JPH0721355A - Intra-picture position transformation method - Google Patents

Abstract

PURPOSE:To provide an intra-picture position transformation method capable of providing the degree of freedom in the arrangement of index points by specifying a transformation formula for transforming the position of the optional point of a reference coordinate system to the corresponding position of a picture coordinate system. CONSTITUTION:Pictures 2 are photographed from multiple directions by a picture photographing device 1 so as to pick up four index points (markers) stuck on the optional positions of the head of a testee. Then, the positions of the markers pick up in the picture 2 stored in a memory 7 in the intrinsic picture coordinate system provided in the picture photographing device 1 for gathering data are specified. Successively, the positions of the markers in the reference coordinate system inside a real space are specified. Then, the transformation formula for transforming the optional position in the reference coordinate system to the corresponding position of the picture coordinate system is specified based on the specified positions of the markers in the picture coordinate system and the positions of the markers in the reference coordinate system. Further, the optional position of the reference coordinate system is transformed to the corresponding position of the picture coordinate system by the specified transformation formula.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting the position of an arbitrary point in a reference coordinate system in real space into a corresponding position in an image coordinate system, for example, a nuclear magnetic tomography apparatus (MRI apparatus). Regarding the intra-image position conversion method used in a stereotactic brain surgery assisting device, etc., which enables to confirm on a monitor the correspondence between the lesion site projected on the image obtained by .

[0002]

2. Description of the Related Art In recent years, with the progress of image diagnostic techniques such as an X-ray CT apparatus and an MRI apparatus (hereinafter collectively referred to as a CT apparatus), for example, a lesion site in the skull has become high. You can now decide with precision. However, at the stage of applying a surgical operation to the determined lesion site,
The craniotomy position is determined and the lesion site is extracted while considering the rough correspondence between the CT image and the actual surgical position based on anatomical knowledge. In order to make such an accurate correspondence between the actual surgical operation position and the lesion site on the CT image, for example, Japanese Patent Laid-Open No. 3-2670
There is a stereotactic brain surgery support device disclosed in Japanese Patent Publication No. 54 and the like.

In this stereotactic brain surgery support device, a plurality of index points (markers) are attached to the head, an image in which the marker is imprinted is photographed by a CT device, and the marker imprinted in the image is recorded. The coordinates in the CT coordinate system (image coordinate system) and the real space of the marker (MS coordinate system) measured by a three-dimensional coordinate measuring device including a magnetic field source, a magnetic field sensor attached to a surgical probe, and a three-dimensional digitizer. ), The conversion formula from the MS coordinate system to the image coordinate system is obtained, the position of the tip of the surgical probe on the MS coordinate is measured by a three-dimensional coordinate measuring device, and the position is calculated. It is converted into an image coordinate system using the above conversion formula, and the tip position of the probe is superimposed and displayed on the image displayed on the monitor, which is useful for specifying the surgical operation position.

[0004]

However, the conventional example having such a structure has the following problems. For conversion from the MS coordinate system of the conventional apparatus to the image coordinate system, it is necessary that all the markers are imprinted on the image obtained from a single direction with a single CT apparatus. But,
Depending on the subject, it may be difficult or impossible to arrange the markers so as to imprint all the markers in an image obtained from a single direction with a single CT apparatus.

The present invention has been made in view of the above circumstances, and in the conversion from the reference coordinate system in the real space to the image coordinate system, the degree of freedom in arranging the index points on the subject is increased. It is an object of the present invention to provide an in-image position conversion method that can be provided.

[0006]

The present invention has the following constitution in order to achieve such an object. That is, the present invention includes a step of capturing a plurality of index points arranged in a space on one of images captured from multiple directions by the same image capturing device to capture the image, and the image capturing device. In the image coordinate system unique to, the step of specifying the position of each of the index points imaged in the image captured from the multi-direction, and the position of each index point in the reference coordinate system in the real space Based on the step of specifying, the position of each index point in the reference coordinate system, and the position of each index point in the image coordinate system, the position of an arbitrary point in the reference coordinate system is set in the image coordinate system. And a step of converting a position of an arbitrary point of the reference coordinate system to a corresponding position of the image coordinate system by the conversion equation.

[0007]

The operation of the present invention is as follows. First, an image that captures multiple index points placed in space
Images are taken from multiple directions with the same image taking device. At this time,
The index point may be imprinted on the image taken from any direction. Next, with reference to the image coordinate system unique to the image capturing apparatus, the position of each index point imaged in the image captured from multiple directions is specified. On the other hand, the position of each index point in the reference coordinate system in the real space is specified. Then, based on the position of each index point in the reference coordinate system and the position of each index point in the image coordinate system, a conversion formula for converting the position of an arbitrary point in the reference coordinate system to the corresponding position in the image coordinate system is created. Identify. That is, the correspondence between the reference coordinate system and the image coordinate system is obtained via the index points. The position of an arbitrary point in the reference coordinate system is converted into the corresponding position in the image coordinate system by the calculated conversion formula.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a stereotactic brain surgery support device incorporating an intra-image position conversion device that implements an intra-image position conversion method according to an embodiment of the present invention, and FIG. It is a flow chart which shows the position conversion processing procedure in a picture by a device.

The structure of each part will be described below with reference to the flowchart of FIG. First, image 2 is captured from multiple directions by the image capturing device 1 to imprint the arbitrary four index points affixed to a position (marker) M ₁ ~M ₄ of the head portion of the test subject (step S1).

The image capturing apparatus 1 is composed of, for example, an MRI apparatus capable of capturing images from multiple directions. As shown in FIG. 3, the image capturing device 1 captures an image 2 by placing a subject M lying on a top plate 4 slidably mounted on a vertically movable base 3 on a subject 6 in a cavity 6 of a gantry 5.
It is performed by inserting inside. At this time, as shown in FIG. 3, markers M _{1 to} M ₄ are attached to the head of the subject M at arbitrary positions. The image 2 is photographed from multiple directions, for example, two directions, α direction and β direction, as shown in FIG. Image 2 (2 ₁ , 2 ₂ ) taken is shown in FIG. FIG. 5A shows the image 2 ₁ photographed from the α direction, and FIG. 5B shows the image 2 ₂ photographed from the β direction. As shown in the figure, the images 2 ₁ photographed from the α direction include the markers M ₁ and M ₂ , and the image 2 ₂ photographed from the β direction includes the markers M ₃ and M _4. Has been done.
That is, the markers M _{1 to} M ₄ may be included in any of the images 2 captured from multiple directions. The photographed image 2 is read by an image reading device (not shown) such as a solid-state imaging device (CCD) camera or an image scanner, and stored in the memory 7. Alternatively, the image data may be directly transferred from the image capturing device 1 and stored in the memory 7. Then, the image 2 stored in the memory 7
Is displayed on the monitor 9 by the display control unit 8.

Next, the positions of the markers M _{1 to} M ₄ imprinted on the image 2 stored in the memory 7 in the unique image coordinate system of the image capturing apparatus 1 for collecting data are specified (step S2). ). This process is performed by the image coordinate specifying unit 21.
Performed by.

The image coordinate system unique to the image capturing apparatus 1 will be described with reference to FIG. In FIG. 3, the center line of the cavity 6 of the gantry 5 in the axial direction is the z axis, and the intersection point of the z direction center of the cavity 5 of the gantry 4 of the image capturing apparatus 1 and the z axis is the origin O. (The plane orthogonal to the z axis is the xy plane, and the axis perpendicular to the plane of the drawing is the x axis) is an image coordinate system unique to the image capturing apparatus 1. In this image coordinate system, for example, image 2 ₁ taken from α direction, the tomographic plane is consistent with the x-y plane, the slice direction is equal to z-axis. The image 2 ₂ taken from β direction, the tomographic plane is consistent with the x-z plane, the slice direction is equal to the y-axis.

Image 2 in the image coordinate system as described above
The positions of the markers M _{1 to} M ₄ imprinted on the can be specified as follows. For example, the image 2 ₁ taken from the α direction will be described. In the imaging in the α direction, the first imaging region is aligned with the imaging position of the image capturing apparatus 1 (the position where the origin O of the above-described image coordinate system is in the middle of the slice thickness of the image 2 ₁ to be imaged), and the image 2 is obtained. Shoot ₁ and then
The top plate 4 is moved in the z direction by the slice thickness, and the image 2 ₁ is imaged with the second imaged part aligned with the imaged position. Similarly, the required number of images 2 ₁ are captured. FIG. 6A shows a state where the photographing of the three images 2 ₁₁ to 2 ₁₃ is completed. In the state of FIG. 6A, the arrangement of the captured images 2 ₁₁ to 2 ₁₃ , the image including the origin O of the image coordinate system (the last captured image 2 ₁₃ in the figure), and the slice thickness d. Therefore, it is possible to specify the position (coordinates) of the z-axis image coordinate system of each of the images 2 ₁₁ to 2 ₁₃ . For example, the z coordinate of the image 2 _{11 in} the image coordinate system corresponds to 2 × d. Further, as shown in FIG. 6B, each image 2 ₁₁ (2
_12, 2 ₁₃ fault plane (x-y plane) at a specific position P in x of), y coordinates, image 2 ₁₁ (2 _12, 2 ₁₃₎ and the distance between the intersection zc and P the z axis L Corresponding to the X component L _X and the Y component L _Y. In this way, the markers M _{1 to} M imprinted on the image 2 ₁ photographed from the α direction in the image coordinate system.
₄ coordinates can be specified. It should be noted that the above-mentioned respective information necessary for specifying the z coordinate is set from the input device 10.

An image 2 taken from the β direction₂Nitsu
However, how is image 2 relative to the image coordinate system?₂Taken by
Depending on the information such as the
Image 2 in the standard₂Marker M imprinted on₁~
M_FourThe y coordinate of can be specified, and image 2₂Fault plane (xz flat
Marker M in the plane)₁~ M_FourX and z coordinates of image 2 ₂
And y-axis intersection and marker M₁~ M_FourX distance of distance
Minute, z component.

The image coordinate system unique to the image capturing apparatus 1 is not limited to the above, and for example, as shown in FIG. 7, the origin O'is set on the end face of the cavity 6 of the gantry 5. May be. When the image coordinate system is set in this way, the distance between the origin O of the image coordinate system described above and the origin O ′ of the image coordinate system of FIG. 7 at the z coordinate of the position specified by the image coordinate system described above. By adding OL, the positions of the markers M _{1 to} M ₄ imprinted on the image 2 can be specified. Further, the image coordinate system may be an oblique coordinate system instead of the orthogonal coordinate system as described above.

From the image 2 ₁ taken in the α direction, the positions of the markers M ₁ and M ₂ in the image coordinate system are specified, and β
From the image 2 ₂ taken from the direction, the positions of the markers M ₃ and M ₄ in the image coordinate system are specified. Positions (coordinates) (x _j , y _j , x _j ) of the identified markers M _{1 to} M ₄
(However, j corresponds to each marker, j = 1 to 4) is given to the image coordinate system / reference coordinate system coordinate conversion formula specifying unit 22.

Next, to identify the position of the marker M ₁ ~M ₄ in the reference coordinate system of the real space (step S3). The following three-dimensional spatial position measuring apparatus 11 is used to specify the positions of the markers M _{1 to} M _{4 in} the reference coordinate system. An example of the three-dimensional spatial position measuring device 11 will be described with reference to FIG.

As shown in FIG. 8, the three-dimensional spatial position measuring device 11 is fixed at a predetermined position (for example, the base 3) and emits an alternating electromagnetic wave, and a magnetic field source 31 and an acute-angled triangle for brain surgery. A magnetic field sensor 33 attached to a predetermined position of a probe 32 such as a suction tube type pointer or a puncture needle, and a three-dimensional digitizer 34. A plurality of mutually distinguishable radio frequency electromagnetic fields are radiated from the magnetic field source 31, the magnetic field sensor 33 separates and detects the electromagnetic fields, and the three-dimensional digitizer 34 uses the magnetic field source 31 as a reference based on the received signal. The position of the magnetic field sensor 33 in the reference coordinate system is calculated, and the probe 32 in the reference coordinate system is calculated from the positional relationship between the mounting position of the magnetic field sensor 33 and the position of the tip 35 of the probe 32.
The position of the tip 35 of the is calculated.

The magnetic field source 31 and the magnetic field sensor 33 are each composed of three sets of orthogonal coils.
When the coils are excited, an induced voltage is generated in the three coils of the magnetic field sensor 33 according to the distance from the magnetic field source 31 and the orientation of the magnetic field sensor 33.
A reference coordinate system (XYZ orthogonal coordinate system) analyzed by the three-dimensional digitizer 34 and having the center of the magnetic field source 31 as the origin O _K.
The position coordinates (a, b, c) and direction angles (A, E, R) of the magnetic field sensor 33 at are calculated. Where A, E, R
Indicates the azimuth angle, the rising angle, and the roll angle in Euler angles, respectively. Then, the electromagnetic field is sequentially radiated from the three coils of the magnetic field source 31, and the measurement is performed while correcting the position and direction angle at a rate of several tens of times per second.

[0020] Then, the position and orientation angle of the measured magnetic field sensor 33, and the magnetic field sensor 33 around the magnetic field sensor coordinate system with the origin O _S (U-V-W orthogonal coordinate system) in the tip 35 of the probe 32 Based on the coordinates (u _P , v _P , w _P ), the position coordinates (X, Y, Z) of the tip 35 of the probe 32 in the reference coordinate system are specified by the following equation.

(X, Y, Z) = (a, b, c) + (u _P , v _P , w _P ) * T ₁ * T ₂ * T ₃ (1) where T ₁ , T ₂ and T ₃ are expressed as follows.

[0022]

[Equation 1]

The coordinates (u _P , v _P , w _P ) of the tip 35 of the probe 32 in the magnetic field sensor coordinate system with the center of the magnetic field sensor 33 as the origin O _S are determined according to the shape, size, etc. of the probe 32. 3D digitizer 3 as initial data
It is preset to 4. That is, if the position and the direction angle of the magnetic field sensor 33 are measured, the position coordinate (X, X,
Y, Z) are specified.

Then, with the subject M fixed, a marker M attached to the subject M by the tip 35 of the probe 32.
_{1 to} M ₄ in order, and each marker in the reference coordinate system M ₁ to
Specify the position (coordinates) of M ₄ . The coordinates (X _j , Y _j , Z _j ) of the specified markers M _{1 to} M ₄ (where j corresponds to the marker and j = 1 to 4) is the image coordinate system / reference coordinate system coordinate conversion formula. It is given to the identification unit 22.

Next, another example of the three-dimensional spatial position measuring device 11 will be described below with reference to FIG. The three-dimensional spatial position measuring apparatus 11 shown in FIG. 9 includes arms 42a to 42c that are rotatably connected in predetermined directions by joints 41a to 41e.
The arm base end portion 43 and the searcher 44 are included.
The arm base end portion 43 is fixed at a predetermined position (for example, the base 3), each arm 42a to 42c, and the searcher 44.
Is rotated in a predetermined direction via the joints 41a to 41e, the searcher 44 can be freely moved in the space. The arm 4 is attached to each joint 41a to 41e.
2a to 42c, a searcher 44, and the like are equipped with a potentiometer (not shown) whose resistance value changes depending on the rotation angle. Then, when the searcher 44 is moved to a predetermined position in the space, depending on the output data from each potentiometer, each arm 42a to 42c, the size of the searcher 44, etc., for example,
The position (coordinates) of the tip 45 of the searcher 44 in the reference coordinate system (XYZ orthogonal coordinate system, where the X axis is the direction perpendicular to the paper surface) with the center of the arm base end portion 43 as the origin O _K is specified. can do.

Then, with the subject M fixed, a marker M ₁ attached to the subject M at the tip 45 of the searcher 44.
To M ₄ in order, and each marker M _{1 to} M in the reference coordinate system
Identify the position (coordinates) of ₄ .

The three-dimensional spatial position measuring device 11 may have a configuration other than that described above, and the three-dimensional spatial position measuring device 11 may be used without using the three-dimensional spatial position measuring device 11 in a reference coordinate system arbitrarily determined in the real space. the position of each marker M ₁ ~M ₄ may be identified.

Further, although the orthogonal coordinate system is set as the reference coordinate system in the above description, it may be an oblique coordinate system.

Next, in steps S2 and S3, the positions of the markers M _{1 to} M ₄ in the specified image coordinate system,
Identifying a conversion expression for converting the position of any point in the reference coordinate system corresponding position in the image coordinate system based on the position of the marker M ₁ ~M ₄ in the reference coordinate system (step S4). This process is performed by the image coordinate system / reference coordinate system coordinate conversion formula specifying unit 22.
Performed by.

For example, the coordinates (x _j , y _j , x _j ) and (X _j , Y _j , Z) of the markers M _{1 to} M ₄ specified in each coordinate system are converted from the reference coordinate system to the image coordinate system. _When expressed by a four-dimensional Affine transformation using _j ), the following equation is obtained.

[0031]

[Equation 2]

Here, T represents a transformation matrix, and this transformation matrix T is given by the following equation from the above equation (2).

[0033]

[Equation 3]

Each coordinate (x _1j , y _1j , x _1j ), (X _j , Y
_{Since j} , Z _j ) are specified by the image coordinate specifying unit 21, the three-dimensional spatial position measuring device 11, the transformation matrix T can be obtained.

For example, as shown in FIG. 10, from an arbitrary point P _r (X _a , Y _a , Z _a ) of the reference coordinate system to a corresponding point P _g (x _b , y _b , z _b ) of the image coordinate system. The conversion of (3) above
It can be expressed as follows by using the transformation matrix T obtained in. _{(X b, y b, z} b, 1) = (X a, Y a, Z a, 1) * T ...... (4)

Next, the position of an arbitrary point in the reference coordinate system is converted into the corresponding position in the image coordinate system by the conversion formula specified in step S4 (step S5). This processing is performed by the position conversion unit 23.

For example, when an arbitrary position pointed to by the tip 35 of the probe 32 of the three-dimensional spatial position measuring device 11 shown in FIG. 8 is given to the position conversion section 23, the above equation (4) is used to calculate in the image coordinate system. Convert to the corresponding position (coordinates).

As described above, since an arbitrary point in the real space can be converted into the image coordinate system, the position of the tip 35 of the probe 32 in the real space can be changed to the three-dimensional space position during the operation. If measured by the measuring device 11, the current position of the tip 35 of the probe 32 can be superimposed and displayed in real time on the image 2 displayed on the monitor 9,
The correspondence between the lesion site and the surgical position can be confirmed on the monitor 8. Moreover, in this embodiment, since the position of the tip 35 of the probe 32 can be displayed in a superimposed manner on the image 2 captured from multiple directions, as shown in FIG.
It is also possible to stereoscopically confirm the position Q of the distal end 35 of the, and it is possible to make it easier to recognize the correspondence between the lesion site and the surgical position.

In FIG. 1, a portion 2 surrounded by a one-dot chain line
0 corresponds to the intra-image position conversion device.

Further, the conversion formula for converting the position of the arbitrary point at the reference position in the real space into the corresponding position of the image coordinate system may be specified by a method other than the above.

Further, in the above-mentioned embodiment, the case where the device is incorporated in the stereotactic brain surgery assisting device has been described, but also in the case of converting from the position of an arbitrary point in the real space to the corresponding position of the image coordinate system. It can also be applied.

[0042]

As is apparent from the above description, according to the present invention, the image photographing device is unique in the index points photographed in any one of the images photographed from the same image photographing device from multiple directions. A conversion formula for converting the position of an arbitrary point in the reference coordinate system into the corresponding position in the image coordinate system based on the position in the image coordinate system and the position of the index point in the reference coordinate system. As a result, it becomes possible to give the degree of freedom to the arrangement of the index points as compared with the case where the index points have to be imprinted in the image photographed from a single direction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a stereotactic brain surgery support device incorporating an intra-image position conversion device that implements an intra-image position conversion method according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure of an in-image position conversion processing by the apparatus of the embodiment.

FIG. 3 is a front view showing a schematic configuration of an image capturing device.

FIG. 4 is a diagram for explaining a direction in which an image is captured.

FIG. 5 is a diagram showing images taken from two directions.

FIG. 6 is a diagram for explaining a procedure for specifying the position of a marker in the image coordinate system.

FIG. 7 is a diagram showing a modification of the setting position of the image coordinate system.

FIG. 8 is a diagram showing a schematic configuration of a three-dimensional spatial position measuring device.

FIG. 9 is a diagram showing a schematic configuration of a modified example of the three-dimensional spatial position measuring device.

FIG. 10 is a diagram for explaining conversion from a reference coordinate system to an image coordinate system.

FIG. 11 is a diagram in which the tip position of the probe is superimposed and displayed on the image displayed on the monitor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image photographing device 2 ... Image 11 ... Three-dimensional spatial position measuring device 20 ... In-image position conversion device 21 ... Image coordinate specification part 22 ... Image coordinate system / reference coordinate system coordinate conversion formula specification part 23 ... Position conversion part M ₁ ~ M ₄ ... Marker (index point)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G06T 3/00 8420-5L G06F 15/66 340

Claims (1)

[Claims] 1. A step of photographing a plurality of index points arranged in a space on one of the images photographed from the same image photographing device from a plurality of directions to photograph the image, and the image photographing device. In the unique image coordinate system, the step of specifying the position of each of the index points imaged in the image captured from the multiple directions, and the position of each of the index points in the reference coordinate system in the real space And the position of each index point in the reference coordinate system, and the position of each index point in the image coordinate system, the position of any point of the reference coordinate system of the image coordinate system. An image characterized by including a step of specifying a conversion formula for converting into a corresponding position and a step of converting a position of an arbitrary point in the reference coordinate system into a corresponding position in the image coordinate system by the conversion formula. Position conversion method.