JP5481053B2 - X-ray exposure amount control apparatus and method, and X-ray imaging apparatus - Google Patents

Description

  The present invention relates to an X-ray exposure amount control apparatus and method for automatically controlling X-rays to an appropriate exposure amount using an X-ray flat panel detector (FPD) for detecting X-rays, and these X-rays. The present invention relates to an exposure control apparatus and an X-ray imaging apparatus to which the method is applied.

  For example, Patent Documents 1 and 2 disclose automatic exposure control devices that automatically control X-rays to an appropriate exposure amount using an X-ray flat panel detector. In Patent Document 1, when X-ray exposure is started, the X-ray transmitted through the subject is converted into an optical signal, the optical signal is converted into an electric signal, and a predetermined pixel is set as an X-ray exposure amount detection pixel. Then, it is disclosed that the electric signal of the pixel is read out and accumulated at a predetermined time interval, and the X-ray exposure is stopped when the accumulated electric signal becomes larger than a predetermined value set in advance. In Patent Document 1, as shown in FIG. 5, the electrical signal of each pixel is read and accumulated every predetermined interval, for example, every time t1, t2, t3, etc., and the electrical signal accumulated every predetermined time is stored. Disclosing resetting.

  In Patent Document 2, each time a pixel value is read from a pixel for X-ray irradiation detection of a flat panel detector and the pixel value is stored for each pixel in an L row pixel adder / memory, this L row is stored. The pixel values stored in the pixel adder / memory are added by the ROI total value calculation circuit, and the added value is further compared with the threshold by the threshold comparator. If the added value exceeds the threshold, the X-ray controller is To stop the X-ray exposure from the X-ray tube. In Patent Document 2, as shown in FIG. 3 of the same document, pixel values are read out and stored at predetermined timings from the X-ray irradiation amount detection pixels of the flat panel detector, and electrical signals are reset at each predetermined timing. To disclose.

  In any case, Patent Documents 1 and 2 disclose that electrical signals are periodically (every predetermined time) from a specific detection element, that is, a specific pixel (AEC pixel) in the X-ray flat panel detector during X-ray exposure. The accumulated electric signal from the start of X-ray exposure is calculated by adding the read electric signals each time, and X-ray exposure is stopped when the accumulated signal reaches a threshold value. In Patent Documents 1 and 2, for example, as shown in FIG. 5 of Patent Document 1, the output of the AEC pixel is reset every time the output of the AEC pixel is read.

  That is, an electrical signal from a specific pixel (AEC pixel) is read out several times every predetermined time, A / D (analog / digital) converted, and these digital signals are added to obtain a signal value of the specific pixel. Yes. And X-ray exposure is stopped when this addition value reaches a threshold value. As a result, during the period from the start of X-ray exposure to the stop of X-ray exposure, the electrical signal from the AEC pixel is read out several times every predetermined time, and several times every predetermined time. The output of the AEC pixel is reset once.

For this reason, for example, if the number of times the electrical signal is read from the AEC pixel and the output of the AEC pixel is reset k times, the electrical signals read at k times are A / D converted, and the k digital signals are The S / N value (S / N1) of the signal value of the specific pixel, which is the result of the addition, is the result of reading the electrical signal from the AEC pixel at one time, A / D converting it, and adding these digital signals. It becomes smaller than the S / N value (S / N2) of the signal value of a specific pixel. The relationship between these S / N1 and S / N2 is expressed by the following equation (1).

  Note that the above formula (1) is a case where only circuit noise is considered, and actually includes X-ray quantum noise, so the above formula (1) is not accurate, but (S / N1) < The (S / N2) relationship remains unchanged.

Such a decrease in the S / N value of the signal value of a specific pixel causes a decrease in reliability when the X-ray is automatically controlled to an appropriate exposure amount.
Japanese Patent No. 3466684 (Japanese Patent Laid-Open No. 7-201490) JP 2000-1000059

  An object of the present invention is to provide an X-ray exposure amount control apparatus and method, and an X-ray image pickup apparatus capable of automatically controlling X-rays to an appropriate exposure amount without reducing the S / N value of the signal value of the pixel. is there.

According to a first aspect of the present invention, there is provided an X-ray exposure amount control device in which a plurality of detection elements for detecting X-rays emitted from an X-ray source are arranged on a two-dimensional plane in vertical and horizontal directions perpendicular to each other. The X-ray flat panel detector and a plurality of detection elements arranged on a plurality of horizontal lines among the plurality of detection elements are used as automatic exposure amount control pixels , respectively, from the start of the X-ray exposure of the X-ray source. Te and on the operation portion to be turned on, during the oN operation of the plurality of detector elements, the respective output signals of the plurality of detection elements accumulate respectively, X-rays source at a time when the added value of these accumulated value exceeds the threshold An X-ray exposure stop unit for stopping the X-ray exposure.

According to a fifth aspect of the present invention, there is provided an X-ray exposure amount control method in which a plurality of detection elements for detecting X-rays emitted from an X-ray source are arranged on a vertical and horizontal two-dimensional plane perpendicular to each other. a plurality of detection elements arranged in the horizontal direction on a plurality of lines of the X-ray flat panel detector continuously from the time of X-ray irradiation start of the X-ray source as an automatic exposure control pixel is turned on made, more of during the on-operation of the detection elements, the output signals of the plurality of detection elements accumulate respectively, the sum of these accumulated values stops X-ray radiation from the X-ray source at the time the threshold is exceeded.

X-ray imaging apparatus according to claim 7 of the present invention, the X-ray source for exposure of the X-ray to the subject, a plurality of detecting elements for detecting X-rays transmitted through the subject, perpendicular to each other An X-ray plane detector arranged on a vertical and horizontal two-dimensional plane, an image data generation unit for generating X-ray image data of a subject based on a detection signal output from the X-ray plane detector, An on-operation unit that continuously turns on a plurality of detection elements arranged on a plurality of lateral lines among the plurality of detection elements as automatic exposure amount control pixels from the start of X-ray exposure of the X-ray source; , during the on-operation of a plurality of detector elements, the output signals of the plurality of detection elements accumulate respectively, to stop the irradiation of X-rays from the X-ray source when the added value of these accumulated value exceeds the threshold And an X-ray exposure stop unit.

  ADVANTAGE OF THE INVENTION According to this invention, the X-ray exposure amount control apparatus which can automatically control an X-ray to appropriate exposure amount, without reducing the S / N value of the signal value of a pixel, its method, and an X-ray image pick-up device can be provided.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an X-ray imaging apparatus to which an X-ray exposure amount control apparatus is applied. The X-ray source 1 and the X-ray detector 2 are disposed to face each other. A subject S such as a human body is disposed between the X-ray source 1 and the X-ray detector 2. X-rays exposed from the X-ray source 1 pass through the subject S and enter the X-ray detector 2.

  As shown in FIG. 2, the X-ray detector 2 is formed by arranging a plurality of detection elements 2-11 to 2-nm for detecting X-rays emitted from the X-ray source 1 on a two-dimensional plane. Specifically, the plurality of detection elements 2-11 to 2-nm are arranged in a vertical and horizontal direction perpendicular to each other, for example, on a two-dimensional plane including a plurality of rows N and a plurality of columns M. The plurality of rows each extend in the line direction L and are arranged at regular intervals in the column direction R. The plurality of columns each extend in the column direction R and are arranged at regular intervals in the column direction L. For example, each detection element 2-11, 2-12, 2-13,..., 2-1m forms a first line, and each detection element 2-21, 2-22, 2-23,. 2m forms the second line. The detection elements 2-11, 2-22, 2-33,..., 2-nm form a first column, and the detection elements 2-12, 2-22, 2-32,. n2 forms the second column.

A plurality of gate lines 3-1 to 3-n are arranged along the line direction L. For example, the first gate line 3-1 is connected to each of the detection elements 2-11, 2-12, 2-13,..., 2-1m forming the first line, and the second gate line 3-2 is , Connected to each detection element 2-21, 2-22, 2-23,..., 2-2m forming the second line.
A gate driver 4 is connected to each of the gate lines 3-1 to 3-n. The gate driver 4 sequentially supplies, for example, a high level gate signal to each of the gate lines 3-1 to 3-n, thereby detecting each of the detection elements 2-11 of the first line, for example, the first line. , 2-12, 2-13,..., 2-1m, and the respective charges stored sequentially for each of the detection elements 2-21, 2-22, 2-23,. Operate.

  A plurality of signal output lines 5-1 to 5-m are arranged along the line direction R. For example, the first gate line 5-1 is connected to each of the detection elements 2-11, 2-21, 2-31,..., 2-n1 forming the first column, and the second gate line 5-2 is , 2-n2 are connected to the detection elements 2-12, 2-22, 2-32,. The plurality of gate lines 3-1 to 3-n and the plurality of signal output lines 5-1 to 5-m are electrically separated from each other.

  The image data generation unit 6 is connected to a plurality of signal output lines 5-1 to 5-m. The image data generation unit 6 generates image data of the subject 3 based on the charges read from the plurality of detection elements 2-11 to 2-nm through the signal output lines 5-1 to 5-m. Specifically, the image data generation unit 6 includes a plurality of charge / voltage converters 7-1 to 7-m provided for each of a plurality of rows N. These charge / voltage converters 7-1 to 7-m are connected to signal output lines 5-1 to 5-m, respectively. Among these, for example, the charge / voltage converter 7-1 is read out from the detection elements 2-11, 2-21, 2-31,..., 2-n1 forming the first column through the signal output line 5-1. The generated charge is converted to voltage. The charge / voltage converter 7-2 receives the charges read from the detection elements 2-12, 2-22, 2-32,..., 2-n2 forming the second column through the signal output line 5-2. Convert to analog voltage signal.

A plurality of A / D converters 8-1 to 8-n are connected to output terminals of the charge / voltage converters 7-1 to 7-m, respectively. These A / D converters 8-1 to 8-n convert the analog voltage signals output from the charge / voltage converters 7-1 to 7-m, respectively, into digital voltage signals. The digital voltage signals output from the A / D converters 8-1 to 8-n are sent to the parallel / serial converter 9.
The parallel-serial converter 9 is formed by connecting the converters 9-1 to 9-m for a plurality of columns M in a line shape. The parallel / serial converter 9 simultaneously receives the digital voltage signals sent from the A / D converters 8-1 to 8-n at the converters 9-1 to 9-m, respectively. The signal is converted to serial and output as one line of image data.

  FIG. 3 is a detailed configuration diagram of the X-ray detector 2 and the image data generation unit 6. FIG. 3 shows only four detection elements 2-11, 2-12, 2-21, and 2-11 in the X-ray detector 2 in order to avoid complication of explanation. In the detection element 2-11, a thin film transistor (TFT) 10-1, a photoelectric film 11-1, and a charge storage capacitor 12-1 are formed. A photoelectric film 11-1 and a charge storage capacitor 12-1 are connected in parallel to the drain electrode of the TFT 10-1. The gate electrode of the TFT 10-1 is connected to the gate line 3-1. The source electrode of the TFT 10-1 is connected to the signal output line 5-1.

  Similarly to the detection element 2-11, each of the detection elements 2-12, 2-21, and 2-22 has the respective TFTs 10-2 to 10-4, the respective photoelectric films 11-2 to 11-4, and the respective charge accumulations. Capacitors 12-2 to 12-4 are formed. Photoelectric films 11-2 to 11-4 and charge storage capacitors 12-2 to 12-4 are connected in parallel to the drain electrodes of the TFTs 10-2 to 10-4, respectively. The gate electrode of the TFT 10-2 is connected to the gate line 3-1, and the gate electrodes of the TFTs 10-3 and 10-4 are connected to the gate line 3-2. The source electrodes of the TFTs 10-1 and 10-3 are connected to the signal output line 5-1, and the source electrodes of the TFTs 10-2 and 10-4 are connected to the signal output line 5-2. ing.

The charge / voltage converter 7-1 includes an amplifier 13-1, a feedback capacitor 13-2, and a reset switch 13-3. A feedback capacitor 13-2 and a reset switch 13-3 are connected in parallel to the amplifier 13-1. Such a charge / voltage converter 7-1 accumulates charges from the detection element 2-11 or the detection element 2-21 in the feedback capacitor 13-2 for each line N, and the time elapses in the feedback capacitor 13-2. A voltage corresponding to the amount of charge accumulated together is output through the amplifier 13-1. The reset switch 13-3 discharges the charge accumulated in the feedback capacitor 13-2 and resets the charge amount to “0”.
Similarly to the charge / voltage converter 7-1, the charge / voltage converter 7-2 includes an amplifier 14-1, a feedback capacitor 14-2, and a reset switch 14-3. A feedback capacitor 14-2 and a reset switch 14-3 are connected in parallel. Such a charge / voltage converter 7-2 also accumulates charges from the detection element 2-12 or the detection element 2-22 in the feedback capacitor 13-2 for each line N, and the time elapses in the feedback capacitor 13-2. A voltage corresponding to the amount of charge accumulated together is output through the amplifier 13-1. The reset switch 13-3 discharges the charge accumulated in the feedback capacitor 13-2 and resets the charge amount to “0”.

  An image memory 15 is connected to the output end of the parallel / serial converter 9. The image memory 15 stores the X-ray image data of the subject 3 by sequentially storing the image data for each line output from the parallel / serial converter 9. The X-ray image data of the subject 3 stored in the image memory 15 is sent to the display unit 16 and displayed.

  The imaging control unit 17 sends an X-ray exposure start command to the X-ray source 1 to emit X-rays from the X-ray source 1 and, for example, the amount of X-ray exposure to the X-ray detector 2 When the value reaches an appropriate value set in advance, the X-ray exposure is stopped and a read command is sent to the gate driver 4 of the X-ray detector 2. High-level signals are sequentially sent to the gate lines 3-1 to 3-n at predetermined intervals in the order of −1 to 3-n, and the detection elements for the first to Nth lines in the X-ray detector 2 are transmitted. For example, the detection elements 2-11, 2-12, 2-13,..., 2-1m in the first line, and then the detection elements 2-21, 2-22, 2-23,. The charge is read sequentially for each 2-2m line.

  Further, the imaging control unit 17 sets one line, for example, the gate line 3-2 of the second line, among the plurality of detection elements 2-11 to 2-nm in the X-ray detector 2 as an AEC line, and this gate line. An automatic exposure control signal (AEC control signal) that is continuously at a high level from the start of X-ray exposure is sent to 3-2. The imaging control unit 17 continuously charges accumulated in the detection elements 2-21, 2-22, 2-23,..., 2-2m of the second line during transmission of the high-level AEC control signal. X-rays from the X-ray source 1 at the time when the accumulated value of the electric charge that has been taken in and accumulated continuously reaches the threshold value G, that is, the X-ray dose exposed to the subject S reaches the accumulated value of the electric charge corresponding to the appropriate value. Stop exposure. Specifically, the imaging control unit 17 includes an on operation unit 18 and an X-ray exposure stop unit 19.

  The on-operation unit 18 is shown in FIG. 4 for the gate line 3-2 of the second line set to one line, for example, the AEC line, among the plurality of detection elements 2-11 to 2-nm in the X-ray detector 2. In this way, a command to send an AEC control signal Q that is continuously at a high level “1” from the start time t1 of the X-ray exposure is sent to the gate driver 4 of the X-ray detector 2, and each of the second lines The detection elements 2-21, 2-22, 2-23, ..., 2-2m are turned on.

  The X-ray exposure stop unit 19 is configured to detect each of the detection elements 2-21, 2-22, 2-23,..., 2- on the gate line 3-2 of the second line set to the AEC line by the ON operation unit 18, for example. During the ON operation of 2m, for example, one of the detection elements 2-21, 2-22, 2-23,... 2-2m, for example, the detection element 2-22 is set as the AEC pixel to the detection element 2-22. The amount of charges accumulated continuously is read, the read amount of charges is converted into an analog voltage signal, the analog voltage signal is converted into a digital signal, and this digital signal, that is, the amount of charge accumulated in the detection element 2-22 It is determined whether or not the X-ray dose that H exposes to the subject S has reached the threshold value G of the accumulated charge value corresponding to the appropriate value.

  When the charge accumulation amount H of the detection element 2-22 reaches the threshold G as a result of this determination, the X-ray exposure stop unit 19 has exceeded the threshold G by the charge accumulation amount H of the detection element 2-22. At the time t2, the X-ray exposure from the X-ray source 1 is stopped, the AEC control signal Q is set to low level “0”, and the reset switches of the charge / voltage converters 7-1 to 7-m 13-3, 14-3, etc. are temporarily closed, the charges accumulated in the feedback capacitors 13-2, 14-2 are discharged, and the accumulated charge amount is reset to “0”.

Next, an X-ray image capturing operation by the apparatus configured as described above will be described.
As shown in FIG. 4, the imaging control unit 17 sends an X-ray exposure start command to the X-ray source 1 at time t1, for example. Thereby, the X-ray source 1 starts X-ray exposure from time t1. X-rays emitted from the X-ray source 1 pass through the subject S and enter the X-ray detector 2. As shown in FIG. 2, the X-ray detector 2 accumulates charges according to the X-ray dose transmitted through the subject S in each of the detection elements 2-11 to 2-2 nm.
In order to simplify the description, the X-ray detector 2 shown in FIG. 3 will be described. Each of the detection elements 2-11, 2-12, 2-21, and 2-22 of the X-ray detector 2 is a photoelectric film. 11-1, 11-2, 11-3, and 11-4 receive X-rays that have passed through the subject S and convert them into charge amounts corresponding to the X-ray transmission amounts. 1, 12-2, 12-3, and 12-4 are continuously accumulated.

  In this state, the on-operation unit 18 of the imaging control unit 17 continuously sets the high level “1” to the gate line 3-2 of the AEC line from the start time t1 of the X-ray exposure as shown in FIG. A command for sending the AEC control signal Q is sent to the gate driver 4 of the X-ray detector 2. As a result, the gate driver 4 sends an AEC control signal Q that is continuously at a high level “1” from the time t1 when the X-ray exposure starts to the gate line 3-2 of the AEC line. The TFTs 10-3 and 10-4 connected to the gate line 3-2 are continuously turned on.

  The imaging control unit 17 sends a low level “0” signal to the other gate lines 3-1, 3-3 to 3-n of the gate line 3-2 serving as the AEC line. As a result, the TFTs 10-1, 10-2, etc. of the first line and the third to Nth lines are turned off continuously, and charges are accumulated in the charge storage capacitors 12-1, 12-2, etc. To go.

  The charge stored in the charge storage capacitor 12-3 by the ON operation of the TFT 10-3 on the AEC line passes through the source electrode from the drain electrode of the TFT 10-3, and further passes through the signal output line 5-1 to the charge / voltage converter 7. -1. At the same time, the charge stored in the charge storage capacitor 12-4 by the ON operation of the TFT 10-4 on the AEC line passes through the source electrode from the drain electrode of the TFT 10-4, and further passes through the signal output line 5-2. It is sent to the converter 7-2.

  The charge / voltage converter 7-1 continuously accumulates the charge from the detection element 2-21 input through the signal output line 5-1 in the feedback capacitor 13-2, and accumulates in the feedback capacitor 13-2. A voltage corresponding to the amount of charge to be output is output as an analog voltage signal through the amplifier 13-1. At the same time, the charge / voltage converter 7-2 continuously accumulates the charge from the detection element 2-22 input through the signal output line 5-2 in the feedback capacitor 14-2, and stores the charge in the feedback capacitor 14-2. A voltage corresponding to the amount of stored charge is output as an analog voltage signal through the amplifier 14-1. The voltage values of the analog voltage signals output from the charge / voltage converters 7-1 and 7-2 correspond to the amount of charge that is continuously accumulated in the feedback capacitors 13-1 and 13-2 and increases. Rise.

  Each analog voltage signal whose voltage value increases in accordance with the amount of electric charge accumulated and increased in this way is sent to each A / D converter 8-1, 8-2. The A / D converters 8-1 and 8-2 convert the analog voltage signals output from the charge / voltage converters 7-1 and 7-2, respectively, into digital signals. The digital signals output from the A / D converters 8-1 and 8-2 are stored in, for example, the image memory 15 through the parallel / serial converter 9.

  The X-ray exposure stop unit 19 reads out, for example, the digital signal of the detection element 2-22 of one pixel, that is, the charge accumulation amount H of the detection element 2-22 among the digital signals stored in the image memory 15, It is determined whether or not the charge accumulation amount H of the detection element 2-22 has reached the threshold value G of the charge accumulation value corresponding to the appropriate value.

  If the charge accumulation amount H of the detection element 2-22 has not reached the threshold G as a result of this determination, the X-ray exposure stop unit 19 sends this fact to the on operation unit 18. As a result, the on-operation unit 18 sends a command to the X-ray detector 2 to send an AEC control signal Q that is continuously at a high level “1” to the gate line 3-2 of the AEC line as shown in FIG. Send to the gate driver 4. Since the gate driver 4 continues to send the AEC control signal Q which is continuously at the high level “1” from the time t1 when the X-ray exposure is started to the gate line 3-2 of the AEC line, The TFTs 10-3 and 10-4 connected to the line 3-2 are continuously turned on.

  On the other hand, when the charge accumulation amount H of the detection element 2-22 reaches the threshold G, the X-ray exposure stop unit 19 at time t2 when the charge accumulation amount H of the detection element 2-22 exceeds the threshold G. The X-ray exposure from the X-ray source 1 is stopped, the AEC control signal Q is set to low level “0”, and the reset switches 13-3 of the charge / voltage converters 7-1 to 7-m are set. , 14-3, etc. are temporarily closed, the charges accumulated in the feedback capacitors 13-2, 14-2 are discharged, and the accumulated charge amount is reset to "0".

As a result, the digital signal output from the A / D converter 8-2, that is, the X-ray dose exposed to the subject S when the charge accumulation amount H of the detection element 2-22 reaches the threshold G is an appropriate value. The X-ray exposure from the X-ray source 1 is stopped at a time t2 when the value exceeds.
As described above, according to the first embodiment, with respect to the gate line 3-2 set as one line, for example, an AEC line, among the plurality of detection elements 2-11 to 2-nm in the X-ray detector 2. An AEC control signal that is continuously at a high level from the time t1 when X-ray exposure starts is sent, and during the sending of the AEC control signal, for example, the charge of the detection element 2-22 of one pixel on the AEC line is accumulated X-ray exposure from the X-ray source 1 is stopped at time t2 when the accumulated charge value H reaches a threshold value G, that is, an appropriate value of the X-ray dose to be exposed to the subject S. Thus, the reset switch 14-3 in the charge / voltage converter 7-2 is temporarily set between the time t1 when the X-ray source 1 is exposed and the time t2 when the X-ray exposure is stopped. The operation of closing and resetting the accumulated charge amount accumulated in the feedback capacitor 14-2 to “0” can be performed only once. In other words, the accumulated charge amount is read from the detection element 2-22 on the AEC line in the X-ray detector 2 between the time t1 when the X-ray exposure is started and the time t2 when the X-ray exposure is stopped. Can only be done once.

  However, the S / N value (S / N2) when the accumulated charge amount of, for example, the detection element 2-22 of one pixel on the AEC line is read at a time as expressed in the above equation (1) is For example, the S / N value (S / N1) when the charge amount is read out from the detection element 2-22 is larger.

As a result, it is not necessary to provide an AEC dedicated X-ray detection element, and the S / N value of the pixel signal value can be obtained by using, for example, one pixel detection element 2-22 on the AEC line in the X-ray detector 2. X-rays can be automatically controlled to an appropriate exposure amount without being reduced. Next, a second embodiment of the present invention will be described with reference to the drawings. The second embodiment is substantially the same as the configuration shown in FIG. 1, and will be described with reference to FIG.
The difference of the second embodiment from the first embodiment is an X-ray exposure stop unit 19. As shown in FIG. 5, after the X-ray source 1 starts X-ray exposure at time t1, the X-ray exposure stop unit 19 performs A / D at different times, for example, at least two times t3 and t4. The digital signal output from the converter 8-2, that is, the charge accumulation amounts A1 and A2 continuously accumulated in the detection element 2-22 of one pixel is read, and linear interpolation is performed using these charge accumulation amounts A1 and A2. (Extrapolation) is performed to obtain the estimated value F of the charge accumulation amount.

  Next, the X-ray irradiation stop unit 19 estimates a time point t5 when the estimated value F of the charge accumulation amount reaches the threshold value G, and determines whether or not the simultaneous point t5 has been reached. As a result of this determination, at time t5, the X-ray exposure stop unit 19 stops X-ray exposure from the X-ray source 1 at time t5 and sets the AEC control signal Q to the low level “0”. As shown in FIG. 3, the reset switches 13-3, 14-3, etc. of the charge / voltage converters 7-1 to 7-m are temporarily closed.

Next, an X-ray image capturing operation by the apparatus configured as described above will be described.
As shown in FIG. 4, the imaging control unit 17 sends an X-ray exposure start command to the X-ray source 1 at time t1, for example. Thereby, the X-ray source 1 starts X-ray exposure from time t1. X-rays emitted from the X-ray source 1 pass through the subject S and enter the X-ray detector 2. As shown in FIG. 2, the X-ray detector 2 accumulates charges according to the X-ray dose transmitted through the subject S in each of the detection elements 2-11 to 2-2 nm.
In this state, the on-operation unit 18 of the imaging control unit 17 continuously sets the high level “1” to the gate line 3-2 of the AEC line from the start time t1 of the X-ray exposure as shown in FIG. A command for sending the AEC control signal Q is sent to the gate driver 4 of the X-ray detector 2. As a result, the gate driver 4 sends an AEC control signal Q that is continuously at a high level “1” from the time t1 when the X-ray exposure starts to the gate line 3-2 of the AEC line. The detection elements 2-21, 2-22,..., 2-2m connected to the gate line 3-2 are continuously turned on.

  The charge / voltage converter 7-1 continuously accumulates charges from the detection element 2-21 input through the signal output line 5-1, and uses a voltage corresponding to the accumulated charge amount as an analog voltage signal. Output. At the same time, the charge / voltage converters 7-2 to 7-m respectively receive the charges from the detection elements 2-22,..., 2-2m respectively input through the signal output lines 5-2 to 5-m. Are continuously stored, and each voltage corresponding to the amount of stored charge is output as each analog voltage signal. The voltage value of each analog voltage signal output from these charge / voltage converters 7-1 to 7-m rises according to the amount of electric charge accumulated and increased continuously.

  In this way, each analog voltage signal whose voltage value increases according to the amount of accumulated charge is sent to each A / D converter 8-1 to 8-m. These A / D converters 8-1 to 8-m convert the analog voltage signals output from the charge / voltage converters 7-1 to 7-m, respectively, into digital signals.

  As shown in FIG. 5, after the X-ray source 1 starts X-ray exposure at time t1, the X-ray exposure stop unit 19 performs, for example, A / D at different times, for example, at least two times t3 and t4. The digital signal output from the converter 8-2, that is, the charge accumulation amounts A1 and A2 continuously accumulated in the detection element 2-22 of one pixel is read, and linear interpolation is performed using these charge accumulation amounts A1 and A2. (Extrapolation) is performed to obtain the estimated value F of the charge accumulation amount.

  Next, the X-ray irradiation stop unit 19 estimates a time point t5 when the estimated value F of the charge accumulation amount reaches the threshold value G, and determines whether or not the simultaneous point t5 has been reached. As a result of this determination, at time t5, the X-ray exposure stop unit 19 stops X-ray exposure from the X-ray source 1 at time t5 and sets the AEC control signal Q to the low level “0”. As shown in FIG. 3, the reset switches 13-3, 14-3, etc. of the charge / voltage converters 7-1 to 7-m are temporarily closed. As a result, for example, the charges accumulated in the feedback capacitors 13-2 and 14-2 shown in FIG. 3 are discharged, and the accumulated charge amount is reset to “0”.

  As a result, X-ray exposure from the X-ray source 1 is stopped at time t5 when the X-ray dose exposed to the subject S exceeds the appropriate value.

  As described above, according to the second embodiment, after the X-ray source 1 starts the X-ray exposure, for example, at each time t3 and t4, each pixel is continuously accumulated in the detection element 2-22. Charge accumulation amounts A1 and A2 are obtained, linear interpolation (extrapolation) is performed using these charge accumulation amounts A1 and A2, and an estimated value F of the charge accumulation amount is obtained. The time t5 when the threshold value G is reached is estimated, and when the simultaneous point t5 is reached, the X-ray exposure from the X-ray source 1 is stopped, the AEC control signal Q is set to the low level “0”, and FIG. As shown, the reset switches 13-3 and 14-3 of the charge / voltage converters 7-1 to 7-m are temporarily closed.

  Thus, as in the first embodiment, each charge / voltage converter 7 is between the time t1 when the X-ray source 1 is exposed and the time t2 when the X-ray exposure is stopped. -1, 7-2 temporarily close the reset switches 13-3, 14-3, etc., and reset the accumulated charge amount accumulated in the feedback capacitors 13-2, 14-2, etc. to "0". Can only be done once. In other words, each detection element 2-21, 2-22 on the AEC line in the X-ray detector 2 between the time t1 when the X-ray exposure is started and the time t2 when the X-ray exposure is stopped. 2-23,... 2-2m can be read only once from each charge.

  However, the S / N value (S / N2) when the accumulated charge amount of, for example, the detection element 2-22 of one pixel on the AEC line is read at a time as expressed in the above equation (1) is For example, the S / N value (S / N1) when the charge amount is read out from the detection element 2-22 is larger.

  As a result, it is not necessary to provide an AEC dedicated X-ray detection element, and the S / N value of the pixel signal value can be obtained by using, for example, one pixel detection element 2-22 on the AEC line in the X-ray detector 2. X-rays can be automatically controlled to an appropriate exposure amount without being reduced.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  For example, in the first and second embodiments, an AEC control signal Q that is continuously at a high level “1” is sent to the gate line 3-2 serving as an AEC line, and the gate line of this AEC line is transmitted. For example, X-rays are accumulated at time t2 when the charge of the detection element 2-22 connected to 3-2 is accumulated, for example, and the accumulated value reaches the threshold G, that is, the appropriate value of the X-ray dose to be exposed to the subject S. Although the X-ray exposure from the source 1 is stopped, the present invention is not limited to this, and a plurality of pixels on the AEC line, for example, the detection elements 2-21, 2-22,. It may be used. In this case, the added value of each charge accumulation value of each detection element 2-21, 2-22,..., 2-3m is compared with a threshold value.

  The AEC line may be set to a plurality of lines, for example, an arbitrary number of the gate lines 3-1 to 3-n.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows 1st Embodiment of the X-ray image imaging device to which the X-ray exposure amount control apparatus based on this invention is applied. The block diagram which shows the X-ray detector and image data generation part in the same apparatus. FIG. 2 is a detailed configuration diagram of an X-ray detector and an image data generation unit in the apparatus. The figure which shows the reset timing of the electric charge accumulate | stored in the feedback capacity | capacitance by the reset switch of the electric charge / voltage converter in the apparatus. The figure which shows the operation | movement timing of 2nd Embodiment of the X-ray imaging device to which the X-ray exposure amount control apparatus which concerns on this invention is applied.

Explanation of symbols

S: subject, 1: X-ray source, 2: X-ray detector, 2-11 to 2-nm: detection element, 3-1 to 3-n: gate line, 4: gate driver, 5-1 to 5- m: signal output line, 6: image data generation unit, 7-1 to 7-m: charge / voltage converter, 8-1 to 8-n: A / D converter, 9: parallel / serial converter, 9 -1 to 9-m: converter, 10-1 to 10-4: thin film transistor (TFT), 11-1 to 11-4: photoelectric film, 12-1 to 12-4: charge storage capacity,
13-1, 14-1: Amplifier, 13-2, 14-2: Feedback capacity, 13-3, 14-3: Reset switch, 15: Image memory, 16: Display unit, 17: Imaging control unit, 18: ON operation part, 19: X-ray exposure stop part.

Claims (9)

An X-ray flat panel detector in which a plurality of detection elements for detecting X-rays emitted from an X-ray source are arranged on a vertical and horizontal two-dimensional plane perpendicular to each other ;
The plurality of detection elements arranged on the plurality of horizontal lines among the plurality of detection elements are each turned on continuously from the start of the X-ray exposure of the X-ray source as an automatic exposure amount control pixel . An on-operation unit;
During the on operation of said plurality of detector elements, the output signals of said plurality of detector elements accumulate each曝of the X-ray from the X-ray source when the added value of these accumulated value exceeds the threshold An X-ray exposure stop unit for stopping the irradiation;
An X-ray exposure amount control apparatus comprising: A capacitor for accumulating electric charges output from the at least one detection element;
A charge-voltage converter that converts a charge amount accumulated in the capacitor into a voltage value;
Have
The X-ray exposure stop unit starts accumulation of the electric charge in the capacitor from the start of the exposure of the X-ray from the X-ray source, and the accumulated value of the electric charge continuously accumulated in the capacitor Stopping exposure of the X-ray from the X-ray source when the threshold exceeds the threshold and resetting the charge accumulation of the capacitor;
The X-ray exposure amount control apparatus according to claim 1, wherein:   The X-ray exposure stop unit captures the accumulated value of the output signal of the detection element at least twice from the start of the X-ray exposure, and the accumulated value of the output signal of the detection element is determined based on these accumulated values. The X-ray exposure control apparatus according to claim 1, wherein a time point at which the threshold value is reached is estimated, and the X-ray exposure from the X-ray source is stopped when the time point is reached.   4. The X-ray exposure control apparatus according to claim 3, wherein the X-ray exposure stop unit estimates a time point at which the X-ray exposure is stopped by linearly interpolating at least two accumulated values. A plurality of detection elements for detecting X-rays emitted from an X-ray source are arranged on a plurality of horizontal lines in an X-ray plane detector formed by arranging a plurality of detection elements on a vertical and horizontal two-dimensional plane perpendicular to each other. Each of the arrayed detection elements is continuously turned on as an automatic exposure amount control pixel from the start of X-ray exposure of the X-ray source,
During the on operation of the plurality of the detecting elements, the output signals of said plurality of detector elements accumulate each of the X-ray from the X-ray source when the added value of these accumulated value exceeds the threshold Stop exposure,
An X-ray exposure amount control method characterized by the above. The X-ray exposure is stopped by capturing the accumulated value of the output signal of the detection element at least twice from the start of the X-ray exposure, and linearly interpolating these accumulated values to obtain the output signal of the detection element. Estimating the time when the accumulated value reaches the threshold, and when the time reaches that time,
The X-ray exposure amount control method according to claim 5. An X-ray source for exposing the subject to X-rays;
An X-ray flat panel detector formed by arranging a plurality of detection elements for detecting the X-rays transmitted through the subject on a two-dimensional plane in vertical and horizontal directions perpendicular to each other ;
An image data generation unit that generates X-ray image data of the subject based on a detection signal output from the X-ray flat panel detector;
At the start of X-ray exposure of the X-ray source, with the plurality of detection elements arranged on the plurality of horizontal lines among the plurality of detection elements arranged in the vertical and horizontal directions as automatic exposure amount control pixels , respectively. An on-operation unit for continuously on-operation, and
During the on operation of said plurality of detector elements, the output signals of said plurality of detector elements accumulate each曝of the X-ray from the X-ray source when the added value of these accumulated value exceeds the threshold An X-ray exposure stop unit for stopping the irradiation;
An X-ray imaging apparatus comprising:   The X-ray exposure stop unit captures the accumulated value of the output signal of the detection element at least twice from the start of the X-ray exposure, and the accumulated value of the output signal of the detection element is determined based on these accumulated values. The X-ray imaging apparatus according to claim 7, wherein a time point at which the threshold value is reached is estimated, and exposure of the X-ray from the X-ray source is stopped when the time point is reached.   The X-ray exposure apparatus according to claim 8, wherein the X-ray exposure stop unit estimates a time point at which the X-ray exposure is stopped by linearly interpolating at least two of the accumulated values.

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