JP2003135438A - Method, device, and program for image generation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate an inverse projection function by using a radiograph obtained at a plurality of photographing positions and to accurately generate phase contrast images by using the inverse projection function. SOLUTION: While moving a detection panel 31, the detection panel 31 is irradiated with an X-ray 12 transmitted through an object 21 and image data Sn indicating the X-ray image of the object 21 are obtained at a plurality of the photographing positions. In an arithmetic part 40, the inverse projection function for calculating the fluctuation components of a spatial frequency is calculated from the image data Sn. In the case that a denominator of the inverse projection function becomes 0 and the inverse projection function diverges, the fluctuation components to be calculated are defined as 0. By Fourier transforming the calculated fluctuation components, the image data Sp indicating the phase contrast images are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects radiation applied to a subject at a plurality of positions at different distances from the subject to obtain a plurality of radiation images, and calculates a backprojection function based on the plurality of radiation images. The present invention relates to an image generation method and apparatus for calculating and generating a phase contrast image based on this backprojection function, and a program for causing a computer to execute the image generation method.

[0002]

2. Description of the Related Art Conventionally, radiation (X-ray, α
Rays, β rays, γ rays, electron rays, ultraviolet rays, etc.) to radiate the radiation that has passed through the subject, and the detector is a stimulable phosphor sheet or a radiation detection panel in which a plurality of detection elements are two-dimensionally arranged. The image data representing the radiation image of the object is obtained by performing the image detection, the image data is subjected to various image processing, and then the image data is reproduced.

Here, in the method using the stimulable phosphor sheet, a part of the radiation energy transmitted through the subject is accumulated, and when excitation light is irradiated thereafter, stimulated emission light of a light amount corresponding to the accumulated energy is emitted. Using the stimulable phosphor (stimulable phosphor), the radiation image information of the subject is recorded on the sheet-shaped stimulable phosphor (that is, the stimulable phosphor sheet), and the stimulable phosphor sheet is used as a laser beam. Is a method of generating stimulated emission light by scanning with excitation light such as, and photoelectrically reading the generated stimulated emission light to obtain image data representing a radiation image of a subject. Further, 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 in each detection element according to the radiation dose applied to the radiation detection panel. This is a method of obtaining image data representing a radiation image of a subject based on this electric signal.

By the way, the radiation image thus obtained represents the difference in the intensity of the transmitted radiation in the subject as an image. For example, when a subject including a bone part and a soft part is photographed, the radiation that has passed through the bone part is greatly attenuated, so that the amount of radiation that reaches the detector is small, but the radiation that has passed through the soft part is not significantly attenuated, so that the detection is performed. The radiation dose reaching the vessel is relatively high. Therefore, in the case of such a subject, a radiographic image in which the bone portion is white and the soft portion is black and the contrast difference is large, that is, a large amount of information is obtained. Note that such a radiation image is referred to as an intensity information radiation image.

However, for example in breast cancer diagnosis,
When the subject is mainly composed of only the soft part, the difference in radiation attenuation amount due to the tissue is not so large, so that only a radiation image with a small contrast difference, that is, a small amount of information can be obtained.

Therefore, there has been proposed a phase contrast imaging method for visualizing a phase difference of radiation caused by passing through a subject. In this phase contrast imaging method, since radiation is an electromagnetic wave similar to light and a wave propagates and propagates, when two different substances are irradiated with radiation, the difference in how the radiation propagates in the substance causes The subject is photographed based on the fact that the phases of the radiation waves are different before and after the transmission of the substance, resulting in a phase difference. Here, when the subject is a soft part, the phase difference of the radiation becomes larger than the difference of the attenuation amount of the radiation, so the phase contrast imaging method is used to capture the phase difference of the radiation as a phase contrast image. This makes it possible to visualize a subtle difference in tissues contained in the soft part. For the phase contrast imaging method, see `` 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) "for details.

According to these documents, image data representing a plurality of radiation images is obtained by performing imaging using a two-dimensional detector at a plurality of imaging positions having different distances from the subject, and using the plurality of image data. A phase contrast image can be generated by performing an operation based on a predetermined algorithm.

By the way, when a phase contrast image is generated from image data representing a plurality of radiation images obtained by the phase contrast imaging method, a method of calculating a back projection function to generate the phase contrast image has also been proposed. There is. Hereinafter, this method will be described. This method is described in "M.Op de Beeck, D.Van Dyck, W.Coene," Wav
e function reconstruction in HRTEM: the parabola m
ethod ", Ultramicroscopy 64 (1996), 167-183 (reference 3)" is applied to a two-dimensional image.

FIG. 6 is a diagram for explaining phase contrast imaging. As shown in FIG. 6, by changing the distance z between the two-dimensional detector and the object from z ₁ to z _N and performing imaging, N X-ray images (hereinafter referred to as X-ray intensity images) I ₁ ，
It is assumed that I ₂ , ... _IN are obtained. Then, it is considered that the transmittance q of the subject 101 is obtained using the X-ray intensity image. The X-ray intensity image I _n (n = 1 to N) corresponds to the value of each pixel on the image, and strictly speaking, I _n (x, y) (x, y are positions on the image. However, in FIG. 6, (x, y) is omitted. Here, since the relation between the image data obtained by the two-dimensional detector and the intensity of the radiation applied to the two-dimensional detector is known in advance, a table showing the relation is prepared and the table is referred to. Thereby, an X-ray intensity image can be obtained from the image data obtained by the two-dimensional detector.

According to the Fresnel diffraction formula, the transmittance q
The wave Ψ _z (x, y) of the X-ray that passes through the object (x, y) and reaches the distance z from the object is represented by the following equation (1).

[0011]

[Equation 1] In Expression (1), * represents convolution integral, and h _z (x,
y) is the Fresnel propagation equation shown in the following equation (2). In the formula (2), i represents an imaginary unit and λ represents the wavelength of X-ray.

[0012]

[Equation 2]

By the way, X-ray is a kind of electromagnetic wave like visible light, and has a wavelength of several tens to 0.01 nm. Electromagnetic waves have two characteristics of particle nature and wave nature, but X-ray waves represent the nature of X-ray waves. Usually, a wave has two pieces of information, an amplitude and a phase (a phase from a certain reference position), but what can be actually detected is the energy of the wave represented by the square of the amplitude, that is, the intensity of the X-ray, and the equation ( The X-ray wave as shown in 1), that is, the amplitude and phase of the X-ray cannot be directly detected. Using equation (1), the distance z _n from the subject 101
The X-ray intensity I _n (x, y) obtained at the imaging positions (n = 1 to N) is represented by the following equation (3).

[Equation 3]

Here, the transmittance q (x, y) is converted into a constant component α
And the fluctuation component Φ (x, y), that is, the component having a spatial frequency of 0 and the other components are decomposed and expressed as the following formula (4).

[0015]

[Equation 4]

By using the equation (4), the equation (3) can be transformed into the following equation (5).

[0017]

[Equation 5]

Further, the equation (5) can be transformed into the following equation (6). In addition, in Formula (6), * attached to the right shoulder of α, Φ (x, y) and h _zn (x, y) means that it is a complex conjugate.

[0019]

[Equation 6]

Further, the following equation (7) can be obtained by Fourier transforming equation (6).

[0021]

[Equation 7] Where u, v: spatial frequency δ (u, v): delta function Φ (u, v): fluctuation component in frequency space H _zn (u, v): Fresnel propagation formula in frequency space F []: Fourier transform

Considering only the DC component, the equation (7) becomes the following equation (8).

[0023]

[Equation 8]

From equation (2), H _zn (u, v) becomes equation (9).

[0025]

[Equation 9]

Therefore, the equation (8) is given by the following equation (10).
Becomes

[0027]

[Equation 10] Then, the equation (10) becomes the following equation (1)
It becomes 1).

[0028]

[Equation 11]

[0029]

[Equation 12]

[Equation 13]

When the equation (13) is added for n = 1, 2, ... N, the following equation (14) is obtained.

[0031]

[Equation 14]

When the right side of the equation (14) is transformed using the equation (12), the following equation (15) is obtained.

[0033]

[Equation 15]

The left side is given by the following equation (16).

[0035]

[Equation 16]

If the nonlinear term NL in the equation (15) is ignored, the following equation (1) is obtained from the equations (15) and (16).
7) can be obtained.

[0037]

[Equation 17]

If the object is a phase object, it can be considered that α≈1. Further, the phase change appears in the fluctuation component, and the relationship of Φ (u, v) ≈iψ (u, v) is established.
Therefore, if the phase difference ψ (u, v) is used for the transmittance q (x, y), from the above formula (4),

[Equation 18] It can be expressed as. Therefore, the variation component Φ (u, v) in the frequency space is obtained from the equation (17), the phase difference ψ (u, v) is further obtained using the relationship of the equation (18), and the obtained phase difference ψ (u , V), the phase difference ψ (x, y) in the real space can be obtained. This phase difference ψ (x, y) represents a phase contrast image.

Further, in consideration of the case where the object is a phase object, the phase contrast image can be obtained by a simplified algorithm. Hereinafter, the simplified algorithm will be described. The algorithm of the above equation (17) is referred to as algorithm 1, and the algorithm described below is referred to as algorithm 2.

Phase object transmittance q (x, y) and phase difference ψ
The relationship shown in the above equation (18) is established with (x, y). In equation (18)

[Formula 19] It can be expressed as.

Further, when the equation (19) is Fourier transformed, the following equation (20) is obtained.

[0042]

[Equation 20]

Substituting equation (20) into equation (10) yields equation (21) below.

[0044]

[Equation 21]

For simplicity, if the second and third terms, which are nonlinear terms, are sufficiently small, equation (21) can be transformed into equation (22) below.

[0046]

[Equation 22]

Therefore, the fluctuation component α ^* Φ (u, v) can be expressed by the following equation (23).

[0048]

[Equation 23]

In order to improve the accuracy, equation (23) is changed to n
= 1, 2, ... N averaged, the following formula (24)
Becomes

[0050]

[Equation 24]

By the way, when the object is a phase object and the fluctuation of the phase is not so large, the phase difference ψ (u, v) in the frequency space is obtained from the relationship shown in the above equation (18).
Can be expressed by the following equation (25).

[0052]

[Equation 25]

In the equation (25),

[Equation 26] Then,

[Equation 27] It can be expressed as. Therefore, Algorithm 2 is
The phase difference ψ (u, v) in the frequency space is represented by the distance z ₁ ,
X-ray intensities I ₁ (x, y), I _{2 at} z ₂ , z ₃ , ... Z _N
(X, y), I ₃ (x, y), ... _IN (x, y) and F ₁ (u, v), F ₂ (u, v), corresponding to the respective distances.
That is, the average value of the fluctuation components calculated based on F ₃ (u, v), ... F _N (u, v) is obtained.

Therefore, the phase difference ψ (x, y) in the real space can be calculated by calculating the spatial frequency component ψ (u, v) of the phase difference from the equation (25) and performing the inverse Fourier transform.

[0055]

However, in the above algorithm 1, when the value of the denominator of equation (17) becomes 0 or a value close to 0, the value of the variation component becomes very large at that spatial frequency. , The phase difference, that is, the phase contrast image cannot be accurately obtained. Also, in the above algorithm 2, the expression (2
When the denominator of 3) becomes 0 or a value close to 0, the value of F _n (u, v) at the time of _n diverges, so that the value of the fluctuation component becomes very large, and the fluctuation component is increased to improve accuracy. Even if the average value of is obtained, the phase difference, that is, the phase contrast image cannot be obtained accurately.

The present invention has been made in view of the above circumstances, and an object thereof is to accurately obtain a phase contrast image.

[0057]

A first image generation method according to the present invention is to irradiate a subject with radiation and detect the radiation transmitted through the subject at a plurality of photographing positions at different distances from the subject. Based on a plurality of radiographic images obtained by calculating a backprojection function corresponding to each spatial frequency in the frequency space, based on each radiographic image and each backprojection function, of the radiation transmitted through the subject. In an image generation method of calculating a variation component of a phase in the frequency space for each of the spatial frequencies and generating a phase contrast image of the subject in the real space based on the variation component, each of the spatial frequencies It is determined whether or not the backprojection function diverges, and the determination result is based on only the fluctuation component calculated based on the negative backprojection function. There are, it is characterized in that to generate the phase contrast image.

The "back projection function" is used to estimate the intensity and phase of radiation at a position where an object, which is a subject, exists from the intensity of radiation obtained at a plurality of photographing positions when a phase contrast image is generated. Function, specifically, in the case of Algorithm 1, in the above equation (17)

[Equation 28] Etc., in the case of Algorithm 2,

[Equation 29] Alternatively, the right side of the above equation (27) or the like can be used as the backprojection function.

A second image generation method according to the present invention irradiates a subject with radiation and detects the radiation transmitted through the subject at a plurality of photographing positions at different distances from the subject. Based on the radiographic image
A backprojection function corresponding to each spatial frequency in the frequency space is calculated for each of the plurality of imaging positions, and based on each of the radiation images and the backprojection function, the phase of the radiation that passes through the subject in the frequency space. A variation component is calculated for each of the spatial frequencies, an average value of the variation components corresponding to the plurality of imaging positions is calculated, and a phase contrast image of the subject in the real space is generated based on the average value of the variation components. In the image generating method, it is determined whether or not each of the backprojection functions corresponding to each of the spatial frequencies at each of the photographing positions diverges, and the determination result is calculated based on the denied backprojection function. It is characterized in that the phase contrast image is generated by calculating an average value of the fluctuation components only based on the fluctuation components.

The first image generating apparatus according to the present invention irradiates a subject with radiation and detects the radiation transmitted through the subject at a plurality of photographing positions having different distances from the subject. Based on the radiographic image
A backprojection function corresponding to each spatial frequency in the frequency space is calculated, and based on each of the radiation images and each of the backprojection functions, a variation component of the phase of the radiation passing through the subject in the frequency space is calculated in each of the spaces. In an image generating apparatus including a generating unit that calculates for each frequency and generates a phase contrast image of the subject in the real space based on the fluctuation component, the generating unit includes the back projections corresponding to the spatial frequencies. A means for determining whether or not the function diverges, and for generating the phase contrast image based only on the fluctuation component calculated based on the back projection function for which the determination result is denied. To do.

The second image generating apparatus according to the present invention irradiates a subject with radiation and detects the radiation transmitted through the subject at a plurality of photographing positions having different distances from the subject. Based on the radiographic image
A backprojection function corresponding to each spatial frequency in the frequency space is calculated for each of the plurality of imaging positions, and based on each of the radiation images and the backprojection function, the phase of the radiation that passes through the subject in the frequency space. A variation component is calculated for each of the spatial frequencies, an average value of the variation components corresponding to the plurality of imaging positions is calculated, and a phase contrast image of the subject in the real space is generated based on the average value of the variation components. In the image generating apparatus including the generating unit, the generating unit determines whether or not the backprojection functions corresponding to the spatial frequencies at the photographing positions diverge, and the determination result is denied. Means for calculating the average value of the fluctuation components based on only the fluctuation components calculated based on the back projection function to generate the phase contrast image It is characterized in that.

The first and second image generation methods according to the present invention may be provided as a program for causing a computer to execute.

[0063]

According to the first image generation method and apparatus of the present invention, it is determined whether or not each backprojection function corresponding to each spatial frequency diverges, and the determination result is denied, that is, divergence does not occur. The phase contrast image is generated based only on the fluctuation component calculated based on the back projection function determined to be. That is, the fluctuation component calculated based on the divergent backprojection function when the absolute value of the denominator becomes less than the predetermined threshold value is not used when generating the phase contrast image. . Therefore, the fluctuation component having an extremely large value is not used for generating the phase contrast image, and thus the phase contrast image can be accurately generated.

According to the second image generating method and apparatus of the present invention, it is judged whether or not each backprojection function corresponding to each spatial frequency at each photographing position diverges, and the judgment result is denied, that is, The average value of the variation components is calculated based on only the variation components calculated based on the backprojection function determined not to diverge, and the phase contrast image is generated. That is, the fluctuation component calculated based on the divergent backprojection function when the absolute value of the denominator becomes less than the predetermined threshold value is not used when generating the phase contrast image. . Therefore, the fluctuation component having an extremely large value is not used for generating the phase contrast image, and thus the phase contrast image can be accurately generated.

[0065]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing the configuration of a photographing device to which an image generating device according to the first embodiment of the present invention is applied. As shown in FIG. 1, this imaging apparatus includes an X-ray source 10 that irradiates an object 21 with X-rays, an object support unit 20 that supports the object 21, and an X-ray that has passed through the object 21 from the object 21. A recording unit 30 that obtains image data Sn (n = 1 to N) representing a plurality of X-ray images of the subject 21 by detecting at a plurality of imaging positions with different z _n (n = 1 to N), and a plurality of images. And a calculation unit 40 that generates image data Sp representing a phase contrast image using the data Sn.

The subject 21 is a phase object whose shape can be expressed mainly by a phase change.

The X-ray source 10 includes a radiation source 11 which emits synchrotron radiation, and a crystal 13 such as silicon which monochromates the synchrotron radiation into monochromatic X-rays (hereinafter simply referred to as X-rays) 12. The synchrotron radiation emitted from the radiation source 11 is reflected by the crystal 13 to obtain a monochromatic X-ray 12.

The subject support section 20 includes a support base 24 for supporting the subject 21.

The recording section 30 moves the detection panel 31 composed of a plurality of detection elements arranged two-dimensionally and the detection panel 31 in a direction parallel to the traveling direction of the X-rays 12 transmitted through the subject 21. Moving means 32 and detection panel 31
Read-out means 33 which obtains the image data Sn at each photographing position by reading electric signals from a plurality of detection elements constituting the detection panel 31 at a plurality of photographing positions set in advance on the moving path.

The moving means 32 supports the detection panel 31 and a support portion 35 formed with a female screw portion, and the X-ray 1
The support portion 3 extends in a direction parallel to the traveling direction of 2 and
5, a male screw portion 36 to be screwed into the female screw portion, and a male screw portion 36.
Is provided with a motor 37 for rotating about a rotating shaft extending in the traveling direction of the X-ray 12, and a control unit 38 for controlling driving and stopping of the motor 37. Then, by driving the motor 37 by the control unit 38, the male screw portion 36 is rotated, and the support portion 35, that is, the detection panel 31 is moved in a direction approaching the subject 21 and a direction away from the subject 21 depending on the rotating direction.

Using the algorithm 1 described above, the calculation section 40 calculates the backprojection function corresponding to each spatial frequency in the frequency space of each X-ray image represented by the plurality of image data Sn, and calculates each X-ray ray. The fluctuation component of the phase in the frequency space is calculated based on the image and each backprojection function, and the image data Sp representing the phase contrast image in the real space is generated based on the fluctuation component.

Therefore, the calculation unit 40 calculates the backprojection function corresponding to each spatial frequency from the plurality of image data Sn, and the backprojection function calculating means 41 calculates the phase fluctuation component in the frequency space based on the backprojection function. The fluctuation component calculating means 42 for calculating and the real space image generating means 4 for generating the image data Sp representing the phase contrast image in the real space.
3 is provided.

The backprojection function calculation means 41 uses the algorithm 1 described above to calculate the backprojection function F shown in the following equation (28).
_n (u, v) (n = 1 to N) is calculated for each photographing position.

[0074]

[Equation 30]

The detection panel 31 is provided at each photographing position.
The relationship between the intensity of the X-rays radiated on the image and each pixel value of the image represented by the image data Sn can be detected in advance. Therefore, from this relationship, a conversion table for converting the pixel value of the image represented by the image data Sn into the intensity of the X-ray is created, and by referring to this conversion table, the image data acquired at the distance z _n is obtained. X from the pixel value at the position (x, y) of the image represented by Sn
The intensity I _n (x, y) of the line can be determined. Further, the intensity I _n (x, y) can be Fourier transformed to obtain the X-ray intensity I _n (u, v) in the frequency space.

In the above equation (28), the denominator of the back projection function F _n (u, v) corresponding to each photographing position is
It is the same regardless of each shooting position, and the denominator is G (u, v).
Then, G (u, v) can be expressed by the following equation (29).

[0077]

[Equation 31]

The fluctuation component calculating means 42 has a threshold value Δ having a value in which the absolute value of the denominator G (u, v) of the backprojection function is close to 0 calculated in advance at a certain spatial frequency (u, v).
It is determined whether it is less than. That is, the fluctuation component calculating means 42 has a certain spatial frequency (ui, vj) (i = 1 to 1).
U, j = 1 to V, U and V are the highest reproducible frequencies in this embodiment, and it is determined whether or not the condition of the following formula (30) is satisfied.

[0079]

[Equation 32]

Here, when the condition of expression (30) is satisfied,
Since the value of the backprojection function F _n (ui, vj) diverges, the spatial frequency (ui, vj) in that case does not contribute to the calculation of the phase contrast image, and the following equation (3)
As shown in 1), the fluctuation component α ^* Φ in equation (17)
The value of (ui, vj) is treated as 0.

[0081]

[Expression 33]

Then, the value of the spatial frequency (ui, vj) is sequentially changed, and the variation component α ^* Φ (u, v) is calculated for all the spatial frequencies (u, v).

The real space image generation means 43 has a fluctuation component α ^* Φ generated by the frequency space image generation means 42.
From (u, v), the subject 21 is a phase object and the phase difference ψ (u, v) in the frequency space is obtained using the relationship shown in the above equation (18), and the obtained phase difference ψ
The phase difference ψ (x, y) in the real space is obtained by inverse Fourier transforming (u, v). This phase difference ψ (x,
y) is the image data Sp representing the phase contrast image.

Next, the operation of the first embodiment will be described. FIG. 2 is a flowchart showing the operation of this embodiment. First, the X-ray source 1 is driven by driving the radiation source 11 to reflect the synchrotron radiation on the crystal 13.
The monochromatic X-rays 12 are emitted from 0, and the X-rays 1 are emitted to the subject 21.
Irradiate 2 (step S1). 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, the electric signals of the plurality of detection elements forming the detection panel 31 are read by the reading means 33 at the plurality of photographing positions according to the movement, and the image data Sn at each photographing position is acquired (step S).
3).

The acquired image data Sn is input to the arithmetic unit 40, and the spatial frequency (ui, vj) is set to an initial value (for example, i
= 0, j = 0) (step S4) and the backprojection function F corresponding to the set spatial frequency (ui, vj)
_n (ui, vj) is calculated (step S5). Then, the denominator G of the calculated backprojection function F _n (ui, vj)
It is determined whether or not (ui, vj) is less than the threshold value Δ (step S6), and when step S6 is affirmed, the fluctuation component α ^* Φ (ui, vj) = 0 is set ( Step S7). When step S6 is denied, the fluctuation component α ^* Φ (ui, vj) is calculated (step S8).

Then, it is judged whether or not the variation component α ^* Φ (u, v) has been calculated for all spatial frequencies (u, v) (step S9), and if step S9 is negative, then The spatial frequency (eg (ui + 1, vj)) is set as a function for calculating the fluctuation component α ^* Φ (ui + 1, vj) (step S10), and the process returns to step S5. When step S9 is affirmed, the phase difference ψ is calculated from the fluctuation components α ^* Φ (u, v) in all the calculated frequency components.
(U, v) is calculated, and the phase difference ψ (u, v) is inverse-Fourier-transformed to obtain the phase difference ψ (x, x in real space.
y) is obtained, the image data Sp representing the phase contrast image is generated (step S11), and the process ends. The image data Sp is used for reproduction by a monitor or print output by a printer.

As described above, in this embodiment, the back projection function F _n (u) corresponding to a certain spatial frequency (ui, vj) is used.
When the absolute value of the denominator G (ui, vj) of (i, vj) is less than the threshold value Δ, the variation component α ^* Φ of the spatial frequency
The value of (ui, vj) is set to 0, and the image data Sp representing the phase contrast image in the real space is generated. Here, the backprojection function F _n (ui, v) in which the absolute value of the denominator G (ui, vj) is less than the threshold value Δ
Since j) is divergent, the value of the fluctuation component α ^* Φ (ui, vj) becomes very large, and as a result, the phase contrast image cannot be obtained accurately. In the present embodiment, when the back projection function F _n (ui, vj) diverges,
Since the value of the variation component α ^* Φ (ui, vj) calculated by the back projection function F _n (ui, vj) is set to 0 so as not to be used for generating the phase contrast image, the phase contrast image is accurately generated. can do.

Next, a second embodiment of the present invention will be described. FIG. 3 is a schematic block diagram showing the configuration of a photographing device to which the image generating device according to the second embodiment of the present invention is applied. In the second embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The second embodiment calculates the backprojection function in each frequency space of each X-ray image represented by a plurality of image data Sn using Algorithm 2 described above, and based on each X-ray image and backprojection function. This is different from the first embodiment in that a calculation unit 140 that calculates a phase variation component in the frequency space and generates image data Sp representing a phase contrast image in the real space based on the variation component is provided.

The operation unit 140 calculates the backprojection function corresponding to each spatial frequency from a plurality of image data Sn, the backprojection function calculating means 141, and the fluctuation for calculating the phase fluctuation component in the frequency space based on the backprojection function. Component calculation means 1
42, and real space image generation means 143 for generating image data Sp representing a phase contrast image in the real space.
Equipped with.

The backprojection function calculating means 141 calculates the backprojection function F ′ _n (u, v) shown in the following equation (32) by the above-mentioned algorithm 2.

[0091]

[Equation 34]

Here, in the above equation (32), the denominator of the backprojection function F ′ _n (u, v) corresponding to each shooting position differs for each shooting position, and the backprojection function corresponding to each shooting position. F _'n (u, v) the denominator of G of' _n (u, v) and when,
The denominator G ′ _n (u, v) can be expressed by the following equation (33).

[0093]

[Equation 35]

The fluctuation component calculating means 142 calculates the absolute value of the denominator G ′ _n (u, v) of the backprojection function F ′ _n (u, v) corresponding to a certain photographing position at a certain spatial frequency (u, v). Is less than a threshold value Δ having a value close to 0 calculated in advance. That is, the fluctuation component calculating means 14
2 is the spatial frequency at a photographing position z _n (ui,
vj) (i = 1 to U, j = 1 to V, U and V are the highest reproducible frequencies in this embodiment), it is determined whether or not the condition of the following expression (34) is satisfied.

[0095]

[Equation 36]

Here, when the condition of the expression (34) is satisfied,
Since the value of the backprojection function F ′ _n (ui, vj) diverges, the spatial frequency (ui, vj) at the imaging position z _n in that case
With respect to, the value of the fluctuation component α ^* Φ (ui, vj) in Expression (23) is treated as 0 so as not to contribute to the calculation of the phase contrast image, as shown in Expression (35) below.

[0097]

[Equation 37]

Then, the fluctuation component α ^* Φ (u having a value of 0
i, vj) is excluded from the calculation of the average value by the equation (24), and the average value of the fluctuation component α ^* Φ (ui, vj) is calculated. Here, when the values of the backprojection function F ′ _n (u, v) at all imaging positions do not diverge at a certain spatial frequency (u, v), the variation component α ^* Φ is calculated by the following equation (36).
The average value of (u, v) is calculated.

[0099]

[Equation 38]

On the other hand, when the value of the backprojection function F ′ _n (u, v) at a certain spatial frequency (u, v) at the shooting position where the distance from the subject 21 is zk is divergent, the following equation (37) ), The average value of the fluctuation component α ^* Φ (u, v) is calculated.

[0101]

[Formula 39]

Then, the value of the spatial frequency (ui, vj) is sequentially changed, and the average value of the fluctuation components α ^* Φ (u, v) is obtained for all the spatial frequencies (u, v).

The real space image generation means 143 has a fluctuation component α ^* Φ generated by the frequency space image generation means 42.
The phase difference ψ in the frequency space from the average value of (u, v)
(U, v) is obtained, and the obtained phase difference ψ (u, v) is inverse Fourier transformed to obtain the phase difference ψ in the real space.
Find (x, y). This phase difference ψ (x, y) becomes the image data Sp representing the phase contrast image.

Next, the operation of the second embodiment will be described. FIG. 4 is a flowchart showing the operation of the second embodiment. First, the radiation source 11 is driven so that the synchrotron radiation light is reflected by the crystal 13, whereby monochromatic X-rays 12 are emitted from the X-ray source 10 and X-rays the subject 21.
The line 12 is irradiated (step S21). At the same time,
The control unit 38 drives the motor 37 to drive the detection panel 3
1 is moved in a direction away from the initial position closest to the subject 21 (step S22). Then, the detection panel 3 is read by the reading means 33 at a plurality of photographing positions according to the movement.
By reading the electric signals of the plurality of detection elements constituting
The image data Sn at each shooting position is acquired (step S23).

The acquired image data Sn is stored in the calculation unit 140.
, The spatial frequency (ui, vj) is set to an initial value (step S24), and the photographing position is set to an initial value (that is, n = 1) (step S25). Then, at the shooting position, the set spatial frequency (u
i, the inverse projection function F _'n (ui corresponding to vj), vj) is calculated (step S26). The calculated inverse projection function F _'n (ui, vj) of the denominator G' _n (ui, vj) it is determined whether it is less than the threshold delta (step S2
7) If the result at step S27 is affirmative, the fluctuation component α ^* Φ (ui, vj) = 0 is set (step S28).
When the step S27 is denied, the fluctuation component α ^* Φ
(Ui, vj) is calculated (step S29).

Whether or not the shooting position at which the current fluctuation component α ^* Φ (u, v) is calculated is the final shooting position,
That is, it is determined whether or not n = N (step S3
0), if step S30 is denied, the value of n is incremented by 1 (step S31), and the process returns to step S27. If the result at step S30 is affirmative, the average value of the fluctuation components α ^* Φ (ui, vj) at all the shooting positions is calculated (step S32).

Subsequently, it is judged whether or not the average value of the fluctuation components α ^* Φ (u, v) has been calculated for all the spatial frequencies (u, v) (step S33), and when the step S33 is denied. Has the following spatial frequency (eg (ui + 1, v
j)) is set as a function for calculating the average value of the fluctuation component α ^* Φ (ui + 1, vj) (step S34), and step S34
Return to 25. When step S33 is affirmed, the phase difference ψ (u, v) is calculated from the average value of the fluctuation components α ^* Φ (u, v) in all the frequency components, and the phase difference ψ (u, v) is calculated.
The phase difference ψ (x, y) in the real space is obtained by performing the inverse Fourier transform on (u, v), and the image data Sp representing the phase contrast image is generated (step S
35), the process ends. The image data Sp is used for reproduction by a monitor or print output by a printer.

Here, in the second embodiment, the backprojection function F'corresponding to a certain spatial frequency (ui, vj).
_If the denominator G ′ _n (ui, vj) of _n (ui, vj) is less than the threshold Δ, the backprojection function F ′ _n (ui, vj) diverges,
As a result, the value of the calculated fluctuation component α ^* Φ (ui, vj) becomes very large. Therefore, the fluctuation component α ^* Φ (u,
Even if the average value of the fluctuation component α ^* Φ (u, v) calculated at each imaging position is calculated in order to improve the calculation accuracy of v), the value becomes very large α ^* Φ (u, v). ), The accuracy of the average value decreases.

In the second embodiment, the backprojection function F _n (ui, vj) corresponding to a certain spatial frequency (ui, vj) is used.
, The backprojection function F _n (ui, vj) of
The value of the fluctuation component α ^* Φ (ui, vj) calculated by
As a result, I did not use it to calculate the average value.
It is possible to accurately generate a phase contrast image.

In each of the above-mentioned embodiments, one detection panel 31 in the recording unit 30 is moved by the moving means 32 in a direction parallel to the traveling direction of the X-rays 12, and images are taken at a plurality of photographing positions. However, as shown in FIG. 5, a plurality of (here, three) stimulable phosphor sheets 61, 62, 63 are used in place of the detection panel 31, and these are placed at a plurality of predetermined photographing positions. The stimulable phosphor sheets 61, 62, 63 may be respectively provided to simultaneously perform image capturing at a plurality of image capturing positions.

When X-ray images are accumulated and recorded on the stimulable phosphor sheets 61, 62 and 63 in this way,
A plurality of image data S representing an X-ray image is read in the reading unit 70 that irradiates each sheet 61, 62, 63 with excitation light to generate stimulated emission light and photoelectrically reads the stimulated emission light.
n is obtained. The obtained plurality of image data Sn are input to the calculation unit 40 (or 140) as in the above embodiments, and the image data Sp representing the phase contrast image is generated.

In each of the above embodiments, the radiation source 1
Although the one that emits the synchrotron radiation is used as No. 1, it is not limited to this. Also, subject 2
Although a monochromatic X-ray is used as the X-ray 12 for irradiating 1
It is not limited to monochromatic X-rays.

In each of the above embodiments, the subject 21 is irradiated with X-rays, but radiation other than X-rays (α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is used. Good.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing a configuration of a photographing device to which an image generating device according to a first embodiment of the present invention is applied.

FIG. 2 is a flowchart showing the operation of the first embodiment.

FIG. 3 is a schematic block diagram showing a configuration of a photographing device to which an image generating device according to a second embodiment of the present invention is applied.

FIG. 4 is a flowchart showing the operation of the second embodiment.

FIG. 5 is a schematic block diagram showing the configuration of a photographing device to which an image generating device according to another embodiment of the present invention is applied.

FIG. 6 is a diagram for explaining phase contrast imaging.

[Explanation of symbols]

10 X-ray source 11 radiation sources 12 X-ray 13 crystals 20 Subject support 21 subject 30 recording section 31 Detection panel 32 means of transportation 33 reading means 40,140 arithmetic unit 61,62,63 Accumulative phosphor sheet 70 reading means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G06T 5/00 100 G06T 7/40 B 7/40 G21K 4/00 L G21K 4/00 A61B 6/00 350Z F-term (reference) 2G083 AA03 BB03 BB05 CC10 DD13 EE02 2H013 AC06 4C093 AA26 AA30 CA50 EA01 EB17 FC16 FD03 FD20 FF50 5B057 AA08 BA03 CA02 CA08 CA12 CA06 DA06 A06 DB03 A06 DB03 A06 DB03 A05 DB06 DB03 A05 DB06 DB03 DB05 CE02 CE02 CE02 CE02 FA32 GA59

Claims (6)

[Claims] 1. A frequency space based on a plurality of radiographic images obtained by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of imaging positions at different distances from the subject. A backprojection function corresponding to each spatial frequency is calculated, and based on each of the radiation images and each of the backprojection functions, a variation component of the phase of the radiation passing through the subject in the frequency space is determined for each of the spatial frequencies. In the image generation method of calculating and generating the phase contrast image of the subject in the real space based on the fluctuation component, it is determined whether or not each of the backprojection functions corresponding to each of the spatial frequencies diverges, Generating the phase contrast image based only on the fluctuation component calculated based on the back projection function for which the result is denied. Image generation method for the butterflies. 2. A frequency space based on a plurality of radiation images obtained by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of photographing positions at different distances from the subject. A backprojection function corresponding to each spatial frequency is calculated for each of the plurality of imaging positions, and based on each of the radiation images and the backprojection function, a variation component of the phase of the radiation passing through the subject in the frequency space is calculated. Image generation that calculates for each spatial frequency, calculates an average value of the fluctuation components corresponding to the plurality of shooting positions, and generates a phase contrast image of the subject in real space based on the average value of the fluctuation components In the method, it is determined whether or not each of the backprojection functions corresponding to each of the spatial frequencies at each of the imaging positions diverges, and the determination result is negative. Based only on the variation component calculated based on the backprojection functions, image generation method characterized by generating the phase contrast image and calculates the average value of the fluctuation component. 3. A frequency space based on a plurality of radiation images obtained by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of imaging positions at different distances from the subject. A backprojection function corresponding to each spatial frequency is calculated, and based on each of the radiation images and each of the backprojection functions, a variation component of the phase of the radiation passing through the subject in the frequency space is determined for each of the spatial frequencies. In the image generation device including a generation unit that calculates and generates a phase contrast image of the subject in the real space based on the fluctuation component, the generation unit is configured to diverge each backprojection function corresponding to each spatial frequency. Whether or not to perform the phase determination based on only the fluctuation component calculated based on the back projection function for which the determination result is denied. Image generating apparatus, characterized in that contrast is a means for generating an image. 4. A frequency space based on a plurality of radiation images obtained by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of imaging positions at different distances from the subject. A backprojection function corresponding to each spatial frequency is calculated for each of the plurality of imaging positions, and based on each of the radiation images and the backprojection function, a variation component of the phase of the radiation passing through the subject in the frequency space is calculated. A generating unit that calculates for each of the spatial frequencies, calculates an average value of the fluctuation components corresponding to the plurality of photographing positions, and generates a phase contrast image of the subject in the real space based on the average value of the fluctuation components. In the image generating apparatus including: the generating unit diverges each of the backprojection functions corresponding to each of the spatial frequencies at each of the photographing positions. By means of determining whether or not, and based on only the fluctuation component calculated based on the back projection function for which the judgment result is denied, an average value of the fluctuation component is calculated to generate the phase contrast image. An image generating apparatus characterized by being present. 5. A frequency space based on a plurality of radiation images obtained by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of imaging positions at different distances from the subject. A backprojection function corresponding to each spatial frequency is calculated, and based on each of the radiation images and each of the backprojection functions, a variation component of the phase of the radiation passing through the subject in the frequency space is determined for each of the spatial frequencies. A program for causing a computer to execute an image generation method for calculating and generating a phase contrast image of the subject in the real space based on the variation component, whether each backprojection function corresponding to each spatial frequency diverges? A procedure for determining whether or not the determination result and only the variation component calculated based on the back projection function for which the determination result is denied Zui, the program having a step of generating the phase contrast image. 6. A frequency space based on a plurality of radiographic images obtained by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of imaging positions having different distances from the subject. A backprojection function corresponding to each spatial frequency is calculated for each of the plurality of imaging positions, and based on each of the radiation images and the backprojection function, a variation component of the phase of the radiation passing through the subject in the frequency space is calculated. Image generation that calculates for each of the spatial frequencies, calculates an average value of the fluctuation components corresponding to the plurality of shooting positions, and generates a phase contrast image of the subject in real space based on the average value of the fluctuation components A program for causing a computer to execute the method, wherein each backprojection function corresponding to each spatial frequency at each imaging position The procedure for determining whether or not to diverge, and the phase contrast image by calculating an average value of the variation components only based on the variation components calculated based on the back projection function for which the determination result is denied. A program having a procedure for generating.