JP2017228863A - Radiation imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation imaging apparatus capable of suppressing noise generation in a radiation image more stably.SOLUTION: A radiation imaging apparatus 1 includes a radiation detector 3 having multiple radiation detection elements arranged two-dimensionally and outputting a pixel image according to the incident radiation dose, a signal extraction unit 19 for extracting the pixel signals outputted from the multiple radiation detection elements by correlation double sampling, a voltage conversion unit 24 for outputting an inputted DC voltage while converting into a predetermined power supply voltage, by switching the configuration of a circuit to which the DC voltage is inputted by a predetermined switching frequency, and a control unit 22 for operating the signal extraction unit in multiple operation modes where the sampling interval are different from each other in the correlation double sampling, and controlling the gain of the signal extraction unit for the switching frequency below a predetermined upper limit smaller than 1, in the period where the signal extraction unit is operating in any one of the multiple operation modes.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a radiographic image capturing apparatus.

  Conventionally, a radiation image in which radiation such as X-rays irradiated through a subject is detected by a two-dimensionally arranged radiation detection element and image data of a radiation image used for diagnosis of the subject is generated from the detection result There is a photographing device. Generation of image data of a radiographic image in the radiographic imaging device is performed by, for example, extracting a pixel signal output from a radiation detection element according to an incident radiation dose by correlated double sampling, and converting the extracted signal into a digital signal. This is done by converting. Here, the sampling interval in correlated double sampling can be changed as appropriate according to the radiographic image capturing conditions. For example, the sampling interval in the case of continuously capturing radiographic images is set to be smaller than the sampling interval in the case of capturing a still image in order to shorten the generation processing time of image data related to the radiographic image.

  In addition, the radiographic imaging apparatus includes a DC-DC converter that converts an input DC voltage into a predetermined power supply voltage and outputs the power supply voltage, and the radiation detection element and its drive circuit are operated by the converted power supply voltage. It can be set as the structure to do. Here, as the DC-DC converter, a system that converts a voltage by switching supply and stop of a DC voltage to a circuit combining a coil and a diode at a predetermined switching frequency by a switching element is used (for example, a patent) Reference 1).

JP 2002-341043 A

  However, in the conventional radiographic imaging apparatus, when the sampling interval of the correlated double sampling is changed in the signal extracting unit that performs correlated double sampling, the gain of the signal corresponding to the frequency in the signal extracting unit varies. Depending on the changed sampling interval, noise of the switching frequency caused by the operation of the DC-DC converter is amplified in the signal extraction unit. As a result, there is a problem that the noise of the switching frequency included in the signal extracted by the signal extraction unit increases and the image quality of the radiographic image decreases.

  An object of the present invention is to provide a radiographic imaging apparatus that can more stably suppress the generation of noise in a radiographic image.

In order to achieve the above object, the invention of the radiographic imaging device according to claim 1 comprises:
A radiation detector having a plurality of two-dimensionally arranged radiation detection elements each outputting a pixel signal corresponding to an incident radiation dose;
A signal extraction unit for extracting the pixel signals output from the plurality of radiation detection elements by correlated double sampling;
A voltage converter that converts the input DC voltage into a predetermined power supply voltage by switching the configuration of the circuit to which the DC voltage is input at a predetermined switching frequency; and
The signal extraction unit is operated in a plurality of operation modes having different sampling intervals in the correlated double sampling, and the signal extraction unit is operated in any operation mode of the plurality of operation modes. A control unit for controlling the gain of the signal extraction unit with respect to a switching frequency to be equal to or lower than a predetermined upper limit gain smaller than 1;
It is characterized by having.

The invention according to claim 2 is the radiographic imaging device according to claim 1,
The radiation detection unit includes a plurality of scanning lines extending in a first direction and a plurality of signal lines extending in a second direction intersecting the first direction,
Each of the plurality of radiation detection elements is connected to any one of the plurality of scanning lines and any one of the plurality of signal lines,
The controller is
The radiation detection element connected to the scanning line to which the selection signal is supplied by sequentially supplying a predetermined selection signal to the plurality of scanning lines at a selection period corresponding to an operation mode of the signal extraction unit. Output the pixel signal to the signal line from
The switching frequency during a period in which the signal extraction unit is operating in the one operation mode is greater than a Nyquist frequency related to the selection period corresponding to the one operation mode.

The invention according to claim 3 is the radiographic imaging device according to claim 1 or 2,
The control unit causes the voltage conversion unit to switch the configuration of the circuit at the same switching frequency when the signal extraction unit is operated in any of the plurality of operation modes. It is a feature.

The invention according to claim 4 is the radiographic imaging device according to claim 1 or 2,
When the operation mode of the signal extraction unit is switched, the control unit adjusts the switching frequency in the voltage conversion unit so that the gain in the operation mode after switching is equal to or lower than the upper limit gain. .

The invention according to claim 5 is the radiographic imaging device according to claim 2,
When the control unit switches the operation mode of the signal extraction unit, the gain in the operation mode after switching is less than or equal to the upper limit gain, and the switching frequency corresponds to the operation mode after switching The switching frequency in the voltage converter is adjusted so as to be higher than the Nyquist frequency related to the period.

The invention according to claim 6 is the radiographic imaging device according to claim 4 or 5,
A storage unit that stores a plurality of the switching frequencies that are predetermined in association with the plurality of operation modes;
When the operation mode of the signal extraction unit is switched, the control unit refers to the storage unit and selects the switching frequency associated with the switched operation mode.

The invention according to claim 7 is the radiographic imaging device according to claim 4 or 5,
The control unit calculates the switching frequency at which the gain in the operation mode after switching is equal to or lower than the upper limit gain based on the sampling interval in the operation mode after switching.

The invention according to claim 8 is the radiographic imaging device according to claim 7,
The control unit calculates the gain in the operation mode after switching with respect to the switching frequency in a period in which the signal extraction unit is operating in the operation mode before switching, and the calculated gain is the upper limit gain. The switching frequency at which the gain in the operation mode after switching is less than or equal to the upper limit gain is calculated.

The invention according to claim 9 is the radiographic imaging device according to claim 7 or 8,
The control unit adjusts the switching frequency so that a product of the sampling interval and the switching frequency in the operation mode after the switching approaches an integer.

The invention according to claim 10 is the radiographic imaging device according to claim 5,
The control unit calculates the switching frequency corresponding to the operation mode after switching based on the sampling interval in the operation mode after switching and the selection cycle corresponding to the operation mode after switching. It is a feature.

The invention according to claim 11 is the radiographic imaging apparatus according to any one of claims 1 to 10,
An image data generation unit that generates image data of a radiographic image based on the extraction result of the pixel signal by the signal extraction unit;
The controller is
In the still image shooting mode in which the image data generating unit generates radiographic image data of a still image, the signal extraction unit is operated in a predetermined first operation mode among the plurality of operation modes, and the image data generation is performed. In the continuous imaging mode in which the image data of the radiation image is continuously generated by the unit, the signal extraction is performed in the second operation mode in which the sampling interval is smaller than the sampling interval in the first operation mode among the plurality of operation modes. Operating part
When switching between the still image shooting mode and the continuous shooting mode, the operation mode of the signal extraction unit is switched.

  According to the present invention, there is an effect that generation of noise in a radiographic image can be suppressed more stably.

It is a perspective view which shows the external appearance of a radiographic imaging apparatus. It is a block diagram which shows the structure of a radiographic imaging apparatus. It is a block diagram which shows the structure of the part corresponding to the said one radiation detection element among the one radiation detection element and readout IC. It is a timing chart explaining the operation | movement in a reset process. It is a timing chart explaining the operation | movement in a read-out process. It is a figure explaining the structure and operation | movement of a DC-DC converter in a power supply circuit. It is a figure which shows the example of the gain of the signal according to the frequency in CDS. It is a figure which shows the example of the table data used for the setting of a switching frequency. It is a flowchart which shows the control procedure of a radiographic imaging process. 10 is a flowchart showing a control procedure of radiographic image capturing processing according to Modification 1;

  Embodiments of the radiation image capturing apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an appearance of a radiographic image capturing apparatus according to an embodiment of the present invention.
The radiographic imaging device 1 is configured by housing a sensor panel in which radiation detection elements 7 (FIG. 2) are arranged, a control circuit for controlling the operation of each part of the radiographic imaging device 1, and the like in a housing 2. Yes. On one side of the housing 2, a power switch 25, a changeover switch 26 for switching the radiographing mode of the radiographic imaging device 1, a connector 27 used for wired communication with an external device, a battery state and radiographic imaging An indicator 28 composed of LEDs or the like for displaying the operating state of the apparatus 1 is provided. An antenna 29 (FIG. 2) used for wireless communication with an external device is provided on the opposite side surface of the housing 2.

  FIG. 2 is a block diagram showing a configuration of the radiographic image capturing apparatus 1. The radiographic imaging device 1 includes a radiation detection unit 3, a scanning line driving circuit 15, a readout IC 16, a control unit 22 (image data generation unit), a storage unit 23, a power supply circuit 24 (voltage conversion unit), A communication unit 30 is provided.

  The radiation detection unit 3 has a plurality of scanning lines 5 formed so as to extend in the left-right direction (first direction) in FIG. 2 and extends in the up-down direction (second direction) in FIG. A plurality of signal lines 6 formed, and a plurality of radiation detection elements 7 provided in positions corresponding to the intersections of the plurality of signal lines 6 and the plurality of signal lines 6 are arranged in a two-dimensional matrix. The scanning line 5, the signal line 6, and the radiation detection element 7 are formed on, for example, a glass substrate that is a base material. The plurality of radiation detection elements 7 may be two-dimensionally arranged in another form such as a honeycomb form instead of the matrix form.

  The radiation detection element 7 generates a charge corresponding to the amount of radiation incident on the formation region of the radiation detection element 7. The radiation detection element 7 can be composed of, for example, a pin type photodiode. Further, as the radiation detecting element 7, a radiation detecting element 7 that converts radiation into an electromagnetic wave in the wavelength range of visible light by a scintillator (not shown) provided on the radiation incident side of the radiation detecting element 7 and detects the amount of the electromagnetic wave. It may be used, or a system that generates radiation by directly detecting radiation may be used.

  Each radiation detection element 7 is connected to one scanning line 5 and one signal line 6 through a thin film transistor 8 (hereinafter referred to as TFT). That is, the first electrode 7 a of the radiation detection element 7 is connected to the source S of the TFT 8, the gate G of the TFT 8 is connected to the scanning line 5, and the drain D is connected to the signal line 6. The second electrode 7 b of the radiation detection element 7 is connected to the bias line 9, and a reverse bias voltage is applied from the power supply circuit 24 through the connection 10 connected to the bias line 9. .

The plurality of scanning lines 5 are connected to the scanning line driving circuit 15. The scanning line drive circuit 15 sequentially selects the scanning lines 5 by supplying an ON voltage (selection signal) to the plurality of scanning lines 5 in order at a predetermined selection cycle. Further, the scanning line driving circuit 15 supplies an off voltage to the scanning lines 5 that are not selected.
When an on-voltage is supplied to the scanning line 5, the source S-drain D of the TFT 8 having the gate G connected to the scanning line 5 becomes conductive (hereinafter, this state is also referred to as an on-state), and radiation. The charge accumulated in the detection element 7 is released to the signal line 6, whereby a pixel signal is output from the radiation detection element 7. Thereafter, when an off voltage is supplied to the scanning line 5, the source S and the drain D of the TFT 8 are brought into a non-conductive state, and the charge generated in the radiation detection element 7 is accumulated in the radiation detection element 7.

Here, the scanning line driving circuit 15 according to the present embodiment sequentially selects the scanning lines 5 at different selection periods according to the imaging mode of the radiation image capturing apparatus 1. For example, when the imaging mode of the radiographic image capturing apparatus 1 is a still image capturing mode for capturing a radiographic image of a still image, the scanning line 5 is selected at the first selection period Tg1, and the radiographic image capturing apparatus 1 When the imaging mode is a continuous imaging mode in which radiographic images are continuously generated, a scanning line is selected at the second selection cycle Tg2 (<Tg1). Thereby, the frame rate of the moving image generated in the continuous shooting mode can be increased.
Note that the selection cycle of the scanning line 5 by the scanning line driving circuit 15 is not limited to the first and second selection cycles. For example, the selection cycle when the radiographic imaging device 1 is in the continuous imaging mode may have different values depending on the frame rate of the radiographic image generated in the radiographic imaging device 1.

The read IC 16 includes a plurality of read circuits 17 corresponding to the plurality of signal lines 6, an analog multiplexer 20, and an A / D converter 21. Among these, each of the plurality of readout circuits 17 is connected to a corresponding one of the signal lines 6, and includes an amplifier circuit 18 and a correlated double sampling circuit 19 (signal extraction unit) (hereinafter referred to as “CDS 19 (Correlated Double Sampling)”. ").)
The amplifier circuit 18 outputs a voltage signal corresponding to the electric charge emitted from the radiation detection element 7 to the CDS 19.
The CDS 19 extracts (samples) the voltage signal output from the amplifier circuit 18 by correlated double sampling, and outputs it to the analog multiplexer 20 as pixel data of an analog signal.
The analog multiplexer 20 sequentially transmits the pixel data output from the CDS 19 to the A / D converter 21.
The A / D converter 21 converts the pixel data of the input analog signal into pixel data of a digital signal and outputs it to the control unit 22.

  FIG. 3 is a block diagram showing a configuration of one radiation detection element 7 and a portion corresponding to the one radiation detection element 7 in the readout IC 16. In FIG. 3, the analog multiplexer 20 is omitted.

  In this embodiment, the amplifier circuit 18 switches between conduction and non-conduction between the operational amplifier 18a operating with the power supply voltage supplied from the power supply circuit 24, the capacitor 18b provided in parallel with the operational amplifier 18a, and the electrodes of the capacitor 18b. The charge amplifier circuit includes a charge reset switch 18c and a switch 18d for switching between conduction and non-conduction between the operational amplifier 18a and the CDS 19. The signal line 6 is connected to the inverting input terminal on the input side of the operational amplifier 18a.

  On / off of the charge reset switch 18 c of the amplifier circuit 18 is controlled by the control unit 22. The switch 18d is switched so as to be interlocked with the charge reset switch 18c, and is turned off when the charge reset switch 18c is on, and when the charge reset switch 18c is off. It is controlled by the control unit 22 so as to be in the ON state.

  In the radiographic imaging device 1, when resetting each radiation detection element 7 to remove the charge remaining in the radiation detection element 7, the charge reset switch 18 c is turned on as shown in FIG. 4. Each TFT 8 is turned on in the state (the switch 18d is turned off). Then, charges are emitted from the radiation detection element 7 to the signal line 6 through the TFTs 8 that are turned on, pass through the charge reset switch 18c of the amplifier circuit 18, and pass through the operational amplifier 18a from the output terminal side of the operational amplifier 18a. As a result, it comes out of the non-inverting input terminal and is grounded or flows out to the power supply circuit 24 connected to the operational amplifier 18a. In this way, reset processing of each radiation detection element 7 is performed.

  Further, when the pixel signal is read out from the radiation detection element 7, as shown in FIG. 5A, the charge reset switch 18c of the amplifier circuit 18 is in the off state (the switch 18d is in the on state). ), The charge is released from the radiation detection element 7 to the signal line 6 through the TFT 8 turned on, and the charge is accumulated in the capacitor 18b of the amplifier circuit 18.

  In the amplifier circuit 18, a voltage value corresponding to the amount of electric charge accumulated in the capacitor 18b is output from the output terminal of the operational amplifier 18a. That is, in the amplification circuit 18, the amount of charge flowing out from the radiation detection element 7 is converted into a voltage signal.

The CDS 19 provided on the output side of the amplifier circuit 18 is subjected to the reset process described above and before the charge flows out from the radiation detection element 7 in accordance with the input of the pulse signal Sp1 (FIG. 5) from the control unit 22. The voltage value V1 output from the amplifier circuit 18 at the time is held by a first sample hold circuit (not shown). Further, at a time after the electric charge flowing out from the radiation detection element 7 by the reading process described above is accumulated in the capacitor 18b of the amplifier circuit 18 in response to the input of the pulse signal Sp2 (FIG. 5) from the control unit 22. The voltage value V2 output from the amplifier circuit 18 is held by a second sample hold circuit (not shown). Then, the CDS 19 calculates a difference V2-V1 between the voltage values held by the first and second sample-and-hold circuits, and uses the difference V2-V1 as pixel data of the analog value as a subsequent circuit (analog multiple in FIG. 2). Output to the kusar 20).
In this way, the CDS 19 extracts the pixel signal output from the radiation detection element 7 by correlated double sampling. Hereinafter, the time interval at which the pulse signal Sp1 and the pulse signal Sp2 are input is also referred to as a sampling interval of correlated double sampling.

Here, the CDS 19 of the present embodiment operates in a plurality of different operation modes depending on the imaging mode of the radiation image capturing apparatus 1 and the like. That is, the CDS 19 operates in the first operation mode in which the sampling interval is Tc1, as shown in FIG. 5A, when the radiographic image capturing apparatus 1 is in the still image capturing mode. When the radiographic image capturing apparatus 1 is in the continuous image capturing mode, as shown in FIG. 5B, the radiographic image capturing apparatus 1 operates in the second operation mode in which the sampling interval is Tc2 (<Tc1).
Note that the operation mode of the CDS 19 is not limited to the first and second operation modes. For example, the operation mode of the CDS 19 when the imaging mode of the radiographic imaging device 1 is the continuous imaging mode is two or more operations with different sampling intervals according to the frame rate of the radiographic image generated in the radiographic imaging device 1. The mode may be selected corresponding to the frame rate.

  The control unit 22 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a bus connecting these, and the like. The CPU reads various control programs and setting data stored in the ROM, stores them in the RAM, executes the programs, and performs various arithmetic processes. Further, the CPU performs overall control of operations of the respective units of the radiographic image capturing apparatus 1 such as the scanning line driving circuit 15, the readout IC 16, the storage unit 23, and the power supply circuit 24. The RAM provides a working memory space for the CPU and stores temporary data. The ROM stores various control programs executed by the CPU, setting data, and the like. This setting data includes table data, which will be described later, stored in association with the sampling interval in the CDS 19 and the selection cycle of the scanning line 5 and the switching frequency of the DC-DC converter 24a. Instead of the ROM, a rewritable nonvolatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used. Moreover, the control part 22 may be comprised by FPGA (Field Programmable Gate Array).

  The storage unit 23 is connected to the control unit 22 and stores image data of a radiographic image including pixel data output from the readout IC 16 to the control unit 22. For example, an SRAM (Static Random Access Memory) or an SDRAM (Synchronous Dynamic Random Access Memory) is used as the storage unit 23.

  The power supply circuit 24 is connected to an external power supply 40 provided outside the radiographic image capturing apparatus 1, and converts a DC voltage input from the external power supply 40 into a plurality of predetermined power supply voltages by a DC-DC converter, thereby scanning lines. This is supplied to each unit such as the drive circuit 15, the readout IC 16, the control unit 22, and the storage unit 23. Instead of the external power supply 40, a battery or a battery provided inside the radiographic image capturing apparatus 1 may be used.

FIG. 6 is a diagram illustrating the configuration and operation of the DC-DC converter 24 a in the power supply circuit 24.
The DC-DC converter 24a shown in FIG. 6A includes a triangular wave oscillation circuit 241, a comparator 242 to which the output of the triangular wave oscillation circuit 241 is input to one input terminal, and an output voltage of the comparator 242. The TFT 243 as a switching element that performs on / off operation, a diode 244 provided between the drain of the TFT 243 and the ground potential, a coil 245 having one end connected to the drain of the TFT 243, and the other end of the coil 245 and the ground potential And resistors 246 and 247 provided in series. A DC voltage is input from the external power supply 40 to the source of the TFT 243. A voltage obtained by dividing the voltage at the other end of the coil 245 by the resistors 246 and 247 is input to the other input terminal of the comparator 242. The oscillation frequency of the triangular wave oscillation circuit 241 is controlled by the control unit 22.
The comparator 242 alternately outputs a voltage that turns on the TFT 243 and a voltage that turns it off according to the value of the voltage output from the triangular wave oscillation circuit 241.
When the TFT 243 is in the on state, energy is stored in the coil by the current flowing from the external power supply 40 to the coil 245, and when the TFT 243 is in the off state, the induced current due to the induced electromotive force of the coil 245 becomes the diode 244 and the coil. 245. In the DC-DC converter 24a, by repeating this operation, the input voltage is stepped down and output from the output terminal according to the ratio of the period in which the TFT 243 is off.

FIG. 6B is a diagram illustrating a signal output from the comparator 242 to the gate of the TFT 243. In this manner, the comparator 242 outputs a rectangular wave having a switching frequency corresponding to the oscillation frequency of the triangular wave oscillation circuit. In the present embodiment, the oscillation frequency of the triangular wave oscillation circuit 241 is controlled by the control unit 22, and the switching frequency in the DC-DC converter 24a is changed according to the control.
The power supply circuit 24 includes a number of DC-DC converters 24a corresponding to the type of power supply voltage to be output. In the power supply circuit 24, a step-up DC-DC converter may be used. Also, other types of DC-DC converters such as a charge pump may be used.

  The communication unit 30 performs wireless communication with the outside via the antenna 29 and performs wired communication with the outside via the connector 27. In the radiographic image capturing apparatus 1, transmission of image data of the generated radiographic image and reception of a control command instructing the operation of the radiographic image capturing apparatus 1 are performed via the communication unit 30.

Next, adjustment of the switching frequency of the power supply circuit 24 in the radiation image capturing apparatus 1 will be described.
In the radiographic imaging device 1, the gain of the signal corresponding to the frequency in the CDS 19 varies according to the sampling interval of correlated double sampling in the CDS 19. For this reason, when the sampling interval in the CDS 19 is changed by switching the shooting mode or the like, depending on the sampling interval after the change, noise of the switching frequency caused by the operation of the DC-DC converter 24a of the power supply circuit 24 is caused in the CDS 19. Amplified. As a result, the noise of the switching frequency included in the signal extracted in the CDS 19 is increased, and the image quality of the radiation image is degraded.
Therefore, in the radiographic image capturing apparatus 1 of the present embodiment, the switching frequency of the DC-DC converter 24a is adjusted so that the generation of noise in the CDS 19 is suppressed. Hereinafter, a method for adjusting the switching frequency will be described.

The gain g of the signal of frequency F in the CDS 19 is expressed by the following equation (1), where Tc is the sampling interval of correlated double sampling.
g = [2-2 cos {2π (F × Tc)}] ^ (1/2) (1)
As shown in the equation (1), the gain g is the minimum due to the signal being canceled when calculating the difference V2-V1 in the CDS 19 when the product of the frequency F and the sampling interval Tc is an integer. Value (0). On the other hand, the gain g has a maximum value (2) when the product of the frequency F and the sampling interval Tc is an odd multiple of 1/2.

  FIG. 7 is a diagram illustrating an example of signal gain according to the frequency in the CDS 19. FIG. 7A shows the gain when the radiographic image capturing apparatus 1 is in the still image capturing mode, and FIG. 7B shows the gain when the radiographic image capturing apparatus 1 is in the continuous capturing mode. In the still image shooting mode of the present embodiment, the sampling interval Tc is set to 175 [μs], and in the continuous shooting mode, the sampling interval Tc is set to 31.6 [μs]. In the still image shooting mode, the selection cycle Tg of the scanning line 5 is set to 280 [μs], and in the continuous shooting mode, the selection cycle Tg of the scanning line 5 is set to 50 [μs].

  As shown in FIG. 7A, the gain g in the CDS 19 when the radiographic image capturing apparatus 1 is in the still image capturing mode fluctuates periodically between 0 and 2 with respect to the frequency F. 0 when the frequency F is an integral multiple of 1/175 [μs] ≈5.7 [kHz]. For this reason, the switching frequency in the DC-DC converter 24a is adjusted within a range where the gain g is less than 1 in FIG. 7A (for example, the frequency ranges R1a, R1b, R1c, etc. in FIG. 7A). Thus, the switching frequency noise generated by the operation of the DC-DC converter 24a can be reduced in the CDS 19. In particular, by setting the switching frequency to a frequency at which the gain g becomes 0, that is, an integer multiple of 5.7 [kHz], noise at the switching frequency can be most effectively reduced.

In the present embodiment, the switching frequency is adjusted within a range of frequencies larger than the Nyquist frequency Fn = 1 / (2Tg) related to the selection cycle Tg of the scanning line 5. By making the switching frequency higher than the Nyquist frequency Fn, when noise of the switching frequency is mixed (sampled) in the pixel signal in the selection period Tg, aliasing occurs in the frequency component exceeding the Nyquist frequency. The spatial frequency of the noise mixed in the signal can be suppressed to less than the frequency corresponding to the Nyquist frequency Fn.
In the present embodiment, the Nyquist frequency Fn1 in the still image shooting mode is 1 / (2 × 280 [μs]) ≈1.8 [kHz], and the switching frequency is adjusted in a frequency range larger than this frequency. .

  Further, as shown in FIG. 7B, the gain F in the CDS 19 when the radiographic imaging apparatus 1 is in the continuous imaging mode has a frequency F of 1 / 31.6 [μs] ≈31.6 [ 0] when it is an integral multiple of [kHz]. Even in the continuous shooting mode, the gain g is less than 1, and the range is larger than the Nyquist frequency Fn2 (Fn2 = 1 / (2 × 50) = 10 [kHz]) (for example, the frequency range R2 in FIG. 7B). Etc.), the switching frequency is adjusted. In particular, by setting the switching frequency to a frequency at which the gain g becomes 0, that is, an integer multiple of 31.6 [kHz], noise at the switching frequency can be most effectively reduced.

FIG. 8 is a diagram illustrating an example of table data used for setting the switching frequency.
In this table data, the sampling interval (a1, a2,..., CDS 19 set in each of a plurality of imaging modes (still image shooting 1, 2, continuous shooting 1, 2,..., M) of the radiation image capturing apparatus 1 is performed. an) and the selection cycle (b1, b2,..., bn) of the scanning line 5 are associated with the optimum switching frequency of the DC-DC converter 24a determined by the above method. The table data is stored in the ROM of the control unit and is referred to by the CPU when the shooting mode is switched, and is used for setting the sampling interval, the selection cycle, and the switching frequency in the shooting mode after switching.

As an example in which two types of still image capturing modes (still image capturing 1 and 2) are provided as shown in FIG. 8, the radiation image capturing apparatus 1 is linked with the radiation irradiation start operation in an external radiation irradiation apparatus. Radiographic imaging device when the imaging operation is started (when linked) and when the radiation operation is detected and the imaging operation is started without linkage with an external radiation irradiation device (when not linked) There is a case where the operation setting of 1 is changed. In this example, the sampling interval of the CDS 19 and the selection cycle of the scanning line 5 are set to relatively large values compared with the time of cooperation in order to increase the sensitivity by increasing the interval for detecting radiation exposure at the time of non-cooperation. The
Further, as an example in which a plurality of continuous imaging modes (moving image shooting 1, 2,..., M) are provided, the operation setting of the radiographic image capturing apparatus 1 is set according to the size of the frame rate of the radiographic image generated at the time of continuous imaging May be different. In this example, the sampling interval of the CDS 19 and the selection cycle of the scanning line 5 are set to smaller values as the frame rate increases.
FIG. 8 shows an example of the table data, and the present invention is not limited to this. Any data may be used as long as at least two switching frequencies are determined. For example, the radiographic image capturing apparatus 1 may have two (for example, one still image capturing mode and one continuous image capturing mode) or any number of three or more. In addition, for the same shooting mode, two settings with different sampling intervals and at least a sampling interval are prepared according to parameters other than the shooting mode, and a switching frequency is determined for each setting. good.

  Subsequently, a control procedure by the control unit 22 of the radiographic image capturing process executed by the radiographic image capturing apparatus 1 will be described. Here, the processing at the time of cooperation described above will be described as an example.

FIG. 9 is a flowchart showing a control procedure of the radiographic image capturing process.
When the radiographic image capturing process is started, the control unit 22 receives an input of setting of an imaging mode (step S101). The input of the shooting mode setting is performed by an input operation using the changeover switch 26, for example.

  The control unit 22 determines whether or not the shooting mode setting is input (step S102). If it is determined that the shooting mode setting is not input ("NO" in step S102). ), The process proceeds to step S105.

  If it is determined that the shooting mode setting has been input ("YES" in step S102), the control unit 22 switches from the table data stored in the storage unit 23 to the switching corresponding to the switched shooting mode. A frequency is acquired (step S103). Moreover, the control part 22 changes the setting of the switching frequency in the DC-DC converter 24a, and operates the DC-DC converter 24a with the switching frequency acquired by step S103 (step S104).

  When the process of step S104 is completed, the control unit 22 determines whether or not a shooting start command is input from the external control device via the communication unit 30 (step S105). If the shooting start command is not input. If it is determined (“NO” in step S105), the process proceeds to step S101.

When it is determined that an imaging start command has been input (“YES” in step S105), the control unit 22 captures a radiographic image (step S106). That is, the control unit 22 completes the reset process of the radiation detection elements 7, supplies an off voltage to all the scanning lines 5, and accumulates charges corresponding to the radiation dose in the radiation detection elements 7. Subsequently, the control unit 22 executes the above-described reading process, extracts the pixel signal output from the radiation detection element 7, and generates image data of the radiation image. The control unit 22 stores the generated image data in the storage unit 23 according to the setting of the shooting mode, and outputs it to the outside via the communication unit 30.
In step S106, when imaging of the number of radiographic images corresponding to the setting of the imaging mode is completed, the control unit 22 ends the radiographic image imaging processing.

(Modification 1)
Next, the modification 1 of the said embodiment is demonstrated. In this modification, the table frequency is not referred to in the adjustment of the switching frequency, and the switching frequency is directly calculated from the sampling interval and the selection cycle of the scanning line 5 set corresponding to the imaging mode of the radiographic image capturing apparatus 1. Different from the above embodiment. Since the other points are the same as those in the above embodiment, differences from the above embodiment will be described below.

  FIG. 10 is a flowchart illustrating a control procedure of the radiographic image capturing process according to the present modification. In this flowchart, step S103 in the flowchart of FIG. 9 according to the above embodiment is changed to step S103a, and step S107 is added. Hereinafter, description of the same steps as those in FIG. 9 will be omitted.

  In the radiographic image capturing process of the present modification, when the setting of the imaging mode is input (“YES” in step S102), the control unit 22 gains the CDS 19 with respect to the current switching frequency in the imaging mode after switching. It is determined whether or not is 1 or more (step S107). That is, the control unit 22 obtains the gain g when Tc in the above equation (1) is the sampling interval related to the shooting mode after switching, and F in the equation (1) is the switching frequency according to the current setting. Whether or not is 1 or more. When it is determined that the gain g is less than 1 (“NO” in step S107), the control unit 22 shifts the processing to step S105.

  When it is determined that the gain g is 1 or more (“YES” in step S107), the control unit 22 selects the sampling interval and the scanning line 5 set corresponding to the imaging mode after switching. Based on the period, the switching frequency at which the gain g in the CDS 19 is less than 1 is calculated (step S103a). That is, the control unit 22 determines that the gain g is less than 1 and the Nyquist frequency related to the selection period of the scanning line 5 when Tc in the above equation (1) is the sampling interval related to the imaging mode after switching. The frequency F that is greater than is calculated. Typically, the minimum frequency F that satisfies the above-described conditions and at which the gain g is 0 is calculated. And the control part 22 changes the setting of the switching frequency in the DC-DC converter 24a, and operates the DC-DC converter 24a with the switching frequency calculated by step S103a (step S104).

(Modification 2)
Next, Modification 2 of the above embodiment will be described. In this modification, the gain of the CDS 19 with respect to the switching frequency is less than 1 and the switching frequency is higher than the Nyquist frequency related to the selection cycle of the scanning line 5 in all imaging modes that can be set in the radiographic image capturing apparatus 1. In addition, one switching frequency is set in advance, and the DC-DC converter 24a operates at the one switching frequency in each photographing mode. That is, the DC-DC converter 24a operates at the same switching frequency regardless of the operation mode of the CDS 19. Other points are the same as in the above embodiment.

  Here, the radiographic image capturing apparatus 1 has only one image capturing mode and one continuous image capturing mode, and the signal gain g in the CDS 19 in the still image capturing mode is represented by FIG. The case where the signal gain g in the CDS 19 in the continuous shooting mode is represented by FIG. 7B will be described as an example.

  In this case, a frequency range in which the Nyquist frequency Fn1 in the still image shooting mode and the Nyquist frequency Fn2 in the continuous shooting mode are larger than each other, and the gain g in the still image shooting mode and the continuous shooting mode is both less than 1. That is, the one switching frequency is set from the frequency ranges R1b and R1c in FIG. This switching frequency is set to a frequency at which the gain g in FIG. Alternatively, the frequency may be set such that the gains g in the still image shooting mode and the continuous shooting mode are equal.

As described above, the radiation image capturing apparatus 1 according to the present embodiment includes a plurality of radiation detection units 3 each having a plurality of two-dimensionally arranged radiation detection elements 7 that output pixel signals corresponding to incident radiation doses, and a plurality of radiation detection units 3. The CDS 19 that extracts the pixel signal output from the radiation detection element 7 by correlated double sampling and the configuration of the circuit to which the DC voltage is input are switched at a predetermined switching frequency, whereby the input DC voltage is converted to a predetermined power source. A period in which the CDS 19 is operated in a plurality of operation modes having different sampling intervals in the correlated double sampling, and the power supply circuit 24 that converts the voltage into voltage and outputs, and the CDS 19 is operating in any one of the plurality of operation modes. The control unit 22 controls the gain of the CDS 19 with respect to the switching frequency in the period to be less than 1.
According to such a configuration, the gain of the CDS 19 with respect to the switching frequency is less than 1 regardless of the sampling interval in the CDS 19, so that the power supply circuit 24 in the CDS 19 can be operated in any operating mode. The noise of the switching frequency caused by the operation can be reduced. As a result, the generation of noise in the radiographic image generated by the radiographic imaging device 1 can be more stably suppressed.

  The radiation detection unit 3 includes a plurality of scanning lines 5 extending in the first direction and a plurality of signal lines 6 extending in the second direction intersecting the first direction. Each of the detection elements 7 is connected to any one of the plurality of scanning lines 5 and any one of the plurality of signal lines 6, and the control unit 22 selects the plurality of scanning lines at a selection cycle corresponding to the operation mode of the CDS 19. By sequentially supplying an ON voltage to 5, the pixel signal is output from the radiation detection element 7 connected to the scanning line 5 to which the ON voltage is supplied to the signal line 6, and the CDS 19 is in one operation mode. The switching frequency in the operating period is higher than the Nyquist frequency related to the selection period corresponding to one operation mode. As a result, when the switching frequency noise is mixed (sampled) in the pixel signal in the selection cycle, aliasing occurs in the frequency component exceeding the Nyquist frequency, so the spatial frequency of the noise mixed in the pixel signal is reduced. The frequency can be suppressed below the frequency corresponding to the Nyquist frequency. As a result, it is possible to further reduce noise in the radiographic image and make it difficult to view.

  Further, the control unit 22 causes the power supply circuit 24 to switch the circuit configuration at the same switching frequency when the CDS 19 is operated in any of the plurality of operation modes. According to such a configuration, when the operation mode of the CDS 19 is switched in accordance with the switching of the imaging mode or the like, the generation of noise in the radiation image can be stably suppressed without changing the switching frequency in the power supply circuit 24. Therefore, generation of noise in the radiographic image can be suppressed by simpler control.

  In addition, when the operation mode of the CDS 19 is switched, the control unit 22 adjusts the switching frequency in the power supply circuit 24 so that the gain in the operation mode after switching is less than 1. Thereby, according to switching of the operation mode of the CDS 19, the power supply circuit 24 can be operated at an appropriate switching frequency capable of reducing noise. Therefore, even when the CDS 19 operates at a number of different sampling intervals in a plurality of operation modes, the generation of noise in the radiation image can be suppressed stably.

  Further, when switching the operation mode of the CDS 19, the control unit 22 has a gain in the operation mode after switching of less than 1, and the switching frequency is higher than the Nyquist frequency related to the selection cycle corresponding to the operation mode after switching. The switching frequency in the power supply circuit 24 is adjusted so as to increase. According to such a configuration, even when the CDS 19 operates at a number of different sampling intervals in a plurality of operation modes, it is possible to stably reduce noise in the radiographic image and make it difficult to view.

  Further, the storage unit 23 stores a plurality of predetermined switching frequencies associated with a plurality of operation modes, and the control unit 22 refers to the storage unit 23 when switching the operation mode of the CDS 19. A switching frequency associated with the operation mode after switching is selected. Thereby, when the operation mode of the CDS 19 is switched, it is possible to operate the power supply circuit 24 by selecting an appropriate switching frequency that can reduce noise by a simple process.

  Further, the control unit 22 calculates a switching frequency at which the gain in the operation mode after switching is less than 1 based on the sampling interval in the operation mode after switching. Thereby, an appropriate switching frequency that can reduce noise can be set according to the sampling interval in the CDS 19.

  Further, the control unit 22 calculates the gain in the operation mode after switching with respect to the switching frequency in the period in which the CDS 19 is operating in the operation mode before switching, and when the calculated gain is 1 or more, A switching frequency at which the gain in the operation mode after switching is less than 1 is calculated. According to this, the switching frequency is adjusted only when the noise of the switching frequency is not reduced in the CDS 19 that operates in the operation mode after switching. Therefore, the adjustment frequency of the switching frequency can be reduced.

  Further, the control unit 22 adjusts the switching frequency so that the product of the sampling interval and the switching frequency in the operation mode after switching approaches an integer. Thereby, the gain of the switching frequency can be brought close to 0 in the CDS 19 that operates in the operation mode after switching. As a result, generation of noise in the radiation image can be more effectively suppressed.

  Further, the control unit 22 calculates a switching frequency corresponding to the operation mode after switching based on the sampling interval in the operation mode after switching and the selection cycle corresponding to the operation mode after switching. Thus, an appropriate switching frequency that can reduce noise can be set according to the sampling interval in the CDS 19 and the selection cycle of the scanning line 5.

  In addition, the control unit 22 generates radiographic image data based on the pixel signal extraction result by the CDS 19 (image data generation unit), and in the still image capturing mode that generates the radiographic image data of the still image, In the continuous imaging mode in which the CDS 19 is operated in the predetermined first operation mode among the operation modes and the image data of the radiation image is continuously generated, the sampling interval of the plurality of operation modes is the sampling in the first operation mode. When the CDS 19 is operated in the second operation mode smaller than the interval and the still image shooting mode and the continuous shooting mode are switched, the operation mode of the CDS 19 is switched. With such a configuration, it is possible to stably suppress the generation of noise in the radiation image in both the still image shooting mode and the continuous shooting mode.

Note that the present invention is not limited to the above-described embodiments and modifications, and various modifications can be made.
For example, in the above-described embodiment and each modification, the switching frequency is set so that the gain g of the CDS 19 with respect to the switching frequency is less than 1. However, the present invention is not limited to this, and the predetermined frequency less than 1 is used. The switching frequency may be set to be equal to or less than the upper limit gain. Such an upper limit gain is not particularly limited, but can be set to “0.3” that can reduce noise to 30% or less, for example.

  Further, in the above embodiment and each modification, the switching frequency is set such that the gain g of the CDS 19 with respect to the switching frequency is equal to or lower than the predetermined upper limit gain and is higher than the Nyquist frequency related to the selection cycle of the scanning line 5. However, the present invention is not limited to this. For example, the switching frequency may be set considering only the condition that the gain g of the CDS 19 with respect to the switching frequency is equal to or less than a predetermined upper limit gain.

  Further, in the above embodiment and each modification, the sensor panel is housed in the housing and can be carried, and the so-called portable radiographic imaging device has been described as an example. However, the present invention is not limited to this. For example, the present invention can also be applied to a radiographic imaging apparatus that is installed in an imaging room and formed integrally with a support base or the like.

  Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, and includes the scope of the invention described in the claims and equivalents thereof. .

DESCRIPTION OF SYMBOLS 1 Radiation imaging device 3 Radiation detection part 5 Scan line 6 Signal line 7 Radiation detection element 8 TFT
14 Power supply circuit (voltage converter)
15 Scanning Line Driving Circuit 17 Reading Circuit 18 Amplifying Circuit 19 CDS (Signal Extraction Unit)
20 Analog multiplexer 21 A / D converter 22 Control unit (image data generation unit)
23 Storage Unit 24 Power Supply Circuit 24a DC-DC Converter 40 External Power Supply

Claims (11)

A radiation detector having a plurality of two-dimensionally arranged radiation detection elements each outputting a pixel signal corresponding to an incident radiation dose;
A signal extraction unit for extracting the pixel signals output from the plurality of radiation detection elements by correlated double sampling;
A voltage converter that converts the input DC voltage into a predetermined power supply voltage by switching the configuration of the circuit to which the DC voltage is input at a predetermined switching frequency; and
The signal extraction unit is operated in a plurality of operation modes having different sampling intervals in the correlated double sampling, and the signal extraction unit is operated in any operation mode of the plurality of operation modes. A control unit for controlling the gain of the signal extraction unit with respect to a switching frequency to be equal to or lower than a predetermined upper limit gain smaller than 1;
A radiographic imaging apparatus comprising: The radiation detection unit includes a plurality of scanning lines extending in a first direction and a plurality of signal lines extending in a second direction intersecting the first direction,
Each of the plurality of radiation detection elements is connected to any one of the plurality of scanning lines and any one of the plurality of signal lines,
The controller is
The radiation detection element connected to the scanning line to which the selection signal is supplied by sequentially supplying a predetermined selection signal to the plurality of scanning lines at a selection period corresponding to an operation mode of the signal extraction unit. Output the pixel signal to the signal line from
The switching frequency during a period in which the signal extraction unit is operating in the one operation mode is greater than a Nyquist frequency related to the selection period corresponding to the one operation mode. Radiographic imaging device.   The control unit causes the voltage conversion unit to switch the configuration of the circuit at the same switching frequency when the signal extraction unit is operated in any of the plurality of operation modes. The radiographic imaging apparatus according to claim 1 or 2, characterized in that   When the operation mode of the signal extraction unit is switched, the control unit adjusts the switching frequency in the voltage conversion unit so that the gain in the operation mode after switching is equal to or lower than the upper limit gain. The radiographic imaging apparatus according to claim 1 or 2.   When the control unit switches the operation mode of the signal extraction unit, the gain in the operation mode after switching is less than or equal to the upper limit gain, and the switching frequency corresponds to the operation mode after switching The radiographic image capturing apparatus according to claim 2, wherein the switching frequency in the voltage conversion unit is adjusted to be higher than a Nyquist frequency related to the period. A storage unit that stores a plurality of the switching frequencies that are predetermined in association with the plurality of operation modes;
The said control part selects the said switching frequency matched with the said operation mode after the switching with reference to the said memory | storage part, when switching the operation mode of the said signal extraction part. Or the radiographic imaging apparatus of 5.   The said control part calculates the said switching frequency from which the said gain in the said operation mode after the said switching becomes below the said upper limit gain based on the said sampling interval in the said operation mode after the switching. 5. The radiographic image capturing apparatus according to 5.   The control unit calculates the gain in the operation mode after switching with respect to the switching frequency in a period in which the signal extraction unit is operating in the operation mode before switching, and the calculated gain is the upper limit gain. The radiographic imaging apparatus according to claim 7, wherein the switching frequency at which the gain in the operation mode after switching is equal to or lower than the upper limit gain is calculated when the switching frequency is greater than the upper limit gain.   The radiographic imaging according to claim 7 or 8, wherein the control unit adjusts the switching frequency so that a product of the sampling interval and the switching frequency in the operation mode after switching approaches an integer. apparatus.   The control unit calculates the switching frequency corresponding to the operation mode after switching based on the sampling interval in the operation mode after switching and the selection cycle corresponding to the operation mode after switching. The radiographic imaging device according to claim 5, wherein An image data generation unit that generates image data of a radiographic image based on the extraction result of the pixel signal by the signal extraction unit;
The controller is
In the still image shooting mode in which the image data generating unit generates radiographic image data of a still image, the signal extraction unit is operated in a predetermined first operation mode among the plurality of operation modes, and the image data generation is performed. In the continuous imaging mode in which the image data of the radiation image is continuously generated by the unit, the signal extraction is performed in the second operation mode in which the sampling interval is smaller than the sampling interval in the first operation mode among the plurality of operation modes. Operating part
The radiographic image capturing apparatus according to claim 1, wherein an operation mode of the signal extraction unit is switched when switching between the still image capturing mode and the continuous capturing mode.

Images