JP4400225B2 - Radiation imaging device - Google Patents

Description

  The present invention relates to a radiation imaging apparatus used in the medical field, industrial fields such as non-destructive inspection, RI (Radio isotope) inspection, and optical inspection, and in the nuclear power field. About.

  Conventionally, as a typical shielding object for shielding radiation, an X-ray grid that removes scattered X-rays, a compensation filter that performs filtering on pixels of a captured image, and a top plate (bed) on which a subject is placed There is. The X-ray grid is configured by alternately arranging lead (Pb) and aluminum (Al), and scattered X-rays are blocked by lead. The X-ray grid is disposed adjacent to the X-ray irradiation side (detection side) of radiation detection means represented by, for example, a flat panel radiation detector (FPD) (see, for example, Patent Document 1).

  By the way, the above-mentioned FPD is configured by laminating a sensitive film on a substrate, detects the radiation incident on the sensitive film, converts the detected radiation into electric charges, and arranges it in a two-dimensional array. Charge is stored in the capacitor. The accumulated charge is read by turning on the switching element, and sent to the image processing means as an electric signal. Therefore, there is a variation in the amount of charge accumulated for each detection element constituting the capacitor or the switching element, and accordingly, there is also a variation for pixels based on the electrical signal for each detection element. In order to eliminate such variations, for example, calibration is performed to adjust the gain of an amplifier for each detection element to align the output side.

Each X-ray grid used for imaging differs depending on the imaging region of the subject and the subject to be imaged. At the time of calibration, the calibration data (correction coefficient) differs depending on each X-ray grid. Therefore, the calibration is performed by switching to the X-ray grid corresponding to the imaging region of the subject or the subject to be imaged. (For example, refer to Patent Document 2).
Japanese Unexamined Patent Publication No. 2000-139887 (page 4-5, FIG. 1-7) JP 2000-245719 A (page 3-7, FIGS. 5, 8, and 9)

  However, when performing a new calibration, the currently used X-ray grid must be retracted, the retracted X-ray grid removed, a new X-ray grid attached, and returned to the imaging position. I must. When calibration data (correction table in Patent Document 2) is stored in advance as in Patent Document 2 described above, it is not necessary to move the X-ray grid in the above-described operation unless calibration is newly performed. Another problem is that calibration data has to be stored for the number of X-ray grids. As described above, a shield represented by an X-ray grid or the like must be considered every time calibration is performed.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the radiation imaging device which can be calibrated without considering a shielding object.

  As a result of intensive studies to solve the above problems, the inventors have obtained the following knowledge.

  In other words, we changed the idea from the conventional technique of keeping the shielding object at the imaging position at the time of calibration (calibration), and focused on moving the shielding object to the retreat position outside the imaging position at the time of calibration. Thus, calibration can be performed without considering the shielding object.

  The present invention based on such knowledge has the following configuration.

That is, the invention according to claim 1 is a pixel detection unit that calibrates each detection element constituting the radiation detection unit with respect to a radiation detection unit that detects radiation transmitted through the subject and a pixel based on the detected radiation. And a radiographic imaging device that images a subject by calibrating the pixel by the pixel calibration unit and performing the image processing by the image processing unit, and image processing unit that performs image processing based on the detected radiation a is provided with a movable shield which shields radiation in front of the detection side of the radiation detecting means, and control means for controlling the moving between an imaging position and a retracted position of the obstacle, the control means , based on the pixel calibration unit initiates the calibration of the pixels, shield was moved to the retracted position from the imaging position, the shield, the scattered radiation removing means for removing the scattering radiation (a), ( B) Examination That it includes top plate for placing a body in which characterized.

  [Operation and Effect] According to the invention described in claim 1, the moving means for moving the shielding object between the imaging position and the retracted position and the control means for controlling the moving means are provided. Based on the pixel calibration means starting the pixel calibration, the control means moves the shielding object from the imaging position to the retracted position, and the control means controls the moving means so as to keep the shielding object in the retracted position at the time of calibration. The shield remains in the retracted position during calibration. Therefore, calibration can be performed without considering the shielding object.

In the above-described invention, the shielding object includes a scattered radiation removing unit that removes scattered radiation, a compensation filter that performs a filter related to pixels of a captured image, and a top plate (bed) on which a subject is placed. In the case of scattered radiation removing means for removing scattered radiation, the scattered radiation removing means is moved from the imaging position to the retracted position based on the pixel calibration means starting the pixel calibration, and the scattered radiation removal is performed at the time of calibration. control means to keep the means in the retracted position, that controls the movement means. In such a case, calibration can be performed without considering the scattered radiation removing means.

In each invention, the control means controls the moving means so as to move the shielding object (for example, the scattered radiation removing means described above) from the retracted position to the imaging position based on completion of the pixel calibration by the pixel calibration means . Is preferred. By controlling in this way, the shielding object returns to the imaging position at the end of calibration, and normal radiation imaging can be performed.

  According to the radiation imaging apparatus of the present invention, based on the pixel calibration means starting the calibration of the pixel, the shielding object is moved from the imaging position to the retracted position, and the shield is kept at the retracted position during calibration. The control means controls the moving means, so that the shield stays in the retracted position during calibration, and calibration can be performed without considering the shield.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 is a block diagram of an X-ray diagnostic apparatus according to an embodiment, FIG. 2 is a plan view of an X-ray grid and a grid driving mechanism used in the X-ray diagnostic apparatus, and FIG. 3 is an X-ray diagnostic apparatus. 4 is an equivalent circuit of the flat panel X-ray detector as viewed from the side, and FIG. 4 is an equivalent circuit of the flat panel X-ray detector as viewed from above. In this embodiment, a flat panel X-ray detector (hereinafter referred to as “FPD” as appropriate) is taken as an example of radiation detection means, and an X-ray diagnostic apparatus is taken as an example of a radiation imaging apparatus.

  As shown in FIG. 1, the X-ray diagnostic apparatus according to the present embodiment includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that irradiates the subject M with X-rays, and a subject. An FPD 3 that detects X-rays transmitted through M, an X-ray grid 4 that removes scattered X-rays, a grid drive mechanism 5 that moves the X-ray grid 4, and the like are provided. The X-ray grid 4 is disposed adjacent to the detection side (X-ray irradiation side) of the FPD 3. The grid drive mechanism 5 is a mechanism that moves the X-ray grid 4 between the imaging position and the retracted position. The FPD 3 corresponds to the radiation detection means in the present invention, the top plate 1 and the X-ray grid 4 correspond to the shield in the present invention, the grid driving mechanism 5 corresponds to the moving means in the present invention, and the X-ray grid 4 corresponds to this This corresponds to the scattered radiation removing means in the invention. The shield is the top plate 1 or the X-ray grid 4. In this embodiment, the only object to be moved between the imaging position and the retracted position during calibration is the X-ray grid 4. Does not move.

  In addition, the X-ray diagnostic apparatus includes a top plate control unit 7 that controls the elevation and horizontal movement of the top plate 1, a unit control unit 8 that controls scanning of the detection unit 6, the tube voltage and tube of the X-ray tube 2 An X-ray tube control unit 10 having a high voltage generation unit 9 that generates a current, a calibration unit 11 that calibrates an X-ray detection signal that is a charge signal from the FPD 3, and a digital signal that has been calibrated. An A / D converter 12 that is extracted and converted, an image processing unit 13 that performs various processes based on an X-ray detection signal output from the A / D converter 12, a controller 14 that supervises these components, A memory unit 15 for storing processed images, an input unit 16 for input setting by an operator, a monitor 17 for displaying processed images, and the like. The calibration unit 11 corresponds to the pixel calibration unit in the present invention, and the A / D converter 12 and the image processing unit 13 correspond to the image processing unit in the present invention.

  The top board control unit 7 moves the top board 1 horizontally to accommodate the subject M up to the imaging position, moves up and down and horizontally moves the subject M to a desired position, or performs imaging while horizontally moving the subject M. Or performing horizontal control after the completion of imaging and retreating from the imaging position. The unit control unit 8 performs control related to scanning by moving the FPD 3 horizontally or rotating around the body axis of the subject M. The high voltage generator 9 generates a tube voltage and a tube current for irradiating X-rays and applies them to the X-ray tube 2. The X-ray tube controller 10 moves the X-ray tube 2 horizontally, Control relating to scanning by rotating around the axis of the body axis of M, control of the setting of the irradiation field of the collimator (not shown) on the X-ray tube 3 side, and the like are performed. When scanning the X-ray tube 2 or the FPD 3, the X-ray tube 2 and the FPD 3 move while facing each other so that the FPD 3 can detect the X-rays emitted from the X-ray tube 2.

  The calibration unit 11 calibrates the charge signal output from the FPD 3, that is, the pixel. In this embodiment, the gain of an amplifier (amplifier) 38 (see FIG. 4) for each switching element 32 described later is set. Adjust to align the output side. The A / D converter 12 converts the calibrated charge signal from analog to digital, and outputs a digitized X-ray detection signal. The controller 14 is configured by a central processing unit (CPU) and the like, and the memory unit 15 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Yes. The input unit 16 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. In the X-ray diagnostic apparatus, the FPD 3 detects X-rays transmitted through the subject M, performs calibration by the calibration unit 11 based on the detected X-rays, and performs image processing by the image processing unit 13. The sample M is imaged.

  In the present embodiment, the controller 14 moves (ejects) the X-ray grid 4 that is one of the shielding objects from the imaging position to the retracted position based on the start of calibration by the calibration unit 11 to perform calibration. It also has a function of controlling the grid driving mechanism 5 so as to keep the X-ray grid 4 in the retracted position at the time. Therefore, the controller 14 corresponds to the control means in this invention. In this embodiment, the calibration unit 11 has a function of controlling the grid driving mechanism 5 so as to move (load) the X-ray grid 4 from the retracted position to the imaging position based on completion of the calibration. I have.

  The X-ray grid 4 described above is configured by alternately arranging lead (Pb) and aluminum (Al), and scattered X-rays are blocked by lead. As shown in FIG. 2, the grid drive mechanism 5 includes a tray 21 on which the X-ray grid 4 is placed, and a round shaft 22 and a round shaft 22 attached to the tray 21 and provided along the longitudinal direction of the top plate 1. The motor 23 is configured to be rotated. When the motor 23 is driven, the shaft 22 rotates around the axis, and the accompanying tray 21 moves along with the X-ray grid 4 along the longitudinal direction. The detection unit 6 is provided with an opening (not shown) on the retreat position B side shown in FIG. 2, and the tray 21 and the X-ray grid 4 pass through the opening between the imaging position A and the retreat position B. Reciprocate between. Here, the imaging position A is located immediately above the FPD 3.

  As shown in FIG. 3, the FPD 3 includes a glass substrate 31 and a thin film transistor TFT formed on the glass substrate 31. As shown in FIGS. 3 and 4, the thin film transistor TFT has a large number of switching elements 32 (for example, 1024 × 1024) formed in a vertical / horizontal two-dimensional matrix arrangement. The switching elements 32 are formed separately from each other. That is, the FPD 3 is also a two-dimensional array radiation detector.

  As shown in FIG. 3, an X-ray sensitive semiconductor 34 is stacked on the carrier collection electrode 33, and the carrier collection electrode 33 is connected to the source S of the switching element 32 as shown in FIGS. 3 and 4. Has been. A plurality of gate bus lines 36 are connected from the gate driver 35, and each gate bus line 36 is connected to the gate G of the switching element 32. On the other hand, as shown in FIG. 4, a multiplexer 37 that collects charge signals and outputs them to one is connected with a plurality of data bus lines 39 via amplifiers 38, and also shown in FIGS. Thus, each data bus line 39 is connected to the drain D of the switching element 32.

  With the bias voltage applied to the common electrode (not shown), the gate of the switching element 32 is turned on by applying the voltage of the gate bus line 36 (or 0 V), and the carrier collection electrode 33 is on the detection surface side. The charge signal (carrier) converted from the incident X-ray through the X-ray sensitive semiconductor 34 is read out to the data bus line 39 via the source S and drain D of the switching element 32. Until the switching element is turned on, the charge signal is temporarily accumulated and stored in a capacitor (not shown). The charge signals read to the respective data bus lines 39 are amplified by the amplifiers 38 and are collectively output as one charge signal by the multiplexer 37. The output charge signal is digitized by the A / D converter 8 and output as an X-ray detection signal.

  Next, a series of calibration control sequences in the apparatus of this embodiment will be described with reference to the flowchart of FIG.

(Step S1) Calibration start?
The controller 14 determines whether or not the calibration unit 11 is performing calibration. Except for calibration, the present embodiment loops the process of step S1 until a calibration start instruction is given in the standby state or during imaging. If there is an instruction to start calibration, the process proceeds to the next step S2. In this embodiment, the calibration start instruction is given by outputting a start command signal from the calibration unit 11 to the controller 14 and receiving the signal.

(Step S2) Ejection When the controller 14 receives the start command signal, the controller 14 grid-drives the eject command signal in order to move the X-ray grid 4 from the imaging position to the retracted position, that is, eject the X-ray grid 4. Output to the motor 23 of the mechanism 5. When the motor 23 receives the signal, the motor 23 is driven to rotate forward (or reversely), and the tray 21 moves from the imaging position to the retracted position together with the X-ray grid 4.

(Step S3) Calibration When the X-ray grid 4 moves to the retracted position, an ejection end signal is output to the controller 14 from a sensor (not shown). When the controller 14 receives the signal, it outputs a drive stop signal to the motor 23. When the motor 23 receives the signal, the motor 23 stops driving. With this driving stop, the tray 21 and the X-ray grid 4 remain in the retracted position. The above-described sensor is composed of, for example, an optical sensor or a contact type sensor, and is disposed near the retracted position. The sensor detects the tray 21 or the X-ray grid 4 that moves to the retracted position. It is only necessary to detect that has moved to the retracted position.

  Further, calibration is executed simultaneously with the movement of the X-ray grid 4 to the retracted position. The calibration unit 11 adjusts the gain of the amplifier 38 according to the value of the charge signal. That is, the gain is adjusted and adjusted so that the pixels for each switching element 32 on the output side are the same. During calibration, the X-ray grid 4 may be removed from the tray 21 and replaced with another type of X-ray grid 4.

(Step S4) Calibration finished?
The controller 14 determines whether or not the calibration unit 11 is performing calibration. If calibration is in progress, the process of step S4 is looped until an instruction to end calibration is given. In the present embodiment, the calibration end instruction is given by outputting an end command signal from the calibration unit 11 to the controller 14 and receiving the signal.

(Step S5) Loading When the controller 14 receives the termination command signal, the controller 14 drives the loading command signal to grid drive in order to move the X-ray grid 4 from the retracted position to the imaging position, that is, to load the X-ray grid 4. Output to the motor 23 of the mechanism 5. When the motor 23 receives the signal, the motor 23 is driven to rotate backward (forward rotation in the case of reverse rotation at the time of ejection), and the tray 21 moves from the retracted position to the imaging position together with the X-ray grid 4.

  When the X-ray grid 4 moves to the imaging position, a loading end signal is output to the controller 14 from a sensor (not shown). When the controller 14 receives the signal, it outputs a drive stop signal to the motor 23. When the motor 23 receives the signal, the motor 23 stops driving. With this drive stop, the tray 21 and the X-ray grid 4 stop at the imaging position. The above-described sensor may be configured similarly to the sensor provided in the vicinity of the retracted position. After loading, the present embodiment returns to the standby state or imaging. In this way, a series of calibration control sequences is completed.

  According to the apparatus of the present embodiment configured as described above, the grid driving mechanism 5 that moves (ejects) the X-ray grid 4 that is one of the shielding objects between the imaging position and the retracted position, and the grid driving mechanism. 5 and a controller 14 for controlling 5. Based on the start of calibration by the calibration unit 11, the controller 14 moves the X-ray grid 4 from the imaging position to the retracted position, and the controller 14 uses a grid drive mechanism so that the X-ray grid 4 remains at the retracted position during calibration. By controlling 5, the X-ray grid 4 remains in the retracted position during calibration. Therefore, calibration can be performed without taking into consideration a shielding object such as the X-ray grid 4.

  Further, based on the start of calibration by the calibration unit 11, the X-ray grid 4 moves from the imaging position to the retracted position, and a series of control sequences in which the X-ray grid 4 remains at the retracted position at the time of calibration, Since it is performed by transmission / reception of each signal input to the control 14 or output from the control 14, there is also an effect of preventing the operator from forgetting to remove the X-ray grid 14 during calibration.

  In the present embodiment, the calibration is performed by controlling the grid driving mechanism 5 to move (load) the X-ray grid 4 from the retracted position to the imaging position based on the end of calibration by the calibration unit 11. At the end, the X-ray grid 4 returns to the imaging position, and normal imaging can be performed.

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

  (1) In the above-described embodiment, the X-ray diagnostic apparatus as shown in FIG. 1 has been described as an example. However, the present invention is also applied to an X-ray diagnostic apparatus disposed on a C-type arm, for example. Also good. The present invention may also be applied to an X-ray CT apparatus.

  (2) In the above-described embodiment, the flat panel X-ray detector (FPD) 3 has been described as an example. However, the present invention is applicable to any X-ray detector configured from each detection element. be able to.

  (3) In the above-described embodiments, the X-ray detector for detecting X-rays has been described as an example. However, in the present invention, a radioisotope (RI) is administered like an ECT (Emission Computed Tomography) apparatus. The radiation detector is not particularly limited as long as it is a radiation detector that detects radiation, as exemplified by a γ-ray detector that detects γ-rays emitted from a subject. Similarly, the present invention is not particularly limited as long as it is an apparatus that performs imaging by detecting radiation, as exemplified by the ECT apparatus described above.

  (4) In the above-described embodiment, the FPD 3 includes a radiation (in the embodiment, X-ray) sensitive semiconductor and directly converts the incident radiation into a charge signal by the radiation sensitive semiconductor. However, instead of the radiation-sensitive type, it is equipped with a light-sensitive semiconductor and a scintillator, and the incident radiation is converted into light by the scintillator, and the converted light is converted into a charge signal by the light-sensitive semiconductor. It may be an indirect conversion type detector.

  (5) In the above-described embodiment, the object to be moved between the imaging position and the retracted position at the time of calibration is only the X-ray grid 4 and the top plate 1 is not moved. At the same time, the top plate 1 may also be moved. The top plate 1 may be moved together with the X-ray grid 4 even after the calibration is completed.

  Further, the X-ray grid 4 may be fixed and only the top plate 1 may be moved, but it is more preferable to move at least the X-ray grid 4 at the time of calibration in consideration of the influence on the shield in the calibration.

  Further, the shielding object is not limited to the X-ray grid 4 or the top plate 1 described above, and is exemplified by a radiation detection unit (FPD in the embodiment) as exemplified by a compensation filter that performs a filter related to pixels of the captured image. Since radiation is shielded before the detection side, the object to be moved between the imaging position and the retracted position during calibration is not particularly limited as long as it is a shield.

  (6) In the embodiment described above, based on the start of calibration, the X-ray grid 4 that is one of the shielding objects is moved (ejected) from the imaging position to the retracted position, and the X-ray grid is used during calibration. Although the controller 14 controls the grid driving mechanism 5 so as to move (load) the X-ray grid 4 from the retracted position to the imaging position based on the fact that 4 is kept at the retracted position and the calibration is finished, only at the time of ejection The grid drive mechanism 5 is controlled by the controller 14, and the X-ray grid 4 is manually moved at the time of loading or not synchronized at the end of calibration. 4 may be moved from the retracted position to the imaging position.

  (7) In the above-described embodiment, the retracted position is the longitudinal direction of the top plate 1 with respect to the imaging position. However, the retracted position may be a direction orthogonal to the longitudinal direction in the horizontal plane. Thus, the direction opposite to the detection surface side of the FPD 3 may be used.

1 is a block diagram of a flat panel X-ray detector and an X-ray diagnostic apparatus according to an embodiment. It is a top view of the X-ray grid and grid drive mechanism which are used for an X-ray diagnostic apparatus. It is the equivalent circuit of the flat panel type X-ray detector used for the X-ray diagnostic apparatus viewed from the side. 2 is an equivalent circuit of a flat panel X-ray detector in plan view. It is a flowchart which shows a control sequence of a series of calibrations.

Explanation of symbols

1 ... Top plate 3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 4 ... X-ray grid 5 ... Grid drive mechanism 11 ... Calibration part 12 ... A / D converter 13 ... Image processing part 14 ... Controller M ... Subject

Claims (3)

Radiation detection means for detecting radiation transmitted through the subject, pixel calibration means for calibrating each detection element constituting the radiation detection means for pixels based on the detected radiation, and an image based on the detected radiation An image processing unit that performs processing, calibrates the pixel by the pixel calibration unit, and performs image processing by the image processing unit, thereby imaging the subject, from the detection side of the radiation detection unit comprising: a movable shield which shields radiation in front, and control means for controlling the moving between an imaging position and a retracted position of the shield,
Control means, based on the pixel calibration unit initiates the calibration of the pixels, is moved to the retracted position of the shield from the imaging position,
The shield, (A) the scattered radiation removing means for removing the scattering radiation, (B) a radiation imaging device comprising that you include top plate for placing the object.   The radiographic apparatus according to claim 1,
  The shielding apparatus further includes (C) a compensation filter that performs a filter related to pixels of a captured image. The radiation imaging apparatus according to claim 1 or 2 ,
Wherein the control section, based on the pixel calibration unit is completed the calibration of the pixels, the radiation imaging apparatus according to claim and Turkey is moved to the imaging position said shield from the retracted position.

Images