JP2004313546A - X-ray photographing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray photographing device in which an X-ray magnification ratio can be reduced by reducing a deformation amount when the focusing distance of a scattered-ray removing grid is changed. <P>SOLUTION: A focusing grid 31 is provided in the vicinity of an incident face of an image receiving part 15 for receiving an image of the X-rays irradiated from an X-ray tube 13 to remove the X-rays scattering inside a subject. Both end parts in the grid arrangement direction of the focusing grid 31 are vertically moved by a grid driving device 40 to deform the focusing grid 31 into a cylindrical shape with a prescribed curvature. The prescribed curvature is determined so that an X-ray cutoff amount at both end parts in the grid arrangement direction becomes minimum corresponding to the SID. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray imaging apparatus including a scattered radiation removal grid that absorbs X-rays scattered in a subject.
[0002]
[Prior art]
Conventionally, parallel grids and focusing grids have been known as scattered radiation removal grids. Here, the parallel grid is a grid in which X-ray absorbing members alternately arranged with an intermediate substance that is an X-ray transmitting member are arranged in parallel. The focusing grid is a grid in which the intermediate substance and the X-ray absorbing member are arranged so as to face the center (focusing point) of the X-ray source.
[0003]
When the distance between the grid and the X-ray source changes from the ideal state, the cutoff amount of X-rays by the X-ray absorbing member increases in both the parallel grid and the focusing grid. In particular, the cutoff amount increases as the distance from the end of the grid perpendicular to the grid extending direction increases. In view of this, there has been proposed a grid having flexibility as a whole in which flexible X-ray transmitting members and X-ray absorbing members are alternately juxtaposed (Patent Document 1).
[0004]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-217813
[Problems to be solved by the invention]
The grid of Patent Document 1 has the following problem.
(1) The grid is deformed into a spherical shape according to the distance to the X-ray source. The grid before the deformation is a so-called parallel grid, and the thickness after the deformation is large in order to focus on a desired X-ray source. Become. Therefore, the magnification of the X-ray image increases.
(2) Since stripes are observed on a monitor when a grid is used, the Bucky method of thinning the stripes observed on the monitor by swinging the grid left and right may be adopted. In this case, it is difficult to eliminate the stripes in the grid of Patent Literature 1 deformed into a spherical surface.
[0006]
The present invention provides a focusing grid capable of reducing the amount of deformation in the thickness direction when changing the focusing distance, and an X-ray imaging apparatus using the focusing grid.
[0007]
[Means for Solving the Problems]
(1) An X-ray imaging apparatus according to a first aspect is provided with an X-ray source for irradiating X-rays, image receiving means for receiving X-rays emitted from the X-ray source, and an image receiving means provided near an incident surface of the image receiving means. A focusing grid for removing X-rays scattered inside the sample; and a driving unit for transforming the focusing grid into a cylindrical shape having a predetermined curvature with the longitudinal direction of the grid as a longitudinal axis. .
(2) The predetermined curvature is preferably determined in accordance with the distance between the X-ray source and the center of the image receiving means so that the X-ray cutoff amounts at both ends in the grid arrangement direction of the focusing grid are minimized. .
(3) The driving means includes first and second driving devices for respectively displacing both ends of the focusing grid in the grid arrangement direction. The first and second driving devices can each have a driving actuator. Alternatively, a driving actuator may be provided in one of the first and second driving devices, and the driving force of the driving actuator may be transmitted to the other driving device by a transmission unit.
(4) It is preferable to further provide a swinging means for swinging the focusing grid in the grid arrangement direction.
(5) When the angle at which X-rays from the X-ray source enter the focusing grid exceeds 0 degrees, the amount of deformation of both ends of the grid by the first and second driving devices is determined based on the relative position change between the two. Make it different.
(6) An X-ray absorbing member and an X-ray transmitting member are alternately arranged to form a scattered X-ray removal grid, and the transmitting member is selected from aluminum, carbon fiber reinforced resin, and synthetic resin. Is preferred.
(7) In the focusing grid of the ninth aspect, the X-ray transmitting members and the X-ray absorbing members are alternately juxtaposed, and each of the X-ray transmitting members and each of the X-ray absorbing members in the arrangement direction have a predetermined focusing. A X-ray transmitting member and an X-ray absorbing member, wherein the X-ray transmitting member and the X-ray absorbing member have a cylindrical shape having a predetermined curvature with a longitudinal axis extending in the extending direction of the X-ray transmitting member and the X-ray absorbing member. It is characterized in that it is made of a material that deforms into a shape.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an X-ray imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating details of a grid device.
[0009]
As shown in FIG. 1, an X-ray imaging apparatus 10 according to the present embodiment includes an X-ray tube holding unit 12 that moves on a rail 11 and an X-ray source (hereinafter, referred to as an X-ray source) held by the X-ray tube holding unit 12. An X-ray tube 13, a collimator 14 that narrows down the X-rays emitted from the X-ray tube 13, an image receiving unit 15 for the X-rays emitted from the X-ray tube 13, and an image receiving unit that holds the image receiving unit 15 so as to be able to move up and down. A holding unit 16 and a control unit 17 that controls various controls of the X-ray imaging apparatus 10 are provided.
[0010]
The X-ray tube 13 rotates around the axis AX1 and moves along the rail 11 in the direction of arrow D1. In addition, it also moves in directions D2 and D3 orthogonal to the direction D1. The X-ray image receiving unit 15 includes a recording medium for recording an X image, such as a flat panel disk or a cassette (not shown), and a grid device shown in FIG. 2 disposed on the X-ray incident surface side of the recording medium. The X-ray receiving unit 15 moves in the direction of the arrow D4 according to the physique of the subject. Here, the entire length of a line connecting the X-ray tube 13 and the center of the recording medium of the image receiving unit 15 is a SID (Source Image Distance).
[0011]
As shown in FIG. 2, the grid device 30 includes a focusing grid 31 and a grid driving device 40. The grid driving device 40 deforms the focusing grid 31 into a cylindrical shape having a predetermined curvature with the longitudinal direction of the grid extending, and swings the focusing grid 31 in the grid arrangement direction.
[0012]
As shown in FIG. 3, the focusing grid 31 alternates between an absorbing member 311 made of an X-ray absorbing material (for example, lead) and a transmitting member 312 made of an X-ray transmitting material (for example, aluminum, carbon fiber reinforced resin, and synthetic resin). In addition, the members 311 and 312 are arranged side by side so as to face the center (focusing point) of the X-ray source. Therefore, those members 311 and 312 have an inclination angle θn of 90 degrees at the center of the convergence grid 31 in the grid arrangement direction, and the inclination angle θn decreases as the distance from both ends increases. The absorbing member 311 and the transmitting member 312 are sandwiched between protective plates 313 made of aluminum or the like. In the drawing, Xn is the distance from the center of the focusing grid 31 to the X-ray absorbing member 311, d is its thickness, D is the thickness of the X-ray transmitting member 312, h0 is the protection plate of the absorbing member 311 and the X-ray transmitting member 312. The thickness between them, t, indicates the thickness of the protection plate 313.
[0013]
As described above, the focusing grid 31 has a predetermined focusing distance by the absorbing member 311 and the transmitting member 312. For example, before the focusing grid 31 is deformed into a cylindrical shape, the focusing distance of the planar focusing grid 31 is represented by f0 as shown in FIG. As shown in FIG. 5, the convergence distance of the convergence grid 31 after being deformed into a cylindrical shape is represented by f1 (<f0).
[0014]
2, a grid driving device 40 includes a pair of left and right vertical driving devices 41 that deform the focusing grid 31 into a cylindrical shape, a swing device 42 that swings the focusing grid 31 left and right in FIG. 2, and these devices. And a frame 43 for accommodating the same.
[0015]
The left and right ends of the focusing grid 31 are held by a grid holding frame 32, and the upper and lower ends are constrained in the thickness direction (vertical direction) by rollers 33 at the center. The pair of grid holding frames 32 are connected to the vertical driving device 41 via the support fittings 51, and by moving each of the support fittings 51 in the vertical direction in FIG. The grid 31 is deformed into a cylindrical shape whose longitudinal axis is the grid extending direction. Further, the grid holding frame 32 is connected to the swinging device 42 via a support fitting 52, and by moving the support fitting 52 right and left in FIG. Swings in a direction perpendicular to the direction.
[0016]
The vertical drive device 41 includes a motor 411, a bevel gear 412 that rotates integrally with the output shaft of the motor 411, a bevel gear 413 that meshes with the bevel gear 412, a screw rod 414 that rotates integrally with the bevel gear 413, And a square nut 415 screwed to the screw rod 414. The screw rod 414 is rotatably supported on the die 416. As described above, the vertical driving device 41 moves the both ends of the focusing grid 31 up and down via the support fittings 51 to form a cylindrical shape.
[0017]
The support fitting 51 has a substantially U-shape in plan view, and has a pair of forks 511 and a base 512. On the side surface of the fork portion 511, an elongated hole 511a extending in the grid arrangement direction is formed. A roller 513 is movably supported by the elongated hole 511a, and the roller 513 is connected to the square nut 415 by a screw 514. Therefore, the rotation of the square nut 415 is restricted between the fork portions 511 of the support bracket 51, and the support bracket 51 is configured to be guided by the square nut 415 and slidable in the grid arrangement direction.
[0018]
When the motor 411 rotates, the screw rod 414 rotates. The rotation of the square nut 415 into which the tip of the screw rod 414 is screwed is restricted by the fork 511, and the square nut 415 is connected to the roller 513 provided in the long hole 511a of the fork 511, and the left and right movement in FIG. Have been. Accordingly, the support fitting 51 moves up and down in response to the rotation of the screw rod 414, whereby the end of the focusing grid 31 also moves up and down. At this time, since the displacement in the vertical direction is restricted by the rollers 33 at the center of the focusing grid 31, the focusing grid 31 is deformed into a cylindrical shape around the rollers 33.
[0019]
The focusing grid 31 is swung right and left in FIG. 2B by a swing device 42 via a support fitting 52. The oscillating device 42 includes a motor 421 and a disk 422 that rotates integrally with the output shaft of the motor 421 and has an eccentric pin 423 implanted therein. The support fitting 52 has a long hole 52 a extending vertically in the rotation plane of the disk 422. The pin 423 of the disk 422 is fitted in the long hole 52 a of the support fitting 52. When the motor 421 rotates, the disk 422 rotates, and the eccentric pin 423 rotates while moving up and down in the long hole 52a. As a result, the focusing grid 31 swings right and left via the support fitting 52.
[0020]
FIG. 6 is a block diagram of the control unit 17 of the grid driving device 40. The control unit 17 includes an arithmetic processing unit 171 including a CPU, a ROM, a RAM, and the like, drive circuits 172 and 173 of the vertical drive motor 411, a drive circuit 174 of the swing motor 421, and a monitor that displays an X-ray image. Device 178. The arithmetic processing unit 171 includes an angle detection unit 175 for detecting the rotation angle of the X-ray tube 13, a detection unit 176 for detecting the three-dimensional position of the X-ray tube holding unit 12, and a position for detecting the position of the image receiving unit 15. Position signals detected by the detection unit 177 are input. Based on these input detection signals, the arithmetic processing unit 171 calculates the SID, that is, the focusing distance of the focusing grid 31. Then, the calculation unit 171 calculates the curvature of the cylindrical shape corresponding to the calculated convergence distance, and calculates the height positions at both ends of the convergence grid 31 for realizing the curvature. Further, the motor 411 is rotationally driven via the drive circuits 172 and 173 so as to be at this height position. Further, the swing motor 421 is rotationally driven via the drive circuit 174.
[0021]
The deformation operation of the focusing grid 31 by the focusing grid driving device configured as described above will be described.
The position detecting unit 176 detects the three-dimensional position of the X-ray tube holding unit 12, the angle detecting unit 175 detects the rotation angle of the X-ray tube 13, and the position detecting unit 177 detects the position of the image receiving unit 15. I do. These detection signals are input to the arithmetic processing unit 171 and the arithmetic processing unit 171 calculates the SID. Based on the SID, the arithmetic processing unit 171 calculates the focal distance f1 of the focusing grid 31 such that the cutoff by the X-ray absorbing member 311 at the end of the focusing grid 31 is minimized. Then, the deflection amount Yn is calculated from the convergence distance f1 using Expression (7) described later. Further, in order to realize the deflection amount Yn, the drive motor 411 is rotated by a predetermined amount. By the rotation of the motor 411, the square nut 415, that is, the support fitting 51 is moved upward, and both ends of the focusing grid 31 are bent by Yn. As a result, the focusing distance of the X-ray absorbing members 311 at both ends of the grid becomes f1.
[0022]
When the X-ray tube 13 irradiates the subject with X-rays in a state in which the deflection amount at both ends of the grid is set to Yn, the X-ray image scattered in the subject is absorbed by the X-ray absorbing member 311 and the X-rays travel straight. Only the line image is received by the image receiving unit 15 through the X-ray transmitting member 312. At this time, the focusing grid 31 is deformed into a cylindrical shape having a desired curvature so that the X-ray cutoff amount at both ends of the grid is minimized. The X-ray image received by the image receiving unit 15 is visualized and displayed on the monitor device 178. At this time, since the focusing grid 31 is swung in the grid arrangement direction by the swing device 42, no grid stripes are displayed on the monitor screen.
[0023]
FIG. 7 is a diagram illustrating the convergence distance and the grid height position. The X axis of the XY coordinate system whose origin is the center 0 of the focusing grid 31 corresponds to the grid arrangement direction, and the Y axis corresponds to the direction orthogonal to the surface of the focusing grid 31. In FIG. 7, when the focusing distance of the planar focusing grid 31 before deformation is f0 and the inclination angle of the X-ray absorbing member 311 at the position P0 Xn from the origin 0 at that time is θn, the deflection of Yn at the position P0 ( When the displacement amount is given, the deflection angle at the position P1 of Xn of the focusing grid 31 deformed into the cylindrical shape is represented by αn, and the focusing distance at the position P1 is represented by f1. At this time, the following equations (1) and (2) hold.
[0024]
(Equation 1)
tan θn = f0 / Xn (1)
(Equation 2)
f1 = Xn · tan (θn−αn) + Yn (2)
However, the amount of displacement of Xn of the X-ray absorbing member 311 after deformation is minute and ignored, and the amount of displacement of the X-ray absorbing member 311 in the Y-axis direction is Yn.
[0025]
FIG. 8 is a view for explaining the cylindrical deformation of the focusing grid 31 as a deformation of a beam in which a one-point concentrated axial load acts on the center of the beam at both ends. Assuming that the deflection angle at a position Xn away from the beam center is αn and the deflection amount is Yn, the following equation is established.
[Equation 3]
αn = W · (Xn ² −L · Xn) / (4 · E · I) (3)
(Equation 4)
Yn = W · Xn ² (3 · L−2 · Xn) / (24 · E · I) (4)
Here, L is the length of the beam, E is the Young's modulus of the grid, and I is the second moment of area.
[0026]
From the expressions (3) and (4), the deflection angle αn is expressed by the following expression (5) using the deflection amount Yn.
(Equation 5)
αn = 6 · Yn · (L−Xn) / (Xn · (3 · L−2 · Xn)) (5)
By substituting equation (5) into equation (2), the following equation is established.
(Equation 6)
f1 = Xn · tan (θn−6 · Yn · (L−Xn) / (Xn · (3 · L−2Xn))) + Yn (6)
[0027]
Thus, for a given SID, the amount of deformation Yn that minimizes the cutoff by the X-ray absorbing member 311 at the end of the focusing grid 31 may be obtained from equation (6). That is, the arithmetic processing unit 171 calculates the SID, and substitutes it into the convergence distance f1 in Expression (6) to calculate Yn.
[0028]
According to the focusing grid deformed into the cylindrical shape as described above, the following operation and effect can be obtained.
(1) When the focusing grid 31 is oscillated by the Bucky method, projection lines of the X-ray on both sides of the focusing grid 31 on the image receiving unit 15 are straight lines at any oscillating positions. No stripes are displayed. In this regard, in the case of the parallel grid deformed into a spherical shape described in Patent Document 1, the projection line becomes a curve having a different shape depending on the swing position, and an image corresponding to the grid stripe is displayed on the monitor screen.
(2) The convergence grid 31 has a smaller deflection amount per unit deformation amount of the convergence distance than the parallel grid, and the image enlargement ratio can be suppressed to be small.
[0029]
In the above, the case where the X-rays emitted from the X-ray tube 13 are perpendicularly incident on the image receiving unit 15, that is, the case where the X-ray incident angle is 0 degree has been described. The same operation and effect can be obtained also when the focusing grid 31 is deformed into a cylindrical shape according to the SID by the grid driving device 40 in the case where the light is incident. In this case, the right and left deflection amounts may be optimized according to the incident angle, instead of uniformly deforming both ends of the grid. Since the up-down driving device of FIG. 2 can be controlled independently of the left and right, the amount of deformation at both ends of the grid can be set individually.
[0030]
-Second embodiment-
When it is not necessary to set the amount of deflection independently for the left and right, a grid device 30A shown in FIG. 9 can be used. The same parts as those in the first embodiment are denoted by the same reference numerals, and differences will be mainly described.
[0031]
The grid device 30A according to the second embodiment includes a convergence grid 31 similar to that of the first embodiment, and a grid drive device 40A that tilts both ends of the convergence grid 31 via a support fitting 51A. The grid driving device 40A includes a driving-side tilting device 41A that tilts one grid end, a driven-side tilting device 41B that tilts the other grid end, and a driven-side tilting device 41B that drives the driving force of the driving-side tilting device 41A. And a transmission device 45 for transmitting the power to the transmission device.
[0032]
The drive-side tilting device 41A rotates integrally with a motor 411A that rotates by a predetermined angle, a gear 412A that rotates integrally with the output shaft of the motor 411A, and a gear 413A that meshes with the gear 412A to tilt the support bracket 51A. It has a driving body 417 and a bearing 418 that supports a rotation shaft 417a of the driving body 417. The driving body 417 has a cylindrical shape, and a pair of pins 417b is implanted on each of both end faces. The pair of pins 417b are inserted into the elongated holes 511a of the support bracket 51A, and when the drive body 417 rotates, apply a rotational torque to the support bracket 51A about the rotation axis of the drive body 417 supported by the bearing 418 to tilt. At this time, the torque of the drive-side tilting device 41A is transmitted to the transmission device 45.
[0033]
The transmission device 45 has a wire 452 wound around the plurality of pulleys 451, and transmits the driving force to the driven-side tilting device 41B. The driven-side tilting device 41B includes a driving body 419 that tilts the support bracket 51A, and a bearing 420 that supports the rotation of the driving body 419. The driving body 419 rotates in a direction opposite to the driving body 417 of the driving-side tilting device 41A by receiving a rotational force via the transmission device 45. The driven-side tilting device 41B tilts the support fitting 51A by rotating the driving body 419 by applying a rotational torque in a direction opposite to that of the driving-side tilting device 41A.
[0034]
In FIG. 9, the support bracket 51A on the driving side tilts by receiving clockwise rotation torque, and the support bracket 51A on the driven side tilts by receiving clockwise rotation torque. As a result, the focusing grid 31 can be deformed into a cylindrical shape without restricting the central portion of the focusing grid 31 with the rollers.
[0035]
In the grid device according to the second embodiment, the same operation and effect as those of the first embodiment can be obtained, and a rotating torque is applied to both ends of the grid by a single drive motor 411A to transform the grid into a cylindrical shape. Since the rollers required in the first embodiment can be omitted and a single drive motor can be used, the size, the number of parts, and the cost can be reduced. It is preferable that a device for swinging the focusing grid 31 be provided in the same manner as in the first embodiment.
[0036]
The above embodiment is merely an example, and the X-ray imaging apparatus according to the present invention is not limited to the above configuration as long as the features of the present invention are not impaired.
[0037]
【The invention's effect】
As described in detail above, according to the present invention, the focusing grid is deformed into a cylindrical shape to change the focusing distance, so that the grid deformation is reduced so that the image is not undesirably enlarged. Can be.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an X-ray imaging apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a grid device according to a first embodiment, where (a) is a plan view and (b) ) Is a front view, and (c) is a right side view of (a). FIG. 3 is a diagram illustrating a focusing grid 31. FIG. 4 is a diagram illustrating a focusing distance of the focusing grid 31 before being deformed into a cylindrical shape. FIG. 5 is a view for explaining a focusing distance of a focusing grid 31 after being deformed into a cylindrical shape. FIG. 6 is a block diagram of a control unit 17 of a grid driving device 40. FIG. FIG. 8 is a diagram illustrating the deformation of the cylindrical shape of the focusing grid 31 as the deformation of a beam in which a one-point concentrated axial load is applied to the center of the support beam at both ends. FIG. 9 is a grid device according to a second embodiment. It is a figure explaining (a), a top view and (b) are the sides. DESCRIPTION OF SYMBOLS
10: X-ray imaging apparatus 11: X-ray tube holding device 12: rail 13: X-ray tube 14: collimator 15: image receiving unit 16: image receiving unit holding unit 17: control unit 30: grid device 31: focusing grid 32: frame 40 , 40A: Grid drive device 41: Vertical drive device, 41A, 41B: Tilt device 42: Swing device 45: Transmission device 51, 51A, 52: Support bracket 311: X-ray absorbing member 312: X-ray transmitting member 411, 411A , 421: drive motor

Claims (9)

An X-ray source for irradiating X-rays,
Image receiving means for receiving X-rays emitted from an X-ray source;
A focusing grid that is provided near the incident surface of the image receiving unit and removes X-rays scattered inside the subject;
An X-ray imaging apparatus comprising: a driving unit configured to deform the focusing grid into a cylindrical shape having a predetermined curvature with a longitudinal axis of the grid extending. The X-ray imaging apparatus according to claim 1,
The driving unit determines the predetermined curvature according to a distance between the X-ray source and the center of the image receiving unit such that X-ray cutoff amounts at both ends of the focusing grid in the grid arrangement direction are minimized. An X-ray imaging apparatus, comprising: The X-ray imaging apparatus according to claim 1 or 2,
The X-ray imaging apparatus according to claim 1, wherein the driving unit includes first and second driving devices for displacing both ends of the focusing grid in the grid arrangement direction. The X-ray imaging apparatus according to claim 3,
An X-ray imaging apparatus, wherein each of the first and second driving devices has a driving actuator. The X-ray imaging apparatus according to claim 3,
A drive actuator is provided on one of the first and second drive devices, and a drive force of the drive actuator is transmitted to a drive device not provided with the drive actuator via a transmission unit. X-ray equipment. The X-ray imaging apparatus according to any one of claims 3 to 5,
An X-ray imaging apparatus, comprising: a swinging unit that swings the focusing grid in the grid arrangement direction. The X-ray imaging apparatus according to any one of claims 3, 4, and 5,
An X-ray imaging apparatus, wherein the amount of driving by the first and second driving devices is made different based on the amount of change in the relative position between the X-ray source and the focusing grid in the grid arrangement direction. The X-ray imaging apparatus according to any one of claims 1 to 6,
The focusing grid forms a scattered X-ray removal grid by alternately arranging an absorbing member that absorbs X-rays and a transmitting member that transmits X-rays, and the transmitting member is made of aluminum, carbon fiber reinforced resin, and synthetic resin. An X-ray imaging apparatus, which is any one of the above. An X-ray transmitting member and an X-ray absorbing member are alternately juxtaposed, and a convergence arranged such that each of the X-ray transmitting members and each of the X-ray absorbing members in the arrangement direction converge at a predetermined convergence point. A grid,
The X-ray transmitting member and the X-ray absorbing member are made of a material that is deformed into a cylindrical shape having a predetermined curvature with the longitudinal direction of the X-ray transmitting member and the X-ray absorbing member as a longitudinal axis. A focusing grid.

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