JP2014083143A - Collimator mechanism for radiographic device and radiographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a collimator mechanism for a radiographic device and a radiographic device capable of variedly shielding X-ray in a wide range despite a simple configuration.SOLUTION: A collimator unit includes a first collimator mechanism and a second collimator mechanism 92. The second collimator mechanism 92 includes a pair of shielding leaves 105 and 106 for one-side diaphragms. The one-side diaphragm shielding leaf 105 and the one-side diaphragm shielding leaf 106 each independently reciprocate by driving of a single motor 64 and a tensile force of a spring so as to come close to or separate from an axis line of X-ray applied from an X-ray tube.

Description

  The present invention relates to a collimator mechanism of an X-ray imaging apparatus that regulates an X-ray irradiation field irradiated from an X-ray tube, and an X-ray imaging apparatus using the collimator mechanism.

  In the X-ray imaging apparatus, a collimator mechanism is used to regulate the X-ray irradiation field irradiated from the X-ray tube. This collimator mechanism is generally provided with two pairs of shielding leaves that move in opposite directions around the X-ray axis from the X-ray tube to the X-ray detector in directions orthogonal to each other. These two sets of shielding leaves are moved to form a rectangular X-ray irradiation field.

  FIG. 8 is a perspective view showing an arrangement of shielding leaves 101, 102, 103, 104 used in such a general collimator mechanism.

  This collimator mechanism is for restricting the X-ray irradiation field E emitted from the X-ray tube 10, and includes four shielding leaves 101, 102, 103, and 104. The shielding leaf 101 and the shielding leaf 102 are synchronously moved in opposite directions so as to be close to or separated from each other about the axis of the X-ray irradiated from the X-ray tube 10 by driving a single motor. . Similarly, the shielding leaf 103 and the shielding leaf 104 are synchronously reversed in directions so as to be close to or separated from each other around the axis of the X-ray irradiated from the X-ray tube 10 by driving a single motor. Move to.

  In the collimator mechanism having such a configuration, the pair of shielding leaves shields the X-rays uniformly around the axis of the X-rays irradiated from the X-ray tube 10. On the other hand, in such an X-ray imaging apparatus, in order to prevent unnecessary X-ray exposure or to prevent halation at the end of the X-ray imaging region, It may be necessary to narrow down only one side.

  Patent Document 1 discloses a configuration in which X-rays can be irradiated while being biased with respect to the axis of X-rays emitted from the X-ray tube in a collimator device of an X-ray computed tomography (CT) apparatus. ing.

JP 2009-526 A

  In order to bias the X-ray irradiation area with respect to the X-ray axis by narrowing only one side of the rectangular X-ray irradiation field, the four shielding leaves 101 and 102 shown in FIG. , 103, 104 may be individually moved by four motors. However, when such a configuration is adopted, four motors, which are double the usual, are required, which not only increases the manufacturing cost of the apparatus, but also increases the size of the apparatus and complicates its control. The problem occurs.

  For this reason, it is conceivable to use a shielding leaf provided with a rectangular opening separately from the collimator mechanism shown in FIG. FIG. 9 is a schematic diagram of the collimator unit 11 having such a configuration, and FIG. 10 is a schematic diagram of the shielding leaf 109 used in the collimator unit 11 shown in FIG.

  As shown in FIG. 10, the collimator unit 11 has a configuration using a shielding leaf 109 having an opening 108 formed in the center thereof, as shown in FIG. 10, together with the four shielding leaves 101, 102, 103, and 104 shown in FIG. . As shown in FIG. 9, the X-rays emitted from the X-ray tube 10 are shielded by the four shielding leaves 101, 102, 103, 104 shown in FIG. 8 to form an X-ray irradiation field, The shielding leaf 109 shown in FIG. 10 is reciprocated in one direction by a motor to narrow down only one side of the rectangular X-ray irradiation field E formed by the four shielding leaves 101, 102, 103, 104. Thus, X-rays can be irradiated while being biased with respect to the X-ray axis.

  However, when such a configuration is adopted, as is apparent from FIG. 9, in order to increase the stroke of the shielding leaf 109, it is necessary to increase the size of the shielding leaf 109, and the entire apparatus is large. Turn into. On the other hand, in order to make the device compact, the stroke of the shielding leaf has to be shortened, resulting in a problem that the shielding range becomes small.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object thereof is to provide a collimator mechanism and an X-ray imaging apparatus for an X-ray imaging apparatus capable of shielding X-rays in a wide range with a simple configuration. To do.

  According to the first aspect of the present invention, in the collimator mechanism of the X-ray imaging apparatus that regulates the X-ray irradiation field irradiated from the X-ray tube, the collimator mechanism is supported so as to be movable in one direction by the guide member, and the moving direction thereof. A pair of one-side aperture shielding leaves formed in parallel with each other, and a pair of engagements movable within the elongated holes in a state of being engaged with the respective elongated holes formed in the pair of one-side aperture shielding leaves. A moving member provided with a joint, driving means for reciprocating the moving member in parallel with the elongated hole, and a biasing member for biasing the pair of one-side aperture shielding leaves in a direction away from each other. A distance between a pair of engaging portions attached to the moving member is a length formed on the pair of one-side diaphragm shielding leaves when the pair of one-side diaphragm shielding leaves are arranged at the most separated positions. Distance equivalent to the distance between holes Characterized in that there.

  According to a second aspect of the present invention, in the first aspect of the present invention, the longitudinal length of the long hole formed in the pair of one-side aperture shielding leaves is the moving distance of the pair of one-side aperture shielding leaves. It is the above.

  According to a third aspect of the present invention, there is provided an X-ray imaging apparatus for detecting, with an X-ray detector, X-rays that have been irradiated from an X-ray tube and have passed through a subject, and X extending from the X-ray tube to the X-ray detector. A first collimator mechanism that includes two pairs of shielding leaves that move in opposite directions in synchronization with each other about the axis of the line in a direction orthogonal to each other, and forms a rectangular X-ray irradiation field; A second collimator mechanism for further narrowing one side of the rectangular X-ray irradiation field formed by the one collimator mechanism to the inside, and the second collimator mechanism can be moved in one direction by a guide member. The pair of one-side aperture shielding leaves formed with a long hole parallel to the moving direction and the elongated holes formed in the pair of one-side aperture shielding leaves are respectively engaged with the long holes. A pair of engagements that can move in the hole A driving member that reciprocates the moving member in parallel with the elongated hole, and a biasing member that biases the pair of one-side aperture shielding leaves in a direction away from each other. The distance between the pair of engaging portions attached to the moving member is between the long holes formed in the pair of one-side aperture shielding leaves when the pair of one-side aperture shielding leaves are disposed at the most separated positions. It is a distance corresponding to the distance.

  According to a fourth aspect of the present invention, in the invention of the third aspect, the length in the longitudinal direction of the long hole formed in the pair of one-side aperture shielding leaves is the moving distance of the pair of one-side aperture shielding leaves. It is the above.

  According to the first and third aspects of the present invention, it is possible to reciprocate the pair of one-side aperture shielding leaves independently of each other using only one driving means such as a motor. For this reason, in the case where the X-ray irradiation region is biased with respect to the X-ray axis by narrowing down only one side of the rectangular X-ray irradiation field, the X-ray is It is possible to shield in a wide range.

  According to the second and fourth aspects of the present invention, it is possible to prevent the pair of one-side aperture shielding leaves from moving over the entire reciprocating stroke of the one-side aperture shielding leaf.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the X-ray imaging apparatus to which this invention is applied, and is a front view when the top plate 13 is arrange | positioned in the supine position. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the X-ray imaging apparatus to which this invention is applied, and is a front view when the top plate 13 is arrange | positioned in a standing position. It is a schematic diagram of the X-ray imaging apparatus to which this invention is applied, and is a right side view when the top plate 13 is disposed at the standing position. 3 is a schematic diagram of a collimator unit 11 having a first collimator mechanism 91 and a second collimator mechanism 92. FIG. 5 is a perspective view of a second collimator mechanism 92. FIG. 5 is a perspective view of a second collimator mechanism 92. FIG. FIG. 10 is a perspective view of a main part of a mechanism that moves a pair of one-side aperture shielding leaves 105 and 106 from a second collimator mechanism 92. 3 is a perspective view showing the arrangement of shielding leaves 101, 102, 103, 104 used in the first collimator mechanism 91. FIG. 2 is a schematic diagram of a collimator unit 11. FIG. 3 is a schematic diagram of a shielding leaf 109. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 3 are schematic views of an X-ray imaging apparatus to which the present invention is applied. In addition, FIG. 1 is a front view when the top plate 13 is disposed at the prone position. FIG. 2 is a front view when the top plate 13 is disposed at the standing position. Furthermore, FIG. 3 is a right side view when the top plate 13 is disposed at the standing position.

  This X-ray imaging apparatus is called an X-ray fluoroscopic imaging table, and includes a top plate 13, a slide arm 15 connected to the top plate 13, and an X disposed at the tip of the slide arm 15. An image intensifier (II) or a flat panel detector (on the opposite side of the X-ray tube 10 with respect to the X-ray tube 10 with respect to the X-ray tube 10, the collimator unit 11 which is a characteristic part of the present invention, And an X-ray detector 12 such as an FPD). The slide arm 15 is provided with a compression cylinder mechanism 20 for pressing the diagnosis part of the subject as necessary. Further, the step board 30 and the grip bar 40 are fixed to the top plate 13.

  The top plate 13, the slide arm 15, the X-ray tube 10 and the like are placed in a prone position as shown in FIG. 1 where the top plate 13 is in the horizontal direction, as shown in FIG. And the top plate 13 shown in FIG. 3 can rotate between the standing positions where it becomes a perpendicular direction. Further, the rotation mechanism 16 itself can be moved up and down with respect to the main column 17 erected on the base plate 18.

  When the top 13 is in the prone position, the subject in the prone position is seen through or photographed. At this time, the subject is placed on the top board 13. Further, when the top plate 13 is in the standing position, the subject in the standing position is seen through or photographed. Further, when performing fluoroscopy or photographing while changing the angle of the top plate 13, the subject stands on the step platform 30 fixed to the top plate 13. Then, the angle of the top plate 13 is changed while the subject is still on the top plate 13 and the platform 30. At this time, the subject holds a pair of grip bars 40 disposed on the top board 13 to support his body.

  Next, the configuration of the collimator unit 11 that is a characteristic part of the present invention will be described. FIG. 4 is a schematic diagram of the collimator unit 11 having the first collimator mechanism 91 and the second collimator mechanism 92.

  The first collimator mechanism 91 used in the collimator unit 11 has the configuration shown in FIG. That is, the first collimator mechanism 91 includes four shielding leaves 101, 102, 103, and 104 as shown in FIG. 8 (only the shielding leaves 101 and 102 are shown in FIG. 4). The shielding leaf 101 and the shielding leaf 102 are synchronously moved in the opposite directions so as to be close to or separated from each other around the X-ray axis irradiated from the X-ray tube 10 by a single motor (not shown). . Similarly, the shield leaf 103 and the shield leaf 104 are synchronously reversed in directions so as to be close to or separated from each other around the axis of the X-ray irradiated from the X-ray tube 10 by a single motor (not shown). Move to.

  On the other hand, the second collimator mechanism 92 includes a pair of one-side aperture shielding leaves 105 and 106. As will be described later, the one-side aperture shielding leaf 105 and the one-side aperture shielding leaf 106 are close to or close to the X-ray axis irradiated from the X-ray tube 10 by driving of a motor 64 and tension of a spring 76 described later. Move independently of each other so that they are separated. The reciprocating direction of the pair of one-side aperture shielding leaves 105 and 106 is parallel to the top plate 13 shown in FIGS. 1 to 3 and the body axis direction of the subject on the top plate 13 surface. The directions are perpendicular to each other (the direction perpendicular to the paper surface in FIGS. 1 and 2, the left-right direction in FIG. 3).

  5 and 6 are perspective views of the second collimator mechanism 92. FIG. FIG. 7 is a perspective view of the main part of the mechanism that moves the pair of one-side aperture shielding leaves 105 and 106 from the second collimator mechanism 92. 5 shows the front side of the second collimator mechanism 92, and FIG. 6 shows the back side of the second collimator mechanism 92. 5, 6, and 7 show a pair of one-side aperture shielding leaves 105 and 106 in a fully opened state, that is, a state where they are arranged at the most separated positions.

  As shown in FIGS. 5 and 6, the second collimator mechanism 92 has a pair of one-side aperture shielding leaves 105 supported at both ends by guide rails 60 and 62 fixed to the base member 61 and reciprocally movable. , 106. As shown in FIG. 7, one of the one-side aperture shielding leaves 105 includes a flange portion 51, and a long hole 53 parallel to the moving direction of the one-side aperture shielding leaf 105 is formed in the flange portion 51. Yes. Similarly, the other one-side aperture shielding leaf 106 includes a flange portion 52, and a long hole 54 is formed in the flange portion 52 parallel to the moving direction of the one-side aperture shielding leaf 106.

  Further, as shown in FIG. 7, the second collimator mechanism 92 includes a moving plate 70 provided with a pair of bosses 71 and 72 at both ends thereof. One of the bosses 71 and 72 is movable in the long hole 53 while being engaged with the long hole 53 formed in the flange portion 51 of the one-side diaphragm shielding leaf 105. It has become. Similarly, the other boss 72 is movable in the long hole 54 in a state where the other boss 72 is engaged with the long hole 54 formed in the flange portion 52 of the other one-side diaphragm shielding leaf 106.

  As shown in FIG. 7, the distance D between the pair of bosses 71 and 72 corresponds to the distance between the long holes 53 and 54 when the pair of one-side aperture shielding leaves 105 and 106 are arranged at the most separated positions. To do. That is, when the pair of one-side aperture shielding leaves 105 and 106 are fully opened, the end portion of the elongated hole 53 on the one-side aperture shielding leaf 106 side and the end portion of the elongated hole 54 on the one-side aperture shielding leaf 105 side And the distance D between the end of the boss 71 on the one-side aperture shielding leaf 106 side and the end of the boss 72 on the one-side aperture shielding leaf 105 side coincide with each other.

  The length L1 in the longitudinal direction of the long hole 53 formed in the flange portion 51 of the one-side diaphragm shielding leaf 105 is equal to or longer than the moving distance of the other one-side diaphragm shielding leaf 106. Similarly, the length L2 in the longitudinal direction of the long hole 54 formed in the flange portion 52 of the one-side aperture shielding leaf 106 is equal to or longer than the moving distance of the one-side aperture shielding leaf 105. In this embodiment, the moving distances of the pair of one-side aperture shielding leaves 105 and 106 are the same, and the longitudinal lengths of the pair of long holes 53 and 54 are the same (that is, L1 = L2). ing.

  As shown in FIG. 7, the wire wound around a pair of driven pulleys 73 and 74 rotatably disposed on a base member 61 (see FIGS. 5 and 6) is provided on one one-side diaphragm shielding leaf 105. One end of the wire 75 is fixed, and the other end of the wire 75 is fixed to the other one-side diaphragm shielding leaf 106. A spring 76 is disposed at the center of the wire 75 (position between the driven pulley 73 and the driven pulley 74).

  As shown in FIGS. 5 and 6, the second collimator mechanism 92 includes a drive pulley 65 that is rotated by driving of a motor 64, and four driven pulleys 58 and 66 that are rotatably disposed on the base member 61. , 67, 68. A wire 69 is wound around the drive pulley 65 and the driven pulleys 58, 66, 67 and 68. A part of the wire 69 is fixed to the drive pulley 65, and moves by the rotation of the drive pulley 65. The four driven pulleys 58, 66, 67, 68 are only along the wire 69, and serve to change the direction of the wire 69. And the wire 69 is connected with the moving board 70 by the connection member 59 shown in FIG. Both ends of the moving plate 70 are supported by guide rails 60 and 63 fixed to the base member 61 and reciprocate in the same direction as the moving direction of the one-side aperture shielding leaves 105 and 106. For this reason, when the drive pulley 65 is rotated by driving the motor 64, the moving plate 70 moves as the wire 69 moves.

  In the second collimator mechanism 92, when the moving plate 70 is moved from the one-side diaphragm shielding leaf 105 side to the other one-side diaphragm shielding leaf 106 side by driving the motor 64, Since the attached one boss 71 is engaged with the end of the long hole 53, the one-side aperture shielding leaf 105 moves to the one-side aperture shielding leaf 106 side together with the moving plate 70. At this time, since the other boss 72 moves in the long hole 54, the one-side aperture shielding leaf 106 does not move. Therefore, by moving the moving plate 70 from the one-side aperture shielding leaf 105 side to the one-side aperture shielding leaf 106 side, it is possible to move only one of the one-side aperture shielding leaves 105 in the closing direction. In this state, the spring 76 is extended.

  When the moving plate 70 is moved from the one-side diaphragm shielding leaf 106 side to the one-side diaphragm shielding leaf 105 side by driving the motor 64 in a state where the one-side diaphragm shielding leaf 105 is closed, the spring 76 is used. As a result, the one-side aperture shielding leaf 105 moves in the opening direction. Also at this time, since the boss 72 moves in the long hole 54, the other one-side aperture shielding leaf 106 does not move. For this reason, by moving the moving plate 70 from the one-side aperture shielding leaf 106 side to the one-side aperture shielding leaf 105 side, only one of the one-side aperture shielding leaves 105 can be moved in the opening direction.

  On the other hand, in the fully opened state as shown in FIGS. 5 to 7 again, when the moving plate 70 is moved from the one-side diaphragm shielding leaf 106 side to the other one-side diaphragm shielding leaf 105 side by driving the motor 64. Since one boss 72 attached to the moving plate 70 is engaged with the end of the long hole 54, the one-side aperture shielding leaf 106 is moved together with the moving plate 70 toward the one-side aperture shielding leaf 105 side. Moving. At this time, since the other boss 71 moves in the elongated hole 53, the one-side aperture shielding leaf 105 does not move. Therefore, by moving the moving plate 70 from the one-side aperture shielding leaf 106 side to the one-side aperture shielding leaf 105 side, only the one-side aperture shielding leaf 106 can be moved in the closing direction. Even in this state, the spring 76 is extended.

  Further, when the moving plate 70 is moved from the one-side diaphragm shielding leaf 105 side to the one-side diaphragm shielding leaf 106 side by driving the motor 64 in a state where one one-side diaphragm shielding leaf 106 is closed, By the action of the spring 76, the one-side aperture shielding leaf 106 moves in the opening direction. Also at this time, since the boss 71 moves in the long hole 53, the other one-side aperture shielding leaf 105 does not move. For this reason, by moving the moving plate 70 from the one-side aperture shielding leaf 105 side to the one-side aperture shielding leaf 106 side, only one of the one-side aperture shielding leaves 106 can be moved in the opening direction.

  As described above, the length L1 in the longitudinal direction of the long hole 53 formed in the flange portion 51 of the one-side diaphragm shielding leaf 105 and the long hole 54 formed in the flange section 52 of the one-side diaphragm shielding leaf 106. The length L2 in the longitudinal direction is equal to or longer than the moving distance of the one-side aperture shielding leaves 105 and 106. For this reason, it is possible to prevent the pair of one-side aperture shielding leaves 105 and 106 from moving when either of the one-side aperture shielding leaves 105 and 106 moves.

  When the length L1 in the longitudinal direction of the long hole 53 and the length L2 in the longitudinal direction of the long hole 54 are shorter than the moving distance of the one-side aperture shielding leaves 105, 106, When one of them moves in the closing direction, the other of the one-side aperture shielding leaves 105 and 106 moves together from the middle. However, if there is no problem even with such a configuration, the length L1 in the longitudinal direction of the long hole 53 or the length L2 in the longitudinal direction of the long hole 54 is changed to move the shielding leaves 105 and 106 for one-side diaphragms. It may be set shorter than the distance.

  In the collimator unit 11 having the above-described configuration, by using the first collimator mechanism 91, a rectangular shape centering on the axis of the X-ray irradiated from the X-ray tube 10 indicated by a one-dot chain line in FIG. An X-ray irradiation field can be formed. By using the second collimator mechanism 92, it is possible to narrow down only one side of the rectangular X-ray irradiation field. For this reason, it becomes possible to prevent unnecessary exposure to X-rays or to prevent halation at the end of the X-ray imaging region as necessary.

  In the second collimator mechanism 92, as described above, the reciprocating direction of the pair of one-side aperture shielding leaves 105 and 106 is parallel to the top plate 13 shown in FIGS. It is a direction orthogonal to the body axis direction of the subject on the surface of the plate 13 (a direction perpendicular to the paper surface in FIGS. 1 and 2 and a left-right direction in FIG. 3). For this reason, in the second collimator mechanism 92, it is possible to narrow down one side of the rectangular X-ray irradiation field in a direction orthogonal to the body axis direction of the subject. In the axial direction, one side of the rectangular X-ray irradiation field cannot be narrowed down. However, in order to narrow down one side of the rectangular X-ray irradiation field in the body axis direction of the subject, a method of moving the X-ray tube 10 in the body axis direction of the subject or the X-ray tube 10 There is a method of changing the X-ray irradiation direction by rotating the X-ray in the body axis direction of the subject.

DESCRIPTION OF SYMBOLS 10 X-ray tube 11 Collimator part 12 X-ray detector 13 Top plate 15 Slide arm 16 Rotating mechanism 17 Main strut 18 Base plate 20 Compression cylinder mechanism 30 Footrest 40 Grasping rod 51 Flange part 52 Flange part 53 Long hole 54 Long hole 58 Driven pulley 59 connecting member 60 guide rail 61 base member 62 guide rail 63 guide rail 64 motor 65 driving pulley 66 driven pulley 67 driven pulley 68 driven pulley 69 wire 70 moving plate 71 boss 72 boss 73 driven pulley 74 driven pulley 75 wire 76 spring 91 first 1 collimator mechanism 92 2nd collimator mechanism 101 shielding leaf 102 shielding leaf 103 shielding leaf 104 shielding leaf 105 shielding leaf for one side diaphragm 106 shielding leaf for one side diaphragm 108 opening 109 shielding shield Full

Claims (4)

In the collimator mechanism of the X-ray imaging apparatus that regulates the X-ray irradiation field irradiated from the X-ray tube,
A pair of one-side aperture shielding leaves that are supported by the guide member so as to be movable in one direction and in which a long hole parallel to the moving direction is formed,
A moving member provided with a pair of engaging portions capable of moving in the long holes in a state of being engaged with the long holes formed in the pair of one-side aperture shielding leaves,
Drive means for reciprocating the moving member in parallel with the elongated hole;
A biasing member that biases the pair of one-side aperture shielding leaves in a direction away from each other;
With
The distance between the pair of engaging portions attached to the moving member is between the long holes formed in the pair of one-side aperture shielding leaves when the pair of one-side aperture shielding leaves are disposed at the most separated positions. A collimator mechanism for an X-ray imaging apparatus, wherein the collimator mechanism is a distance corresponding to the distance of. In the collimator mechanism of the X-ray imaging apparatus according to claim 1,
A collimator mechanism for an X-ray imaging apparatus, wherein a length of a long hole formed in the pair of one-side aperture shielding leaves is longer than a moving distance of the pair of one-side aperture shielding leaves. In an X-ray imaging apparatus that detects X-rays irradiated from an X-ray tube and passing through a subject with an X-ray detector,
Centering on the X-ray axis extending from the X-ray tube to the X-ray detector, two pairs of shielding leaves that move in opposite directions in synchronization with each other are provided in two directions orthogonal to each other. A first collimator mechanism for forming an irradiation field;
A second collimator mechanism for further narrowing one side of the rectangular X-ray irradiation field formed by the first collimator mechanism to the inside;
The second collimator mechanism is
A pair of one-side aperture shielding leaves that are supported by the guide member so as to be movable in one direction and in which a long hole parallel to the moving direction is formed,
A moving member provided with a pair of engaging portions capable of moving in the long holes in a state of being engaged with the long holes formed in the pair of one-side aperture shielding leaves,
Drive means for reciprocating the moving member in parallel with the elongated hole;
A biasing member that biases the pair of one-side aperture shielding leaves in a direction away from each other;
With
The distance between the pair of engaging portions attached to the moving member is between the long holes formed in the pair of one-side aperture shielding leaves when the pair of one-side aperture shielding leaves are arranged at the most separated positions. An X-ray imaging apparatus having a distance corresponding to The X-ray imaging apparatus according to claim 3,
An X-ray imaging apparatus, wherein a length of a long hole formed in the pair of one-side aperture shielding leaves is longer than a moving distance of the pair of one-side aperture shielding leaves.

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