A three-dimensional image registration method

Abstract

The application discloses a three-dimensional image registration method, comprising the steps of: obtaining the position of a mark point on a phantom in a phantom coordinate system; obtaining a three-dimensional image of the phantom through a C-arm scanner, periodically obtaining the pose of the C-arm in the scanning process, and constructing a C-arm coordinate system; identifying the position of the mark point in the three-dimensional image, and calculating the transformation relationship between the image coordinate system and the phantom coordinate system; calculating the transformation relationship between the C-arm coordinate system and the phantom coordinate system according to the pose of the C-arm and the phantom identified by an optical tracking system, and calculating the transformation relationship between the C-arm coordinate system and the image coordinate system. In the application, the use of intraoperative positioning mark points is removed, the registration accuracy is ensured, the surgical process is simplified, and the surgical efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of image registration technology, and in particular to a three-dimensional image registration and registration method. Background Technology

[0002] In recent years, with the rapid development of medical surgical robots, orthopedic navigation technology has become increasingly mature in the medical field. Image registration, one of its core technologies, plays a decisive role in the reliability of navigation. Through image registration technology, doctors can easily plan surgical procedures for patient lesions on images. Combined with navigation and positioning technology, they can accurately locate the actual lesion site without the need for open incisions, achieving minimally invasive surgery. The essence of image registration is to establish a mapping relationship between the image coordinate system and the surgical space coordinate system, thereby enabling planning on three-dimensional images. This reduces the exposure time of patients and doctors under X-rays and also reduces the difficulty of traditional surgery.

[0003] Image registration technology has brought great convenience to surgery, but it also has certain limitations. For example, in the navigation and positioning process of surgical robots, positioning markers need to be placed in the scene. A 3D C-arm is used to reconstruct the positioning markers in 3D, and then image processing algorithms are used to identify the markers in the 3D image. The markers are then used to achieve image registration. This process requires that the object with the markers be close to the affected area and that it not move during the image scanning process. Any movement will greatly affect the registration accuracy. Secondly, it is necessary to ensure that both the markers and the patient's lesion vertebra are completely in the image. When obese patients are present, it is difficult to meet the requirements. Therefore, alternative registration methods are needed to overcome the current limitations of intraoperative registration. Summary of the Invention

[0004] Purpose of the invention: This invention provides a simple and efficient method for preoperative three-dimensional image registration and alignment, which not only realizes the alignment process but also eliminates the use of intraoperative markers, simplifying the surgical procedure and having a wide range of applications in the field of surgical planning.

[0005] Technical solution:

[0006] A three-dimensional image registration and alignment method includes the following steps:

[0007] Obtain the position of the marked point on the model in the model coordinate system;

[0008] The three-dimensional image of the phantom is obtained by scanning with a C-arm, and the pose of the C-arm is periodically acquired during the scanning process to construct the C-arm coordinate system.

[0009] Identify the positions of marker points in a 3D image and calculate the transformation relationship between the image coordinate system and the phantom coordinate system;

[0010] Based on the poses of the C-arm and the phantom identified by the optical tracking system, the transformation relationship between the C-arm coordinate system and the phantom coordinate system is calculated, and the transformation relationship between the C-arm coordinate system and the image coordinate system is also calculated.

[0011] The step of obtaining the position of the marked point on the phantom in the phantom coordinate system includes:

[0012] Obtain the spatial positions of the marker points on the phantom and the tracer, construct the phantom coordinate system based on the coordinates of the tracer, and then calculate the position of the marker points in the phantom coordinate system.

[0013] The transformation relationship between the phantom coordinate system and the image coordinate system obtained by the calculation includes:

[0014] Based on the position of the marker points in the 3D image and their spatial position, the position transformation matrix between the 3D image and the marker points in physical space is calculated, which is the transformation relationship between the image coordinate system and the phantom coordinate system.

[0015] The position transformation matrix between the 3D image and the marker points in physical space is calculated using the rigid body registration method.

[0016] The rigid body registration method is either the SVD decomposition method or the QR decomposition method.

[0017] The spatial positions of the marker points and tracers on the phantom were obtained by measuring with a coordinate measuring machine.

[0018] The periodic acquisition of the C-arm pose during the scanning process includes:

[0019] While receiving the exposure signals periodically sent by the C-arm boom, the position and pose of the tracer on the C-arm boom are obtained through the optical tracking system.

[0020] The C-arm machine sends exposure signals at both the start and end positions during the scanning process.

[0021] The C-arm scanner is an isocentric C-arm scanner, and the phantom is located at the isocentric point of the C-arm scanner during scanning.

[0022] The construction of the C-arm coordinate system includes:

[0023] Acquire the discrete point set of the pose of the tracer on the C-arm during the scanning process;

[0024] A plane is obtained by fitting all discrete points, and the normal vector of the plane is used as the z-axis direction of the C-arm coordinate system;

[0025] Project all discrete points onto the fitted plane, and fit a circle with the projected points, using the center of the circle as the origin of the C-arm coordinate system.

[0026] Select the start and end positions during the scanning process, and connect them to the origin respectively. Use the angle bisector of the two lines as the x-axis direction of the C-arm coordinate system.

[0027] The y-axis is obtained by cross-product of the x-axis and z-axis directions.

[0028] There are 5 marker points.

[0029] It also includes the following steps:

[0030] The patient's lesion area is scanned by a C-arm scanner to obtain intraoperative three-dimensional images; the pose of the C-arm scanner is periodically acquired during the scanning process to obtain the intraoperative C-arm scanner coordinate system;

[0031] Based on the poses of the intraoperative C-arm machine and patient tracker identified by the optical tracking system, and the transformation relationship between the image coordinate system and the C-arm machine coordinate system, the pose of the intraoperative three-dimensional image in the patient tracker coordinate system is calculated.

[0032] It also includes the following steps:

[0033] Obtain the pose of the C-arm tracker at the scanning start position, and obtain the intraoperative C-arm coordinate system based on the positional relationship between the C-arm tracker and the C-arm coordinate system.

[0034] The patient's lesion area was scanned using a C-arm scanner to obtain intraoperative three-dimensional images;

[0035] Based on the poses of the C-arm machine and the patient tracker identified by the optical tracking system, and the transformation relationship between the image coordinate system and the C-arm machine coordinate system, the pose of the intraoperative three-dimensional image in the patient tracker coordinate system is obtained.

[0036] Beneficial effects: This invention only requires 3D image registration during preoperative calibration to obtain the transformation relationship between the image coordinate system and the C-arm coordinate system, eliminating the need for recalculation during the actual surgical procedure. The elimination of intraoperative positioning markers in this invention ensures registration accuracy while simplifying the surgical process and improving efficiency. Attached Figure Description

[0037] Figure 1 A schematic diagram showing the connection between the surgical robot and the C-arm machine;

[0038] Figure 2 This is a flowchart of the registration method of the present invention;

[0039] Figure 3 This is a schematic diagram of the mold assembly.

[0040] Figure 4 A schematic diagram of isocentric C-arm scanning;

[0041] Figure 5 This is a schematic diagram of the construction of the coordinate system for a C-arm crane.

[0042] Wherein, 1 is the model body, 2 is the C-arm machine, 3 is the industrial control computer, and 4 is the optical tracking system (NDI); A is the starting position and B is the ending position. Detailed Implementation

[0043] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0044] In this invention, the apparatus for implementing the three-dimensional image registration and alignment method includes: a phantom 1, a C-arm 2, an industrial control computer 3, and an optical tracking system 4, such as... Figure 1 As shown; among them, C-arm 2 is an isocentric C-arm to ensure that it can perform uniform scanning of circular trajectories.

[0045] The phantom 1 is equipped with a phantom tracer and several marker points. Specifically, the marker points are five solid steel balls with a diameter of 4mm, used for marking the 3D image. The phantom tracer includes several tracer balls, which are reflective spheres that can be identified and positioned by the optical tracking system 4 for marking the phantom 1. Specifically, there are four tracer balls, each with a diameter of 16mm. Both the marker points and the phantom tracer are fixed to the phantom 1, and the area between the marker points and the phantom tracer is also a rigid body.

[0046] Since the C-arm boom 2 requires regular maintenance and accuracy calibration, its image accuracy needs to be calibrated using a calibration fixture to ensure that the image accuracy of the C-arm boom 2 is always in optimal operating condition. In this embodiment, the phantom is the calibration fixture for the C-arm boom, and the marker points and phantom tracer are fixed on this calibration fixture.

[0047] In another embodiment, the phantom can also be a patient, with markers and a phantom tracer attached to the patient via a registration plate.

[0048] The device also includes a device tracer, identical to the phantom tracer described above, for mounting on the C-arm 2. The three-dimensional image registration and registration method of the present invention is as follows: Figure 2 As shown, it includes the following steps:

[0049] (1) Obtain the spatial coordinates of the marker points on the phantom and the spatial coordinates of the phantom tracer, as follows:

[0050] The spatial coordinates of the marker points and phantom tracers are obtained by measuring the marker points and each tracer ball of the phantom tracer using a coordinate measuring machine. Then, a new coordinate system is constructed using the spatial coordinates of each tracer ball as the phantom coordinate system. Thus, the coordinates of each marker point in the phantom coordinate system can be obtained through transformation.

[0051] (2) Install the equipment tracer onto the C-arm crane, place the phantom at the isocenter point of the C-arm crane, and perform a three-dimensional image scan on it, as follows:

[0052] The equipment tracer is installed on the C-arm machine 2, making the two a rigid body to ensure stability and no shaking during the operation of the C-arm machine 2. Specifically, the equipment tracer can be installed on the C-arm of the C-arm machine 2 near the flat panel detector.

[0053] Place the model 1 at the center point of the C-arm, such as... Figure 3 As shown, the isocenter point of the C-arm can be found through laser alignment of the C-arm;

[0054] like Figure 4 As shown, a three-dimensional image of the device is scanned, and the device tracer and phantom tracer are tracked by an optical tracking system 4.

[0055] (3) During the scanning process, the pose of the tracer on the C-arm is periodically acquired, and the C-arm coordinate system is established accordingly; as follows:

[0056] During the scanning process, the C-arm 2 sends exposure signals to the industrial control computer 3 at regular frame intervals. Exposure signals are also sent at the start position A and end position B. Simultaneously with receiving each exposure signal, the optical tracking system acquires the pose information of the device tracker, thus obtaining a series of discrete points representing the device tracker's pose, such as... Figure 5 As shown; specifically, the pose set P of all discrete points. i ={p1,p2,…,p i}, where i is the number of discrete points to be obtained, p i The pose of the device tracer at point i is represented; where i ≥ 3, and in this embodiment of the invention, i is taken as 8 to reduce the influence of outliers on the fitting plane and ensure fitting accuracy.

[0057] The C-arm coordinate system is constructed based on the pose information from the device tracer, specifically as follows:

[0058] According to the least squares method, a plane is obtained by fitting all discrete points, and the normal vector of the plane is used as the z-axis direction of the C-arm coordinate system.

[0059] Project all discrete points onto the fitted plane, and use the least squares method to fit a circle with the projected points, and use the center of the circle as the origin O of the C-arm coordinate system.

[0060] Select the start and end positions during the scanning process, and connect them to the origin respectively. Use the angle bisector of the two lines as the x-axis direction of the C-arm coordinate system.

[0061] The y-axis is obtained by cross-product of the x-axis and z-axis directions, such as... Figure 5 As shown, the coordinate system of the C-arm crane is now complete.

[0062] (4) Extract the marker points from the 3D image, and calculate the transformation relationship between the image coordinate system and the phantom coordinate system based on the spatial coordinates of each marker point obtained in step (1) in the phantom coordinate system; specifically:

[0063] The point cloud data of the 3D image is processed to obtain the position of each marker point in the 3D image, and thus obtain the coordinates of each marker point in the image coordinate system;

[0064] Based on the coordinates of each marker point in the phantom coordinate system obtained in step (1), the position transformation matrix between each marker point in the three-dimensional image and the marker point in the physical space is calculated using the rigid body registration method. This position transformation matrix is ​​also the transformation matrix between the image coordinate system and the phantom coordinate system. Among them, the rigid body registration method usually adopts methods such as SVD decomposition and QR decomposition.

[0065] (5) Calculate the transformation relationship between the image coordinate system and the C-arm coordinate system to complete the preoperative registration;

[0066] Using the pose information of the phantom tracer and the device tracer obtained through the optical tracking system, and taking the optical tracking system coordinate system as the reference coordinate system, the transformation matrices T1 and T2 from the phantom coordinate system and the C-arm coordinate system to the optical tracking system coordinate system are calculated based on the previously established phantom coordinate system and C-arm coordinate system. Therefore, the transformation matrix T3 from the phantom coordinate system to the C-arm coordinate system can be calculated.

[0067]

[0068] Based on the transformation matrix T4 from the image coordinate system to the phantom coordinate system obtained in step (4), the transformation matrix T from the image coordinate system to the C-arm coordinate system is calculated:

[0069] T = T3 * T4

[0070] The subsequent steps in the actual surgery also include:

[0071] The patient's lesion area is scanned by a C-arm scanner to obtain intraoperative three-dimensional images. During the scanning process, the pose of the C-arm scanner is periodically acquired, and the intraoperative C-arm scanner coordinate system is obtained as described above. Specifically, while receiving the exposure signals periodically sent by the C-arm scanner, the pose of the tracer on the C-arm scanner is acquired through an optical tracking system. In another embodiment, only the pose of the tracer on the C-arm scanner at the start of the scan can be acquired, and the intraoperative C-arm scanner coordinate system can be obtained based on the pose of the tracer on the C-arm scanner in the preoperative C-arm scanner coordinate system.

[0072] Based on the poses of the C-arm machine and the patient tracker identified by the optical tracking system, and the transformation relationship between the aforementioned image coordinate system and the C-arm machine coordinate system, the pose of the intraoperative three-dimensional image in the patient tracker coordinate system is calculated.

[0073] The transformation matrix T can be used to transform the 3D image into the C-arm coordinate system. Since the C-arm and the reconstructed image area are rigid bodies, T is a constant value that only needs to be calculated once when calibrating the C-arm or scanning the first patient. In subsequent actual surgeries, it is not necessary to recalculate the image. The pose of the 3D image can be calculated based on the pose of the C-arm. Therefore, the use of intraoperative positioning markers is eliminated, the surgical procedure is simplified, and the efficiency of the surgery is improved.

[0074] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations (such as quantity, shape, position, etc.) can be made to the technical solution of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A three-dimensional image registration and alignment method, characterized in that: Including the following steps: Obtain the position of the marked point on the model in the model coordinate system; The phantom is placed at the isocenter point of the C-arm machine, and a three-dimensional image of the phantom is obtained by scanning with the C-arm machine. While receiving the exposure signals periodically sent by the C-arm machine, the pose of the tracer on the C-arm machine is obtained through the optical tracking system. Acquire the discrete point set of the pose of the tracer on the C-arm during the scanning process; A plane is obtained by fitting all discrete points, and the normal vector of the plane is used as the z-axis direction of the C-arm coordinate system; Project all discrete points onto the fitted plane, and fit a circle with the projected points, using the center of the circle as the origin of the C-arm coordinate system. Select the start and end positions during the scanning process, and connect them to the origin respectively. Use the angle bisector of the two lines as the x-axis direction of the C-arm coordinate system. The cross product of the x-axis and z-axis directions is used to obtain the y-axis direction, thereby constructing the C-arm coordinate system; Identify the positions of marker points in a 3D image and calculate the transformation relationship between the image coordinate system and the phantom coordinate system; Based on the poses of the C-arm and the phantom identified by the optical tracking system, the transformation relationship between the C-arm coordinate system and the phantom coordinate system is calculated, and then the transformation relationship between the C-arm coordinate system and the image coordinate system is calculated.

2. The three-dimensional image registration and alignment method according to claim 1, characterized in that: The step of obtaining the position of the marked point on the phantom in the phantom coordinate system includes: The spatial positions of the marker points and the tracer on the phantom are obtained. A phantom coordinate system is constructed based on the coordinates of the tracer, thereby calculating the position of the marker points in the phantom coordinate system.

3. The three-dimensional image registration and alignment method according to claim 2, characterized in that: The transformation relationship between the phantom coordinate system and the image coordinate system obtained by the calculation includes: Based on the position of the marker points in the 3D image and their spatial position, the position transformation matrix between the 3D image and the marker points in physical space is calculated, which is the transformation relationship between the image coordinate system and the phantom coordinate system.

4. The three-dimensional image registration and alignment method according to claim 3, characterized in that: The position transformation matrix between the 3D image and the marker points in physical space is calculated using the rigid body registration method.

5. The three-dimensional image registration and alignment method according to claim 4, characterized in that: The rigid body registration method is as follows: SVD Decomposition method or QR Decomposition method.

6. The three-dimensional image registration and alignment method according to claim 2, characterized in that: The spatial positions of the marker points and tracers on the phantom were obtained by measuring with a coordinate measuring machine.

7. The three-dimensional image registration and alignment method according to claim 1, characterized in that: The C-arm machine sends exposure signals at both the start and end positions during the scanning process.

8. The three-dimensional image registration and alignment method according to claim 1, characterized in that: There are 5 marker points.

9. The three-dimensional image registration and alignment method according to claim 1, characterized in that: It also includes the following steps: The patient's lesion area is scanned by a C-arm scanner to obtain intraoperative three-dimensional images; the pose of the C-arm scanner is periodically acquired during the scanning process to obtain the intraoperative C-arm scanner coordinate system; Based on the poses of the intraoperative C-arm machine and patient tracker identified by the optical tracking system, and the transformation relationship between the image coordinate system and the C-arm machine coordinate system, the pose of the intraoperative three-dimensional image in the patient tracker coordinate system is calculated.

10. The three-dimensional image registration and alignment method according to claim 1, characterized in that: It also includes the following steps: Obtain the pose of the C-arm tracker at the scanning start position, and obtain the intraoperative C-arm coordinate system based on the positional relationship between the C-arm tracker and the C-arm coordinate system. The patient's lesion area was scanned using a C-arm scanner to obtain intraoperative three-dimensional images; Based on the poses of the C-arm machine and the patient tracker identified by the optical tracking system, and the transformation relationship between the image coordinate system and the C-arm machine coordinate system, the pose of the intraoperative three-dimensional image in the patient tracker coordinate system is obtained.

Images