A method and system for registering pre-operative CT images with intra-operative ultrasound images

Abstract

The application discloses a preoperative CT image and intraoperative ultrasound image registration method and system, comprising S1. generating a three-dimensional model of a CT image, acquiring corresponding point coordinates of a surgical site marker point in a CT image coordinate system and a world coordinate system respectively, registering the preoperative CT image coordinate system and the world coordinate system, and acquiring a space conversion matrix between the CT image coordinate system and the world coordinate system; S2. obtaining a conversion matrix from an ultrasound image coordinate system to an ultrasound probe coordinate system through an N-shaped calibration model; S3. collecting an intraoperative ultrasound image and an ultrasound probe pose, measuring a conversion matrix between the ultrasound probe coordinate system and the world coordinate system through electromagnetic positioning technology, and registering the preoperative CT image and the intraoperative ultrasound image according to the conversion matrix of the ultrasound image coordinate system and the ultrasound probe coordinate system, the conversion matrix of the ultrasound probe coordinate system and the world coordinate system, and the conversion matrix of the world coordinate system and the CT image coordinate system, to obtain a slice of the CT image corresponding to the ultrasound image.

Description

Technical Field

[0001] This invention relates to the field of assistive medical technology, and more specifically to a method and system for registering preoperative CT images with intraoperative ultrasound images. Background Technology

[0002] Currently, medical image navigation has been widely used in various minimally invasive surgeries. The mainstream intraoperative real-time image navigation methods are mainly divided into X-ray-based navigation and ultrasound-based navigation. In order to reduce X-rays during surgery, ultrasound has obvious advantages over CT and X-ray: First, ultrasound detection is low-cost and does not cause radiation damage, so doctors and patients can avoid direct contact with radiation equipment; second, ultrasound equipment is developing towards miniaturization and portability, saving a lot of surgical space, which makes medical surgery more flexible in various situations.

[0003] However, ultrasound images have relatively poor image quality and cannot accurately provide intraoperative navigation information. At the same time, in surgery, doctors need to perform CT scans on patients before surgery to understand the condition of the surgical site, so as to diagnose the patient and determine the surgical plan. However, during surgery, doctors need to rely on experience to judge the correspondence between the lesion and the CT image, which will put some pressure on the doctors.

[0004] In addition, the current volume navigation system of General Electric in the United States can use the "point-to-surface" method to register CT and ultrasound images. The process is to use an ultrasound probe to scan in the same direction as the CT scan, calculate the CT slice number corresponding to the ultrasound image, and then match it after the doctor selects a matching point. However, it is very difficult to keep the ultrasound slice in the same direction as the CT cross section, and manually selecting the matching point is troublesome and requires a high level of skill from the doctor, which limits the clinical application of this method.

[0005] Therefore, how to provide a method and system for registering preoperative CT images with intraoperative ultrasound images is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method and system for registering preoperative CT images and intraoperative ultrasound images to solve the problems mentioned in the background art, so as to provide high-precision automatic registration of preoperative CT and intraoperative ultrasound images.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for registering preoperative CT images with intraoperative ultrasound images includes the following steps:

[0009] S1. Generate a 3D model from the CT image, obtain the corresponding coordinates of the surgical site markers in the CT image coordinate system and the world coordinate system, register the preoperative CT image coordinate system and the world coordinate system, and obtain the spatial transformation matrix between the CT image coordinate system and the world coordinate system.

[0010] S2. Perform preoperative ultrasound probe calibration: Obtain the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system through the N-shaped calibration model;

[0011] S3. Acquire intraoperative ultrasound images and ultrasound probe pose. Measure the transformation matrix between the ultrasound probe coordinate system and the world coordinate system in real time using electromagnetic positioning technology. Based on the transformation matrices between the ultrasound image coordinate system and the ultrasound probe coordinate system, between the ultrasound probe coordinate system and the world coordinate system, and between the world coordinate system and the CT image coordinate system, register the preoperative CT images with the intraoperative ultrasound images to obtain slices of the CT images corresponding to the ultrasound images.

[0012] Preferably, before S1, the procedure also includes marking the patient's surgical site and performing a CT scan on the patient's surgical site to obtain CT images.

[0013] Preferably, the specific content of S1 includes:

[0014] S11. Separate the marker points from the CT image using threshold segmentation, and calculate the marker point coordinates P in the CT image coordinate system based on the positions of the segmented marker points. (CT) ,

[0015] S12. Obtain the coordinates P of the surgical site marker in the world coordinate system. (W) ,

[0016] S13. Calculate the transformation matrix between the CT image coordinate system and the world coordinate system. W T CT :

[0017] The ICP iterative nearest point algorithm is used to match the coordinates of the marker points in the CT image coordinate system with their coordinates in the world coordinate system, resulting in the following correspondence:

[0018]

[0019] The objective function to be optimized is:

[0020]

[0021] Solve the rotation matrix using the SVD decomposition method. W R CT Translation vector Wt CT Calculate the spatial transformation matrix between the CT image coordinate system and the world coordinate system. W T CT for:

[0022]

[0023] Preferably, the specific content of the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system obtained through the N-shaped calibration model in S2 includes:

[0024] Obtain the coordinates of four points A, B, C, and D in the world coordinate system of the N-type model. By combining the proportional relationship between the distances between the three intersection points E, F, and G of the ultrasound image and the N-type model image, and using the principle of similar triangles, the coordinates of points E, F, and G in the world coordinate system can be determined. Then there is

[0025] P i (W) = W T S S T US P i (US)

[0026] W T S This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system, measured using electromagnetic positioning technology.

[0027] The objective function to be optimized is:

[0028]

[0029] The rotation matrix can be obtained using the SVD decomposition method. S R US Translation vector S t US Then, the spatial transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system is calculated. S T US ,in:

[0030]

[0031] Preferably, the registration of preoperative CT images and intraoperative ultrasound images in S3 is specifically performed as follows:

[0032] p (CT) = CT T US P (US) = CT T WW T S S T US P (US)

[0033] Where, p (CT) Points in a CT image CT T W This is the transformation matrix between the world coordinate system and the CT image spatial coordinate system. W T S This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system. S T US p is the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system. (CT) Points in an ultrasound image.

[0034] Preferably, the method for registering preoperative CT and intraoperative ultrasound images further includes S4 tracking and locating the surgical site, responding to changes in the movement of the surgical site, acquiring the pose of the surgical site before and after movement, updating the transformation matrix between the world coordinate system and the CT image spatial coordinate system, and registering the preoperative CT image and the intraoperative ultrasound image.

[0035] Preferably, after the surgical site markers have moved, the transformation matrix between the world coordinate system and the CT image space coordinate system is:

[0036] CT T W ′= CT T W ·T change

[0037] Among them, T change The transformation matrix for the pose of the surgical site before and after movement:

[0038] T change =T0T1 -1

[0039] T1 = T change T0

[0040] Where T0 is the initial pose and T1 is the pose after the movement;

[0041] The registration of preoperative CT images with intraoperative ultrasound images is specifically performed as follows:

[0042] p (CT) = CT T W T change W T S S T US P (US)

[0043] Where, p (CT) Points in a CT image CT T W T is the transformation matrix between the world coordinate system and the CT image space coordinate system. change This is the transformation matrix of the surgical site pose before and after movement. W T S This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system. S T US P is the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system. (CT) Points in an ultrasound image.

[0044] A registration system for preoperative CT images and intraoperative ultrasound images includes an electromagnetic tracker, a graphics workstation electrically connected to the electromagnetic tracker, a 5-DOF electromagnetic positioning probe connected to the electromagnetic tracker, a marker fixed to the patient's surgical site, an ultrasound probe, an ultrasound graphics workstation connected to both the ultrasound probe and the graphics workstation, and a first 6-DOF electromagnetic positioning sensor fixed to the ultrasound probe and connected to the electromagnetic tracker.

[0045] A 5-DOF electromagnetic positioning probe is used to obtain the coordinates of the corresponding points of the surgical site markers in the world coordinate system and transmit them to the graphics workstation.

[0046] The electromagnetic tracker is used to acquire the coordinates of the corresponding points of the surgical site markers in the CT image coordinate system and transmit them to the graphics workstation.

[0047] The graphics workstation is used to generate 3D models from CT images. Based on the corresponding coordinates of the surgical site markers in the CT image coordinate system and the world coordinate system, it registers the preoperative CT image coordinate system with the world coordinate system and obtains the spatial transformation matrix between the CT image coordinate system and the world coordinate system. It is also used for preoperative ultrasound probe calibration. Through an N-shaped calibration model, it obtains the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system, obtains the measured transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and combines it with the spatial transformation matrix between the CT image coordinate system and the world coordinate system. It receives intraoperative ultrasound images and ultrasound probe pose and registers the preoperative CT images with the intraoperative ultrasound images.

[0048] An ultrasound probe is used to acquire intraoperative ultrasound images, which are then transmitted to a graphics workstation via an ultrasound graphics workstation.

[0049] The first 6-DOF electromagnetic positioning sensor is used to acquire the pose of the ultrasound probe in the world coordinate system, acquire the pose of the ultrasound probe during surgery, measure the transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and transmit it to the graphics workstation.

[0050] Preferably, the registration system for preoperative CT images and intraoperative ultrasound images further includes a CT scanner, which is used to mark the surgical site of the patient, perform a CT scan on the surgical site to obtain CT images, and transmit them to a graphics workstation.

[0051] Preferably, the registration system for preoperative CT images and intraoperative ultrasound images further includes a second 6-DOF electromagnetic positioning sensor, which is fixed to the patient's surgical site and connected to an electromagnetic tracker.

[0052] The second 6-DOF electromagnetic positioning sensor is used to track and locate the surgical site, respond to changes in the movement of the surgical site, collect the pose of the surgical site before and after movement, and transmit it to the graphics workstation.

[0053] The graphics workstation is also used to update the transformation matrix between the world coordinate system and the CT image spatial coordinate system based on the surgical site pose before and after movement, and to match the preoperative CT images with the intraoperative ultrasound images.

[0054] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method and system for registering preoperative CT images and intraoperative ultrasound images. By determining the transformation relationship between the ultrasound image coordinate system and the CT image coordinate system, the corresponding CT two-dimensional slice image can be directly obtained. This allows doctors to observe the tissue structure of the surgical site in greater detail during surgery without manually searching for CT slices, thereby improving the automation level of the surgery. The accurate position of the CT slice can be calculated, improving the automation level and registration accuracy of the registration process, facilitating its application in surgery, and contributing to improving the quality of medical images in the field of medical image navigation, thereby reducing the surgical burden on doctors. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0056] Figure 1 The attached figure is a schematic diagram of the registration method between preoperative CT images and intraoperative ultrasound images provided by the present invention;

[0057] Figure 2 The attached figure is a schematic diagram of the structure provided by the present invention for registering the preoperative CT image coordinate system with the world coordinate system;

[0058] Figure 3The attached figure is a schematic diagram of the system structure for registering preoperative CT images and intraoperative ultrasound images provided by the present invention;

[0059] Figure 4 The attached figure is a schematic diagram of the N-shaped calibration model provided in an embodiment of the present invention;

[0060] Among them, 1-electromagnetic tracker, 2-graphics workstation, 3-5-DOF electromagnetic positioning probe, 4-surgical site marker, 5-ultrasound probe, 6-first 6-DOF electromagnetic positioning sensor, 7-ultrasound graphics workstation, 8-second 6-DOF electromagnetic positioning sensor. Detailed Implementation

[0061] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] This invention discloses a method for registering preoperative CT images with intraoperative ultrasound images, such as... Figure 1 This includes the following steps:

[0063] S1. Generate a 3D model from the CT image, obtain the corresponding coordinates of the surgical site markers in the CT image coordinate system and the world coordinate system, register the preoperative CT image coordinate system and the world coordinate system, and obtain the spatial transformation matrix between the CT image coordinate system and the world coordinate system.

[0064] S2. Perform preoperative ultrasound probe calibration: Obtain the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system through the N-shaped calibration model;

[0065] S3. Acquire intraoperative ultrasound images and ultrasound probe pose. Measure the transformation matrix between the ultrasound probe coordinate system and the world coordinate system in real time using electromagnetic positioning technology. Based on the transformation matrices between the ultrasound image coordinate system and the ultrasound probe coordinate system, between the ultrasound probe coordinate system and the world coordinate system, and between the world coordinate system and the CT image coordinate system, register the preoperative CT images with the intraoperative ultrasound images to obtain slices of the CT images corresponding to the ultrasound images.

[0066] In this embodiment, the electromagnetic positioning system Aurora of NDI establishes a transformation relationship between the CT image coordinate system and the world coordinate system, and regards the coordinate system of the electromagnetic positioning system as the world coordinate system, so that a transformation bridge can be established between the CT image coordinate system and the real physical space through the electromagnetic positioning sensor.

[0067] To further implement the above technical solution, S1 also includes marking the patient's surgical site before the operation and performing a CT scan on the patient's surgical site to obtain CT images.

[0068] In practical applications, the marking method adopts the method of posting manual markers before surgery. The spacing between the posted manual markers should be sufficient to prevent multiple or incorrect solutions when matching marker points later.

[0069] To further implement the above technical solution, the specific content of S1 includes:

[0070] S11. Due to the significant difference between the material of the marker points and the composition of human tissue, the marker points are separated from the CT image using threshold segmentation. The coordinates P of the marker points in the CT image coordinate system are then calculated based on the positions of the separated marker points. (CT) ,

[0071] S12. Obtain the coordinates P of the surgical site marker in the world coordinate system. (W) ,

[0072] In this embodiment, by pointing the tip of the 5-DOF electromagnetic positioning probe at the marked point on the patient's surgical site, the coordinates P of the marked point in the world coordinate system can be obtained. (W) .

[0073] S13. Calculate the transformation matrix between the CT image coordinate system and the world coordinate system. W T CT :

[0074] The ICP iterative nearest point algorithm is used to match the coordinates of the marker points in the CT image coordinate system with their coordinates in the world coordinate system, resulting in the following correspondence:

[0075]

[0076] The objective function to be optimized is:

[0077]

[0078] Solve the rotation matrix using the SVD decomposition method. W R CT Translation vector W t CT Calculate the spatial transformation matrix between the CT image coordinate system and the world coordinate system. W T CT for:

[0079]

[0080] To further implement the above technical solution, the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system is obtained through measurement output, and the transformation matrix from the ultrasonic image coordinate system to the ultrasonic probe coordinate system is obtained through the N-shaped calibration model.

[0081] In this embodiment, the purpose of ultrasound probe calibration is to solve the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system. S T US In the actual calibration process, the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system can be obtained from the electromagnetic positioning system. W T S The N-shaped model used for calibration is fixed in the water tank. In practical applications, the N-shaped model is composed of bent nylon ropes. After fixing, fixed model geometry is established. The two base edges of the N-shaped model are parallel, and the oblique line forms a fixed angle with the two parallel base edges. At this time, the N-shaped model is imaged above the water tank. The imaging process is as follows: Figure 4 As shown in (a), the imaging process can be understood as the ultrasound imaging plane forming three intersection points E, F, and G with the three sides of the N-shaped model. Figure 4 As shown in (b), a 5-DOF positioning probe can be used to obtain... Figure 4 (b) Coordinates of points A, B, C, and D in the world coordinate system By utilizing the proportional relationship between points E, F, and G, and applying the principle of similar triangles, the coordinates of points E, F, and G in the world coordinate system can be determined.

[0082] Then we have:

[0083] P i (W) = W T S S T US P i (US)

[0084] W T S This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system, measured using electromagnetic positioning technology.

[0085] The objective function to be optimized is:

[0086]

[0087] The rotation matrix can be obtained using the SVD decomposition method. S R US Translation vector s t US Then, the spatial transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system is calculated.s T US ,in:

[0088]

[0089] Since the first 6-DOF electromagnetic positioning sensor (6) is fixed on the ultrasonic probe (5), after one calibration, as long as the position of the first 6-DOF electromagnetic positioning sensor (6) relative to the ultrasonic probe (5) remains unchanged in subsequent use, there is no need to perform calibration again.

[0090] To further implement the above technical solution, the registration of preoperative CT images and intraoperative ultrasound images in S3 is specifically performed as follows:

[0091] p (CT) = CT T US P (US) = CT T W W T S S T US P (US)

[0092] Where, p (CT) Points in a CT image CT T W This is the transformation matrix between the world coordinate system and the CT image spatial coordinate system. W T S This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system. S T US p is the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system. (CT) Points in an ultrasound image.

[0093] During surgery, the patient's surgical site may move, thus altering the transformation matrix between the world coordinate system and the CT image space coordinate system. CT T W Things have changed.

[0094] To further implement the above technical solution, a registration method for preoperative CT and intraoperative ultrasound images also includes S4 tracking and locating the surgical site, responding to changes in the movement of the surgical site, acquiring the pose of the surgical site before and after movement, updating the transformation matrix between the world coordinate system and the CT image spatial coordinate system, and registering the preoperative CT image and the intraoperative ultrasound image.

[0095] To further implement the above technical solution, after the surgical site markers are moved, the transformation matrix between the world coordinate system and the CT image space coordinate system is as follows:

[0096] CT T W ′= CT T W ·T change

[0097] Among them, T change The transformation matrix for the pose of the surgical site before and after movement:

[0098] T change =T0T1 -1

[0099] T1 = T change T0

[0100] Where T0 is the initial pose and T1 is the pose after the movement;

[0101] The registration of preoperative CT images with intraoperative ultrasound images is specifically performed as follows:

[0102] p (CT) = CT T W T change W T S ST US P (US)

[0103] Where, p (CT) Points in a CT image CT T W T is the transformation matrix between the world coordinate system and the CT image space coordinate system. change This is the transformation matrix of the surgical site pose before and after movement. W T S This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system. S T US p is the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system. (CT) Points in an ultrasound image.

[0104] A registration system for preoperative CT images and intraoperative ultrasound images, such as Figure 2 and Figure 3 It includes an electromagnetic tracker 1, a graphics workstation 2 electrically connected to the electromagnetic tracker 1, a 5-DOF electromagnetic positioning probe 3 connected to the electromagnetic tracker, a marker 4 fixed to the surgical site of the patient, an ultrasound probe 5, an ultrasound graphics workstation 7 connected to both the ultrasound probe 5 and the graphics workstation 3, and a first 6-DOF electromagnetic positioning sensor 8 fixed to the ultrasound probe 5 and connected to the electromagnetic tracker 1.

[0105] The 5-DOF electromagnetic positioning probe 3 is used to obtain the coordinates of the corresponding point of the surgical site marker 4 in the world coordinate system and transmit them to the graphics workstation 2.

[0106] Electromagnetic tracker 1 is used to acquire the coordinates of the corresponding point of surgical site marker 4 in the CT image coordinate system and transmit it to graphics workstation 2;

[0107] The graphics workstation is used to generate 3D models from CT images. Based on the coordinates of the corresponding point 4 of the surgical site marker in the CT image coordinate system and the world coordinate system, it registers the preoperative CT image coordinate system with the world coordinate system and obtains the spatial transformation matrix between the CT image coordinate system and the world coordinate system. It is also used for preoperative ultrasound probe calibration. Through the N-shaped calibration model, it obtains the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system, obtains the measured transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and combines it with the spatial transformation matrix between the CT image coordinate system and the world coordinate system. It receives intraoperative ultrasound images and ultrasound probe pose and registers the preoperative CT images with the intraoperative ultrasound images.

[0108] Ultrasonic probe 5 is used to acquire intraoperative ultrasound images, which are then transmitted to graphics workstation 2 via ultrasound graphics workstation 7.

[0109] The first 6-DOF electromagnetic positioning sensor 6 is used to acquire the pose of the ultrasound probe 5 in the world coordinate system, acquire the pose of the ultrasound probe during the operation, measure and obtain the transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and transmit it to the graphics workstation.

[0110] To further implement the above technical solution, a registration system for preoperative CT images and intraoperative ultrasound images also includes a CT scanner, which is used to mark the surgical site of the patient, perform a CT scan on the surgical site to obtain CT images, and transmit them to a graphics workstation 2.

[0111] To further implement the above technical solution, a registration system for preoperative CT images and intraoperative ultrasound images also includes a second 6-degree-of-freedom electromagnetic positioning sensor 8, which is fixed at the patient's surgical site and connected to the electromagnetic tracker 1.

[0112] The second 6-DOF electromagnetic positioning sensor 8 is used to track and locate the surgical site, respond to changes in the movement of the surgical site, collect the pose of the surgical site before and after movement, and transmit it to the graphics workstation 2.

[0113] The graphics workstation 2 is also used to update the transformation matrix between the world coordinate system and the CT image spatial coordinate system based on the pose of the surgical site before and after movement, and to match the preoperative CT image with the intraoperative ultrasound image.

[0114] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0115] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for registering preoperative CT images with intraoperative ultrasound images, characterized in that, Includes the following steps: S1. Generate a 3D model from the CT image, obtain the corresponding coordinates of the surgical site markers in the CT image coordinate system and the world coordinate system, register the preoperative CT image coordinate system and the world coordinate system, and obtain the spatial transformation matrix between the CT image coordinate system and the world coordinate system. S2. Perform preoperative ultrasound probe calibration: Obtain the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system through the N-shaped calibration model; S3. Acquire intraoperative ultrasound images and ultrasound probe pose. Measure the transformation matrix between the ultrasound probe coordinate system and the world coordinate system in real time using electromagnetic positioning technology. Based on the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system, the transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and the transformation matrix between the world coordinate system and the CT image coordinate system, register the preoperative CT images with the intraoperative ultrasound images to obtain slices of the CT images corresponding to the ultrasound images. It also includes S4 tracking and locating the surgical site, responding to changes in the movement of the surgical site, collecting the pose of the surgical site before and after movement, updating the transformation matrix between the world coordinate system and the CT image spatial coordinate system, and registering the preoperative CT image with the intraoperative ultrasound image. After the surgical site markers have moved, the transformation matrix between the world coordinate system and the CT image space coordinate system is: ； in, The transformation matrix for the pose of the surgical site before and after movement: ； ； in, This is the initial pose. The pose after the movement; The registration of preoperative CT images with intraoperative ultrasound images is specifically performed as follows: ； in, Points in a CT image This is the transformation matrix between the world coordinate system and the CT image spatial coordinate system. This is the transformation matrix of the surgical site pose before and after movement. This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system. This is the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system. Points in an ultrasound image.

2. The registration method for preoperative CT images and intraoperative ultrasound images according to claim 1, characterized in that, S1 also includes marking the patient's surgical site before surgery and performing a CT scan of the surgical site to obtain CT images.

3. The registration method for preoperative CT images and intraoperative ultrasound images according to claim 1, characterized in that, The specific content of S1 includes: S11. Separate the marker points from the CT image using thresholding, and calculate the marker point coordinates in the CT image coordinate system based on the positions of the separated marker points. , ; S12. Obtain the coordinates of the surgical site marker in the world coordinate system. , ; S13. Calculate the transformation matrix between the CT image coordinate system and the world coordinate system. : The ICP iterative nearest point algorithm is used to match the coordinates of the marker points in the CT image coordinate system with their coordinates in the world coordinate system, resulting in the following correspondence: ； The objective function to be optimized is: ； Solve the rotation matrix using the SVD decomposition method. Translation vector Calculate the spatial transformation matrix between the CT image coordinate system and the world coordinate system. for: 。 4. The registration method for preoperative CT images and intraoperative ultrasound images according to claim 1, characterized in that, The specific contents of the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system obtained through the N-shaped calibration model in S2 include: Obtain the coordinates of four points A, B, C, and D in the world coordinate system of the N-type model. , , , By combining the proportional relationship between the distances between the three intersection points E, F, and G of the ultrasound image and the N-type model imaging, and using the principle of similar triangles, the coordinates of points E, F, and G in the world coordinate system can be determined. , , Then there is ； This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system, measured using electromagnetic positioning technology. The objective function to be optimized is: ； The rotation matrix can be obtained using the SVD decomposition method. Translation vector Then, the spatial transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system is calculated. ,in: 。 5. The method for registering preoperative CT images and intraoperative ultrasound images according to claim 1, characterized in that, The registration of preoperative CT images and intraoperative ultrasound images in S3 is specifically performed as follows: ； in, Points in a CT image This is the transformation matrix between the world coordinate system and the CT image spatial coordinate system. This is the transformation matrix between the ultrasonic probe coordinate system and the world coordinate system. This is the transformation matrix between the ultrasound image coordinate system and the ultrasound probe coordinate system. Points in an ultrasound image.

6. A registration system for preoperative CT images and intraoperative ultrasound images, based on the registration method for preoperative CT images and intraoperative ultrasound images according to any one of claims 1-5, characterized in that, It includes an electromagnetic tracker, a graphics workstation electrically connected to the electromagnetic tracker, a 5-DOF electromagnetic positioning probe connected to the electromagnetic tracker, a marker fixed to the patient's surgical site, an ultrasound probe, an ultrasound graphics workstation connected to both the ultrasound probe and the graphics workstation, and a first 6-DOF electromagnetic positioning sensor fixed to the ultrasound probe and connected to the electromagnetic tracker. A 5-DOF electromagnetic positioning probe is used to obtain the coordinates of the corresponding points of the surgical site markers in the world coordinate system and transmit them to the graphics workstation. The electromagnetic tracker is used to acquire the coordinates of the corresponding points of the surgical site markers in the CT image coordinate system and transmit them to the graphics workstation. The graphics workstation is used to generate 3D models from CT images. Based on the corresponding coordinates of the surgical site markers in the CT image coordinate system and the world coordinate system, it registers the preoperative CT image coordinate system with the world coordinate system and obtains the spatial transformation matrix between the CT image coordinate system and the world coordinate system. It is also used for preoperative ultrasound probe calibration. Through an N-shaped calibration model, it obtains the transformation matrix from the ultrasound image coordinate system to the ultrasound probe coordinate system, obtains the measured transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and combines it with the spatial transformation matrix between the CT image coordinate system and the world coordinate system. It receives intraoperative ultrasound images and ultrasound probe pose and registers the preoperative CT images with the intraoperative ultrasound images. An ultrasound probe is used to acquire intraoperative ultrasound images, which are then transmitted to a graphics workstation via an ultrasound graphics workstation. The first 6-DOF electromagnetic positioning sensor is used to acquire the pose of the ultrasound probe in the world coordinate system, acquire the pose of the ultrasound probe during surgery, measure and obtain the transformation matrix between the ultrasound probe coordinate system and the world coordinate system, and transmit it to the graphics workstation. It also includes a second 6-DOF electromagnetic positioning sensor, which is fixed to the patient's surgical site and connected to the electromagnetic tracker. The second 6-DOF electromagnetic positioning sensor is used to track and locate the surgical site, respond to changes in the movement of the surgical site, collect the pose of the surgical site before and after movement, and transmit it to the graphics workstation. The graphics workstation is also used to update the transformation matrix between the world coordinate system and the CT image spatial coordinate system based on the surgical site pose before and after movement, and to register the preoperative CT images with the intraoperative ultrasound images.

7. The registration system for preoperative CT images and intraoperative ultrasound images according to claim 6, characterized in that, It also includes a CT scanner, which is used to mark the surgical site of the patient, perform a CT scan on the surgical site to obtain CT images, and transmit them to a graphics workstation.

Images