body reconstruction coordinate system C (recovery) by taking a calibrated simulated body as a reference, establishing a receiver coordinate system R (recovery) by taking a magnetic navigation positioning receiver as a reference, establishing an image coordinate system I (image) by taking a cross section ultrasonic image and a sagittal plane ultrasonic image as references, and carrying out coordinate transformation on any characteristic point: p is a radical of_c＝T_ct*T_tr*T_ri*p_i；

Step (4.2) knowing parameter information of the calibration phantom, and calculating a transformation matrix Tct from a transmitter (transmitter) coordinate system to a phantom reconstruction coordinate system (reconstruction) by using coordinates of the magnetic field generator of 30 points on the right surface, the upper surface and the front surface of the cuboid phantom;

step (4.3) screening outliers according to 5-point coplanarity, wherein 5 characteristic points in the calibrated picture belong to the same plane, fitting the plane by using the coordinates of the magnetic field generator coordinate system of the 5 points, and discarding the picture data of the frame if the distance between any one point and the plane is calculated to be larger than a specific threshold value;

step (4.4) using iterative least squares fitting to transform matrix Tri from image (image) coordinate system to sensor/receiver (receiver) coordinate system;

step (4.5) using the calibration matrix T _ { ri } obtained in the step 6 to perform coordinate transformation on the existing key points and reconstruct the coordinates of the simulated coordinate system of the key points;

step (4.6) for the calculated coordinates of the imitation coordinate system, points with larger difference with the true values are taken as outliers to be screened out;

step (4.7) repeating steps (4.4) - (4.6) until no outlier is screened out, and obtaining the calibration matrix T of the cross section or the sagittal plane_ri。

10. The calibration method based on the biplane ultrasonic probe calibration system as claimed in claim 6, wherein the specific process of the step (5) is as follows:

step (5.1), regarding the cross section and the sagittal plane, the calibration matrix form is 4-4 matrix

Wherein

The physical meanings of the ultrasonic probe are direction vectors of the ultrasonic probe in the axis direction, right above and right to the receiver coordinate system respectively;

step (5.2), order

Construct new cross section, sagittal plane calibration matrix

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