JP2012090872A - Radiographic device - Google Patents

Abstract

There is provided a radiographic apparatus capable of acquiring a subtraction image with excellent visibility by overlapping a fluoroscopic image of a subject without overlapping a stripe pattern derived from a radiation grid.
According to the present invention, a subtraction image P3 is taken while an X-ray grid 5 that absorbs scattered radiation is moved with respect to an FPD 4. This subtraction image P3 is generated by superimposing a plurality of perspective images P1, P2. The most characteristic configuration of the present invention is a series of perspective images P1 that are superimposed when the single subtraction image P3 is generated while the X-ray grid 5 is moved from one end side to the other end side of the movable range. , P is taken. In this way, a subtraction image P3 with excellent visibility can be provided.
[Selection] Figure 1

Description

  The present invention relates to a radiation imaging apparatus that images a fluoroscopic image of a subject using radiation, and particularly relates to a radiation imaging apparatus including a radiation grid that removes scattered radiation components of radiation.

  A medical institution is equipped with a radiation imaging apparatus that acquires an image of the subject M with radiation. Such a radiation imaging apparatus 51 includes a top plate 52 on which the subject M is placed, a radiation source 53 for irradiating radiation, and a radiation detector 54 for detecting radiation (FIG. 12, Patent Document 1). reference). Based on the detection signal output from the radiation detector 54, an image in which a fluoroscopic image of the subject M is reflected is acquired.

  A radiation grid 55 for removing scattered radiation generated in the subject M is provided on an incident surface (detection surface) on which radiation of the radiation detector 54 is incident. The radiation grid 55 is configured by arranging elongated absorbing foils like a blind. When scattered radiation strikes this absorbing foil, most of the radiation is absorbed by the absorbing foil and does not enter the radiation detector 54.

  By providing the radiation grid 55, a clear fluoroscopic image from which scattered radiation has been removed can be acquired, but the following problems arise. That is, the shadow of the absorbing foil is reflected on the radiation detector 54. Then, a striped pattern with dark pixel values appears in the fluoroscopic image, which deteriorates the visibility of the fluoroscopic image.

  Therefore, according to the conventional configuration, imaging is performed while moving the radiation grid 55 in a direction orthogonal to the direction in which the absorption foil extends with respect to the radiation detector 54. As a result, the position at which the shadow of the absorbing foil in the radiation detector 54 changes during photographing, so that a clear striped pattern does not appear in the fluoroscopic image, and the visibility of the fluoroscopic image is improved.

  The radiation grid 55 is set to reciprocate with respect to the radiation detector 54. The radiation source 53 emits radiation while the radiation grid 55 moves from one end side to the other end side of the movable range. The radiation detector 54 detects the radiation that has passed through the subject M so that a single fluoroscopic image can be acquired. In order to prevent the stripe pattern of the radiation grid 55 from appearing in the fluoroscopic image, it is necessary to move the radiation grid 55 as much as possible with respect to the radiation detector 54 during irradiation of radiation.

  By the way, in the conventional configuration, there are cases in which a subtraction image in which the bone part or soft tissue of the subject M is emphasized is obtained by superimposing two images having different imaging conditions. In order to capture the subtraction image, the radiation grid 55 is moved with respect to the radiation detector 54, and the imaging is performed twice while changing the intensity of the radiation.

JP 2008-114083 A

However, the conventional configuration has the following problems.
That is, according to the conventional radiographic apparatus, there is a problem that a clear subtraction image cannot be acquired.

  According to the conventional configuration, it is set so that the radiation grid 55 is moved as much as possible with respect to the radiation detector 54 during irradiation of radiation in order to prevent a stripe pattern derived from the radiation grid 55 from being reflected in the image. . Therefore, when trying to acquire a subtraction image with the conventional configuration, two images with different shooting conditions are shot as follows.

  That is, in the first imaging, the radiation grid 55 is moved from one end of the movable range to the other end with respect to the radiation detector 54, and in the second imaging, the radiation grid 55 is moved to the radiation detector 54. Is moved from the other end of the movable range toward one end. That is, the moving direction of the radiation grid 55 when viewed from the radiation detector 54 is reversed every time imaging is performed.

  The radiation grid 55 is moved relative to the radiation detector 54 by a moving mechanism provided between the radiation detector 54 and the radiation grid 55. Therefore, when the radiation grid 55 is moved from one end side to the other end side of the movable range, a reaction caused by the movement is applied to the radiation detector 54, and contrary to the radiation grid 55, one end side from the other end side is applied. Try to move on. Although the radiation detector 54 is fixed by the support member, the position of the radiation detector 54 is slightly shifted according to this reaction. When photographing is performed in this state, the position of the fluoroscopic image of the subject M reflected in the image is slightly shifted according to the above-described deviation of the radiation detector 54.

  When taking a subtraction image, according to the conventional configuration, the moving direction of the radiation grid 55 in the first shooting and the moving direction in the second shooting are different from each other. The directions of the reaction applied to the detector 54 are different from each other. As a result, the direction in which the subject M shifts between the two images acquired by the two photographings is different from each other. For example, if the subject M is reflected to the right with respect to the image in the first imaging, the sample is reflected to the left with respect to the image in the second imaging.

  As described above, in the conventional configuration, the movement of the radiation grid 55 is reversed every time imaging is performed, so that the position where the subject M is reflected in the images acquired by both imaging is greatly shifted. When the subtraction image is generated by superimposing, the fluoroscopic image of the subject M is shifted and superimposed on the image. Therefore, according to the conventional configuration, a subtraction image with excellent visibility cannot be obtained.

  A configuration is also possible in which the fluoroscopic images of the subject M are aligned on both images by image processing, and then the two images are superimposed on each other to generate a subtraction image. It will deteriorate. In addition, since it is necessary to calculate how much the fluoroscopic image of the subject M is shifted between the two images to be superimposed, the display speed of the subtraction image is reduced.

  The present invention has been made in view of such circumstances, and the purpose of the present invention is to visually recognize that the striped pattern derived from the radiation grid does not appear and the fluoroscopic images of the subject are superimposed without being displaced. An object of the present invention is to provide a radiation imaging apparatus capable of acquiring a subtraction image having excellent properties.

The present invention has the following configuration in order to solve the above-described problems.
That is, the radiographic apparatus according to the present invention includes a radiation source that irradiates radiation, a radiation source control unit that controls the radiation source, a detection unit that detects the irradiated radiation on a detection surface and outputs a detection signal; A radiation grid that is disposed in front of the detection surface and removes scattered radiation generated inside the subject, a radiation grid moving means that reciprocates the radiation grid with respect to the detection means, and a radiation grid that controls the radiation grid moving means The movement control means, the image generation means for generating a fluoroscopic image based on the detection signal output from the detection means, and a plurality of fluoroscopic images photographed under different radiation irradiation conditions are controlled by the radiation source control means. And a subtraction image generating means for generating a subtraction image in which the tissue of the subject is emphasized, and the control of the radiation grid movement control means. Thus, a series of fluoroscopic images that are superimposed when a single subtraction image is generated while the radiation grid is moved from one end side to the other end side of the movable range are photographed. .

  [Operation / Effect] According to the present invention, the subtraction image is taken while the radiation grid that absorbs the scattered radiation is moved with respect to the detection means. Therefore, the acquired subtraction image is suppressed from the appearance of a striped pattern derived from the radiation grid, and is suitable for diagnosis. This subtraction image is generated by superimposing a plurality of fluoroscopic images. The most characteristic configuration of the present invention is that a series of perspective images that are superimposed when a single subtraction image is generated while the radiation grid is moved from one end side to the other end side of the movable range are captured. There is. When the radiation grid is moved relative to the detection means, the detection means moves relative to the subject due to the reaction. When a series of fluoroscopic images are captured while reversing the moving direction of the radiation grid as in the conventional configuration, the position where the subject is reflected changes greatly between the acquired fluoroscopic images. This is because the direction of reaction applied to the detection means is different each time a fluoroscopic image is taken. According to the present invention, since the direction of the reaction applied to the detection unit does not change in the series of fluoroscopic image capturing, the position of the subject in the series of fluoroscopic images becomes more consistent. If such a fluoroscopic image is superimposed to generate a subtraction image, the images of the subject are superimposed without being displaced, and thus an image with excellent visibility can be provided.

  Further, in the above-described radiation imaging apparatus, the radiation grid movement control unit controls the radiation grid to move at a constant speed while the radiation grid is moved from one end of the movable range to the other end, and the radiation source control unit It is more desirable that the detection means perform a series of imaging while the radiation grid is moving at a constant speed.

  [Operation / Effect] The above-described configuration shows a more specific configuration of the radiation imaging apparatus of the present invention. When photographing is performed in a state where the speed of the radiation grid is changed, the false image derived from the radiation grid cannot be erased from the obtained fluoroscopic image. This is because if the radiograph is taken while the speed of the radiation grid is changed, the time during which the shadow of the radiation grid is reflected varies depending on the detection means. If a series of imaging is performed while the radiation grid is moving at a constant speed as in the present invention, the shadow of the radiation grid is reliably dispersed on the detection surface of the detection means, and the radiation grid is displayed on the fluoroscopic image. The striped pattern does not appear.

  Further, in the above-described radiation imaging apparatus, the radiation grid movement control unit controls the radiation grid movement unit so that the radiation grid moves at a constant speed when the first radiation irradiation in a series of fluoroscopic image capturing is started. This is more desirable.

  Further, in the above-described radiographic apparatus, the radiation grid movement control unit controls the radiation grid movement unit so that the radiation grid moves at a constant speed when the last radiation irradiation in a series of fluoroscopic imaging is completed. More desirable.

  [Operation / Effect] The above-described configuration shows a more specific configuration of the radiation imaging apparatus of the present invention. If comprised as mentioned above, a series of fluoroscopic images can be reliably taken while the radiation grid is moving at a constant speed.

  The radiation imaging apparatus includes an input unit that inputs an operator's instruction, and the radiation grid movement control unit performs radiation so that the time during which the radiation grid moves at a constant speed is shortened according to the input of the input unit. It is more desirable to control the grid moving means.

  [Operation / Effect] The above-described configuration shows a more specific configuration of the radiation imaging apparatus of the present invention. If comprised as mentioned above, the speed when the radiation grid is moving at constant speed can be made the fastest. By doing so, the shadow of the radiation grid is reliably dispersed on the detection surface of the detection means, and the striped pattern of the radiation grid does not appear in the fluoroscopic image.

  Further, in the above-described radiation imaging apparatus, it is more desirable if it is for standing position imaging.

  [Operation / Effect] The above-described configuration shows a more specific configuration of the radiation imaging apparatus of the present invention. If comprised as mentioned above, it will be easy to wobble a detection means with the movement of a radiation grid. This is because the radiation grid is supported by an upright member. The present invention is suitable for such a radiation imaging apparatus for standing imaging.

The present invention also discloses the following inventions.
A radiation source for irradiating radiation, a radiation source control means for controlling the radiation source, a detection means for detecting the irradiated radiation on the detection surface and outputting a detection signal, and a cover for covering the detection surface The absorbing foils extending in the extending direction are arranged in an arrangement direction orthogonal to the extending direction, a radiation grid that absorbs scattered radiation generated inside the subject, and the arrangement of the radiation grid with respect to the detection means A radiation grid moving means for reciprocating in a direction, a radiation grid movement controlling means for controlling the radiation grid moving means, an image generating means for generating a fluoroscopic image based on a detection signal output from the detecting means, and the radiation source A subtractor that emphasizes the tissue of a subject by superimposing a plurality of fluoroscopic images taken under different irradiation conditions under the control of the control means. Subtraction image generation means for generating a traction image, and a single subtraction image is generated while the radiation grid is moved from one end side to the other end side of the movable range under the control of the radiation grid movement control means. A radiation imaging apparatus characterized in that a series of fluoroscopic images that are superimposed upon generation are captured.

  [Operation / Effect] The above-described configuration is a configuration more specifically showing the moving direction of the radiation grid and the like in the configuration of the present invention. If the radiation grid is moved as described above, a clear subtraction image can be acquired more reliably.

  According to the present invention, the subtraction image is captured while the radiation grid that absorbs the scattered radiation is moved with respect to the detection means. This subtraction image is generated by superimposing a plurality of fluoroscopic images. The most characteristic configuration of the present invention is that a series of perspective images that are superimposed when a single subtraction image is generated while the radiation grid is moved from one end side to the other end side of the movable range are captured. That is. In this way, since the direction of reaction applied to the detection means does not change in a series of fluoroscopic image capturing, the images of the subject are superimposed without deviation when generating a subtraction image, and an image with excellent visibility is obtained. Can be provided.

1 is a functional block diagram illustrating a configuration of a radiation imaging apparatus according to Embodiment 1. FIG. 3 is a plan view illustrating an X-ray grid according to Embodiment 1. FIG. 1 is a cross-sectional view illustrating an X-ray grid according to Example 1. FIG. 3 is a flowchart for explaining the operation of the radiation tomography apparatus according to Embodiment 1. FIG. 3 is a schematic diagram for explaining the operation of the radiation tomography apparatus according to the first embodiment. FIG. 3 is a schematic diagram for explaining the operation of the radiation tomography apparatus according to the first embodiment. It is a schematic diagram explaining the effect of the structure of the radiation tomography apparatus which concerns on Example 1. FIG. It is a schematic diagram explaining the effect of the structure of the radiation tomography apparatus which concerns on Example 1. FIG. It is a schematic diagram explaining the effect of the structure of the radiation tomography apparatus which concerns on Example 1. FIG. It is a schematic diagram explaining the effect of the structure of the radiation tomography apparatus which concerns on Example 1. FIG. It is a schematic diagram explaining the effect of the structure of the radiation tomography apparatus which concerns on Example 1. FIG. It is a schematic diagram explaining the structure of the radiography apparatus of a conventional structure.

  Hereinafter, examples of the present invention will be described. X-rays in the examples correspond to the radiation of the present invention. FPD is an abbreviation for flat panel detector.

  First, the configuration of the X-ray imaging apparatus 1 according to the first embodiment will be described. The X-ray imaging apparatus 1 is configured to image a subject M in a standing position. As shown in FIG. 1, as shown in FIG. 1, a support column 2 extending in the vertical direction v from the floor surface, and X for irradiating X-rays It has a line tube 3, an FPD 4 supported by the support column 2, and a suspension support 7 that extends in the vertical direction v and is supported by the ceiling. The suspension support 7 supports the X-ray tube 3 in a suspended manner. The X-ray tube 3 corresponds to the radiation source of the present invention, and the FPD 4 corresponds to the detection means of the present invention.

  The FPD 4 can slide in the vertical direction v with respect to the column 2. Moreover, the suspension support body 7 is extendable in the vertical direction v, and the position of the X-ray tube 3 in the vertical direction v is changed as the suspension support body 7 expands and contracts. The movement of the FPD 4 in the vertical direction v with respect to the column 2 is executed by an FPD moving mechanism 15 provided between the two and the four. This is controlled by the FPD movement control unit 16.

  The movement of the X-ray tube 3 will be described. The X-ray tube 3 is performed by an X-ray tube moving mechanism 11 provided on the suspension support 7. The X-ray tube movement control unit 12 is provided for the purpose of controlling the X-ray tube movement mechanism 11. The X-ray tube 3 is moved by the X-ray tube moving mechanism 11 (1) in the vertical direction v, (2) in the approach / separation direction with respect to the FPD 4, and (3) in the horizontal direction s orthogonal to the direction from the X-ray tube 3 toward the FPD 4 (see FIG. 1 in the paper surface penetrating direction in 1 and the body side direction of the subject M). When the X-ray tube 3 moves in the vertical direction v, the suspension support 7 expands and contracts.

  The FPD 4 has a detection surface 4a (see FIG. 1) for detecting X-rays. The detection surface 4a is arranged in the X-ray imaging apparatus 1 upright in the vertical direction v. Thereby, the standing subject M can be efficiently imaged. The detection surface 4 a is disposed so as to face the X-ray irradiation port of the X-ray tube 3. In other words, the detection surface 4a is arranged along a plane formed by two directions of the horizontal direction s and the vertical direction v. Further, the detection surface 4a is rectangular, and one side is in the horizontal direction s and the other side orthogonal to the one side is in the vertical direction v.

  The X-ray grid 5 is provided for the purpose of acquiring clear fluoroscopic images P1 and P2 by absorbing and removing scattered X-rays generated inside the subject. The X-ray grid 5 is disposed so as to cover the front surface of the detection surface 4 a of the FPD 4, and the X-rays cannot enter the detection surface 4 a of the FPD 4 unless they pass through the X-ray grid 5. ing. The X-ray grid 5 corresponds to the radiation grid of the present invention.

  The configuration of the X-ray grid 5 will be described. As shown in FIG. 2, the X-ray grid 5 has a plurality of absorbent foils 5a extending in the vertical direction and arranged in the horizontal direction perpendicular to the vertical direction. The longitudinal direction corresponds to the stretching direction of the present invention. The absorption foil 5a has a strip shape in which the direction from the X-ray tube 3 toward the FPD 4 (more precisely, the traveling direction of the X-rays irradiated from the X-ray tube 3) is a short direction. Since the X-rays irradiated from the X-ray tube 3 spread radially, the X-rays enter the detection surface 4a from an oblique direction at the end of the FPD 4. Accordingly, the lateral direction of the absorbent foil 5a is inclined following the X-ray inclination. The X-ray grid 5 is arranged in the FPD 4 so that the vertical direction coincides with the vertical direction of the X-ray grid 5. FIG. 3 is a cross-sectional view showing the relationship between the absorbent foil 5a and the FPD 4. As shown in FIG. In FIG. 3, the direction away from the detection surface 4a of the FPD 4 coincides with the short direction of the absorbent foil 5a.

  The absorbent foil 5a is made of a member that absorbs X-rays such as a molybdenum alloy. Therefore, X-rays whose traveling direction does not follow the direction from the X-ray tube 3 toward the FPD 4 are absorbed and removed by the absorbing foil 5a. In this way, scattered X-rays generated inside the subject by irradiating the subject M with X-rays are absorbed and removed by the absorbing foil 5a and do not reach the detection surface 4a of the FPD 4. Therefore, the visibility of the acquired fluoroscopic images P1 and P2 is not deteriorated by scattered X-rays.

  The X-ray grid moving mechanism 13 is provided between the FPD 4 and the X-ray grid 5, and reciprocates in the horizontal direction with respect to the FPD 4 (the arrangement direction of the absorbent foil 5 a: the horizontal direction in FIG. 3). It is provided for the purpose of moving. The X-ray grid movement control unit 14 controls this. When the fluoroscopic images P1 and P2 are photographed while moving the X-ray grid 5 with respect to the FPD 4, the photographing is performed while the shadow of the absorbing foil 5a projected on the detection surface 4a of the FPD 4 is moved. Then, an image suitable for diagnosis can be acquired without a striped pattern appearing in the perspective images P1 and P2. The X-ray grid movement mechanism 13 corresponds to the radiation grid movement means of the present invention, and the X-ray grid movement control unit 14 corresponds to the radiation grid movement control means of the present invention.

  If an image is taken without moving the X-ray grid 5 with respect to the FPD 4, a shadow of the absorbing foil 5a appears at the same position on the detection surface 4a of the FPD 4 during X-ray irradiation. This shadow will appear. However, if the X-ray grid 5 is moved as in the configuration of the first embodiment, the shadow of the absorbing foil 5a moves on the detection surface 4a of the FPD 4 during the X-ray irradiation. If the detection pixels arranged in a two-dimensional manner are provided on the detection surface 4a, photographing is performed while changing the detection pixels in which the shadow appears. Therefore, the shadow of the absorbing foil 5a is dispersed in the perspective images P1 and P2, and no shadow appears clearly in the perspective images P1 and P2. In order to make the shadow of the absorbing foil 5 a less noticeable, the X-ray grid 5 is moved at a higher speed with respect to the FPD 4.

  The X-ray tube controller 6 controls the tube voltage, tube current, and X-ray irradiation time of the X-ray tube 3. The X-ray tube control unit 6 controls the X-ray tube 3 so as to output radiation with a predetermined tube current, tube voltage, and pulse width. Parameters such as tube current are stored in the storage unit 24. The X-ray tube control unit 6 corresponds to the radiation source control means of the present invention.

  The image generation unit 21 assembles the detection data output from the FPD 4 and generates perspective images P1 and P2 in which the projection image of the subject M is reflected. The subtraction image generation unit 22 generates a subtraction image P3 in which the tissue of the subject M is emphasized by superimposing a plurality of fluoroscopic images P1, P2 imaged under different imaging conditions (different X-ray irradiation conditions). The image generation unit 21 corresponds to the image generation unit of the present invention, and the subtraction image generation unit 22 corresponds to the subtraction image generation unit of the present invention.

  The subtraction image P3 will be described. The subtraction image P3 is generated by taking two shots and taking the difference between the two fluoroscopic images obtained by shooting.

  The output of the X-ray tube 3 differs between the first imaging and the second imaging. For example, in the first imaging, the output of the X-ray source is high, and in the second imaging, the output of the X-ray source is low. In both radiographs, the bone tissue and soft tissue of the subject M are reflected.

  In the first imaging, the degree of X-ray transmission differs between bone tissue and soft tissue. Similarly, in the second imaging, the degree of X-ray transmission differs between bone tissue and soft tissue. The difference in X-ray transmission in the first imaging does not match the difference in X-ray transmission in the second imaging. For example, in the first imaging under the high output condition, although there is a considerable difference in the pixel value between the bone tissue portion and the soft tissue portion, the bone tissue in the second imaging under the low output condition. There is a phenomenon in which the difference in pixel values is not so much seen between the portion and the soft tissue portion. When the difference between two fluoroscopic images having such characteristics is taken, for example, the soft tissue portion reflected in the two fluoroscopic images is offset, the bone tissue portion is emphasized, and the bone tissue becomes clearer. The reflected subtraction image P3 can be acquired.

  Similarly, if two fluoroscopic images are subjected to gradation correction and superimposed, a subtraction image P3 in which a soft tissue portion is reflected more clearly can be acquired. The subtraction image generation unit 22 may be configured to superimpose two fluoroscopic images after log conversion. By doing so, the difference between the subject images reflected in the two fluoroscopic images becomes clearer, and a subtraction image P3 suitable for diagnosis can be acquired.

  The console 27 is provided for the purpose of inputting each instruction of the operator, and the storage unit 24 is control information of the X-ray tube 3, position information of the X-ray tube 3, position information of the FPD 4 in the vertical direction v, and the like. All of various parameters used for X-ray imaging are stored. As shown in FIG. 1, the X-ray imaging apparatus 1 includes a main control unit 41 that comprehensively controls the units 6, 12, 14, 16, 18, 21, 22, and 24. The main control unit 41 is constituted by a CPU, and realizes each unit by executing various programs. Further, each of the above-described units may be divided and executed by an arithmetic device that takes charge of them. The display unit 26 is provided for the purpose of displaying the captured subtraction image P3. The console 27 corresponds to the input means of the present invention.

<Operation of X-ray imaging apparatus>
Next, the operation of the X-ray imaging apparatus 1 will be described. In order to generate the subtraction image P3 using the X-ray imaging apparatus 1 according to the first embodiment, as shown in FIG. 4, first, the subject M is placed on the apparatus (subject placement step S1), and X-rays are obtained. The movement of the grid 5 is started (X-ray grid movement start step S2). Then, X-ray irradiation is started (irradiation start step S3), and fluoroscopic images P1 and P2 are generated (fluoroscopic image generation step S4). Finally, the perspective images P1 and P2 are superimposed to generate a subtraction image P3 (subtraction image generation step S5). Hereinafter, these steps will be described in order.

<Subject placement step S1>
Prior to imaging, the subject M is erected at a position between the X-ray tube 3 and the FPD 4. As a result, the subject M is placed on the X-ray imaging apparatus 1. When the operator adjusts the positions of the X-ray tube 3 and the FPD 4 through the console 27, the X-ray tube 3 and the FPD 4 reach the imaging region of the subject M according to the control of the control units 12 and 16 that control the respective movements. Moving.

<X-ray grid movement start step S2>
When the surgeon gives an instruction to start photographing the fluoroscopic images P1 and P2 through the console 27, the X-ray grid movement control unit 14 starts to move the X-ray grid 5. The X-ray grid 5 is located at one end of the movable range of the X-ray grid 5 in the initial state before being moved. This is because it is necessary to make the distance that the X-ray grid 5 moves at a constant speed as long as possible. When the X-ray grid 5 is moved greatly during photographing, the reflection of the shadow of the X-ray grid 5 in the perspective images P1 and P2 is further suppressed.

  A change in position of the FPD 4 accompanying the start of movement of the X-ray grid 5 will be described. FIG. 5 shows a state of the X-ray grid 5 at the time when the movement is started. In FIG. 5, the X-ray grid 5 is about to move from the initial position on the left side of the drawing to the right side of the drawing. This movement is performed by the X-ray grid moving mechanism 13. If the X-ray grid moving mechanism 13 tries to move the X-ray grid 5 to the left side of the page as indicated by the arrow, the reaction indicated by the dashed arrow is applied to the FPD 4. Since the reaction accompanying the movement of the X-ray grid 5 is opposite to the movement direction of the X-ray grid 5, the FPD 4 tries to move in the left direction in FIG. 5 according to this reaction. Although the movement of the FPD 4 is prohibited by the support 2, the FPD 4 still moves slightly to the left along with the support 2 as the X-ray grid 5 moves.

<Irradiation start step S3>
After the movement of the X-ray grid 5 is started, the X-ray tube control unit 6 emits X-rays according to the irradiation time, tube current, and tube voltage stored in the storage unit 24. Since the irradiation start time t1 is related to the movement mode of the X-ray grid 5, this relationship will be described. FIG. 6 is a timing chart showing the relationship between movement of the X-ray grid 5 and X-ray irradiation.

  As shown in the upper side of FIG. 6, the movement pattern of the X-ray grid 5 is such that the relative movement speed of the X-ray grid 5 with respect to the FPD 4 increases from the start of movement of the X-ray grid 5 to time ta. And from time ta to time tb, the X-ray grid 5 moves at a constant speed. Finally, the relative movement speed of the X-ray grid 5 with respect to the FPD 4 decreases when the time tb elapses. The reason why the moving speed decreases is due to the limitation of the movable range of the X-ray grid 5. That is, in the vicinity of time tb, the X-ray grid 5 approaches the other end side of the movable range, and the X-ray grid 5 cannot move in the same direction any more. Therefore, the X-ray grid 5 is temporarily stopped so that it can be moved in the reverse direction at the next imaging.

  The movement of the X-ray grid 5 is desirable if the speed is changed rapidly so that the time in the constant speed state is maximized. That is, it is desirable that the acceleration be performed at a high acceleration when attempting to accelerate and a negative acceleration having a high absolute value when decelerating. In the configuration of the first embodiment, imaging is not performed during the acceleration / deceleration of the X-ray grid 5. When the X-ray grid 5 is accelerating or decelerating, the movement of the X-ray grid 5 relative to the FPD 4 is not uniform. Therefore, when photographing is performed in this state, a striped pattern derived from the X-ray grid 5 is superimposed on the image portion. Resulting in. Therefore, the configuration of the first embodiment is not suitable for imaging during the acceleration / deceleration period of the X-ray grid 5. According to the configuration of the first embodiment, the time during which the X-ray grid 5 is shifted is suppressed as much as possible, so that the time that can be used for imaging is increased accordingly.

  During the period in which the X-ray grid 5 is at a constant speed, the fluoroscopic images P1 and P2 are captured twice. That is, two X-ray pulses p1 and p2 are irradiated from the X-ray tube 3 during a constant speed movement time from time ta to time tb in FIG. 6, and two fluoroscopic images P1 and P2 are emitted for each pulse irradiation. P2 is irradiated. That is, the start time t1 of the first X-ray pulse p1 is later than the start time ta of the constant speed movement time. Further, the end time t2 of the second X-ray pulse p2 is earlier than the end time tb of the constant speed movement time. That is, while the X-ray pulses p1 and p2 are being irradiated, the X-ray grid 5 is moving at a constant speed with respect to the FPD 4.

  That is, a series of images superimposed when the single subtraction image P3 is generated while the X-ray grid 5 is moved from one end side to the other end side of the movable range under the control of the X-ray grid movement control unit 14. The fluoroscopic images P1 and P2 are taken. Moreover, a series of imaging is performed while the X-ray grid 5 is moving at a constant speed. Further, the X-ray grid moving mechanism 13 is controlled so that the X-ray grid 5 moves at a constant speed at the time when the first X-ray irradiation in the series of fluoroscopic images P1 and P2 is started. The X-ray grid moving mechanism 13 is controlled so that the X-ray grid 5 moves at a constant speed when the final X-ray irradiation in the fluoroscopic imaging is completed.

  Further, the distance that the X-ray grid 5 moves per acquisition of the subtraction image P3 is constant. Specifically, the movement of the X-ray grid 5 starts from one end of the movable range, and a single subtraction image P3 is acquired while it ends at the other end.

  Note that the control (irradiation time, tube current, tube voltage) of the X-ray tube 3 when taking fluoroscopic images P1, P2 is different from each other. As a result, two types of fluoroscopic images P1 and P2 with different fluoroscopic methods are obtained.

<Transparent Image Generation Step S4>
The FPD 4 detects X-rays and outputs detection signals to the image generation unit 21 every time the X-ray pulses p1 and p2 are irradiated toward the subject M. The image generation unit 21 generates perspective images P1 and P2 in which a perspective image of the subject M is reflected based on each detection signal. The two fluoroscopic images P1 and P2 are sent to the subtraction image generation unit 22.

<Subtraction image generation step S5>
The two fluoroscopic images P1 and P2 generated by the image generation unit 21 are sent to the subtraction image generation unit 22. The subtraction image generation unit 22 generates a subtraction image P3 by superimposing the two fluoroscopic images P1 and P2 with each other. As a method for superimposing images, the other perspective image is subtracted from one perspective image. The subtraction image P3 is displayed on the display unit 26, and the inspection ends.

<Effects of Configuration of Example 1>
Finally, the effect of the configuration of the first embodiment will be described. The most characteristic feature of the configuration of the first embodiment is that, as shown in FIG. 6, all of the photographing related to the generation of the subtraction image P3 is completed while the X-ray grid 5 is moving at a constant speed. . With this configuration, there is no discrepancy between the positions where the subject M is reflected in the two fluoroscopic images P1 and P2. Therefore, when the fluoroscopic images P1 and P2 are superimposed, an image of the subject M is obtained. It is possible to generate a subtraction image P3 that is superimposed without being displaced and excellent in visibility.

  In the generation of the subtraction image P3 according to the conventional configuration, first, the first imaging is performed while moving the X-ray grid 5 in one direction, and then the second imaging is performed while the X-ray grid 5 is moved in the opposite direction. That is, the X-ray grid 5 is reciprocated to take two images. This is because the X-ray grid 5 is moved as much as possible with respect to the FPD 4 by moving the entire range of the movable range during one imaging, so that the striped pattern of the X-ray grid 5 is a fluoroscopic image. This is the result of not superimposing it on.

  FIG. 7 shows a fluoroscopic image taken for the first time in the conventional configuration. For convenience of explanation, it is assumed that a circular subject is reflected in the fluoroscopic image. The position of the FPD 4 viewed from the subject M is shifted in the direction opposite to the movement direction of the X-ray grid 5 due to the influence of the movement of the X-ray grid 5. An image ma indicated by a broken line in FIG. 7 is a subject that appears in the fluoroscopic image when the X-ray grid 5 does not move. Actually, since the X-ray grid 5 is moving, the subject appears in the position of the image m1 indicated by the solid line in FIG.

  FIG. 8 shows a fluoroscopic image taken for the second time in the conventional configuration. An image ma indicated by a broken line in FIG. 8 is a subject that appears in the fluoroscopic image when the X-ray grid 5 does not move. Actually, since the X-ray grid 5 is moving, the subject appears in the position of the image m2 indicated by the solid line in FIG.

  As can be seen by comparing the two fluoroscopic images with reference to FIGS. 7 and 8, the direction in which the subject image shifts in the fluoroscopic image is reverse with respect to the image ma. This is because the moving direction of the X-ray grid 5 is reversed between the two images and the reaction force applied to the FPD 4 is also reversed. In addition, in the second shooting, in addition to the reaction applied to the FPD 4, the reaction applied to the FPD 4 at the previous shooting is also added, and the FPD 4 moves more greatly than the first shooting. That is, when a reaction in a certain direction is applied to the FPD 4 at the time of the first photographing, a force is exerted on the FPD 4 to return to the opposite direction due to the reaction. This force is based on the elasticity of the column 2. Since this force is in the same direction as the reaction newly received by the FPD 4 in the second shooting, the forces strengthen each other and try to move the FPD 4 greatly. Therefore, the image m2 in FIG. 8 is more deviated from the image ma than m1 in FIG.

  When the two fluoroscopic images shown in FIGS. 7 and 8 are overlapped in order to generate a subtraction image, the images of the subject are greatly shifted from each other as shown in FIG. Therefore, the visibility of the obtained subtraction image is poor.

  Next, acquisition of the subtraction image P3 according to the configuration of the first embodiment will be described. In the first embodiment, the first fluoroscopic image taken is the same as that shown in FIG.

  FIG. 10 shows a fluoroscopic image taken for the second time in the configuration of the first embodiment. An image ma indicated by a broken line in FIG. 8 is a subject that appears in the fluoroscopic image when the X-ray grid 5 does not move. Actually, since the X-ray grid 5 is moving, the subject appears in the position of the image m2 indicated by the solid line in FIG.

  As can be seen from a comparison between FIG. 7 and FIG. 10, the direction in which the subject image shifts in the fluoroscopic image is the same direction with reference to the image ma. This is because the moving direction of the X-ray grid 5 is not reversed between the two photographings, and the reaction force applied to the FPD 4 is not reversed. It is true that the position of the FPD 4 in the second shooting may have moved slightly compared to the first shooting, but this is not a large movement. This is because the FPD 4 cannot move greatly in the same direction from the position when the image of FIG.

  When the two fluoroscopic images shown in FIGS. 7 and 10 are overlapped in order to generate a subtraction image, as shown in FIG. 11, the deviation of the subject image is suppressed to the minimum.

  As described above, according to the configuration of the first embodiment, the subtraction image P3 is captured while the X-ray grid 5 that absorbs scattered X-rays is moved with respect to the FPD 4. Therefore, the acquired subtraction image P3 is suppressed from the striped pattern derived from the X-ray grid 5, and is suitable for diagnosis. This subtraction image P3 is generated by superimposing a plurality of perspective images P1, P2. The most characteristic configuration of the configuration of the first embodiment is a series of superimposed images when the single subtraction image P3 is generated while the X-ray grid 5 is moved from one end side to the other end side of the movable range. The perspective images P1 and P2 are to be taken. That is, the configuration of the first embodiment is characterized by the moving method of the X-ray grid moving mechanism 13. When the X-ray grid 5 is moved relative to the FPD 4, the FPD 4 moves relative to the subject M due to the reaction. When a series of fluoroscopic images P1 and P2 are captured while reversing the moving direction of the X-ray grid 5 as in the conventional configuration, the position where the subject M is reflected changes greatly between the acquired fluoroscopic images P1 and P2. End up. This is because the direction of reaction applied to the FPD 4 is different each time the fluoroscopic images P1 and P2 are photographed. According to the configuration of the first embodiment, since the direction of the reaction applied to the FPD 4 does not change in capturing a series of fluoroscopic images P1 and P2, the position of the subject M in the series of fluoroscopic images P1 and P2 becomes more consistent. . If the subtraction image P3 is generated by superimposing such fluoroscopic images P1 and P2, the images of the subject M are superimposed without being displaced, so that an image with excellent visibility can be provided.

  Further, if an image is taken with the speed of the X-ray grid 5 being changed, the false image derived from the X-ray grid cannot be erased from the obtained fluoroscopic images P1 and P2. This is because the time during which the shadow of the X-ray grid 5 is reflected varies depending on the portion of the FPD 4 when imaging is performed while changing the speed of the X-ray grid 5. If a series of imaging is performed while the X-ray grid 5 is moving at a constant speed as in the configuration of the first embodiment, the shadow of the X-ray grid 5 is reliably dispersed on the detection surface of the FPD 4. The striped pattern of the X-ray grid 5 does not appear in the perspective images P1 and P2.

  Further, if the time during which the X-ray grid 5 is moving at a constant speed during imaging is shortened, the speed when the X-ray grid 5 is moving at a constant speed can be maximized. By doing so, the shadow of the X-ray grid 5 is reliably dispersed on the detection surface of the FPD 4 so that the striped pattern of the X-ray grid 5 does not appear in the fluoroscopic images P1 and P2.

  Further, the standing position FPD 4 is likely to wobble as the X-ray grid 5 moves. This is because the X-ray grid 5 is supported by the upright support 2. The configuration of the first embodiment is suitable for such an X-ray imaging apparatus for standing imaging.

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

  (1) According to the configuration of the embodiment, the subtraction image P3 is generated by superimposing the two fluoroscopic images P1 and P2, but the subtraction image P3 is superposed on two or more fluoroscopic images. You may make it produce | generate.

  (2) According to the configuration of the embodiment, the configuration for determining the movement mode of the X-ray grid 5 was not mentioned, but the movement mode was determined in accordance with the shooting mode of the subtraction image. Also good. In other words, according to an instruction from the operator through the console 27, the X-ray grid movement control unit 14 is from the start of irradiation of the first X-ray pulse p1 to the end of irradiation of the second X-ray pulse p2. May be configured to move relative to the FPD 4 at a constant speed and as fast as possible. When the operator selects the type of subtraction image to be imaged through the console 27, the imaging condition corresponding to this type is read from the storage unit 24, and the X-ray tube control unit 6 performs X-ray irradiation according to the imaging condition. Let it be done. At the same time, this imaging condition is also sent to the X-ray grid movement control unit 14, and the time required from the start of the first X-ray pulse p1 irradiation to the end of the second X-ray pulse p2 is calculated. Then, the X-ray grid movement control unit 14 shortens the time between the time ta at which the X-ray grid 5 starts moving at a constant speed and the imaging start time t1, and the imaging end time t2 and the X-ray grid. The X-ray grid moving mechanism 13 is controlled so that the time from the time tb until the constant-velocity movement 5 ends is shortened. Then, the time during which the X-ray grid 5 is moving at a constant speed is minimized.

  Since the moving distance of the X-ray grid 5 for capturing one subtraction image P3 is constant, the time during which the X-ray grid 5 is moving at a constant speed is shortened. Means faster. If the X-ray grid 5 is moved at a high speed, the shadow of the absorbing foil 5a moves greatly on the detection surface 4a of the FPD 4, so that the fringes derived from the X-ray grid 5 appear in the fluoroscopic images P1 and P2. The pattern becomes more difficult to visually recognize and a clear subtraction image P3 can be acquired.

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

  (4) 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 (detection means)
4a Detection surface 5 X-ray grid (radiation grid)
6 X-ray tube control unit (radiation source control means)
13 X-ray grid moving mechanism (radiation grid moving means)
14 X-ray grid movement control unit (radiation grid movement control means)
21 Image generation unit (image generation means)
22 Subtraction image generation unit (subtraction image generation means)
27 Console (input means)

Claims (6)

A radiation source that emits radiation;
Radiation source control means for controlling the radiation source;
Detection means for detecting the irradiated radiation on the detection surface and outputting a detection signal;
A radiation grid disposed in front of the detection surface and removing scattered radiation generated inside the subject;
Radiation grid moving means for reciprocating the radiation grid relative to the detection means;
Radiation grid movement control means for controlling the radiation grid movement means;
Image generating means for generating a fluoroscopic image based on a detection signal output by the detecting means;
Subtraction image generation means for generating a subtraction image in which a plurality of fluoroscopic images photographed under different radiation irradiation conditions are superimposed to emphasize the tissue of the subject under the control of the radiation source control means,
Under the control of the radiation grid movement control means, a series of fluoroscopic images superimposed when a single subtraction image is generated while the radiation grid is moved from one end side to the other end side of the movable range are photographed. A radiation imaging apparatus. The radiographic apparatus according to claim 1,
The radiation grid movement control means controls the radiation grid to move at a constant speed while the radiation grid is moved from one end of the movable range to the other end,
The radiation imaging apparatus according to claim 1, wherein the radiation source control means and the detection means perform a series of imaging while the radiation grid is moving at a constant speed. The radiation imaging apparatus according to claim 2,
The radiation grid movement control unit controls the radiation grid movement unit so that the radiation grid moves at a constant speed when the first radiation irradiation in a series of fluoroscopic images is started. Radiography equipment. In the radiographic apparatus of Claim 2 or Claim 3,
The radiation grid movement control means controls the radiation grid movement means so that the radiation grid moves at a constant speed when the last radiation irradiation in a series of fluoroscopic imaging is completed. Shooting device. The radiation imaging apparatus according to claim 4,
Provide input means to input the surgeon's instructions,
The radiation imaging apparatus according to claim 1, wherein the radiation grid movement control unit controls the radiation grid movement unit so that a time during which the radiation grid is moving at a constant speed is shortened in accordance with an input from the input unit. The radiographic apparatus according to any one of claims 1 to 5,
A radiation imaging apparatus characterized by being for standing position imaging.

Images