Positioning method of sacrum nerve-free channel based on CPD point cloud registration technology

Abstract

The invention relates to the technical field of positioning, and provides a sacrum nerve-free channel positioning method based on a CPD point cloud registration technology, and the method comprises the following steps: 1, data acquisition; step 2, three-dimensional image point cloud processing; step 3, marking the position of a first sacral foramen; 4, point cloud registration is carried out; and step 5, calculating the nerve-free channel. The method has the advantages that the three-dimensional CT image can be processed, the processed three-dimensional model can be completely matched with the sacrum model of the human body, the nerve-free channel can be comprehensively determined from the coronal position, the sagittal position and the transection position, and compared with an X-ray image, the method is more accurate, and the accuracy of the nerve-free channel is improved. And the condition of the channel can be visually seen from the three-dimensional model.

Description

Technical Field

[0001] The present invention relates to the technical field of positioning, and specifically relates to a positioning method for the sacral non-neural channel based on the CPD point cloud registration technology. Background Art

[0002] When performing sacral-related surgeries or operations, accurately positioning the non-neural channel of the sacrum is crucial, which can effectively avoid nerve damage. The nerve structures in the sacral region are complex, such as the sacral plexus nerve and sacral nerve roots, etc., which are densely distributed. Once damaged, it may cause serious functional disorders.

[0003] Specifically, in the current sacral nerve modulation (SNM), it is necessary to puncture and locate the S3 sacral foramen of the sacrum. The main technique is the cross positioning method under X-ray fluoroscopy, that is, under the anteroposterior fluoroscopy of the X-ray image, determine and mark the midline of the sacrum, determine the sacroiliac joint, then make a connection line at the lower ends of the bilateral sacroiliac joints, and then calculate that the positions about 2 cm to the left and right of the intersection point of the connection line and the midline are the positions of the S3 sacral nerve foramina.

[0004] The main disadvantages of this method for locating the sacral foramen include three aspects. First, this method can only be applied to 2D X-ray images, but it cannot be applied to CT data. Second, in this method, the position of the sacral nerve foramen is located at the positions about 2 cm to the left and right of the intersection point of the connection line and the midline. The sacrum of different people varies greatly, and the 2 cm position cannot be applied to all people, so the generalization of this method is poor. Third, this method can only locate the position of the third sacral foramen. When it is necessary to locate above the first sacral foramen and the upper edge position of the sacrum, this method will not work.

[0005] The application number 201710520171.0 provides an S3 sacral nerve cross positioning device and a positioning method, which effectively use the manual touch method or X-ray equipment to determine the lower edge of the sacroiliac joint and the position of the sacrum, and locate the position of the S3 sacral nerve foramen. However, this application is still limited to the positioning method for the position of the third sacral foramen, and it is impossible to locate the non-neural channels above the first sacral foramen and the upper edge position of the sacrum through this method. Summary of the Invention

[0006] Aiming at the problem that the current sacral non-neural channel can only rely on manual calculation based on experience and has a relatively low accuracy.

[0007] The present invention provides a positioning method for the sacral non-neural channel based on the CPD point cloud registration technology, including the following steps: Step 1, data acquisition: Obtain the CT three-dimensional scan image of the sacrum; Step 2, three-dimensional image point cloud processing: Process the obtained CT image into point cloud data through the CPD point cloud registration technology, and map the pixel positions of the CT image into three-dimensional coordinates; Step 3, Marking the position of the first sacral foramen: Mark the first sacral foramen of the sacrum, denoted as hole_target; Step 4, Point cloud registration: Take the sacral point cloud data with the marked sacral foramen as the registration target, denoted as target, and take the sacral point cloud data without the marked sacral foramen as the source. Use the CPD point cloud registration algorithm for point cloud registration to obtain the mapping relationship between the configured source and target, denoted as f(°). Then input the marked data of the first sacral foramen into the mapping relationship f(°) to get hole_source = f(hole_target). Then the coordinates of hole_source are the position of the first sacral foramen of the unmarked sacrum; Step 5, Calculating the nerve-free channel: Solve for the maximum value of the z-axis coordinate of the first sacral foramen, that is, max(hole_source(z)). After obtaining the upper edge coordinates of the first sacral foramen, make cross-sections along the z-axis and y-axis respectively based on the upper edge of the first sacral foramen; then make cross-sections along the z-axis and y-axis based on the tangent line of the minimum value of the y-axis of the sacrum; then make cross-sections along the z-axis respectively based on the leftmost tangent line and the rightmost tangent line of the sacrum. The cross-rectangular area composed of the six cross-sections is the nerve-free area of the sacrum; then calculate the center point coordinates of the leftmost cross-section and the rightmost cross-section in this rectangular area respectively, and connect a straight line through the center points of the two cross-sections. This straight line is the nerve-free channel of the sacrum.

[0008] As a preferred solution, the mapping method is as follows: 1) Calculate the total number of slices in the CT image, denoted as z_max. Calculate the horizontal axis (width) of each slice in the CT image as w_max and the vertical axis (length) as h_max; 2) Convert the pixel positions of each slice in the CT to the coordinates in three-dimensional space. Denote the original pixel point coordinates as p_o=(x_i,y_j,z_k), where z_k represents the k-th slice. The conversion formula is: x_new = x_i-(1+w_max) / 2; y_new = y_j-(1+h_max) / 2; z_new = z_k-(1+z_max) / 2; The converted coordinates p_new=(x_new,y_new,z_new) are the three-dimensional coordinates of each image in the original CT image; 3) Create a three-dimensional matrix point=(w_max,h_max,z_max), assign the points with p_new coordinates to 1, and assign other points to 0, then obtain the discretized point cloud coordinates, that is, the point cloud data of the sacrum.

[0009] As a preferred solution, the three-dimensional matrix point=(w_max, h_max, z_max) is established in the Python programming language environment.

[0010] As a preferred solution, in step 1, the data acquisition uses Python to read a three-dimensional sacral model, and the core command for reading the three-dimensional sacrum is ds = pydicom.dcmread("digu.dcm").

[0011] The beneficial effects of the present invention are as follows: 1. The present invention can process three-dimensional CT images, and the processed three-dimensional model can be completely matched with the human sacral model. The nerve-free channel can be comprehensively determined from three dimensions: the coronal plane, the sagittal plane, and the transverse plane. Compared with X-ray images, this method is more accurate, and the situation of the channel can be intuitively seen from the three-dimensional model.

[0012] 2. The first sacral foramen positioning method based on the point cloud registration technology proposed by the present invention has higher robustness and generalization. Compared with the method of positioning the S3 sacral foramen in X-ray images, it does not require rigid settings such as a fixed width of 2 cm. There are significant differences in the shapes and sizes of the sacra of different individuals, and the rigid distance setting cannot be applied to all sacral models. This method can position the first sacral foramen for any sacral model. Specific implementation mode

[0013] To illustrate the characteristics of the present invention, the present invention will be further described below in conjunction with embodiments.

[0014] Embodiment 1: This embodiment provides a method for automatically calculating the sacral surgical screw channel based on the CPD point cloud registration technology to locate the nerve-free channel of the sacrum; Step 1, data acquisition: Obtain the CT three-dimensional scan image of the sacrum, and use Python to read the three-dimensional sacral model. First, install pydicom (pip install pydicom). The core command for Python to read the three-dimensional sacrum is ds = pydicom.dcmread("digu.dcm"). The Python function for reading the model is as follows: import pydicom import os def read_dicom_series(dicom_dir): series = [] for dcm_file in os.listdir(dicom_dir): if dcm_file.endswith('.dcm'): file_path = os.path.join(dicom_dir, dcm_file) dcm = pydicom.dcmread(file_path) series.append(dcm) return series; Step 2, 3D image point cloud processing: Process the acquired CT images into point cloud data through CPD point cloud registration technology. In the read CT images, each image is a slice in the 3D data. Map the pixel positions of the CT images to 3D coordinates. The mapping method in this embodiment is (taking two points as an example): 1) 50 slices of the CT image are denoted as z_max = 50. The horizontal axis (width) of each slice in the CT image is w_max = 20, and the vertical axis (length) is h_max = 20; 2) Convert the pixel positions of each slice in the CT to 3D space coordinates. The coordinates of a point on the upper edge of the left hole in the first sacral foramen are p1 = (5, 4, 30), and the coordinates of a point on the upper edge of the right hole are p2 = (15, 4, 30). The conversion formula is (rounding down the decimal part): x1_new = 5 - (1 + 20) / 2 = -5 y1_new = 4 - (1 + 20) / 2 = -6 z1_new = 20 - (1 + 50) / 2 = 4 x2_new = 15 - (1 + 20) / 2 = 4 y2_new = 4 - (1 + 20) / 2 = -6 z2_new = 30 - (1 + 50) / 2 = 4 The converted coordinates p_new = (x_new, y_new, z_new) are the 3D coordinates of each image in the original CT image (the center point of the 3D model is the origin). That is, the p1 coordinates will become p1' = (-5, -6, 4), and p2 will become p2' = (4, -6, 4); 3) In the python programming language environment, create a 3D matrix point = (w_max, h_max, z_max), assign the points with p_new coordinates to 1, and assign other points to 0, then the discretized point cloud coordinates are obtained; 4) Save the 3D matrix in the.stl format, then the point cloud data of the sacrum is obtained.

[0015] In this embodiment, the required Python toolkits are pydicom, numpy, and tqdm, and the installation methods are (pip install pydicom, numpy, tqdm) respectively; Step 3, Marking the position of the first sacral foramen: Use cloudcompareV to mark the first sacral foramen of the sacrum, denoted as hole_target; Step 4, Point cloud registration: Use the sacral point cloud data with the marked sacral foramen as the registration target, denoted as target, and use the sacral point cloud data without the marked sacral foramen as the source. Use the CPD point cloud registration algorithm to perform point cloud registration to obtain the mapping relationship between the configured source and target, denoted as f(°). Then, input the marked first sacral foramen data into the mapping relationship f(°) to obtain hole_source = f(hole_target). The coordinates of hole_source are the position of the first sacral foramen of the unmarked sacrum; Step 5, Calculate the nerve-free channel: Solve the maximum value of the z-axis coordinate of the first sacral foramen, that is, max(hole_source(z)). After obtaining the upper edge coordinates of the first sacral foramen, make sections along the z-axis and y-axis respectively based on the upper edge of the first sacral foramen; then make sections along the z-axis and y-axis based on the tangent line of the minimum value of the y-axis of the sacrum; then make sections along the z-axis based on the leftmost tangent line and the rightmost tangent line of the sacrum respectively. Making a section along the z-axis means extending the line connecting the upper edge point p1' of the left foramen in the first sacral foramen and the upper edge p2' of the right foramen in the first sacral foramen along the z-axis. Extend one step, and the z-axis coordinate will increase by 1, that is, the coordinates of p1' will become (-5, -6, 5), and similarly, the coordinates of p2' will become p2'=(4, -6, 5). Making a section along the y-axis means extending the line connecting p1' and p2' along the y-axis. Extend one step, and the y-axis coordinate will decrease by 1, that is, the coordinates of p1' will become (-5, -7, 4), and similarly, the coordinates of p2' will become p2'=(4, -7, 4); Similarly, make sections along the z-axis and y-axis based on the tangent line of the minimum value of the y-axis of the sacrum; then make sections along the z-axis based on the leftmost tangent line and the rightmost tangent line of the sacrum respectively.

[0016] The cross-rectangular area composed of the six sections is the nerve-free area of the sacrum; then calculate the center point coordinates of the leftmost section and the rightmost section in this rectangular area respectively, and connect a straight line through the center points of the two sections. This straight line is the nerve-free channel of the sacrum.

[0017] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. The present invention has been described in detail with reference to the preferred embodiments. Those of ordinary skill in the art should understand that any changes, modifications, additions or substitutions made by those of ordinary skill in the art within the scope of the essence of the present invention do not depart from the purpose of the present invention and should also fall within the scope of protection of the claims of the present invention. Other related technical structures not exhaustively disclosed in the present invention are the prior art in the art.

Claims

1. A method for locating sacral nerve-free channels based on CPD point cloud registration technology, characterized in that: The following steps are involved: Step 1, data acquisition: obtaining a CT three-dimensional scanning image of the sacrum; Step 2, 3D image point cloud processing: The acquired CT image is processed into point cloud data through CPD point cloud registration technology, and the pixel position of the CT image is mapped to 3D coordinates; Step 3, marking the position of the first sacral foramen: marking the first sacral foramen of the sacrum, recorded as hole_target; Step 4, point cloud registration: the sacral point cloud data with marked sacral foramen is used as the registration target, denoted as target, and the sacral point cloud data without marked sacral foramen is used as source. The CPD point cloud registration algorithm is used for point cloud registration to obtain the mapping relationship between the configured source and target, denoted as f(°). Then the data of the first marked sacral foramen is input into the mapping relationship f(°) to obtain hole_source = f(hole_target). The coordinates of hole_source are the position of the first sacral foramen of the unmarked sacrum. Step 5, calculate the nerve-free channel: solve the maximum value of the z-axis coordinate of the first sacral foramen, that is, max(hole_source(z)). After obtaining the coordinates of the upper edge of the first sacral foramen, make sections along the z-axis and y-axis according to the upper edge of the first sacral foramen; then make sections along the z-axis and y-axis according to the tangent of the sacrum with the minimum y-axis value; then make sections along the z-axis according to the leftmost tangent and the rightmost tangent of the sacrum. The crossed rectangular area composed of the six sections is the nerve-free area of ​​the sacrum; then calculate the coordinates of the center points of the leftmost section and the rightmost section in the rectangular area, and connect the center points of the two sections with a straight line. The straight line is the nerve-free channel of the sacrum.

2. The method for locating a sacral nerve-free channel based on CPD point cloud registration technology according to claim 1, characterized in that: The mapping method is: 1) Calculate the total number of slices in the CT image and record it as z_max. Calculate the horizontal axis (width) of each slice in the CT image as w_max and the vertical axis (length) as h_max. 2) Convert the pixel position of each slice in CT into coordinates in three-dimensional space. The original pixel coordinates are recorded as p_o=(x_i, y_j, z_k), where z_k represents the kth slice. The conversion formula is: x_new = x_i-(1+w_max) / 2 y_new = y_j-(1+h_max) / 2 z_new = z_k-(1+z_max) / 2 The converted coordinates p_new = (x_new, y_new, z_new) are the three-dimensional coordinates of each image in the original CT image; 3) Create a new three-dimensional matrix point=(w_max,h_max,z_max), assign the point of p_new coordinates to 1 and the other points to 0, then you will get the discretized point cloud coordinates, that is, the point cloud data of the sacrum.

3. The method for locating a sacral nerve-free channel based on CPD point cloud registration technology according to claim 2, characterized in that: The three-dimensional matrix point=(w_max, h_max, z_max) is established in the python programming language environment.

4. The method for locating a sacral nerve-free channel based on CPD point cloud registration technology according to claim 1, characterized in that: The data acquisition described in step 1 uses Python to read the three-dimensional sacrum model. The core command for reading the three-dimensional sacrum is ds = pydicom.dcmread("digu.dcm").