CN115737144A - Three-dimensional image registration and registration method - Google Patents
Three-dimensional image registration and registration method Download PDFInfo
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- CN115737144A CN115737144A CN202211396882.9A CN202211396882A CN115737144A CN 115737144 A CN115737144 A CN 115737144A CN 202211396882 A CN202211396882 A CN 202211396882A CN 115737144 A CN115737144 A CN 115737144A
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Abstract
The invention discloses a three-dimensional image registration and registration method, which comprises the following steps: acquiring the position of a mark point on a die body under a die body coordinate system; scanning by a C-arm machine to obtain a three-dimensional image of the mold body, periodically acquiring the pose of the C-arm machine in the scanning process, and constructing a coordinate system of the C-arm machine; identifying the position of a mark point in the three-dimensional image, and calculating to obtain a transformation relation between an image coordinate system and a model coordinate system according to the position; and calculating the transformation relation between the coordinate system of the C-arm machine and the coordinate system of the die body according to the positions and postures of the C-arm machine and the die body which are identified by the optical tracking system, and calculating the transformation relation between the coordinate system of the C-arm machine and the image coordinate system according to the transformation relation. The invention removes the use of positioning mark points in the operation, ensures the registration precision, simplifies the operation process and improves the operation efficiency.
Description
Technical Field
The invention relates to the technical field of image registration, in particular to a three-dimensional image registration method.
Background
In recent years, with the rapid development of medical surgical robots, orthopedic navigation technology is mature in the medical field, and image registration, one of the core technologies, plays a decisive role in navigation reliability. Through the image registration technology, a doctor can conveniently perform surgical planning on the focus of a patient on an image, and accurately find the actual focus part by combining the navigation positioning technology without performing open incision processing on the focus part, so that minimally invasive operation is realized. The essence of image registration is to establish a mapping relationship between an image coordinate system and an operation space coordinate system, thereby realizing planning on a three-dimensional image, reducing the exposure time of a patient and a doctor under X-rays and simultaneously reducing the difficulty of the traditional operation.
The image registration technology brings great convenience to the operation, but has certain limitations, for example, in the navigation and positioning process of a surgical robot, positioning mark points need to be placed in a scene, the positioning mark points are subjected to three-dimensional reconstruction by using a three-dimensional C-shaped arm, then the mark points in a three-dimensional image are identified by using an image processing algorithm, and then the image registration is realized by using the mark points. In the process, the object with the mark points is ensured to be close to the affected part, and the object cannot shake in the image scanning process, so that once the object shakes, the registration accuracy is greatly influenced; secondly, the marking point and the pathological vertebral segment of the patient are ensured to be completely in the image, and when the obese patient appears, the requirement is difficult to meet, so that the limitation of the current intraoperative registration needs to be solved by an additional registration mode.
Disclosure of Invention
The invention aims to: the invention provides a simple and efficient preoperative three-dimensional image registration and registration method, which not only realizes the registration process, but also removes the use of intraoperative marker points, simplifies the operation process and has wide application scenes in the field of operation auxiliary planning.
The technical scheme is as follows:
a three-dimensional image registration and registration method comprises the following steps:
acquiring the position of a mark point on a die body under a die body coordinate system;
scanning by a C-arm machine to obtain a three-dimensional image of the mold body, periodically acquiring the pose of the C-arm machine in the scanning process, and constructing a coordinate system of the C-arm machine;
identifying the positions of the marking points in the three-dimensional image, and calculating to obtain a transformation relation between an image coordinate system and a model coordinate system;
and calculating to obtain a transformation relation between a C-arm machine coordinate system and a model coordinate system according to the poses of the C-arm machine and the model identified by the optical tracking system, and calculating to obtain a transformation relation between the C-arm machine coordinate system and an image coordinate system.
The acquiring of the position of the mark point on the mold body under the mold body coordinate system comprises:
and acquiring the space positions of the mark points on the mold body and the tracer, and constructing a mold body coordinate system according to the coordinates of the tracer, so as to calculate the positions of the mark points under the mold body coordinate system.
The step of obtaining the transformation relation between the model coordinate system and the image coordinate system by calculation comprises the following steps:
and calculating to obtain a position transformation matrix between the three-dimensional image and the mark points in the physical space according to the positions of the mark points in the three-dimensional image and the space positions of the mark points, namely the transformation relation between the image coordinate system and the model coordinate system.
And calculating to obtain a position transformation matrix between the three-dimensional image and the mark points in the physical space by adopting a rigid body registration method.
The rigid body registration method is an SVD decomposition method or a QR decomposition method.
And measuring by a three-coordinate measuring instrument to obtain the space positions of the mark points and the tracer on the die body.
The periodically acquiring the pose of the C-arm machine in the scanning process comprises the following steps:
and acquiring the pose of a tracer on the C-arm machine through an optical tracking system while receiving exposure signals periodically sent by the C-arm machine.
And the C-arm machine sends exposure signals at the start position and the end position in the scanning process.
The C-arm machine is an isocentric C-arm machine, and the die body is located at an isocenter of the C-arm machine during scanning.
The constructing the C-arm machine coordinate system comprises:
acquiring a discrete point set of the pose of a tracer on a C-arm machine in the scanning process;
fitting all the discrete points to obtain a plane, and taking a normal vector of the plane as the z-axis direction of the coordinate system of the C-arm machine;
projecting all the discrete points onto a plane obtained by fitting, fitting the projected points to obtain a circle, and taking the center of the circle as the origin of the coordinate system of the C-arm machine;
selecting a start position and a stop position in the scanning process, respectively connecting the start position and the stop position with an original point, and taking the angular bisector direction of the two connecting lines as the x-axis direction of the coordinate system of the C-arm machine;
and performing cross multiplication on the x-axis direction and the z-axis direction to obtain a y-axis direction.
The number of the mark points is 5.
Further comprising the steps of:
scanning a focus area of a patient through a C-arm machine to obtain an intraoperative three-dimensional image; periodically acquiring the pose of the C-arm machine in the scanning process to obtain an intraoperative C-arm machine coordinate system;
and calculating the pose of the intraoperative three-dimensional image in the coordinate system of the patient tracer according to the pose of the intraoperative C-arm machine and the patient tracer identified by the optical tracking system and the transformation relation between the image coordinate system and the coordinate system of the C-arm machine.
Further comprising the steps of:
acquiring the pose of a tracer on the C-arm machine at a scanning start position, and acquiring an intraoperative C-arm machine coordinate system according to the position relation between the tracer on the C-arm machine and the C-arm machine coordinate system;
scanning a focus area of a patient through a C-arm machine to obtain an intraoperative three-dimensional image;
and identifying the obtained poses of the C-arm machine and the patient tracer according to the optical tracking system, and obtaining the pose of the intraoperative three-dimensional image in the patient tracer coordinate system according to the transformation relation between the image coordinate system and the C-arm machine coordinate system.
Has the beneficial effects that: the invention can obtain the transformation relation between the image coordinate system and the C-arm machine coordinate system only by carrying out three-dimensional image registration during preoperative calibration, and does not need to calculate again in the actual operation process. The invention removes the use of positioning mark points in the operation, ensures the registration precision, simplifies the operation process and improves the operation efficiency.
Drawings
FIG. 1 is a schematic view of a surgical robot connected to a C-arm machine;
FIG. 2 is a flow chart of a registration method of the present invention;
FIG. 3 is a schematic view of mold body installation;
FIG. 4 is a schematic illustration of an isocentric C-arm machine scan;
fig. 5 is a schematic diagram of the construction of a coordinate system of the C-arm machine.
Wherein, 1 is a die body, 2 is a C-arm machine, 3 is an industrial personal computer, and 4 is an optical tracking system (NDI); a is the start bit and B is the stop bit.
Detailed Description
The invention is further elucidated with reference to the drawings and the embodiments.
In the invention, the device for realizing the three-dimensional image registration and registration method comprises the following steps: the system comprises a die body 1, a C-arm machine 2, an industrial personal computer 3 and an optical tracking system 4, as shown in figure 1; the C-arm machine 2 is an isocentric C-arm machine so as to ensure that the isocentric C-arm machine can perform uniform scanning on a circular track.
The die body 1 is provided with a die body tracer and a plurality of marking points, and specifically, the marking points adopt 5 solid steel balls with the diameter of 4mm and are used for marking a three-dimensional image; the die body tracer comprises a plurality of tracer balls, and the tracer balls are reflective balls, can be identified and positioned by the optical tracking system 4 and are used for marking the die body 1; specifically, there are 4 tracer balls, and a sphere with a diameter of 16mm is used. The mark point and the die body tracer are fixed on the die body 1, and a rigid body is arranged between the mark point and the die body tracer.
Since the C-arm machine 2 needs to be regularly maintained and accurately calibrated, the image accuracy of the C-arm machine needs to be calibrated by a calibration tool, so that the image accuracy of the C-arm machine 2 is always in an optimal operating state. In this embodiment, the mold body is a calibration fixture of a C-arm machine, and the mark points and the mold body tracer are fixed on the calibration fixture.
In another embodiment, the phantom may also be a patient, and the marker points and phantom tracer are secured to the patient by an registration plate.
The device also comprises an equipment tracer, which is consistent with the die body tracer and is used for being arranged on the C-arm machine 2. The three-dimensional image registration and registration method of the invention is shown in fig. 2, and comprises the following steps:
(1) Respectively acquiring the space coordinates of the mark points on the die body and the die body tracer, and specifically, the method comprises the following steps:
measuring the mark point and the die body tracer by a three-coordinate measuring instrument to respectively obtain the space coordinates of each tracer ball of the mark point and the die body tracer; and then, a new coordinate system is constructed by using the space coordinates of each tracer ball to serve as a model coordinate system, so that the coordinates of each mark point under the model coordinate system can be obtained through conversion.
(2) Installing the equipment tracer on the C arm machine, placing the die body at the isocenter point of the C arm machine, and scanning three-dimensional images of the die body, wherein the method specifically comprises the following steps:
the equipment tracer is arranged on the C-arm machine 2 to form a rigid body, so that the stability and the non-shaking are ensured in the operation process of the C-arm machine 2, and specifically, the equipment tracer can be arranged on a position, close to a flat panel detector, on a C-shaped arm of the C-arm machine 2;
placing the mold body 1 at the isocenter of the C-shaped arm, as shown in fig. 3, finding the isocenter of the C-shaped arm through laser alignment of the C-shaped arm;
as shown in fig. 4, a three-dimensional image is scanned while the device tracer and phantom tracer are tracked using the optical tracking system 4.
(3) In the scanning process, the pose of the tracer of the equipment on the C-arm machine is periodically acquired, and a coordinate system of the C-arm machine is established according to the pose; the method comprises the following specific steps:
in the scanning process, the C-arm machine 2 sends exposure signals to the industrial personal computer 3 at certain intervals, the exposure signals are also sent at the start position A and the end position B, and the pose information of the equipment tracer is acquired through the optical tracking system while each exposure signal is received, so that a series of discrete points of the pose of the equipment tracer can be obtained, as shown in FIG. 5; specifically, a set of poses P of all discrete points i ＝{p 1 ,p 2 ,…,p i I is the number of discrete points acquired, p i Representing the pose of the device tracer at the ith point; wherein i is more than or equal to 3, and i is 8 in the embodiment of the invention, so that the influence of the abnormal point on the fitting plane is reduced, and the fitting precision is ensured.
The method comprises the following steps of constructing and obtaining a C-arm machine coordinate system according to pose information of an equipment tracer, specifically:
according to a least square method, fitting all discrete points to obtain a plane, wherein a normal vector of the plane is used as the z-axis direction of a C-arm machine coordinate system;
projecting all discrete points onto a plane obtained by fitting, fitting the projected points to obtain a circle according to a least square method, and taking the center of the circle as the origin O of the coordinate system of the C-arm machine;
selecting a start position and a stop position in the scanning process, respectively connecting the start position and the stop position with an original point, and taking the angular bisector direction of the two connecting lines as the x-axis direction of the coordinate system of the C-arm machine;
and performing cross multiplication on the x-axis direction and the z-axis direction to obtain a y-axis direction, as shown in fig. 5, and thus, completing the construction of the coordinate system of the C-arm machine.
(4) Extracting mark points in the three-dimensional image, and calculating according to the space coordinates of each mark point obtained in the step (1) in a model coordinate system to obtain a transformation relation from an image coordinate system to the model coordinate system; the method comprises the following specific steps:
processing the point cloud data of the three-dimensional image to obtain the position of each marking point in the three-dimensional image, thereby obtaining the coordinate of each marking point in an image coordinate system;
calculating a position transformation matrix between each mark point in the three-dimensional image and the mark point in the physical space by adopting a rigid body registration method according to the coordinates of each mark point in the model coordinate system obtained in the step (1), wherein the position transformation matrix is also a transformation matrix between the image coordinate system and the model coordinate system; among them, the rigid body registration method generally adopts methods such as SVD decomposition and QR decomposition.
(5) Calculating a transformation relation between an image coordinate system and a C-arm machine coordinate system to complete preoperative registration;
obtaining the position and orientation information of the mold body tracer and the equipment tracer by the optical tracking system, taking the coordinate system of the optical tracking system as a reference coordinate system, and calculating according to the established mold body coordinate system and the C-arm machine coordinate system to obtain a transformation matrix T from the mold body coordinate system and the C-arm machine coordinate system to the coordinate system of the optical tracking system respectively 1 、T 2 (ii) a Therefore, a transformation matrix T from the model coordinate system to the C-arm machine coordinate system can be calculated 3 ：
According to the transformation matrix T from the image coordinate system to the model coordinate system calculated in the step (4) 4 And calculating to obtain a transformation matrix T from the image coordinate system to the C-arm machine coordinate system:
T＝T 3 *T 4
in actual operation, the method also comprises the following steps:
scanning a focus area of a patient through a C-arm machine to obtain an intraoperative three-dimensional image; the pose of the C-arm machine is periodically obtained in the scanning process, and an intraoperative C-arm machine coordinate system is obtained in the manner; specifically, the pose of a tracer on the C-arm machine is obtained through an optical tracking system while exposure signals periodically sent by the C-arm machine are received; in another embodiment, the pose of the tracer on the C-arm machine at the scanning start position can be obtained, and the coordinate system of the C-arm machine in the operation can be obtained according to the pose of the tracer on the C-arm machine under the coordinate system of the C-arm machine constructed before the operation;
and calculating the pose of the intraoperative three-dimensional image in the coordinate system of the patient tracer according to the poses of the C-arm machine and the patient tracer identified by the optical tracking system and the transformation relation between the obtained image coordinate system and the coordinate system of the C-arm machine.
The three-dimensional image can be transformed to a coordinate system of the C-arm machine according to the transformation matrix T, because the C-arm machine and the reconstructed image area are rigid bodies, the T is a fixed value and is calculated only once when the C-arm machine calibrates or scans a first patient, and subsequently, in the actual operation process, the pose of the three-dimensional image can be calculated according to the pose of the C-arm machine without recalculation, so that the use of positioning mark points in the operation is eliminated, the operation flow is simplified, and the operation efficiency is improved.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the foregoing embodiments, and various equivalent changes (such as number, shape, position, etc.) may be made to the technical solution of the present invention within the technical spirit of the present invention, and these equivalent changes are all within the protection scope of the present invention.
Claims (13)
1. A three-dimensional image registration and registration method is characterized in that: the method comprises the following steps:
acquiring the position of a mark point on a die body under a die body coordinate system;
scanning by a C-arm machine to obtain a three-dimensional image of the mold body, periodically acquiring the pose of the C-arm machine in the scanning process, and constructing a coordinate system of the C-arm machine;
identifying the positions of the marking points in the three-dimensional image, and calculating to obtain a transformation relation between an image coordinate system and a model coordinate system;
and calculating to obtain a transformation relation between a C-arm machine coordinate system and a model coordinate system according to the poses of the C-arm machine and the model identified by the optical tracking system, and further calculating to obtain a transformation relation between the C-arm machine coordinate system and an image coordinate system.
2. The three-dimensional image registration and registration method according to claim 1, wherein: the step of acquiring the position of the mark point on the die body under the die body coordinate system comprises the following steps:
and acquiring the space positions of the mark points on the mold body and the tracer, and constructing a mold body coordinate system according to the coordinates of the tracer, thereby calculating to obtain the positions of the mark points under the mold body coordinate system.
3. The method for registering and registering three-dimensional images according to claim 2, wherein: the calculation of the transformation relation between the model coordinate system and the image coordinate system comprises the following steps:
and calculating to obtain a position transformation matrix between the three-dimensional image and the mark points in the physical space according to the positions of the mark points in the three-dimensional image and the space positions of the mark points, namely the transformation relation between the image coordinate system and the model coordinate system.
4. The three-dimensional image registration and registration method according to claim 3, wherein: and calculating to obtain a position transformation matrix between the three-dimensional image and the mark points in the physical space by adopting a rigid body registration method.
5. The three-dimensional image registration and registration method according to claim 4, wherein: the rigid body registration method is an SVD decomposition method or a QR decomposition method.
6. The three-dimensional image registration and registration method according to claim 2, wherein: and measuring by a three-coordinate measuring instrument to obtain the space positions of the mark points and the tracer on the die body.
7. The three-dimensional image registration and registration method according to claim 1, wherein: the periodically acquiring the pose of the C-arm machine in the scanning process comprises the following steps:
and acquiring the pose of a tracer on the C-arm machine through an optical tracking system while receiving exposure signals periodically sent by the C-arm machine.
8. The three-dimensional image registration and registration method according to claim 7, wherein: and the C-arm machine sends exposure signals at the start position and the end position in the scanning process.
9. The three-dimensional image registration and registration method according to claim 1, wherein: the C-arm machine is an isocentric C-arm machine, and the die body is located at an isocentric point of the C-arm machine during scanning.
10. The method for registering and registering three-dimensional images according to claim 9, wherein: the constructing the C-arm machine coordinate system comprises:
acquiring a discrete point set of the pose of a tracer on a C-arm machine in the scanning process;
fitting all the discrete points to obtain a plane, and taking a normal vector of the plane as the z-axis direction of the coordinate system of the C-arm machine;
projecting all the discrete points onto a plane obtained by fitting, fitting the projected points to obtain a circle, and taking the center of the circle as the origin of the coordinate system of the C-arm machine;
selecting a start position and a stop position in the scanning process, respectively connecting the start position and the stop position with an original point, and taking the angular bisector direction of the two connecting lines as the x-axis direction of the coordinate system of the C-arm machine;
and performing cross multiplication on the x-axis direction and the z-axis direction to obtain a y-axis direction.
11. The method for registering and registering three-dimensional images according to claim 1, wherein: the number of the mark points is 5.
12. The three-dimensional image registration and registration method according to claim 1, wherein: further comprising the steps of:
scanning a focus area of a patient through a C-arm machine to obtain an intraoperative three-dimensional image; periodically acquiring the pose of the C-arm machine in the scanning process to obtain an intraoperative C-arm machine coordinate system;
and calculating the pose of the intraoperative three-dimensional image in the coordinate system of the patient tracer according to the pose of the intraoperative C-arm machine and the patient tracer identified by the optical tracking system and the transformation relation between the image coordinate system and the coordinate system of the C-arm machine.
13. The three-dimensional image registration and registration method according to claim 1, wherein: further comprising the steps of:
acquiring the pose of a tracer on the C-arm machine at a scanning start position, and obtaining an intraoperative C-arm machine coordinate system according to the position relation between the tracer on the C-arm machine and the C-arm machine coordinate system;
scanning a focus area of a patient through a C-arm machine to obtain an intraoperative three-dimensional image;
and identifying the obtained poses of the C-arm machine and the patient tracer according to the optical tracking system, and obtaining the pose of the intraoperative three-dimensional image in the patient tracer coordinate system according to the transformation relation between the image coordinate system and the C-arm machine coordinate system.
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