JP2002336229A - Positioning method and device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely position multiple radiation pictures obtained by a phase contrast radiographing method. SOLUTION: An X-ray 12 transmitting through an object 21 and positioning markers 22 and 23 is emitted on a detection panel 31, while moving the detection panel 31 to obtain picture data Sn expressing X-ray pictures of the object in multiple radiographing positions. A positioning part 40 detects central positions of multiple diffraction fringes appearing on the marker pictures, finds a mean value of the multiple central positions, and sets it as the central position of the marker pictures. The central positions of the marker pictures of the multiple data are found, the X-ray pictures expressed by the multiple picture data Sn are positioned based on the central positions, and an arithmetic part 50 obtains picture data S1 expressing the phase contrast picture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting radiation applied to a subject at a plurality of positions at different distances from the subject, obtaining a plurality of radiation images, and forming a phase contrast image using the plurality of radiation images. The present invention relates to a radiographic image registration method and apparatus suitable for generation and a program for causing a computer to execute the registration method.

[0002]

2. Description of the Related Art Conventionally, radiation (X-ray, α
Radiation, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) to irradiate the radiation that has passed through the subject. To obtain image data representing a radiation image of a subject, subject the image data to various image processing, and then subjecting the image data to reproduction.

Here, in the method using a stimulable phosphor sheet, a part of radiation energy transmitted through a subject is accumulated, and then, when irradiated with excitation light, stimulating light is emitted in an amount of light corresponding to the accumulated energy. Using a stimulable phosphor (stimulable phosphor), radiation image information of a subject is recorded on a sheet-shaped stimulable phosphor (ie, a stimulable phosphor sheet), and the stimulable phosphor sheet is irradiated with laser light. In this method, stimulated emission light is generated by scanning with excitation light, and the generated stimulated emission light is photoelectrically read to obtain image data representing a radiation image of the subject. In addition, the method using the radiation detection panel uses a radiation detection panel in which a plurality of detection elements are two-dimensionally arranged, and generates an electric signal corresponding to the amount of radiation applied to each of the detection elements, This is a method of obtaining image data representing a radiation image of a subject based on the electric signal.

[0004] Incidentally, the radiation image obtained in this way represents the intensity difference of the transmitted radiation in the subject as an image. For example, when an image of a subject including a bone and a soft part is taken, radiation transmitted through the bone is greatly attenuated, so that the amount of radiation reaching the detector is small.However, radiation transmitted through the soft part is not significantly attenuated. The radiation dose reaching the vessel is relatively high. Therefore, in the case of such a subject, a radiographic image with a large contrast difference in which the bone part is expressed white and the soft part expressed black is obtained, that is, a large amount of information is obtained.

However, for example, as in breast cancer diagnosis,
If the subject is mainly composed of only soft parts, the difference in radiation attenuation between tissues is not so large, so that only a radiographic image with a small contrast difference, that is, a small amount of information, can be obtained.

For this reason, there has been proposed a phase contrast imaging method for visualizing a phase difference of radiation caused by transmission through a subject. In this phase contrast imaging method, radiation is an electromagnetic wave like light and the wave travels and propagates, so when irradiating two different substances with radiation, due to the difference in the way of transmission of radiation in the substance, The subject is photographed based on the fact that the phase of the radiation wave differs before and after the transmission of a substance, and a phase difference occurs. Here, when the subject is a soft part, the phase difference of the radiation is larger than the difference of the attenuation of the radiation. Thereby, it is possible to visualize a subtle difference in the tissue included in the soft part. For the phase contrast shooting method, refer to “Pe
ter Cloetens, et al., "Quantitative aspects of coh
erent hard X-ray imaging: Talbot image and hologra
phic reconstruction ", Proc, SPIE, Vol.3154 (1977),
72-82 (Reference 1) "and" Peter Cloetens, et al., "
Hard x-ray phase imaging using simple propagation
of a coherent synchrotron radiation beam ", J. Phys.
D: Appl. Phys. 32 (1999), A145-A151 (Reference 2) ". According to these documents, image data representing a plurality of radiographic images is obtained by performing imaging using a two-dimensional detector at a plurality of imaging positions at different distances from a subject, and the image data is predetermined using a plurality of image data. By performing calculations based on the algorithm
A phase contrast image can be generated.

[0007]

By the way, in order to obtain a phase contrast image from a plurality of radiation images obtained by the above-described phase contrast imaging method, it is necessary to align a plurality of radiation images. In this case, it is conceivable to manually align each radiation image while observing a plurality of radiation images, but this imposes a heavy burden on the operator. For this reason, for example, as described in JP-A-58-163338, a marker made of a metal such as tantalum is photographed together with a subject, and a plurality of radiographic images are included in the marker image together with the subject image. It is conceivable to perform positioning of a plurality of radiation images on the basis of the positions.

However, in the phase contrast imaging method, a plurality of radiation images are acquired at a plurality of positions at different distances from the subject. Since the included marker images become unclear, it is difficult to perform accurate alignment using the marker images. As described above, if the alignment cannot be performed accurately, the entire image including the edge of the structure included in the phase contrast image is blurred, and accurate diagnosis using the phase contrast image can be performed. I can no longer do it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to accurately align a plurality of radiation images obtained by a phase contrast imaging method.

[0010]

According to the positioning method of the present invention, a subject and a marker for positioning are irradiated with radiation, and the radiation transmitted through the subject and the marker is transferred to a plurality of positions at different distances from the subject. A positioning method for performing positioning of a plurality of radiation images including a subject image and a marker image at each of the positions obtained by detecting at the positions, wherein diffraction of the marker image included in each of the plurality of radiation images is performed. The positioning of the plurality of radiation images is performed based on an image.

A plurality of image data can be obtained by arranging a plurality of detectors at predetermined photographing positions in the traveling direction of the radiation transmitted through the subject and detecting the radiation by each detector. Alternatively, it may be obtained by moving one detector in the traveling direction of the radiation transmitted through the subject and irradiating the detector with the radiation transmitted through the subject at a predetermined imaging position.

The marker may be arranged at the same position as the object, and when a plurality of detectors are used, the marker may be arranged at the detector closest to the object.

In the positioning method according to the present invention, a plurality of diffraction fringes of the marker image are extracted, and a plurality of reference positions of the marker image are detected based on the extracted plurality of diffraction fringes. A representative position representative of the plurality of reference positions may be determined, and the positions of the plurality of radiation images may be aligned based on the representative positions of the plurality of radiation images.

In this case, it is preferable that the shape of the marker is circular and the reference position is a center position of the diffraction fringes.

"A plurality of reference positions of the marker image" means a plurality of diffraction fringes in the marker image, and the center position, the center of gravity, etc. of the plurality of diffraction fringes can be used.

As the "representative position representing a plurality of reference positions", an average value of a plurality of reference positions, a reference position of an intermediate-size diffraction pattern among a plurality of diffraction patterns, and the like can be used.

Further, in the positioning method according to the present invention, a phase contrast image may be generated based on the plurality of radiation images that have been aligned.

A positioning apparatus according to the present invention irradiates a subject and a positioning marker with radiation, and detects radiation transmitted through the subject and the marker at a plurality of positions at different distances from the subject. A positioning apparatus for performing positioning of a plurality of radiation images including a subject image and a marker image at each of the positions, based on a diffraction image of the marker image included in each of the plurality of radiation images, And a positioning means for positioning a plurality of radiation images.

In the positioning apparatus according to the present invention, the positioning means includes: an extracting means for extracting a plurality of diffraction fringes of the marker image; and a plurality of diffraction fringes extracted by the extracting means. Reference position detection means for detecting a plurality of reference positions for the marker image, and determining means for determining a representative position representing the plurality of reference positions, based on the representative positions of the plurality of radiation images, A means for aligning the plurality of radiation images may be used.

In this case, the marker has a circular shape,
Preferably, the reference position is a center position of the diffraction fringes.

Further, the positioning apparatus according to the present invention may further include an image generating means for generating a phase contrast image based on the plurality of radiation images which have been aligned.

The positioning method according to the present invention may be provided as a program for causing a computer to execute the method.

[0023]

According to the present invention, image data representing a plurality of radiographic images including a subject image and a marker image is obtained, and a plurality of radiographic images based on the diffraction images of the marker images included in the plurality of radiographic images are obtained. Alignment is performed. Here, when only the marker image is used, the marker image is blurred in a radiographic image obtained at a position relatively large from the subject, so that it is difficult to perform accurate alignment. If the positioning is performed based on the diffraction image of the marker image, the positioning accuracy can be improved as compared with the case where only the marker image is used. Therefore, a plurality of radiographic images can be accurately positioned, thereby preventing a phase contrast image from being blurred.

Further, a plurality of diffraction fringes of the marker image are detected,
By detecting a plurality of reference positions of the marker image based on the plurality of diffraction fringes, further determining a representative position representing the plurality of reference positions, and performing alignment of the representative positions for the plurality of radiation images, Since positioning of a plurality of radiation images can be performed by a relatively simple calculation, the calculation time for positioning can be reduced.

Further, by making the shape of the marker circular and setting the reference position to the center position of the diffraction fringe, the reference position can be detected more easily.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing a configuration of a phase contrast imaging apparatus to which a positioning device according to a first embodiment of the present invention is applied. As shown in FIG. 1, the phase contrast imaging apparatus includes an X-ray source 10 for irradiating a subject with X-rays, a subject 21 and a marker 2.
An object support unit 20 supporting the objects 2 and 23; a recording unit 30 for detecting X-rays transmitted through the object 21 to obtain image data Sn (n = 1 to N) representing a plurality of X-ray images of the object; A positioning unit 40 for performing positioning of the X-ray image of
A calculation unit 50 that obtains image data S1 representing a phase contrast image using the aligned image data Sn '.
And

The X-ray source 10 includes a radiation source 11 that emits synchrotron radiation, and a crystal 13 that converts the synchrotron radiation to monochromatic X-rays (hereinafter simply referred to as X-rays) 12. The monochromatic X-rays 12 are obtained by reflecting the synchrotron radiation emitted from the crystal 13 on the crystal 13.

The subject support section 20 has a support 24 for supporting the subject 21 and the two markers 22 and 23. The markers 22, 23 are formed in a ring shape as shown in FIG. 2, and are made of metal such as tantalum.

The recording unit 30 moves the detection panel 31 in a direction parallel to the traveling direction of the X-rays 12 transmitted through the subject 21 and the detection panel 31 including a plurality of detection elements arranged two-dimensionally. Moving means 32 and detection panel 31
At a plurality of photographing positions set in advance on the moving path of the camera, electric signals are read from a plurality of detecting elements constituting the detection panel 31 and image data S at each photographing position
reading means 33 for obtaining n.

The moving means 32 includes a support portion 35 for supporting the detection panel 31 and having a female screw portion formed thereon, and an X-ray 1
A male screw portion 36 extending in a direction parallel to the traveling direction of the screw 2 and screwing into the female screw portion of the support portion;
The motor 37 includes a motor 37 that rotates around a rotation axis extending in the traveling direction of the line 12, and a control unit 38 that controls driving and stopping of the motor 37. Then, the male screw portion 36 is rotated by driving the motor 37 by the control portion 38, and the support portion 35, that is, the detection panel 31 moves in a direction approaching the subject 21 and a direction away from the subject 21 according to the rotating direction.

The positioning unit 40 performs a line extraction process on an image near the marker image included in the X-ray image represented by each image data Sn to extract a plurality of diffraction fringes, A center position detecting unit 42 for detecting the center position of the diffraction fringes; an average value calculating unit 43 for detecting the average value of the center positions of the respective diffraction fringes as the center position of the marker image included in the image data Sn; And a positioning unit 44 for positioning an X-ray image represented by a plurality of image data Sn based on the center position of the marker image.

Here, the diffraction images of the markers 22 and 23 will be described. FIG. 3 is a diagram illustrating a state where the detection panel 31 detects the X-rays 12 transmitted through the subject 21 at a position z = d away from the position of the subject 21 (z = 0). Here, for simplicity, a diffraction image on a cross section passing through the optical axis of the X-ray 12 will be described. The wave of the X-rays 12 reaching the detection panel 31 is given by the following Fresnel diffraction equation (1). When the detection panel 31 detects an edge portion of an object having a steep edge as shown in FIG.
The intensity distribution of the X-ray 12 is as shown in FIG. Therefore, when the X-ray image of the subject 21 is captured using the markers 22 and 23, it is understood that the edge of the marker image included in the X-ray image becomes unclear.

(Equation 1) Here, λ: wavelength of X-ray 12 i: imaginary unit k = 2π / λ g (x): transmittance of object placed at z = 0 x: From intersection of optical axis of X-ray 12 and detection panel 31 On the detection panel 31

Referring to FIG. 4B in detail, it can be seen that the intensity peak of the irradiated X-ray 12 is repeated a plurality of times to form diffraction fringes. As a result, the marker image is detected in a state where a plurality of diffraction fringes are generated as shown in FIG. In the present embodiment, the positions of the markers 22 and 23 are accurately obtained based on the positions of the plurality of diffraction fringes to perform the alignment.

The line extracting means 41 performs a first-order differentiation process on the image data Sn to extract diffraction fringes as lines. Note that template matching using a plurality of circular templates having different radii may be performed to extract diffraction fringes as lines.

The center position detecting means 42 finds a point on the diffraction fringe furthest from each point for a plurality of points on the diffraction fringe, and determines an intersection of a line connecting the corresponding points with the center of the diffraction fringe. Detect as position. When a diffraction pattern is detected by template matching, the center position of the template may be detected as the center position of the diffraction pattern.

The average value calculating means 43 calculates an average value of coordinate values representing the center positions of the plurality of diffraction fringes detected by the center position detecting means 42, and uses this as the center position of the marker image. Note that, instead of the average value, the center position of the diffraction fringe that takes the median of the radius when a plurality of diffraction fringes are arranged in descending order of the radius may be the center position of the marker image.

The positioning means 44 enlarges or reduces an X-ray image (hereinafter referred to as another X-ray image) other than the X-ray image (hereinafter referred to as a reference X-ray image) obtained at a position closest to the subject 21. By performing affine transformation on another X-ray image in order to perform rotation, translation, and translation, the other X-ray image is aligned with the reference X-ray image.

The arithmetic unit 50 obtains image data S1 representing a phase contrast image based on a plurality of image data Sn by the method described in the above-mentioned document 1. Below, Document 1
Will be described. It is assumed that the transmittance of the subject 21 is represented by the following equation (2).

(Equation 2) Here, T (x, y): transmittance function A (x, y): transmittance intensity function ψ (x, y): phase shift amount function (x, y): coordinate value representing a position on the detection panel 31

Here, when the object is a thin object whose transmittance intensity is negligible (that is, A (x, y) is close to 1), the subject 21 and the detection panel 31 are expressed by the following equation (3). And the spatial frequency component I _dn (fx, fy) obtained by Fourier-transforming the image I _dn (x, y) photographed at a distance dn (n = 1 to N) with respect to the space of the phase shift amount. A frequency component is calculated. Here, as the image I _dn (x, y), a pixel value at the position (x, y) of the image represented by the image data Sn acquired at the distance dn may be used.

(Equation 3) N: number of image data Sn f: spatial frequency ψ (fx, fy ≠ 0): spatial frequency component of phase shift amount when frequency is not 0 I _dn (fx, fy): I _dn (x, y) Spatial frequency component of

Then, by subjecting the spatial frequency component of the phase shift amount to the inverse Fourier transform, the phase shift amount, that is, the phase difference ψ (x, y) can be calculated. here,
Since the phase difference ψ (x, y) takes a value in the range of 0 to 2π,
By assigning the calculated phase difference ψ (x, y) to, for example, an 8-bit value, image data S1 representing a phase contrast image can be obtained.

Here, A where the transmittance intensity can be ignored
It is assumed that (x, y) is close to 1, but the phase shift amount can be calculated for a thick object using the same algorithm.

Next, the operation of this embodiment will be described. FIG. 6 is a flowchart showing the operation of the first embodiment. First, the X-ray source 1 is driven by driving the source 11 so that the synchrotron radiation is reflected by the crystal 13.
The monochromatic X-rays 12 are emitted from 0 to irradiate the subject 21 and the markers 22, 23 with the X-rays 12 (step S).
1). At the same time, the control unit 38 drives the motor 37 to move the detection panel 31 in a direction away from the initial position closest to the subject 21 (step S2). Then, at a plurality of photographing positions according to the movement, the reading means 33
, The electrical signals of the plurality of detection elements constituting the detection panel 31 are read out, and the image data Sn at each photographing position is read out.
Is obtained (step S3).

The acquired image data Sn is input to the positioning unit 40, where the positioning is performed, and the aligned image data Sn 'is obtained (step S).
4). Then, the aligned image data Sn 'is input to the arithmetic unit 50, where the image data S1 representing the phase contrast image is obtained as described above (Step S).
5), end the processing. The image data S1 is provided for reproduction on a monitor or printout by a printer.

Here, when positioning is performed using only the marker image in the positioning unit 40, X obtained at a position where the distance from the subject 21 is relatively large is obtained.
Since the marker image is blurred in the line image, it is difficult to perform accurate positioning. In the first embodiment, since the alignment is performed using the diffraction fringes of the marker image, the alignment accuracy can be improved as compared with the case where only the marker image is used. Therefore, a plurality of X-ray images can be aligned with high accuracy, thereby preventing a phase contrast image from being blurred due to a displacement.

Further, since the shape of the markers 22 and 23 is annular and the reference position is the center position of the diffraction fringe, the reference position for alignment can be detected more easily.

In the first embodiment, one detection panel 31 is moved by the moving unit 32 in the recording unit 30.
Moves in a direction parallel to the traveling direction of the X-rays 12 to perform imaging at a plurality of imaging positions. However, as in the second embodiment shown in FIG.
Instead of one, a plurality (three in this case) of stimulable phosphor sheets 61, 62, 63 are used, and these stimulable phosphor sheets 61, 62, 63 are respectively disposed at a plurality of predetermined photographing positions. Then, the photographing at a plurality of photographing positions may be performed simultaneously. In this case, the markers 22 and 23 may be provided on the subject support unit 20, but as shown in FIG.
The markers 22 and 23 may be provided on the stimulable phosphor sheet 61 located at a position closest to 1.

When an X-ray image is accumulated and recorded on the stimulable phosphor sheets 61, 62, 63 in this manner,
The sheets 61, 62, and 63 are irradiated with excitation light to generate stimulated emission light, and a reading unit 70 that reads the stimulated emission light photoelectrically reads a plurality of image data S representing an X-ray image.
n is obtained. The plurality of obtained image data Sn are aligned in the alignment unit 40 in the same manner as in the first embodiment, and the arithmetic unit 50 obtains image data S1 representing the phase contrast.

In the first and second embodiments, a radiation source that emits synchrotron radiation is used as the radiation source 11. However, if the diffraction images of the markers 22 and 23 can be obtained, the radiation However, the present invention is not limited to this. In addition, monochromatic X-rays are used as the X-rays 12 that irradiate the subject 21, but the present invention is not limited to monochromatic X-rays as long as diffraction images of the markers 22 and 23 can be obtained.

In the first and second embodiments, the subject 21 is irradiated with X-rays.
Radiation other than X-rays (α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) as long as they can observe 2, 23 diffraction images
May be used.

Furthermore, in the first and second embodiments, the markers 22 and 23 are annular in shape, but various shapes such as circular, triangular and rectangular can be used. When the shape of the markers 22 and 23 is triangular or rectangular, the alignment can be performed using the position of the center of gravity.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a configuration of a phase contrast imaging device to which a positioning device according to a first embodiment of the present invention is applied.

FIG. 2 is a diagram showing the shape of a marker.

FIG. 3 is a diagram showing a state in which an X-ray transmitted through a subject is detected by a detection panel.

FIG. 4 is a diagram showing states of edges and diffraction.

FIG. 5 shows a diffraction image.

FIG. 6 is a flowchart showing the operation of the first embodiment.

FIG. 7 is a schematic block diagram illustrating a configuration of a phase contrast imaging device to which a positioning device according to a second embodiment of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 X-ray source 11 X-ray source 12 X-ray 13 Crystal 20 Subject support part 21 Subject 22, 23 Marker 30 Recording part 31 Detection panel 32 Moving means 33 Reading means 40 Positioning part 41 Line extraction means 42 Center position detection means 43 Average value Calculating means 44 positioning means 50 calculating part 61,62,63 stimulable phosphor sheet 70 reading means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03B 42/02 G03B 42/02 B F term (Reference) 2F067 AA67 CC19 EE10 HH04 KK06 KK09 LL18 NN07 RR14 RR28 RR35 2G001 AA01 AA02 AA03 AA05 AA07 BA11 CA01 CA02 CA03 CA05 CA07 DA09 HA07 HA12 HA13 JA06 JA13 KA03 LA01 2H013 AC14 4C093 AA07 CA50 DA06 EA05 EA20 EB05 EC29

Claims (12)

[Claims] 1. Each position obtained by irradiating a subject and a marker for positioning with radiation, and detecting radiation transmitted through the subject and the marker at a plurality of positions at different distances from the subject. A positioning method for performing positioning of a plurality of radiation images including a subject image and a marker image in the method, wherein a position of the plurality of radiation images is determined based on a diffraction image of the marker image included in each of the plurality of radiation images. A positioning method characterized by performing alignment. 2. Extracting a plurality of diffraction fringes of the marker image, detecting a plurality of reference positions for the marker image based on the extracted plurality of diffraction fringes, and representing the plurality of reference positions. The method according to claim 1, wherein a representative position is determined, and the plurality of radiation images are aligned based on the representative position of the plurality of radiation images. 3. The alignment method according to claim 2, wherein the shape of the marker is circular, and the reference position is a center position of the diffraction fringes. 4. The alignment method according to claim 1, wherein a phase contrast image is generated based on the plurality of radiation images that have been aligned. 5. Each position obtained by irradiating a subject and a positioning marker with radiation and detecting radiation transmitted through the subject and the marker at a plurality of positions at different distances from the subject. A positioning apparatus for performing positioning of a plurality of radiation images including a subject image and a marker image in the position of the plurality of radiation images based on a diffraction image of the marker image included in each of the plurality of radiation images. A positioning device, comprising: positioning means for performing alignment. 6. The positioning device according to claim 1, wherein the positioning unit extracts a plurality of diffraction fringes of the marker image, and the plurality of diffraction fringes extracted by the extraction unit.
Reference position detecting means for detecting a plurality of reference positions for the marker image, and determining means for determining a representative position representing the plurality of reference positions, based on the representative positions of the plurality of radiation images, 6. The positioning apparatus according to claim 5, wherein the positioning apparatus is means for positioning the plurality of radiation images. 7. The alignment apparatus according to claim 6, wherein the shape of the marker is circular, and the reference position is a center position of the diffraction fringe. 8. The image processing apparatus according to claim 5, further comprising an image generating unit that generates a phase contrast image based on the plurality of radiation images that have been aligned. Positioning device. 9. Each position obtained by irradiating a subject and a positioning marker with radiation and detecting radiation transmitted through the subject and the marker at a plurality of positions at different distances from the subject. A program for causing a computer to execute an alignment method for aligning a plurality of radiation images including a subject image and a marker image in the computer program, based on a diffraction image of the marker image included in each of the plurality of radiation images. A program for aligning the plurality of radiation images. 10. The step of performing the alignment includes the steps of extracting a plurality of diffraction fringes of the marker image, and detecting a plurality of reference positions for the marker image based on the extracted plurality of diffraction fringes. A step of determining a representative position representing the plurality of reference positions; and a step of performing alignment of the plurality of radiation images based on the representative positions of the plurality of radiation images. The described program. 11. The program according to claim 10, wherein when the marker has a circular shape, the reference position is a center position of the diffraction fringe. 12. The method according to claim 9, further comprising a step of generating a phase contrast image based on the plurality of radiation images that have been aligned.
Program described in section.