JP2016156697A - Phase detection type radiographic x-ray apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase detection type radiographic X-ray apparatus with which it is possible to establish an interference condition under different X-ray energies and take a photograph with discretionary X-ray energy.SOLUTION: A radiographic X-ray apparatus includes, between an X-ray source 101 and an X-ray detector 106, first to third grading units 103, 104, and 105 that are arranged in order from the X-ray source. Each of the first and third grating units 103, 105 comprises a plurality of grating members, and the in-plane rotation of the plurality of grating members generates a moire fringe in which an X-ray shielding part and an X-ray transmitting part are alternately arrayed. The repetition cycle of the shielding and transmitting parts of the moire fringe is changed by adjusting the relative rotation angles of the gratings in accordance with X-ray energy, whereby an interference condition is established.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image acquisition apparatus using X-rays, and more particularly to an X-ray differential phase contrast image photographing apparatus.

  Conventional image acquisition technology using X-rays is based on the transmission of X-rays, that is, the distribution of the X-ray absorption rate of the subject, but depends on the tissue when X-rays pass through the subject. It is known that the effect (contrast) of the phase shift of X-rays generated is greater than that of X-ray absorption, and attempts have been made to apply this phase shift imaging technique to medical images. This technique is called a phase contrast imaging technique or a phase detection type imaging technique, and is expected to depict soft tissues that are difficult to draw with an absorption contrast image.

  In the currently known phase contrast imaging technique, an apparatus using a Talbot-Lau interferometer is used. In this apparatus, a first grating composed of an absorption diffraction grating for dividing the X-ray source into minute light sources is disposed between the X-ray source and the subject. Further, a second grating in which materials for changing the phase are arranged at a predetermined period between the subject and the X-ray detector, and a period regulated by the pitch of interference fringes formed by the effect of the second grating. And a third grating having. The structure for establishing the interference condition in such an apparatus is determined by the X-ray energy, the distance between gratings, the period of each grating, and the like. For example, when the X-ray energy used for measurement is changed, it is necessary to change the distance and the period between the gratings.

  In general, when imaging a human body or the like, the optimum X-ray energy for the imaging region is different, so the X-ray energy used for each imaging region is changed. When the X-ray phase contrast imaging device using the Talbot-Lau interferometer described above is applied to the human body, the grating is changed each time the X-ray energy is changed in order to change to the optimum X-ray energy corresponding to the imaging region. There is a need to. This leads to a decrease in convenience of the apparatus and an increase in cost.

  Patent Document 1 proposes a technique for avoiding the change of the grating accompanying the change of the X-ray energy. In this technique, in order to cope with two types of high X-ray energy and low X-ray energy, two gratings disposed between the subject and the X-ray detector are respectively used for high X-ray energy and low X-ray energy. Use a stack of two gratings for energy. The gratings for high X-ray energy and the gratings for low X-ray energy are overlapped with the grating directions orthogonal to each other.

JP 2012-125423 A

  The optimum X-ray energy corresponding to the imaging region exists in a wide range from, for example, a low energy of 20 keV or less to a high energy of 100 keV or more, but in the technique described in Patent Document 1, two predetermined X-ray energies are used. Can only deal with.

  In an X-ray imaging apparatus using a Talbot-Lau interferometer, the interference condition is established by adjusting the distance between the gratings (the distance along the X-ray irradiation direction) to cope with changes in X-ray energy. However, in this case, even in the range of X-ray energy used for general X-ray imaging of the human body, the distance to be adjusted may extend to 1 m or more. Cannot be realized.

  It is an object of the present invention to provide a phase detection type X-ray imaging apparatus that can handle arbitrary X-ray energy.

  In order to solve the above-described problem, the phase detection type X-ray imaging apparatus of the present invention includes two grating sections each composed of an absorption diffraction grating, that is, a first grating disposed between an X-ray source and a subject. And a third grating unit disposed on the X-ray detector side between the subject and the X-ray detector, and provided with means for changing the grating period.

  In the present invention, the second grating unit disposed between the subject and the X-ray detector and on the subject side has a constant grating period and is fixed in position with respect to the first grating unit. Yes.

  The phase detection type X-ray imaging apparatus of the present invention further includes a moving unit that moves the third grating unit along the X-ray irradiation direction with respect to the second grating unit.

  According to the present invention, by providing a mechanism that makes the grating period variable in the two grating parts configured by the absorption diffraction grating, the grating (on the subject side) between the subject and the detector ( The interference condition can be established corresponding to the change of the X-ray energy, that is, X-ray differential phase contrast imaging can be performed while the period and the position of the second grating portion) are fixed.

The figure which shows the outline | summary of the whole structure of the X-ray imaging apparatus of 1st embodiment. FIG. 2 is a front view and an enlarged cross-sectional view showing a structure of a grating constituting the X-ray imaging apparatus, where (a) shows one grating constituting the first grating part, (b) shows the second grating part, and (c) ) Shows one grating constituting the third grating part. This shows a state in which moire is generated due to the in-plane rotation deviation of the two gratings, and the rotation deviation (relative rotation angle) is large in the order of (a) → (b) → (c), and the moire fringe period g1t Shows how it becomes smaller. The figure which shows the relationship between the relative rotation angle of the grating in a 1st grating part, and the grating period g1t. The figure which shows the whole structure of the X-ray imaging apparatus using the conventional Talbot low interferometer The figure which shows the conditions for establishing interference conditions in different X-ray energy in the X-ray imaging apparatus using the conventional Talbot low interferometer Functional block diagram showing the configuration of the control unit of the first embodiment The figure which shows the conditions for satisfy | filling interference conditions in different X-ray energy in the X-ray imaging apparatus of 1st embodiment. (A) is a diagram showing the same graph as FIG. 8, (b) is a diagram showing the relationship between the grating period of the first and third grating parts and the relative rotation angle between the gratings that achieve it. The flow which shows the imaging | photography procedure of 1st embodiment. It is a figure which shows the relationship between the area (opening area) of the permeation | transmission part in the combination of two gratings, and the relative rotation angle of a grating, (a) shows the case of a single opening, (b) shows the case of the whole grating. The figure which shows the outline | summary of the X-ray imaging apparatus of 2nd embodiment. Functional block diagram showing the configuration of the control unit of the second embodiment It is a figure explaining the change of a phase contrast by the difference in X-ray energy, (a) is a graph which shows the relationship between X-ray energy and a phase shift amount, (b) is a phase contrast in case X-ray energy is 20 keV, ( c) shows the phase contrast when the X-ray energy is 100 keV. It is a figure explaining the effect by the X-ray imaging apparatus of 2nd embodiment, (a) is a graph which shows the relationship between X-ray energy and phase shift amount, (b) shows the phase contrast in case X-ray energy is 20 keV. Show. The flow which shows the imaging | photography procedure of 2nd embodiment. The figure which shows the outline | summary of the whole structure of the X-ray imaging apparatus of 3rd embodiment. It is a figure explaining the effect by the X-ray imaging apparatus of 3rd embodiment, (a) shows the change of the image magnification by X-ray energy when the distance of a 2nd grating part and a 3rd grating part is made constant. , (B) shows the change in the distance between the second grating portion and the third grating portion for making the image enlargement ratio constant under different X-ray energy conditions. The figure which shows the example of a change of 1st-3rd embodiment.

  The X-ray imaging apparatus according to this embodiment is arranged to face an X-ray source with an X-ray source (101) that irradiates X-rays and an object (109) interposed therebetween, and detects X-rays that have passed through the object. A first grating unit (103), a second grating unit (104), and a third grating disposed in order from the X-ray source between the X-ray source (106) and the X-ray source. A grating portion (105). Each of the first grating portion (103) and the third grating portion (105) has a structure in which shielding portions that shield X-rays and transmission portions that transmit X-rays are alternately arranged. The repetition period with the transmission part is variable.

  Specifically, each of the first grating portion (103) and the third grating portion (105) includes a plurality of grating members, and adjusts the relative rotation angle by rotating the plurality of grating members in a plane. An angle adjustment mechanism (501-504) is provided. By changing the relative rotation angle of the plurality of grating members by the angle adjusting mechanism, the period of moire fringes generated based on the in-plane displacement of the plurality of grating members, that is, the grating period is changed. The X-ray imaging apparatus of the present embodiment further includes a control unit (107) that controls the angle adjustment mechanism according to the X-ray energy at the time of imaging.

  The X imaging apparatus of the present embodiment further includes a moving stage (508) that moves the third grating part (105) so as to change the distance from the second grating part. The control unit controls the moving stage according to the X-ray energy at the time of imaging.

<First embodiment>
Hereinafter, the X-ray imaging apparatus of this embodiment will be described with reference to the drawings. FIG. 1 shows the overall configuration of the X-ray imaging apparatus of the present embodiment.

  This X-ray imaging apparatus is an apparatus for phase contrast image imaging, and as shown in the figure, an X-ray source 101 and an X-ray detector 106 arranged at a position where X-rays emitted from the X-ray source 101 can be detected. A first grating unit 103 disposed between the X-ray source 101 and the subject 109, a third grating unit 105 disposed between the subject 109 and the X-ray detector, and the subject 109 and the third grating. 2nd grating part 104 arrange | positioned between the parts 105. The X-ray imaging apparatus processes signals detected by the control device (control unit) 107 and the X-ray detector 106 for controlling the operation of each element described above and a mechanism unit (described later) provided in each element. , An arithmetic device (arithmetic unit) 108 for generating an image or the like is provided. The arithmetic unit 108 can be constructed as a single computer system together with the control unit 107. In the following description, when the first to third grating portions are not particularly distinguished, they may be collectively referred to as a grating portion.

  In FIG. 1, the linear direction connecting the X-ray focal point of the X-ray source 101 and the X-ray detector 106 is the z direction, orthogonal to the z direction, the vertical direction in the figure is the y direction, and the direction orthogonal to the y direction is x. Defined as direction.

  The X-ray source 101 includes an X-ray tube, is connected to a power source 102, and emits X-rays having a predetermined X-ray energy. X-ray energy can be changed by changing conditions such as tube current and tube voltage supplied to the X-ray tube. Usually, the X-rays emitted from the X-ray source 101 have an energy distribution, and the X-ray energy at the peak of the distribution is the X-ray energy that mainly plays a role in phase contrast imaging. In the present specification, “predetermined X-ray energy emitted from the X-ray source 101” refers to “X-ray energy having a main function”.

  The X-ray detector 106 can be composed of a known flat detector such as FPD (FLAT PANEL DETECTOR), and its detection surface is substantially orthogonal to the central beam of X-rays irradiated from the X-ray source 101. Is arranged. The X-ray detector 106 is connected to the arithmetic device 108 through a signal processing device inserted as necessary. The signal processing apparatus may be an analog circuit that electrically processes a signal, or may be a processor that processes a digital signal after A / D conversion.

The first grating 103, a pair of grating G1-1, consists G1-2, these gratings G1-1, a grating having a predetermined period _{g 1t} utilizing moire generated by superimposing G1-2 Function as. Although the moire due to the superposition of the gratings G1-1 and G1-2 will be described in detail later, the arrangement direction of the moire fringes generated by the superposition of the gratings is substantially orthogonal to the arrangement direction of the gratings of the gratings G1-1 and G1-2. To do.

Each of the gratings G1-1 and G1-2 has a structure in which linear X-ray shields 202 are arranged at a predetermined period g _1t0 on a substrate 201 that transmits X-rays, as shown in FIG. Have That is, the gratings G1-1 and G1-2 are so-called absorption diffraction gratings, and X-ray transmission parts (hereinafter simply referred to as transmission parts) and X-ray shielding parts (hereinafter simply referred to as shielding parts) are alternately arranged. Has the structure. The gratings G1-1 and G1-2 have the same structure and period, and FIG. 2A shows only one grating.

  The pair of gratings G1-1 and G1-2 are fixed to the rotation adjusting mechanisms 501 and 502, respectively, and the angle between the two (relative rotation angle) can be adjusted by the rotation adjusting mechanism. The rotation adjusting mechanisms 501 and 502 operate under the control of the control device 107. In this embodiment, the respective gratings are rotated by the same angle with the opposite signs with respect to the X axis or the Y axis. In the illustrated embodiment, the case where both of the pair of gratings G1-1 and G1-2 are provided with the rotation adjustment mechanisms 501 and 502, respectively, is realized by a single rotation adjustment mechanism. Is also possible. As the rotation adjusting mechanism, for example, a ring-shaped frame for fixing the grating and a rotating mechanism for rotating the frame on the order of about 1 ° can be employed. Since the rotation mechanism can adopt a known structure, description thereof is omitted here.

  The distance between the grating G1-1 and the grating G1-2 is not particularly limited, but it is preferable that the distance between the grating G1-1 and the grating G1-2 is closely integrated as long as the physical approach of the accompanying mechanism portion is allowed.

The second grating unit 104 is a diffraction grating that generates an X-ray diffraction image. For example, as shown in FIG. 2B, the second grating unit 104 transmits X-rays on a base material 203 such as a silicon substrate that transmits X-rays. The phase change unit 204 made of a material that changes the phase of the phase is arranged with a predetermined period g _2t . The material that changes the phase is a material that changes the phase of the X-ray when the X-ray passes through the material. Generally, a metal such as Au or Ni is used. The amount of phase shift varies depending on the material and its thickness, and can be adjusted by appropriately selecting the material and thickness. A grating having such a structure is also called a phase grating or a phase type diffraction grating, and a diffraction image is generated when X-rays pass through the grating. Here, since the X-ray is an X-ray that is phase-shifted by passing through the subject 109, the diffraction image includes this phase shift.

  The arrangement direction of the phase change sections 204 in the second grating section 104 is the same as the arrangement direction of the transmission section and the shielding section (the arrangement direction of moire fringes) formed by the combination of two gratings in the first grating section 103.

  The first grating unit 103 and the second grating unit 104 include a space in which the subject 109 is disposed between the first grating unit 103 and the second grating unit 104, and are fixed in the apparatus so as to maintain a certain distance L. The distance L is defined as the distance from G1-2 (the one closer to the second grating unit 104) to the second grating unit 104 out of the two gratings of the first grating unit 103.

Similarly to the first grating unit 103, the third grating unit 105 includes a pair of gratings G5-1 and G5-2. The gratings G5-1 and G5-2 are respectively provided with rotation adjusting mechanisms 503 and 504. Is provided. The operations of the rotation adjusting mechanisms 503 and 504 are controlled by the control device 107. The structures of the gratings G5-1 and G5-2 are the same as those of the gratings G1-1 and G1-2 constituting the first grating unit 103, and as shown in FIG. On 205, a shielding part made of a material that shields X-rays is formed in a stripe shape. The two gratings G5-1 and G5-2 have the same grating period. The third grating 105, these gratings G5-1, functions as a grating having a predetermined period g _3t utilizing moire generated by superimposing a relative rotation angle other than zero G5-2.

The third grating unit 105 generates moiré on the diffraction image formed by the second grating unit 104 and renders information on the phase shift included in the X-rays transmitted through the second grating unit 104 as an X-ray transmission amount. It is for making it happen. Therefore, in the third grating, the arrangement direction of the grating (grating by moire) generated by the combination of the two gratings constituting the third grating is the same as the grating arrangement direction of the second grating section 104, and the grating period (transmission section and shielding section). The relative rotation angle of the two gratings is adjusted so that the portion arrangement period) g _3t is the same as the period p of the interference fringes of the second grating unit 104. The distance between the two gratings G5-1 and G5-2 may be a physically minimum distance or a predetermined distance, like the first grating unit 103.

  The third grating unit 105 is mounted on a lateral movement stage 507 that moves the third grating unit 105 in a direction parallel to the grating arrangement direction (x direction) within a plane parallel to the grating surface. The lateral movement stage 507 on which the third grating unit 105 is mounted is further mounted on the vertical movement stage 508. The longitudinal movement stage 508 is a mechanism for moving the third grating in a direction (z direction) orthogonal to the grating surface and adjusting the distance d between the second grating unit 103 and the third grating 103. The distance d in this case is defined as the distance from the second grating section 104 to the grating G5-1 of the third grating section 105.

  The operations of the horizontal movement stage 507 and the vertical movement stage 508 are controlled by the control device 107.

  Next, the adjustment of the grating period in the first grating unit 103 and the third grating unit 105 will be described in detail. The first grating unit 103 and the third grating unit 105 have a common mechanism for forming a moire fringe grating by combining two gratings. Therefore, the first grating unit will be described as a representative in the following description.

  As already described, the gratings G1-1 and G1-2 can change the rotation angle (relative rotation angle) in the plane of each other by the rotation adjusting mechanisms 501 and 502. When these relative rotation angles are not zero, moire occurs when they are superimposed. Moire is an X-ray shading pattern transmitted through the first grating portion 103 and can be regarded as a striped pattern consisting of a shielding portion and a transmission portion, that is, a grating.

  The arrangement direction of the stripes in the moire is a direction substantially orthogonal to the arrangement direction of the gratings of the gratings G1-1 and G1-2. Specifically, for example, when the angles of the gratings G1-1 and G1-2 along the shielding part or the transmission part with respect to the x direction are ± θ (relative rotation angle is 2θ), the moire fringe direction is the y direction, that is, the fringe. The arrangement direction is the x direction.

Further, the moire period can be regarded as the grating period g _1t of the first grating section 103, and differs depending on the angle formed by the two gratings G1-1 and G1-2. FIG. 3 shows moire that occurs when the relative rotational angles formed by the two gratings G1-1 and G1-2 are different. In the figure, the relative rotation angle increases in the order of (a), (b), and (c), and the moire period, ie, the grating period, decreases accordingly. The relationship between the relative rotation angle and the grating period g _1t can be expressed by the following equation (1) as shown in FIG.

[Equation 1]
g _1t = (g _1t0 / 2) ÷ sinθ (1)
In Expression (1), g _1t0 is the period of the gratings G1-1 and G1-2. From equation (1), it can be seen that the grating period g _1t of the first grating unit 103 can be controlled by adjusting the relative rotation angles of the two gratings G1-1 and G1-2.

Similarly, the grating period g _3t can also be controlled by adjusting the relative rotation angle formed by the two gratings G5-1 and G5-2 constituting the third grating unit 105.

  As described above, when the first grating unit 103 and the third grating unit 105 are each regarded as one grating having an adjustable grating period, the X-ray imaging apparatus illustrated in FIG. The configuration is the same as that of the conventional X-ray imaging apparatus shown in FIG. In FIG. 5, the same elements as those of FIG.

  Here, in the measurement technique using the Talbot-Lau interferometer used by the present invention and the conventional X-ray imaging apparatus, the conditions of the apparatus that establish the interference condition are X-ray energy, the second grating section 104 and the third grating section. 105 (grating 405 in the conventional apparatus in FIG. 5) is determined by the distance d and the like, and their relationship is approximated by the equation (2).

式（２）中、ｍは奇数、ηは１又は２、λは主たる働きをするＸ線の波長、ｇ_２ｔは第２グレーティング部１０４のグレーティング周期である。

In equation (2), m is an odd number, η is 1 or 2, λ is the wavelength of X-rays that mainly function, and g _2t is the grating period of the second grating unit 104.

Further, the period p of the diffraction image (interference fringe) of the second grating unit 104 which is a diffraction grating is set such that the distance between the first grating unit 103 (grating 403 in the conventional device of FIG. 5) and the second grating unit 104 is L. Then, it is represented by the following formula (3).

The grating period g _3t of the third grating unit 105 (grating 405 in the conventional apparatus of FIG. 5) is designed to be equal to the period p of this diffraction image. The grating period g _1t of 103 of the first grating unit is approximated by the following expression (4) using the period p.
[Equation 4]
g _1t = p (L / d) (4)

  As can be seen from the equations (2) to (4), when the X-ray energy is determined, the period of each grating necessary for satisfying the interference condition is defined. However, in general, the grating has a periodic structure formed of a metal or the like on a silicon substrate, so that it is necessary to replace the grating in order to cope with a change in X-ray energy. On the other hand, in order to satisfy the interference condition when the X-ray energy is changed while fixing the period of each grating, the change in the distance d between the second and third grating portions is changed to the first and second grating portions. It is conceivable to adjust the distance L between them. However, in this case, since the distance L changes according to the ratio of the X-ray energy that plays a major role in the measurement, it is difficult to cope with a wide X-ray energy in a practical size range. FIG. 6 is a graph showing changes in the distance d and the distance L for satisfying the interference condition when the period of each grating is fixed and the X-ray energy is changed. In FIG. 6, the horizontal axis represents X-ray energy (keV), the right vertical axis represents the grating period (unit: m), and the left vertical axis represents the distance (unit: m). As can be seen from this graph, for example, when the X-ray energy is changed from 20 keV to 40 keV, it is necessary to change the distance L between the first and second grating portions from 1 m to 2 m. It is far from practical as a photographing device.

In the X-ray imaging apparatus of the present embodiment, the X-ray direction of the first grating unit 105 is fixed while the first grating unit 103 and the second grating unit 104 are fixed by the longitudinal movement stage 508 on which the third grating unit 105 is mounted. The position in the (Z direction), that is, the distance d is adjusted, and the grating periods g _1t and g _3t of the first grating unit 103 and the third grating 104 are adjusted to cope with changes in the energy of X-rays that perform the main function. Enables X-ray imaging using a Talbot-Lau interferometer.

  Specifically, in the X-ray imaging apparatus of FIGS. 1 and 5, when the position of the second grating unit 104 is fixed, the change in the X-ray energy (X-ray wavelength λ) in Equation (1) The interference condition can be satisfied by changing the position of the third grating unit 105 (grating 405 in the conventional apparatus of FIG. 5), that is, the distance d with respect to the second grating unit 104.

Further, when the position of the first grating unit 103 (that is, the distance L to the second grating unit 104) and the period g _2t of the second grating unit 104 are fixed, the first grating unit 103 is obtained by the equations (3) and (4). It can be seen that the change in the X-ray energy (X-ray wavelength λ) can be accommodated by changing the period g _1t and the period g _3t of the third grating portion.

Next, the control device 107 for adjusting the period g _1t of the first grating unit 103, the period g _3t of the third grating unit, and the distance d will be described.

  As schematically shown in FIG. 7, the control device 107 mainly includes a measurement control unit 1071, a grating control unit 1075, a calculation unit (calculation device 108), a memory 1078, and a main control unit 1070. . The control device 107 further includes an input device 110 for inputting measurement conditions and commands necessary for its operation, a display device 111 for displaying an image reconstructed by the arithmetic unit 108, a GUI functioning as an input device, and the like. Can be provided. The memory 1078 stores input conditions, data being calculated, calculation results, and the like.

  The measurement control unit 1071 includes an X-ray source control unit 1072, an X-ray detector control unit 1073, and a scan control unit 1074. The X-ray imaging apparatus according to the present embodiment acquires a phase-contrast X-ray image. Each part of the X-ray imaging apparatus is controlled to perform measurement. Specifically, the operation of the power source 102 of the X-ray source 101 is controlled by the X-ray source control unit 1072, and, for example, according to the X-ray conditions such as the X-ray tube voltage and tube current input via the input device 110, X-rays having a predetermined X-ray energy are irradiated from the X-ray source 101. The scanning unit 1074 drives the lateral movement stage 507 while the X-ray source 101 is radiating X-rays, and causes the third grating unit 105 to have a pitch smaller than the grating period along a direction parallel to the grating surface. Scan with. By the scanning of the third grating unit 105, the moire fringes (the fringes formed by the transmission part and the shielding part) generated by the overlapping of the grating of the third grating part 105 and the diffraction image of the second grating part 104 are moved. X-rays corresponding to the stripes are detected by the X-ray detector 106. The X-ray detector control unit 1073 controls the X-ray detector 106 and collects an electrical signal corresponding to the X-ray dose.

The grating control unit 1075 includes a grating angle adjusting unit 1076 and an inter-grating distance adjusting unit 1077. The grating angle adjustment unit 1076 controls the rotation adjustment mechanisms 501 to 504 in accordance with, for example, information on the X-ray energy input via the input device 111, and the gratings G1-1 and G1 constituting the first grating unit 103 are controlled. -2 and the relative rotation angles of the gratings G5-1 and G5-2 constituting the third grating unit 105 are adjusted, and the respective grating periods g _1t and g _3t are controlled. The direction and period of the grating generated by changing the relative rotation angle is as described above.

In the present embodiment, the grating period g _1t of the first grating unit 103 and the second grating are adjusted by the grating control unit 1075 in order to satisfy the interference conditions represented by the above formulas (2) to (4). FIG. 8 shows the relationship between the diffraction pattern pitch p of the section 104, that is, the grating period g _{3t of} the third grating section 105, the distance d between the second grating section 104 and the third grating section 105, and the X-ray energy. FIG. 8 is a graph in which the periods g1t0 of the two gratings G1-1 and G1-2 of the first grating section 103 are 10 μm, and the periods g3t0 of the gratings G5-1 and G5-2 of the third grating section are 2 μm. 8, the horizontal axis represents X-ray energy (keV), the right vertical axis represents the grating period (m), and the left vertical axis represents the distance (m).

As can be seen from FIG. 8, when the X-ray energy range is changed from, for example, 20 keV to 100 keV, the distance d may be adjusted within the range of about 0.1 m to 0.65 m (55 cm), and the practical dimensions of the apparatus. Adjustment is possible in the range. Further, the grating period g _1t may be adjusted within the range of 10 μm to 40 μm, and the grating period g _3t may be adjusted within the range of 4 μm to 7 μm. These adjustment ranges are obtained from the equation (1) at the relative rotation angle 2θ of the two gratings. , G _1t is 15 to 60 degrees, and g _3t is 17 to 30 degrees.

FIG. 9B shows a relationship between the grating periods g _1t and g _3t and the relative rotation angle 2θ. FIG. 9A is the same graph as FIG. 8 and shows changes in g _1t , g _3t, and d with respect to X-ray energy (horizontal axis). Changes in g _1t , g _3t, and d in the X-ray energy range of 20 keV to 100 keV in the graph of FIG. 9A are indicated by double arrows in FIG. 9B. The range indicated by this arrow is the range for adjusting the relative rotation angle 2θ.

Next, an imaging procedure by the X-ray imaging apparatus of this embodiment will be described with reference to FIG.
First, an imaging region is designated via the input device 110 (S1). The optimum X-ray energy for the imaging region is selected (S2). The X-ray energy may be selected by the examiner according to the imaging region, or the measurement control unit 1071 may automatically set the X-ray energy based on the predetermined X-ray energy guide according to the imaging region. You can also. When the X-ray energy is selected, the calculation unit 108 calculates the wavelength (S3), and calculates the apparatus condition for satisfying the interference condition based on the above-described equations (1) to (4) (S4). Among the apparatus conditions, since the period g _2t of the second grating unit 104 and the distance L between the first grating unit 103 and the second grating unit 104 are fixed, the second grating unit 104 and the third grating unit 105 are fixed. , The interference fringe period p of the second grating unit 105, and the grating periods g _1t and g _{3t of} the first and third grating units 103 and 105 are calculated. Incidentally, the period g _3t is set to the period p of the interference fringes. Further, the relative rotation angles of the gratings constituting the first and third grating sections 103 and 105 are calculated using the grating periods g _1t and g _3t (S5).

  The calculation unit 108 sets the calculated value in the grating control unit 1075 (S6). The grating control unit 1075 controls the longitudinal movement stage 108 and the rotation mechanism units 501 to 504 via the inter-grating distance adjustment unit 1077 and the grating angle adjustment unit 1076, respectively, so that the set distance d and the relative rotation angle are obtained. Further, the third grating unit 105 is moved and the two gratings constituting the first and third grating units are rotated. The determination of the distance and the relative rotation angle according to the X-ray energy may be calculated each time, or a predetermined value may be held for each X-ray energy as a table.

  In this manner, the first and third grating units are adjusted so that the interference condition is satisfied by the grating control unit 1075, and then imaging is performed under the control of the measurement control unit 1071 (S7). That is, a signal is measured by the X-ray detector 106 while moving the third grating unit 105 in the x direction while driving the lateral movement stage 507. The moving pitch of the third grating unit 105 by the lateral movement stage 507 is smaller than the grating period g3t of the third grating unit 105, for example, 1 / n (n is an integer of 2 or more). As a result, for each position in the x direction of the third grating, the X-ray detector 106 can obtain a moiré image including phase shift information depending on the subject.

This moire image is a moire image generated by the displacement of the second grating portion 104 and the third grating portion 105 in the x direction, and the diffraction image of the second grating portion includes phase shift information due to the subject. A plurality (n) of moire images are acquired while scanning the third grating unit 105 by the number of pitches corresponding to the grating period _g3t (for example, n times).

  The computing unit 108 processes the plurality of acquired moire images and creates a phase contrast image (S8). Specifically, since the plurality of moire images include a minute change of the phase shift amount, that is, a differential phase, for each pitch in the x direction of the third grating unit 105, the phase shift amount is expressed by contrast by integrating this. The phase contrast image thus obtained is reconstructed. The algorithm for calculating the phase contrast image is the same as that of the conventional X-ray imaging apparatus described in, for example, Japanese Patent Application Laid-Open No. 2007-203074 and the like, and the description thereof is omitted here.

  The image reconstructed by the calculation unit 108 can be displayed on the display device 110 (S9). The phase shift of the X-ray generated in the tissue of the subject takes a large value even in a tissue where X-ray attenuation (absorption) is small. Therefore, in the image representing the phase shift as contrast, weakly absorbed tissues such as living soft tissues are well depicted.

  According to the present embodiment, the grating parts that are two absorption diffraction gratings are configured by combining two gratings, respectively, and the period can be adjusted by the relative rotation angle, so that the first grating that is difficult to adjust is used. The interference condition can be satisfied even if the X-ray energy changes while the distance between the first grating and the second grating and the period of the second grating portion are fixed, and a phase contrast image can be obtained under any X-ray energy condition. Can be taken.

  In the X-ray imaging apparatus according to the present embodiment, a grating composed of a transmission part and a shielding part is created by combining two gratings. Therefore, the area (opening area) of the transmission part changes depending on the angle, and the transmission part is transmitted through the transmission part. X-ray dose to be changed. Looking at a single opening, as shown in FIG. 11A, the opening area decreases as the rotation angle increases, and is minimum when the rotation angle is 90 °. However, looking at the entire grating, as shown in FIG. 11B, when the rotation angle is increased, the moire cycle is shortened, so that the numerical aperture is increased, which acts to compensate for a decrease in the area of a single opening. Therefore, when the X-ray energy is small, the change in the opening area may be ignored. However, when the angle increases, that is, when the energy increases, the opening area as a whole slightly increases. When the energy is set high, the increase in the opening area can be corrected by the tube current and the X-ray generation time, and uniformized.

<Second embodiment>
In 1st embodiment, although the case where the 1st-3rd grating part was arrange | positioned so that the lattice plane was orthogonally crossed with respect to an X-ray irradiation direction (Z direction), this embodiment is 1st-1st. It is characterized in that the grating surface of the 3 grating portion is not parallel to the surface orthogonal to the Z direction but can be inclined.

Since the other configuration is the same as that of the first embodiment, the following description will focus on differences from the first embodiment. FIG. 12 shows the structure of the grating portion of the X-ray imaging apparatus of this embodiment. Although other elements are omitted in FIG. 12, they are the same as those of the X-ray apparatus of the first embodiment shown in FIG. 1, and will be described with the aid of FIG. Also in this embodiment, the first and third grating portions 103 and 105 are absorption diffraction gratings, each of which is composed of a pair of gratings, and relative rotation of the gratings by the rotation adjusting mechanisms 301 to 304 provided in the gratings. The grating periods g _1t and g _3t can be adjusted by changing the angle. The second grating unit 104 is a phase type diffraction grating having a predetermined grating period _g2t . The third grating 105 is mounted on the vertical movement stage 508 together with the horizontal movement stage 507, and the distance d from the second grating 104 can be adjusted.

  The X-ray imaging apparatus according to the present embodiment further includes a mechanism (tilting mechanism) 509 for tilting the grating sections 103 to 105 with respect to the z direction. As the tilt mechanism, a mechanism that rotates the grating portion around an axis parallel to the x direction, the upper end and the lower end in the y direction of each grating portion are connected by two link members, and one or both of these link members are connected. A known mechanism such as a link mechanism that moves along the z direction can be employed.

  The configuration of the control device 107 (FIG. 1) is almost the same as the configuration shown in FIG. 7, but a grating tilt angle adjusting unit 1079 for controlling the tilt mechanism 509 is added to the grating control unit 1075 as shown in FIG. Is done.

  In the present embodiment, by tilting the grating portion, it is possible to prevent the phase difference generated in the second grating portion 104 that is a phase grating from being lowered due to a decrease in X-ray energy. The reason will be described in detail below.

  In the X-ray imaging apparatus of the first embodiment and the present embodiment, the interference condition is established by adjusting the relative rotation angle of the grating overlap, and the transmission part of the moire fringes formed by the grating overlap is the X-ray. The amount (X-ray energy) that passes through changes in accordance with the relative angle. On the other hand, the phase difference generated by the second grating section 104 that is a phase grating depends on the X-ray energy, and when the X-ray energy transmitted through the second grating section 104 decreases, the phase difference generated there decreases.

  This is shown in FIG. FIG. 14A shows the X-ray energy and the phase difference generated in the second grating unit 104. The second grating section 104 has a structure that generates a phase difference of π (rad) when the X-ray energy is 20 keV. FIGS. 14B and 14C respectively simulate the interference fringes generated when the X-ray energy is 20 keV and the X-ray energies generated when the second grating unit 104 is used. Shows the results obtained. In FIG. 14C, the ideal state where the phase shift is π is indicated by a dotted line. In the case of the first embodiment, when the X-ray energy is 100 keV, the phase difference is reduced to 0.2π (rad) compared to the ideal state. For this reason, the interference fringe state is lower in contrast than the ideal interference fringe, although the interference condition is satisfied.

On the other hand, in the present embodiment, since the second grating section 104 is inclined, the distance (passing distance) through which the X-ray passes through the phase change section (204 in FIG. 2B) of the second grating section 104. T varies as shown in equation (5).
[Equation 5]
T = g _2h ÷ cosφ (5)
Here, [g _2h ] is the width of the phase changing unit 204 of the second grating unit 104, and φ is the inclination angle (φ in FIG. 12) of the second grating unit 104.

  That is, the passing distance T can be increased by (1 / cosφ) times when the second grating portion 104 is inclined as compared to when the second grating portion 104 is orthogonal to the Z direction. FIG. 15A shows the relationship between the X-ray energy and the generated phase difference when the second grating section 104 is inclined 45 degrees. In FIG. 15A, the relationship between the X-ray energy and the generated phase difference when the second grating unit 104 is not tilted (same as FIG. 14A) is indicated by a dotted line. FIG. 15B shows the result of simulating the interference fringes generated when the X-ray energy is 100 keV. Again, for comparison, the case of the ideal state and the case of no inclination are indicated by a dotted line and a broken line, respectively. From the comparison of these simulation results, it can be seen that the contrast is improved by inclining the second grating portion.

  The angle φ for inclining the grating portion can be appropriately adjusted according to the X-ray energy used. FIG. 16 shows a photographing procedure of this embodiment including angle adjustment. The same processes as those in FIG. 10 are denoted by the same reference numerals.

First, an imaging region is designated via the input device 110 (S1). The optimum X-ray energy for the imaging region is selected (S2). The X-ray energy may be selected by the examiner according to the imaging region, or the measurement control unit 1071 may automatically set the X-ray energy based on the predetermined X-ray energy guide according to the imaging region. You can also. When the X-ray energy is selected, the calculation unit 108 calculates the wavelength (S3), and calculates the apparatus condition for satisfying the interference condition based on the above-described equations (1) to (4) (S4). Among the apparatus conditions, since the period g _2t of the second grating unit 104 and the distance L between the first grating unit 103 and the second grating unit 104 are fixed, the second grating unit 104 and the third grating unit 105 are fixed. , The interference fringe period p of the second grating unit 105, and the grating periods g _1t and g _{3t of} the first and third grating units 103 and 105 are calculated. Further, using the grating periods g _1t and g _3t , the relative rotation angles of the gratings constituting the first and third grating sections 103 and 105 are calculated (S5).

  Thereafter, the calculation unit 108 determines whether to tilt the grating unit based on the input X-ray energy (S11). For example, when the X-ray energy is relatively low and a sufficient phase contrast is obtained as shown in FIG. In this case, similarly to the first embodiment, the calculation unit 108 sets the results calculated in S4 and S5 in the grating control unit 1075 (the grating angle adjustment unit 1076 and the grating distance adjustment unit 1077), and the rotation adjustment mechanism 501. ˜504 and the longitudinal movement stage 508 are controlled to set the grating section (S6). Thereafter, the X-ray source 101, the X-ray detector 106, and the lateral movement stage 507 are controlled to perform imaging (S7).

  On the other hand, when it is determined in S11 that the grating portion needs to be tilted, the calculation unit 108 further calculates a tilt angle φ (S12). The tilt angle φ may be determined based on, for example, a relationship between the X-ray energy and the tilt angle in advance, or a predetermined constant angle φ may be set if tilt is necessary. May be. Information on the set tilt angle is passed to the grating tilt angle adjusting unit 1079, and the tilt mechanism 509 is driven (S6). Thereafter, the X-ray source 101, the X-ray detector 106, and the lateral movement stage 507 are controlled to execute imaging (S7), image reconstruction as necessary, and image display as shown in FIG. This is the same as the shooting procedure of the first embodiment.

  According to the present embodiment, by adding a mechanism for inclining the grating part, it is possible to suppress and obtain a decrease in the phase shift generated by the second grating part due to a change in the passing X-ray energy. A reduction in the contrast of the image can be suppressed.

<Third embodiment>
The X-ray imaging apparatus according to the present embodiment is characterized in that a mechanism for changing the distance between the third grating unit and the X-ray detector is provided, thereby expanding the phase contrast image detected by the X-ray detector. Keep the rate constant.

  FIG. 17 shows an outline of the X-ray imaging apparatus of the present embodiment. In the figure, the same elements as those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and description of the elements is omitted. In the X-ray imaging apparatus of this embodiment, as shown in FIG. 17, the X-ray detector 106 is fixed to the second longitudinal movement stage 518, and the third grating unit 105 is driven by driving the longitudinal movement stage 518. Distance D can be adjusted. The longitudinal movement stage 518 is driven by a grating controller 1075 shown in FIG.

When the distance D is constant, the enlargement ratio of the image increases as the X-ray energy increases. By changing the distance D, the enlargement ratio can be made constant. The relationship between the distance D and the enlargement ratio will be described with reference to FIG. 18A shows the case where the distance D is fixed, FIG. 18B shows the case where the magnification is fixed, the horizontal axis of the graph is X-ray energy (keV), and the right vertical axis is the second grating portion. -Indicates the distance D (m) between the third grating portions and the magnification rate Mag. For reference, the period p of the interference fringes and the period g _1t of the first gritting unit 103 are shown together in the graph.

  FIG. 18A shows the relationship between the X-ray energy and the magnification factor Mag of the image when the distance D is fixed to 1 cm. As can be seen from this graph, the X-ray energy and the magnification factor are proportional to each other. Assuming that the enlargement factor when the X-ray energy is 40 keV is 1, the X-ray energy is about 1.2 times when the X-ray energy is 100 keV. On the other hand, as shown in FIG. 18B, the enlargement ratio can be kept constant by changing the distance D in the range of about 1.1 m to 0.8 m in the range of X-ray energy of 20 to 100 keV. .

  The X-ray imaging apparatus according to the present embodiment is configured such that, for example, when setting the X-ray energy, the examiner can select whether or not the magnification rate is constant through the input device 110. When it is selected to make the enlargement factor constant, the calculation unit 108 keeps the default enlargement factor (= 1) constant using the X-ray energy set as the default and the set X-ray energy. The distance D (or the movement amount ΔD of the X-ray detector 106) is calculated and set in the control device 107 that controls the second longitudinal movement stage 518, and the position of the X-ray detector 106 relative to the third grating 105 is calculated. Adjust. Alternatively, the calculation unit 108 refers to the X-ray energy and the magnification rate of the previous measurement, and according to the newly set X-ray energy, the magnification rate in the X-ray energy is the same as the previous magnification rate. The distance D may be calculated.

  When the third grating portion is moved (that is, the distance d is adjusted) according to the X-ray energy, the distance D between the X-ray detector 106 and the third grating portion 105 also changes. In this case, the distance D is adjusted in consideration of the change in the distance d.

  This embodiment is effective when a plurality of measurements are performed with different X-ray energies or when measurement is performed with an X-ray energy different from the past X-ray energy. In the present embodiment as well, as in the second embodiment, it is possible to provide a function of inclining each grating portion, and the photographing procedure in this case is the same as the flow shown in FIG.

<Fourth embodiment>
In the X-ray imaging apparatuses of the first to third embodiments, the third grating unit 105 is mounted on the lateral movement stage 507, and measurement is performed while moving the third grating unit 105 in the x direction at a fine pitch. However, the X-ray imaging apparatus of the present embodiment is characterized in that the first grating unit 103 is moved instead of moving the third grating unit 105.

  FIG. 19 shows an outline of the entire apparatus. Elements common to the X-ray imaging apparatus of FIGS. 1 and 17 are denoted by the same reference numerals. As can be seen from a comparison with the X-ray imaging apparatus of FIG. 1 or FIG. 17, the X-ray imaging apparatus is mounted on a lateral movement stage 507 for scanning in the x direction. The 3 grating section 105 is not provided with a lateral movement stage.

The lateral movement stage 507 on which the first grating unit 103 is mounted operates under the control of the scan control unit 1074 of the measurement control unit 1071, moves at a pitch finer than the grating period g _3t of the third grating unit 105, As a result, as in the case where the third grating unit 105 is scanned in the x direction, the X-ray detector 106 can obtain information including a minute phase change (differentiation) at each pitch.

  The X-ray imaging apparatus shown in FIG. 19 is further provided with a mechanism (second longitudinal movement stage) 518 that moves vertically in the X-ray detector 106, so that the X-ray energy is the same as in the third embodiment. Even if it is different, it has a function to maintain a constant magnification. This embodiment can be applied to any of the first to third embodiments, and the same effect can be obtained.

  As mentioned above, although each embodiment of the X-ray imaging apparatus of this invention was described with reference to drawings, the X-ray imaging apparatus of this invention is not limited to these embodiment, A various change is possible. For example, FIG. 1 and the like show the case where the direction of the grating of the second grating portion is the y direction, but the direction of the second grating is arbitrary as long as it is in a plane orthogonal to the z direction, and the y direction It is not limited to. The first and third gratings may be arranged so that moire fringes are generated so as to coincide with the direction of the second grating.

  Moreover, the numerical value quoted in each embodiment is an example, and it cannot be overemphasized that this invention is not limited to these numerical values.

  The present invention can be applied to an X-ray imaging apparatus using the Talbot-Lau interferometry method, and can be suitably applied to an X-ray diagnostic imaging apparatus and an X-ray CT apparatus especially for the human body.

DESCRIPTION OF SYMBOLS 101 ... X-ray source, 102 ... Power supply, 103 ... 1st grating part, 104 ... 2nd grating part, 105 ... 3rd grating part, 106 ... X-ray detector, DESCRIPTION OF SYMBOLS 107 ... Control apparatus, 108 ... Calculation part (calculation apparatus), 109 ... Subject, 110 ... Input device, 111 ... Display apparatus, 201, 203, 304 ... Base material, 202 , 206 ... X-ray shield (absorption type grating), 204 ... Striped grating (phase type grating), 501 to 504 ... Rotation adjustment mechanism, 507 ... Horizontal movement stage, 508 ... Vertical movement stage, 509... Tilting mechanism, 518... Second vertical movement stage, 1071... Measurement control unit, 1075... Grating control unit, 1076.・ ・Computing distance adjusting unit, 1079 ... grating tilt angle adjusting unit.

Claims (13)

An X-ray source that irradiates X-rays, an X-ray detector that is disposed opposite to the X-ray source across the subject and detects X-rays that have passed through the subject, and the X-ray source and the X-ray detection A first grating unit, a second grating unit, and a third grating unit arranged in order from the X-ray source,
Each of the first grating portion and the third grating portion has a structure in which shielding portions that shield X-rays and transmission portions that transmit X-rays are alternately arranged. A phase detection type X-ray imaging apparatus characterized in that a repetition cycle is variable. The phase detection type X-ray imaging apparatus according to claim 1,
Each of the first grating portion and the third grating portion includes a plurality of grating members, and includes an angle adjustment mechanism that adjusts a relative rotation angle by rotating the plurality of grating members in a plane. Phase detection type X-ray imaging apparatus. The phase detection type X-ray imaging apparatus according to claim 2,
The first grating portion and the third grating portion each have a period of moiré fringes generated based on an in-plane shift of the plurality of grating members by changing a relative rotation angle of the plurality of grating members. The phase detection type X-ray imaging apparatus is characterized in that changes. The phase detection type X-ray imaging apparatus according to claim 2,
A phase detection type X-ray imaging apparatus, further comprising a control unit that controls the angle adjustment mechanism in accordance with X-ray energy at the time of imaging. The phase detection type X-ray imaging apparatus according to any one of claims 1 to 4,
A phase detection type X-ray imaging apparatus, further comprising a moving stage that moves the third grating section so that a distance from the second grating section changes. The phase detection type X-ray imaging apparatus according to claim 5,
A phase detection type X-ray imaging apparatus comprising: a control unit that controls the moving stage in accordance with X-ray energy at the time of imaging. The phase detection type X-ray imaging apparatus according to any one of claims 1 to 6,
The first to third grating portions include an inclination mechanism that changes an inclination angle of the principal plane from a position orthogonal to a direction of X-rays irradiated from the X-ray source. A phase detection type X-ray imaging apparatus. A phase detection type X-ray imaging apparatus according to any one of claims 1 to 7,
The phase detection type X-ray imaging apparatus, wherein the second grating section is composed of a phase grating having a fixed grating period, and a distance from the first grating section is fixed. A phase detection type X-ray imaging apparatus according to any one of claims 1 to 8,
Phase detection X-ray imaging characterized in that said X-ray detector further comprises a moving stage that moves relative to said third grating along the direction of X-rays emitted from said X-ray source apparatus. A phase detection type X-ray imaging apparatus according to any one of claims 1 to 9,
A lateral movement stage that moves the first grating part or the third grating part perpendicular to the direction of X-rays emitted from the X-ray source and along the grating arrangement direction of the second grating part; A phase detection X-ray imaging apparatus comprising: The phase detection type X-ray imaging apparatus according to claim 10,
The image processing apparatus further includes a calculation unit that reconstructs a phase contrast image using signals detected by the X-ray detector at different positions in the lateral movement direction of the first grating unit or the third grating unit. A phase detection type X-ray imaging apparatus. A phase detection type X-ray imaging apparatus according to any one of claims 1 to 10,
The X-ray source, the first to third grating sections, and the X-ray detector are centered on a point that is intermediate between the first grating section and the second grating section in a state in which the positional relationship is maintained. A phase detection type X-ray characterized by further comprising: a rotation mechanism that rotates as a rotation unit; and a calculation unit that forms a phase contrast CT image to be inspected using a signal detected by the X-ray detector during the rotation. Shooting device. An X-ray source that irradiates X-rays, an X-ray detector that is disposed opposite to the X-ray source across the subject and detects X-rays that have passed through the subject, and the X-ray source and the X-ray detection Including a first grating portion, a second grating portion and a third grating portion arranged in order from the X-ray source,
Each of the first grating portion and the third grating portion is composed of a plurality of grating members, and a shielding portion that shields X-rays and a transmission that transmits X-rays due to an in-plane angle shift between the plurality of grating members. Which produces a striped structure with alternating parts
A phase detection type X-ray imaging apparatus comprising an angle adjustment mechanism that adjusts a relative rotation angle by rotating the plurality of grating members in a plane.

Images