JP2011024664A - Radiographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic apparatus contrived so that an artifact derived from a radiation grid is prevented from being projected in a perspective image as far as possible even when a radiation detector is moved to a radiation source. <P>SOLUTION: By the configuration of this invention, the width of the shadow in the lateral direction of absorption foil projected to an FPD is equal when the position of the focus of an X-ray tube to an FPD is at the position of P<SB>min</SB>and when it is at the position of P<SB>max</SB>. In such a manner, since the advancing direction of a radiation beam to the absorption foil of the radiation grid is not changed as far as possible regardless of the movement of the FPD, the radiation beam (direct beam) radiated from the X-ray tube reaches the FPD without being obstructed by the absorption foil. Thus, a false image appearing in a radiation perspective image is suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radiation imaging apparatus provided with a radiation source and a radiation detector, and in particular, the radiation detector is provided with a radiation grid, and the relative distance between the radiation source and the radiation detector can be changed. The present invention relates to a radiation imaging apparatus.

  A medical institution is equipped with a radiation imaging apparatus that acquires a radiation image of a subject. Such a radiation imaging apparatus includes a radiation source that irradiates radiation, a radiation detector that detects radiation, and a radiation grid that covers a detection surface of the radiation detector.

  A configuration of a conventional radiation imaging apparatus will be described. A conventional radiation imaging apparatus 51 includes a radiation source 53, a radiation detector 54, and a radiation grid 55 as shown in FIG. The radiation irradiated from the radiation source 53 passes through the subject M and then enters the radiation detector 54. The radiation detector 54 outputs a radiation detection signal, and based on this, a fluoroscopic image of the subject is generated. The radiation grid 55 is fixed to the radiation detector 54.

  As shown in FIG. 16, the radiation grid 55 is configured by arranging elongated absorption foils 55a like a blind. The absorption foil 55a is provided for the purpose of removing scattered radiation generated in the subject.

The radiation detector 54 can be moved forward and backward with respect to the radiation source 53 (see the arrow in FIG. 15). By changing the distance between the radiation detector 54 and the radiation source 53, the size of the projected image of the subject reflected in the radiation detector 54 can be adjusted. When the radiation detector 54 moves, the radiation grid 55 fixed to the radiation detector 54 also moves following this. The distance between the radiation detector 54 and the radiation source 53 can be changed from the shortest SID _min to the longest SID _max . As a radiation imaging apparatus having such a configuration, there is one as described in Patent Document 1.

JP 2005-342522 A

However, the conventional radiographic apparatus has the following problems.
In other words, the conventional radiographic apparatus has a problem that the shadow of the radiation grid 55 is reflected in the radiation detector 54 and the visibility of the fluoroscopic image is deteriorated. The arrangement of the absorption foils 55a of the radiation grid 55 is set assuming that the positions of the radiation source 53 and the radiation detector 54 are at a certain distance. That is, when the distance between the two 53 and 54 is SID ₀ intermediate between SID _min and SID _max , the absorption foil 55a of the radiation grid 55 directly emits radially from the radiation source 53 as shown in FIG. It is inclined so as to follow the direction of traveling to radiation (see arrow in the figure). In the fluoroscopic image acquired at this time, the influence of the shadow S of the radiation grid 55 does not appear so much. In the conventional apparatus, SID ₀ is usually equal to (SID _max + SID _min ) / 2.

However, the radiation detector 54 is moved relative to the radiation source 53, the distance between them 53, 54 is eliminated in SID _0. Then, the direction in which the radiation is applied to the radiation grid 55 changes, so that the shadow S of the absorbing foil 55a of the radiation grid 55 becomes wider and is reflected in the radiation detector 54 (see FIG. 18). Such enlargement of the shadow S of the absorption foil 55a is remarkable at the end portions in the arrangement direction of the absorption foils 55a provided on the radiation grid 55. Further, enlargement of the shadow S of the absorbing foil 55a, the distance between the two 53 and 54 is significant as displaced from SID _0. Such a phenomenon is called a radiation grid cut-off.

  In the fluoroscopic image acquired in the above-described state, a portion where the shadow S of the enlarged absorbent foil 55a is reflected is dark. As the shadow S is reflected in the radiographic image, a striped pattern appears in the radiographic image. It is more preferable to remove as many artifacts as possible in such a diagnosis.

  The present invention has been made in view of such circumstances, and the object thereof is to prevent artifacts derived from the radiation grid from appearing in the fluoroscopic image as much as possible even when the radiation detector moves relative to the radiation source. An object of the present invention is to provide a radiation imaging apparatus devised as described above.

The present invention has the following configuration in order to solve the above-described problems.
That is, the radiation imaging apparatus according to the present invention advances and retreats from a first position closest to the radiation source to a second position farthest from the radiation source that irradiates the radiation, a radiation detection means that detects the radiation, and the radiation detection means. A radiation grid configured to cover a detector moving means to be moved and a detection surface for detecting radiation of the radiation detecting means, and a strip-shaped absorbing foil extending in the first direction arranged in the second direction. And the width of the shadow in the second direction of the absorbing foil reflected on the radiation detecting means when the position of the radiation detecting means relative to the radiation source is at a standard position that is sandwiched between the first position and the second position. The width of the shadow in the second direction of the absorbing foil reflected on the radiation detection means from the standard position toward the first position or the second position from the standard position gradually becomes wider. In the line imaging apparatus, (A) when the position of the radiation detection means with respect to the radiation source is the first position, the width of the shadow in the second direction of the absorbing foil reflected in the radiation detection means, and (B) with respect to the radiation source When the position of the radiation detecting means is the second position, the width of the shadow in the second direction of the absorbing foil reflected on the radiation detecting means is equal.

  [Operation / Effect] According to the present invention, the radiation detecting means moves forward and backward relative to the radiation source. Specifically, the radiation detection means moves from the first position closest to the radiation source to the second position furthest away. The radiation detection means of the present invention is provided with a radiation grid for removing scattered radiation. The radiation grid is configured by arranging strip-shaped absorbing foils extending in the first direction in the second direction.

  When the radiation detection means is at the standard position, the width of the shadow produced by the radiation grid absorbing foil blocking the radiation is the narrowest. The width at this time is substantially the same as the thickness of the absorbent foil. The reason why they are not completely the same is that the radiation beam has a cone shape, and the shadow of the absorbing foil is slightly enlarged until it reaches the radiation detection means.

  When the radiation detection means moves relative to the radiation source, the irradiation direction of the radiation beam on the absorbing foil changes. Then, the width of the shadow generated by the radiation grid absorbing foil blocking the radiation is increased. According to the present invention, when the position of the radiation detection means relative to the radiation source is the first position and when the position is the second position, the shadow of the absorbing foil reflected in the radiation detection means in the second direction is reflected. The widths are equal. On the other hand, since the conventional configuration does not have such a configuration, the width of the shadow of the absorption foil when the position of the radiation detection means with respect to the radiation source is the first position and when the position is the second position. Is different. If it sets in this way, the width | variety of the shadow of the absorption foil reflected on a radiation detection means will become wider when a radiation detection means exists in a 1st position or a 2nd position. This is because when the radiation detection means moves from the standard position to the first position or the second position, the traveling direction of the radiation beam changes more drastically than the setting of the present invention. According to the present invention, since the traveling direction of the radiation beam with respect to the radiation detection means is not changed as much as possible regardless of the movement of the radiation detection means, the change in the width of the shadow of the absorption foil accompanying the movement of the radiation detection means Is minimal. Therefore, the radiation beam (direct line) emitted from the radiation source reaches the radiation detection means without being disturbed by the absorption foil. Thereby, the false image which appears in a radiographic image can be suppressed.

  Moreover, when the absorption foil located in the 2nd direction end part of the above-mentioned radiation grid is made into the endmost part absorption foil, the shadow of the endmost part absorption foil reflected in a radiation detection means is a radiation detection means with respect to a radiation source. It is more desirable if the widths are equal regardless of whether the position is the first position or the second position.

  [Operation / Effect] The absorption foil (absorption foil located at the irradiation limit position of the cone-shaped radiation beam emitted from the radiation source) located at the extreme end in the second direction of the radiation grid is the absorption foil accompanying the movement of the radiation detection means. The change in the shadow width is the most dramatic. According to the above-described configuration, the setting relating to the width of the shadow is performed based on the absorbing foil positioned at the most distal portion of the radiation grid. In this way, a radiographic image from which the influence of the absorbing foil has been removed can be obtained more reliably.

  Further, when the position of the radiation detection means with respect to the radiation source is at the standard position, it is more desirable that each of the extension lines extending in the short direction of the absorption foils constituting the radiation grid intersect at the focal point of the radiation source. .

  [Operation / Effect] The above-described configuration shows a more specific configuration of the radiation imaging apparatus of the present invention. In this way, it is possible to provide a radiation imaging apparatus in which the progress of the radiation beam emitted from the radiation source is not disturbed by the radiation grid as much as possible.

  In addition, the arc-shaped C-arm that supports the radiation source and the radiation detection means at both ends and the plane of the arc of the arc-shaped C-arm are orthogonal to each other, and the center of curvature of the C-arm is A first rotating means for rotating the C-arm around the first axis passing therethrough; a second rotating means for rotating the C-arm around the second axis that is orthogonal to the first axis and extends in the horizontal direction; Is more desirable.

  [Operation / Effect] The above-described configuration shows a more specific configuration of the radiation imaging apparatus of the present invention. Thus, a configuration having a C-arm can be adopted as a specific configuration of the radiation imaging apparatus.

  The radiation detecting means of the present invention is provided with a radiation grid configured by arranging strip-shaped absorbing foils extending in the first direction in the second direction. When the radiation detection means is moved with respect to the radiation source, the direction in which the oblique radiation beam strikes the absorbing foil changes. Thereby, the width of the shadow generated by the radiation foil of the radiation grid blocking the radiation is widened. According to the present invention, when the position of the radiation detection means with respect to the radiation source is at the first position and when the radiation detection means is at the second position, the shadow of the absorbing foil reflected in the radiation detection means in the second direction is reflected. Are equal in width. According to the present invention, since the traveling direction of the radiation beam with respect to the radiation detection means is not changed as much as possible regardless of the movement of the radiation detection means, the change in the width of the shadow of the absorption foil accompanying the movement of the radiation detection means Is minimal. Therefore, the radiation beam (direct line) emitted from the radiation source reaches the radiation detection means without being disturbed by the absorption foil. Thereby, the false image which appears in a radiographic image can be suppressed.

1 is a functional block diagram illustrating a configuration of an X-ray imaging apparatus according to Embodiment 1. FIG. FIG. 3 is a schematic diagram for explaining a configuration of a C-arm according to the first embodiment. It is a perspective view explaining the arm rotation mechanism which concerns on Example 1. FIG. 3 is a schematic diagram illustrating an X-ray grid according to Embodiment 1. FIG. 3 is a schematic diagram illustrating an X-ray grid according to Embodiment 1. FIG. It is a schematic diagram explaining the movement of the relative position of the X-ray tube and FPD which concern on Example 1. FIG. FIG. 3 is a schematic diagram for explaining a positional relationship of each unit according to the first embodiment. FIG. 3 is a schematic diagram for explaining a positional relationship of each unit according to the first embodiment. It is a schematic diagram explaining the shadow of the absorption foil which concerns on Example 1. FIG. FIG. 3 is a schematic diagram for explaining a positional relationship of each unit according to the first embodiment. FIG. 3 is a schematic diagram for explaining a positional relationship of each unit according to the first embodiment. FIG. 6 is a schematic diagram for explaining an effect according to the first embodiment. FIG. 6 is a schematic diagram for explaining an effect according to the first embodiment. It is a mimetic diagram explaining one modification of the present invention. It is a schematic diagram explaining the structure of the X-ray imaging apparatus of a conventional structure. It is a schematic diagram explaining the structure of the X-ray imaging apparatus of a conventional structure. It is a schematic diagram explaining the structure of the X-ray imaging apparatus of a conventional structure. It is a schematic diagram explaining the structure of the X-ray imaging apparatus of a conventional structure.

  Next, an embodiment of the radiation imaging apparatus according to Embodiment 1 will be described with reference to the drawings. The X-ray in Example 1 corresponds to the radiation of the present invention.

<Configuration of X-ray imaging apparatus>
First, the configuration of the X-ray imaging apparatus 1 according to the first embodiment will be described. FIG. 1 is a functional block diagram illustrating the configuration of the radiation imaging apparatus according to the first embodiment. As shown in FIG. 1, the X-ray imaging apparatus 1 according to the first embodiment includes a top plate 2 on which a subject M is placed, an X-ray tube 3 provided below the top plate 2, and a top plate 2. The flat panel detector: FPD4 which detects the X-rays provided on the upper side of the FPD4 and the X-ray grid 5 provided so as to cover the detection surface on which the X-rays of the FPD4 are incident. Detection elements for detecting X-rays are arranged vertically and horizontally on the detection surface of the FPD 4 to constitute a two-dimensional matrix of detection elements. The X-ray tube controller 6 controls the tube current, tube voltage, and X-ray beam pulse width of the X-ray tube 3. The X-ray tube 3 corresponds to the radiation source of the present invention, and the FPD 4 corresponds to the radiation detection means of the present invention. The X-ray grid 5 corresponds to the radiation grid of the present invention.

  The X-ray tube 3 irradiates the cone-shaped radiation beam B toward the X-ray grid 5 and the FPD 4. The central axis of the radiation beam is perpendicular to the X-ray grid 5 and FPD 4 and passes through the center point of the X-ray grid 5 and FPD 4 which are sheet-like vertically and horizontally.

  The C-type arm 7 supports the X-ray tube 3 and the FPD 4 collectively. The C-shaped arm 7 has an arc shape as shown in FIG. 2, and an X-ray tube 3 is provided at one end of the arc and an FPD 4 is provided at the other end. The arm rotation mechanism 9 is provided for the purpose of rotating the C-arm 7 (see FIG. 1). Assuming that the plane in which the arc of the C-shaped arm 7 having an arc exists exists as a reference plane [paper surface in FIG. 2A], the C-shaped arm 7 passes through the center of curvature of the C-shaped arm 7 perpendicular to the reference plane. If it can be rotated around the first central axis E, it can also be rotated around a horizontal second central axis F included in the reference plane, as shown in FIG. The first central axis E and the second central axis F are orthogonal to each other. In this way, the C-shaped arm 7 has two central axes, and the rotation of each is independent. The C-arm 7 is rotated by an arm rotation mechanism 9. The arm rotation control unit 10 controls the arm rotation mechanism 9. The C-arm 7 is supported by a column 8 arranged on the floor surface of the examination room.

  As shown in FIG. 3, the arm rotation mechanism 9 includes a first rotation mechanism 9 a that rotates the C-type arm 7 around the first central axis E, and a second type that rotates the C-type arm 7 around the second central axis F. And a rotation mechanism 9b. The arm rotation control unit 10 includes a first rotation control unit 10a that controls the first rotation mechanism 9a and a second rotation control unit 10b that controls the second rotation mechanism 9b. The second rotating mechanism 9b corresponds to the second rotating means of the present invention, and the first rotating mechanism 9a corresponds to the first rotating means of the present invention.

  The FPD 4 is provided with a shift mechanism 11 that shifts the FPD 4 forward and backward with respect to the X-ray tube 3 (see FIG. 1). The FDP 4 can be moved closer to the X-ray tube 3 by the shift mechanism 11 or can be moved away. The shift control unit 12 controls the shift mechanism 11. The shift mechanism 11 corresponds to the detector moving means of the present invention.

  The image generation unit 21 generates an X-ray fluoroscopic image P in which a fluoroscopic image of the subject is reflected based on the detection signal output from the FPD 4.

  The X-ray grid 5 is provided for the purpose of removing scattered X-rays generated when X-rays pass through the subject M. The X-ray grid 5 has a plate shape that can cover the detection surface of the rectangular FPD 4, and a strip-shaped absorbent foil 5 a extending in the vertical direction p (corresponding to the first direction of the present invention) is in the horizontal direction. q (corresponding to the second direction of the present invention) arranged (see FIG. 4). Each absorbing foil 5a is arranged so as to allow direct X-rays that go straight to the FPD 4 without being scattered on the path. Scattered rays whose traveling direction deviates from the direction in which the radiation beam irradiated from the X-ray tube 3 spreads are absorbed by any of the absorbing foils 5a and cannot reach the FPD 4.

The absorption foil 5a of the X-ray grid 5 is inclined as shown in FIG. That is, each of the absorption foils 5 a is provided so that the short direction of each absorption foil 5 a is along the traveling direction of the cone-shaped radiation beam irradiated from the X-ray tube 3. In other words, an extension to extend the respective absorption foil 5a in the lateral direction, all of the absorbing foil 5a is to intersect the X-ray generating focal point P ₀ of the X-ray tube 3 at a distance standard distance SID ₀ from FPD4 Become. When the position of the FPD 4 with respect to the X-ray tube 3 is the standard position of the present invention, the distance between the FPD 4 and the X-ray tube 3 is SID ₀ .

FIG. 6 illustrates a change in the distance between the FPD 4 and the X-ray tube 3. The FPD 4 is moved forward and backward along the central axis of the X-ray beam emitted from the X-ray tube 3 by the shift mechanism 11. Originally, the FPD 4 moves relative to the X-ray tube 3. However, in FIG. 6 and the subsequent drawings, it is assumed that the X-ray tube 3 moves relative to the FPD 4 for the purpose of brief explanation. The distance between the FPD 4 and the X-ray tube 3 varies from the maximum SID _max to the minimum SID _min . The distance D of the difference between SID _max and SID _min is about 25 cm. When the position of the FPD 4 with respect to the X-ray tube 3 is the first position of the present invention, the distance between the FPD 4 and the X-ray tube 3 is SID _min . When the position of the FPD 4 with respect to the X-ray tube 3 is the second position of the present invention, the distance between the FPD 4 and the X-ray tube 3 is SID _max .

  The X-ray imaging apparatus 1 according to the first embodiment includes a main control unit 41 that comprehensively controls the control units 6 and 10. The main control unit 41 is constituted by a CPU, and realizes the control units 6 and 10 and the image generation unit 21 by executing various programs. In addition, each part is good also as a structure divided | segmented into the control apparatus in charge of each. The display unit 35 displays an X-ray fluoroscopic image, and the console 36 allows an operator's operation to be input.

  The storage unit 37 stores all the set values, reference data, and outputs in the control units 6 and 10 and the image generation unit 21 related to image generation.

<Positional relationship between X-ray grid and each part>
The configuration of the first embodiment has a special relationship between the degree of inclination of the absorption foil 5 a of the X-ray grid 5 and the movable range of the X-ray tube 3 and the FPD 4. For the purpose of explaining this, the positional relationship between the X-ray grid and each part will be described.

FIG. 7 shows the positional relationship of each part when the distance between the X-ray tube 3 and the FPD 4 is SID ₀ . P ₀ is the focal point of the X-ray tube 3 at that time. The width of the X-ray grid 5 in the thickness direction of the X-ray grid 5 (the direction perpendicular to both the vertical direction and the horizontal direction) is 5b, which is the absorption foil positioned at the extreme end in the horizontal direction of the X-ray grid 5. Let L be L. Let h be the distance from the exit surface from which the X-ray grid 5 emits X-rays to the detection surface from which the FPD 4 enters X-rays. Since the X-ray grid 5 is fixed to the FDP 4, this distance h is constant. The absorbent foil 5b corresponds to the endmost absorbent foil of the present invention. Each absorption foils 5a of the X-ray grid 5 is fabricated to orient the focal point P _0, it is attached to the FPD 4.

A center line in the thickness direction of the X-ray grid 5 is defined as C, and a point where the center line C and the absorbent foil 5b intersect is defined as an absorbent foil reference point G. The distance from the focal point P ₀ to the center line C is S ₀ . Further, consider a line segment D ₀ connecting the focal point P ₀ and the absorbing foil reference point G. An angle formed by the line segment D ₀ and the center line C is defined as θ ₀ . When FPD4 for X-ray tube 3 is in the standard position of the present invention, the focal position of the X-ray tube 3 for FPD4 has a position of the focal point P _0.

Further, when the distance between the X-ray tube 3 and the FPD 4 is SID _min , the focus of the X-ray tube 3 is set to P _min (see FIG. 8). When the FPD 4 with respect to the X-ray tube 3 is in the first position of the present invention, the focal position of the X-ray tube 3 with respect to the FPD 4 is the position of the focal point _Pmin .

When the distance between the X-ray tube 3 and the FPD 4 is SID _max , the focal point of the X-ray tube 3 is set to P _max (see FIG. 8). That is, when the FPD 4 with respect to the X-ray tube 3 is in the second position, the focal position of the X-ray tube 3 with respect to the FPD 4 is the position of _Pmax .

As shown in FIG. 8, the feature of the first embodiment is that the angle θA formed by the line segment D ₀ and the line segment D _max is equal to the angle θB formed by the line segment D ₀ and the line segment D _min . When the distance between the X-ray tube 3 and the FPD 4 is SID ₀ , as shown on the left side of FIG. 9 (a), the X-ray is blocked by the absorption foil 5b by the thickness of the absorption foil 5b, and the FPD 4 has a shadow. S is projected. The shadow S is reflected on a single detection element on the detection surface of the FPD 4 as shown in the center of the drawing when the detection elements arranged in the horizontal direction are compared. Such a positional relationship between the shadow S and the detection element is the same in the entire area of the FPD 4. That is, the shadow S does not appear across the two detection elements from the lateral direction.

  9A, the width of the shadow S in the horizontal direction is only the thickness of the absorbing foil 5b and is narrow. Accordingly, in the X-ray fluoroscopic image P generated based on the detection signal output by the FPD 4, dark vertical stripes with a width of one pixel as shown on the right side in the figure appear. The pixel value is dark because the pixel value related to the detection element in which the shadow S is reflected is lower than that in which the shadow S is not reflected, and the vertical line is the shadow on the FPD 4. This is because the detection elements including S are continuously present in the vertical direction.

FIG. 9B shows the state of the shadow S projected on the FPD 4 when the distance between the X-ray tube 3 and the FPD 4 is SID _max . Compared with the case of FIG. 9A, the irradiation direction of the X-ray beam irradiated from the X-ray tube 3 to the absorbing foil 5b is changed by θA (see FIG. 8). Along with this, the traveling direction of the X-ray beam irradiated to the absorption foil 5b is changed, and the shadow S of the absorption foil 5b reflected in the FPD 4 becomes wider in the lateral direction than in the case of FIG.

On the other hand, FIG. 9C shows the state of the shadow S projected on the FPD 4 when the distance between the X-ray tube 3 and the FPD 4 is SID _min . Compared to the case of FIG. 9A, the irradiation direction of the X-ray beam irradiated from the X-ray tube 3 to the absorbing foil 5b is changed by θB (see FIG. 8). Along with this, the traveling direction of the X-ray beam irradiated to the absorption foil 5b is changed, and the shadow S of the absorption foil 5b reflected in the FPD 4 becomes wider in the lateral direction than in the case of FIG.

  In the configuration of the first embodiment, the horizontal width of the shadow S in the case of FIG. 9B is equal to the horizontal width of the shadow S in the case of FIG. 9C. This is because θA and θB have the same angle. Also, θA and θB are appropriately changed so that the horizontal width of the shadow S in FIG. 9B is exactly the same as the horizontal width of the shadow S in FIG. 9C. You may do it. Since the short side direction of the absorbent foil 5b is not orthogonal to the incident surface of the FPD 4, the state of FIG. 9B is closer to the FPD 4 than the state of FIG. 9C. . Since the X-ray beam has a cone shape, the enlargement ratio of the shadow appearing in the FPD 4 is strictly different between FIG. 9B and FIG. 9C. Therefore, by appropriately adjusting θA and θB, the influence of the enlargement ratio can be removed, and the horizontal width of the shadow S can be made more consistent.

Note that the focus Pc in FIG. 8 indicates a position intermediate between the focus P _max and the focus P _min . That is, the focal point Pc is the midpoint of the line segment connecting the focal point P _max and the focal point P _min . The distance from the focal point Pc to the FPD 4 is an average distance between SID _max and SID _min . The focal point P ₀ is closer to the focal point P _min than the focal point Pc. Therefore, SID ₀ is shorter than the average distance between SID _max and SID _min .

Next, how to determine the position of the focal point P ₀ when the positions of the focal point P _max and the focal point P _min are determined will be described. Prior to this, the positional relationship of each part is represented by a symbol. First, as shown in FIG. 7, let R be the distance from the center in the lateral direction q of the FPD 4 to the absorbent foil reference point G. Further, as shown in FIG. 10, the distance from the focal point P _max to the center line C is defined as S _max . A line segment D _max connecting the focal point P _max and the absorbing foil reference point G is considered. An angle formed by D _max and the center line C is defined as θ _max . Similarly, as shown in FIG. 11, the distance from the focal point P _min to the center line C is S _min . Further, consider a line segment D _min connecting the focal point P _min to the absorbing foil reference point G. An angle formed by D _min and the center line C is defined as θ _min . In the following description, P ₀ , S ₀ , D ₀ , and θ ₀ can be understood with reference to FIG. P _max , S _max , D _max , and θ _max can be understood with reference to FIG. P _min , S _min , D _min , and θ _min can be understood with reference to FIG.

S _max and S _min can be expressed as follows.
S _max = SID _max −h−L / 2 (1)
S _min = SID _min −h−L / 2 (2)

Tan θ _max and tan θ _min can be expressed as follows.
tan θ _max = S _max / R (3)
tan θ _min = S _min / R (4)

By the way, θA is equal to θ ₀ −θ _min , and θB is equal to θ _max −θ ₀ . Given that θA = θB, the following equation holds:
θ ₀ = (θ _min + θ _max ) / 2 (6)

SID ₀ and S ₀ can be expressed as follows.
SID ₀ = S ₀ + L / 2 + h (7)
S ₀ = R · tan θ ₀ (8)

From equations (6) to (8), the following equation holds:
SID ₀ = R · tan (θ _min / 2 + θ _max / 2) + L / 2 + h (9)

Here, referring to equations (1) to (4), it can be seen that SID ₀ can be determined using only SID _max , SID _min , L, and h. That is, tan θ _max is represented by S _max and R [see formula (3)], and S _max is represented by SID _max , L, and h [see formula (1)]. Therefore, tan θ _max is represented by SID _max , L, h, and R. Similarly, tan θ _min is expressed by SID _min , L, h, and R [see Formula (2) and Formula (4)]. Here, L, h, and R are constant because they are the arrangement and dimensions of the FPD 4 and the X-ray grid 5. That is, SID ₀ is uniquely determined with the setting of SID _max and SID _min . The inclination of the absorbing foil strips 5a of the X-ray grid 5 will be determined relative to the SID _0. If Prolonged absorption foil 5a in transverse direction, is that all intersect at the focal point P _0.

  Next, the effects of the present invention will be described with reference to FIGS. In the conventional X-ray imaging apparatus, the focal point Pc in FIG. 12 is a reference for the inclination of the absorption foil 5 a of the X-ray grid 5. If the absorbent foil 5a is extended in the short direction, all intersect at the focal point Pc. A line segment connecting the absorbent foil reference point G and the focal point Pc is defined as Dc.

If the angle formed by the line segment _Dmax and the line segment Dc is θP, and the angle formed by the line segment _Dmin and the line segment Dc is θQ, then θP <θQ. This is significantly different from the configuration of the present embodiment in which θA = θB. The angle formed by D _min and D _max is θP + θQ, and as can be seen from FIG. 8, this is θA + θB. That is, the ratio of the angle division formed by the line segment _Dmin and the line segment _Dmax is different from the conventional configuration and the present invention.

When comparing the conventional example with the present embodiment, θQ> θB is satisfied (see FIGS. 8 and 12). That is, when the focal point of the X-ray tube 3 at Pc is moved to _Pmin , the irradiation direction of the X-ray beam changes greatly, as shown in the left and center of FIG. 13, compared to FIG. 9C. A wider shadow S is reflected in the FPD 4 in the width direction. Then, as shown on the right side of FIG. 13, vertical stripes that are darker and more conspicuous than FIG. 9C appear. In the present embodiment, although vertical stripes appear, they are not so conspicuous.

  As described above, according to the configuration of the first embodiment, the FPD 4 moves back and forth with respect to the X-ray tube 3. Specifically, the FPD 4 moves from the position closest to the X-ray tube 3 to the position farthest away. The FPD 4 having the configuration of the first embodiment is provided with an X-ray grid 5 for removing scattered X-rays. The X-ray grid 5 is constituted by strip-shaped absorbent foils 5a extending in the vertical direction and arranged in the horizontal direction.

  When the FPD 4 is in the standard position, the width in the horizontal direction of the shadow caused by the absorption foil 5a of the X-ray grid 5 blocking the radiation is the narrowest. The width at this time is substantially the same as the thickness of the absorbent foil 5a. The reason why they are not completely the same is that the radiation beam has a cone shape, and the shadow of the absorption foil 5a is slightly enlarged until it reaches the FPD 4.

When the FPD 4 moves with respect to the X-ray tube 3, the irradiation direction of the obliquely radiated beam with respect to the absorbing foil 5a changes. Then, the width of the shadow generated by the absorption foil 5a of the X-ray grid 5 blocking the radiation is widened. According to the configuration of the first embodiment, the absorption foil 5a reflected in the FPD 4 is detected when the focal point of the X-ray tube 3 with respect to the FPD 4 is at the position P _min and when it is at the position P _max . The horizontal shadow widths are equal. In the conventional configuration, since such a configuration is not used, the absorption foil 5a has a different position when the focal point of the X-ray tube 3 with respect to the FPD 4 is at the position P _{min and at} the position P _max . The shadow width is different. If set in this way, the width of the shadow of the absorbing foil 5a reflected on the FPD 4 becomes wider when the position of the focal point of the X-ray tube 3 relative to the FPD 4 is at the position P _min or P _max . This is because when the X-ray tube 3 moves from the standard position to the position P _min or the position P _max , the traveling direction of the radiation beam changes more drastically than the setting of the configuration of the first embodiment. According to the configuration of the first embodiment, the traveling direction of the radiation beam with respect to the absorption foil 5a of the X-ray grid 5 does not change as much as possible regardless of the movement of the FPD 4. Therefore, the absorption foil 5a associated with the movement of the FPD 4 The change in shadow width is minimal. Therefore, the radiation beam (direct ray) emitted from the X-ray tube 3 reaches the FPD 4 without being obstructed by the absorption foil 5a. Thereby, the influence of the false image appearing in the radioscopic image can be suppressed.

  The absorption foil 5b (absorption foil existing at the irradiation limit position of the cone-shaped radiation beam emitted from the X-ray tube 3) positioned at the lateral end of the X-ray grid 5 is a shadow of the absorption foil 5a accompanying the movement of the FPD 4. The change in width is the most dramatic. According to the above-described configuration, the setting relating to the width of the shadow S described above is performed with reference to the absorbing foil 5 a located at the most distal portion of the X-ray grid 5. In this way, a radiographic image from which the influence of the absorbing foil 5a has been removed can be acquired more reliably.

Further, when the position of the FPD 4 with respect to the X-ray tube 3 is at the standard position (when the distance between the X-ray tube 3 and the FPD 4 is SID ₀ ), each of the absorption foils 5a constituting the X-ray grid 5 is arranged in the short direction. Each extended line extends at the focal point of the X-ray tube 3. The above configuration shows a more specific configuration of the radiation imaging apparatus having the configuration of the first embodiment. In this way, it is possible to provide a radiation imaging apparatus in which the progress of the radiation beam emitted from the X-ray tube 3 is not disturbed by the X-ray grid 5 as much as possible.

  The present invention is not limited to the above-described configuration, and can be modified as follows.

  (1) Although the configuration of the first embodiment is a configuration having a C-shaped arm, instead of this, as shown in FIG. 14, a type of radiation imaging apparatus in which the X-ray tube 3 is supported by a support (common name: fluoroscopic table) May be adapted. In this case, the X-ray tube 3 moves up and down to set the SID appropriately.

  (2) Although the embodiment described above is a medical device, the present invention can also be applied to industrial and nuclear devices.

  (3) X-rays referred to in the above-described embodiments are an example of radiation in the present invention. Therefore, the present invention can be applied to radiation other than X-rays.

3 X-ray tube (radiation source)
4 FPD (radiation detection means)
5 X-ray grid (radiation grid)
5a Absorbing foil 7 C-type arm 9a First rotation mechanism (first rotation means)
9b Second rotation mechanism (second rotation means)
11 Shift mechanism (detector moving means)

Claims (4)

A radiation source that emits radiation;
Radiation detection means for detecting radiation;
Detector moving means for moving the radiation detecting means forward and backward from a first position closest to the radiation source to a second position furthest away;
A radiation grid provided so as to cover a detection surface for detecting radiation of the radiation detection means, and a strip-shaped absorbing foil extending in the first direction arranged in the second direction,
The width of the shadow in the second direction of the absorbing foil reflected on the radiation detecting means when the position of the radiation detecting means with respect to the radiation source is at a standard position that is sandwiched between the first position and the second position. Is the narrowest,
In the radiation imaging apparatus in which the width of the shadow in the second direction of the absorbing foil reflected on the radiation detection means gradually increases from the standard position toward the first position or the second position from the standard position.
(A) When the position of the radiation detection means with respect to the radiation source is the first position, the width of the shadow in the second direction of the absorption foil reflected on the radiation detection means; and (B) the radiation source. When the position of the radiation detecting means relative to the second position is the second position, the width of the shadow in the second direction of the absorbing foil reflected on the radiation detecting means is equal. . The radiographic apparatus according to claim 1,
When the absorption foil located at the endmost portion in the second direction of the radiation grid is the endmost absorption foil,
The shadow of the outermost absorption foil reflected on the radiation detection means has the same width regardless of whether the position of the radiation detection means relative to the radiation source is the first position or the second position. A radiographic apparatus characterized by comprising: The radiographic apparatus according to claim 1 or 2,
When the position of the radiation detection means with respect to the radiation source is at the standard position, each of the extension lines extending in the short direction of each of the absorption foils constituting the radiation grid intersects at the focal point of the radiation source. Radiography equipment. The radiographic apparatus according to any one of claims 1 to 3,
An arcuate C-shaped arm that supports the radiation source and the radiation detection means at both ends;
First rotating means for rotating the C-shaped arm around a first axis that is orthogonal to a plane on which the arc of the C-shaped arm that is arcuate and passes through the center of curvature of the C-shaped arm;
A radiation imaging apparatus comprising: a second rotation unit that rotates the C-arm around a second axis that is orthogonal to the first axis and extends in the horizontal direction.

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