JP2022107783A - Radiographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in image quality due to a deviation in synchronization between a radiation irradiation period in a radiation source and a charge accumulation period in a radiographic apparatus.

SOLUTION: A control unit of an FPD cassette executes first processing for synchronizing a radiation irradiation period in which a radiation source emits a radiation ray with an accumulation period in which accumulation is made by radiation detection elements before the emission of the radiation source, and then executes second processing for adjusting a deviation in the synchronization on the basis of a charge amount accumulated in at least some of the plurality of radiation detection elements.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a radiation imaging apparatus.

In recent years, portable radiation detection elements that accumulate electric charges according to the radiation emitted from the radiation source and transmitted through the subject are arranged in a two-dimensional pattern, and the electric charges accumulated in the radiation detection elements are read out to generate image data. A radiation imaging system using a radiation imaging device (FPD: Flat Panel Detector) is known. In such a radiography system, a period during which radiation is emitted from the radiation source (a radiation exposure period) is performed so that the radiation source emits radiation during a charge accumulation period (hereinafter referred to as an accumulation period) in the radiography apparatus. ) and the accumulation period in the radiographic apparatus must be synchronized.

However, when wireless communication is used between the radiation imaging apparatus and the radiation control apparatus that controls the radiation source, there is a problem with real-time performance. Synchronization may not be achieved if synchronous communication is performed between the radiation control apparatus and the radiation imaging apparatus for each irradiation of radiation when capturing a moving image in which a plurality of frame images are obtained by using the radiation control apparatus.

Therefore, for example, in Patent Document 1, a timer unit for measuring time is provided in a console as a radiation control apparatus for giving imaging instructions, and an electronic cassette incorporating an FPD measures time synchronized with the timer unit of the console. When the exposure start time predetermined by the console is reached, radiation is emitted from the radiation source for a predetermined time, and the predetermined time elapses from the exposure start time by the electronic cassette. A technique for generating image data representing a radiographic image by reading the electric charges accumulated in the FPD after the radiation has been performed is described.

Japanese Unexamined Patent Application Publication No. 2010-81960

However, the portable radiographic apparatus is often used in an environment where heat is likely to rise, such as between a patient and a bed, and there are cases where sufficient heat dissipation cannot be ensured. On the other hand, the radiation control apparatus naturally dissipates enough heat even during operation, and the influence of heat generation can be ignored. Therefore, even if the clocks of the radiation control device and the radiation imaging device are synchronized in advance, the radiation irradiation period and the charge accumulation period may differ due to the influence of fluctuations in the operating frequency of the oscillator due to temperature rise on the radiation imaging device side. may be out of sync.
Further, when the radiation output emitted from the radiation source fluctuates, the synchronization between the radiation irradiation period and the charge accumulation period may be out of sync.

If, for example, radiation is irradiated during the readout period after the end of the accumulation period due to a shift in synchronization during moving image shooting that generates a plurality of frame images, charges corresponding to the radiation irradiated during the readout period will remain. , image quality deterioration occurs in the next frame image.

SUMMARY OF THE INVENTION An object of the present invention is to suppress deterioration in image quality due to a synchronization deviation between a radiation irradiation period in a radiation source and a charge accumulation period in a radiation imaging apparatus.

In order to solve the above problems, the present invention
a detection portion including a plurality of radiation detection elements that accumulate charge upon irradiation by a radiation source;
a control unit configured to generate a plurality of frame images by repeatedly performing accumulation by the radiation detection elements and reading out of the accumulated charges from the radiation detection elements,
The control unit performs a first process for synchronizing a radiation irradiation period during which the radiation source emits radiation and an accumulation period during which the radiation detecting element accumulates the radiation, before the irradiation with the radiation source. A second process for adjusting the synchronization deviation is performed based on the amount of charge accumulated in at least a part of the radiation detection element.

According to the present invention, it is possible to suppress deterioration in image quality due to the synchronization deviation between the radiation irradiation period in the radiation source and the charge accumulation period in the radiation imaging apparatus.

1 is a diagram showing an example of the overall configuration of a radiation imaging system according to this embodiment; FIG. 2 is a block diagram showing the functional configuration of a radiation control device; FIG. 3 is a block diagram showing the functional configuration of the FPD cassette in the first and second embodiments; FIG. FIG. 10 is a diagram showing an example of the operation of the FPD cassette, readout charge amount, and radiation tube voltage when line L0 (Line0) is subsequently read out again after reading out the charges of the radiation detection elements for frame image generation. An example of the operation of the FPD cassette, the amount of readout charge, and the radiation tube voltage when line L0 (Line0) and line L1 (Line1) are read out again after completion of readout of the charge of the radiation detection element for frame image generation is shown. It is a diagram. FIG. 11 is a block diagram showing the functional configuration of an FPD cassette according to the third embodiment; FIG. FIG. 7 is a block diagram showing the flow of information relating to time measurement and adjustment of the control unit of FIG. 6; FIG. 7 is a flowchart showing clock adjustment processing executed by the control unit of FIG. 6; FIG.

<First embodiment>
(Configuration of radiation imaging system 100)
First, the configuration of the first embodiment according to the present invention will be described.
FIG. 1 shows an example of the overall configuration of a radiation imaging system 100 according to this embodiment.
The radiography system 100 is, for example, a round system for radiography of a patient who is difficult to move, and includes a radiation control device 1, a radiation source 2, and an FPD (Flat Panel Detector).
) cassette 3. The radiation control apparatus 1 has wheels and is configured as a mobile medical vehicle.

As shown in FIG. 1, the radiation imaging system 100 is brought into an operating room, an intensive care unit, a hospital room Rc, or the like, and the FPD cassette 3 is placed, for example, between the subject H lying on the bed B and the bed B, or In this system, a moving image of a subject H is captured by irradiating radiation from a radiation source 2 while being inserted into an insertion opening provided on the opposite side of a bed B to which the subject H is not exposed. In the present embodiment, the moving image capturing means repeatedly irradiating the object H with pulsed radiation such as X-rays at predetermined time intervals (pulse irradiation) in response to one image capturing operation (operation of the exposure switch 102a). ) to obtain moving images. A series of images obtained by moving image shooting is called a moving image. Also, each of the plurality of images forming the moving image is called a frame image.

Each device constituting the radiation imaging system 100 will be described below.
The radiation control device 1 is a device that controls the radiation source 2 based on input radiation irradiation conditions to irradiate radiation, and as shown in FIG. It is composed of a unit 104, a driving unit 105, a wireless communication unit 106, a crystal oscillator 107, and the like.

The control unit 101 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The CPU of the control unit 101 reads the system program and various processing programs stored in the storage unit 104 according to the operation of the operation unit 102, expands them in the RAM, and executes the radiation control apparatus 1 according to the expanded programs. Controls the operation of each part.

The operation unit 102 has a touch panel or the like in which transparent electrodes are arranged in a grid pattern so as to cover the surface of the display unit 103. The operation unit 102 detects a position pressed by a finger or a touch pen, and uses the position information as operation information. output to 101.
The operation unit 102 also includes an exposure switch 102a for the operator to instruct radiation exposure. The exposure switch 102a is a two-stage switch.

The display unit 103 is configured by a monitor such as an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube), and performs display according to instructions of display signals input from the control unit 101 .

The storage unit 104 is configured by a nonvolatile semiconductor memory, hard disk, or the like. The storage unit 104 stores various programs executed by the control unit 101, parameters necessary for executing processing by the programs, or data such as processing results.

The drive unit 105 is a circuit that drives the tube of the radiation source 2 . The drive unit 105 and the radiation source 2 are connected via a cable.
The wireless communication unit 106 has an antenna 108 and wirelessly communicates with an external device such as the FPD cassette 3 .
The crystal oscillator 107 is an element that oscillates by a piezoelectric effect, and its oscillation frequency is input to the CPU of the control unit 101 . The control unit 101 measures time based on the oscillation frequency input from the crystal oscillator 107 .

The radiation source 2 is capable of pulse irradiation, and irradiates the subject H with radiation (X-rays) under the control of the radiation control device 1 .

The FPD cassette 3 is a portable radiation imaging apparatus for moving image imaging. Hereinafter, the FPD cassette 3 will be described as a so-called indirect type that includes a scintillator or the like, converts the irradiated radiation into light of other wavelengths such as visible light with the scintillator, and obtains image data with the radiation detection element. A so-called direct type, in which radiation is directly detected by a radiation detecting element without passing through a radiation detecting element, may be employed.

FIG. 3 is a block diagram showing an equivalent circuit of the FPD cassette 3. As shown in FIG. As shown in FIG. 3, in the FPD cassette 3, a plurality of radiation detection elements 7 are arranged two-dimensionally (in a matrix) on a sensor substrate (not shown) (detection section). Each radiation detection element 7 accumulates electric charge according to the dose of irradiated radiation. A bias line 9 is connected to each radiation detection element 7 , and the bias line 9 is connected to a wire connection 10 . The connection 10 is connected to a bias power supply 14, and a reverse bias voltage is applied from the bias power supply 14 to each radiation detecting element 7 through the bias line 9 and the like.

A thin film transistor (hereinafter referred to as a TFT) 8 is connected to each radiation detection element 7 as a switching element, and the TFT 8 is connected to a signal line 6 . Further, in the scanning driving section 15, the ON voltage and the OFF voltage supplied from the power supply circuit 15a through the wiring 15c are switched by the gate driver 15b and applied to the respective lines L0 to Lx of the scanning lines 5. there is Each TFT 8 is turned on when an ON voltage is applied via the scanning line 5 , and causes the charge accumulated in the radiation detecting element 7 to be discharged to the signal line 6 . When an off-voltage is applied to the radiation detecting element 7, it turns off, cuts off the conduction between the radiation detecting element 7 and the signal line 6, and accumulates the charges generated in the radiation detecting element 7 in the radiation detecting element 7. It's becoming Each radiation detection element 7 and the TFT 8 connected thereto constitute a pixel.

A plurality of readout circuits 17 are provided in the readout IC 16 , and signal lines 6 are connected to the respective readout circuits 17 . When the image data is read out, when charges are emitted from the radiation detection element 7, the charges flow into the readout circuit 17 via the signal line 6, and the amplifier circuit 18 adjusts the amount of A voltage value is output. A correlated double sampling circuit (denoted as “CDS” in FIG. 3) 19 reads out the voltage value output from the amplifier circuit 18 as analog image data and outputs it to the downstream side. The output image data is sequentially transmitted to the A/D converter 20 via the analog multiplexer 21, is sequentially converted into digital image data by the A/D converter 20, and is output to the storage unit 23. They are saved sequentially.

The control unit 22 is a computer connected to a bus with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input/output interface, etc., which are not shown, or an FPGA (Field Programmable Gate Array). It is configured. It may be composed of a dedicated control circuit. The control unit 22 is connected to a storage unit 23 composed of SRAM (Static RAM), SDRAM (Synchronous DRAM), NAND flash memory, etc., and is connected to an external device such as the radiation control apparatus 1 via an antenna 29. A wireless communication unit 30 is connected to wirelessly communicate with the device. Since communication between the radiation control apparatus 1 and the FPD cassette 3 is performed wirelessly, there is no need to connect the radiation control apparatus 1 and the FPD cassette 3 with a cable or the like during imaging in rounds, which is convenient.

Also connected to the control unit 22 are a built-in power supply 24 and the like that supply necessary power to each functional unit such as the scanning drive unit 15 , readout circuit 17 , storage unit 23 , bias power supply 14 , and the like. Then, the control unit 22 controls the operations of the scanning driving unit 15, the readout circuit 17, and the like as described above to cause each radiation detection element 7 to accumulate charges corresponding to the radiation dose, or to signal the accumulated charges. The charge is discharged to the line 6, and the discharged charge is read out as image data by a readout circuit 17 or the like.

Furthermore, a crystal oscillator 25 is connected to the controller 22 . The crystal oscillator 25 is an element that oscillates by a piezoelectric effect, and its oscillation frequency is input to the CPU of the control section 22 . The control unit 22 measures time based on the oscillation frequency input from the crystal oscillator 25 .

The FPD cassette 3 may be brought by a radiographer such as a radiological technologist, but the FPD cassette 3 is relatively heavy and may break or malfunction if dropped. It can be inserted into a cassette pocket 11 provided in the apparatus 1 and carried.

(Operation of radiation imaging system 100)
Next, an imaging operation in the radiation imaging system 100 will be described.
First, the imaging operator prepares for imaging. For example, the radiation irradiation conditions are input (set) via the operation unit 102 in the radiation control apparatus 1 . Radiation irradiation conditions include, for example, tube current, tube voltage, frame rate (number of frame images captured per unit time (1 second)), total imaging time or total number of captured frame images per imaging, additional filter type, radiation exposure time per frame image, and the like. Further, the imaging operator positions the subject H, the radiation source 2 and the FPD cassette 3 .

When the imaging preparation is completed, the imaging operator presses the first stage switch of the exposure switch 102a. When the first stage switch of the exposure switch 102a is pressed, the control unit 101 of the radiation control apparatus 1 activates the radiation source 2, and transmits an activation signal to the FPD cassette 3 via the antenna 108 by the wireless communication unit 106. Send. When the controller 22 of the FPD cassette 3 receives the activation signal from the wireless communication unit 30, the gate driver 15b (see FIG. 3) of the scan drive unit 15 sequentially applies an ON voltage to each of the lines L1 to Lx of the scan lines 5. Then, the reset processing of the radiation detection element 7 is performed to remove the charge remaining in the radiation detection element 7 from the inside of the radiation detection element 7 by, for example, discharging the charge remaining in the radiation detection element 7 to the signal line 6 . When the reset process is completed, the control unit 22 applies an off voltage from the gate driver 15b to each of the lines L1 to Lx of the scanning lines 5 to shift to the charge accumulation state. At the same time, the wireless communication unit 30 transmits an interlock release signal to the radiation control apparatus 1 .

When the second-stage switch of the exposure switch 102a is pressed, the control unit 101 of the radiation control apparatus 1 determines whether or not the wireless communication unit 106 has received an interlock release signal from the FPD cassette 3, and determines whether or not the signal is received. If it is determined that the interlock release signal is not received, it waits for the reception of the interlock release signal. When the interlock release signal is received, the control unit 101 starts reading out the radiation irradiation time from the radiation source 2 and the FPD cassette 3 for generating each frame image for moving image capturing based on the set radiation irradiation conditions. Then, the radio communication unit 106 transmits the reading start time to the FPD cassette 3 . Then, based on the calculated radiation irradiation time, the control unit 101 causes the radiation source 2 to perform radiation irradiation (pulse irradiation) under the radiation irradiation conditions set by the driving unit 105 .

In the FPD cassette 3, when the readout start time transmitted from the radiation control apparatus 1 arrives, the control unit 22 causes the gate driver 15b to sequentially apply the ON voltage to the lines L0 to Lx of the scanning lines 5, as described above. Read processing of the image data of the frame image is performed. When the reading process for the line Lx is completed, the control unit 22 causes the charge of the radiation detection element 7 for one line to be read again, and determines whether the charge amount of the line that has been read again is equal to or greater than a predetermined threshold value. to decide. Note that a representative value (for example, an average value) of the charge amounts of a plurality of pixels on the line on which rereading is performed may be compared with a predetermined threshold value, or the charge amount of one pixel may be compared with a predetermined threshold value. may

FIG. 4(a) shows the operation of the FPD cassette 3, the amount of read charge, and the radiation tube voltage when the first embodiment is normal (that is, when there is no synchronization deviation between the irradiation period and the accumulation period). . FIG. 4(b) shows the operation of the FPD cassette 3, the amount of read charge, and the radiation tube voltage when the radiation irradiation period and the accumulation period are out of synchronization (delay in the radiation irradiation period). In FIGS. 4A and 4B, after the reading of the charges of the radiation detection elements 7 of each line L0 to Lx is finished, the charges of the radiation detection element 7 of the line L0 (Line0) are read again. is shown.

As shown in FIG. 4A, when there is no synchronization deviation between the radiation irradiation period and the accumulation period, the charge of the radiation detection element 7 of the re-read line L0 is approximately zero. However, as shown in FIG. 4B, for example, when the time measured by the radiation control apparatus 1 is later than the time measured by the FPD cassette 3, or when the radiation output of the radiation source 2 fluctuates. If, for example, the end of the radiation irradiation period is delayed and the readout period starts, the charge corresponding to the radiation irradiated during the readout period is accumulated in the radiation detection element 7. If the charge of the radiation detection element 7 of L0 is re-read, the charge equal to or higher than the predetermined threshold is detected.

When determining that the charge amount of the re-read line is not equal to or greater than the predetermined threshold value, the control unit 22 determines that there is no synchronization deviation between the irradiation period and the accumulation period, and continues the imaging sequence. If it is determined that the re-read charge amount of the line is equal to or greater than the predetermined threshold value, the control unit 22 determines that synchronization deviation has occurred between the radiation irradiation period and the accumulation period, and determines that the re-read charge amount of the line Based on this, the imaging sequence is continued after adjusting the synchronization deviation.

Here, FIG. 4B shows an example in which the radiation irradiation period is delayed with respect to the accumulation period, but the radiation irradiation period may be earlier than the accumulation period. , the amount of charge in the re-read line (or pixel) is greater than or equal to a predetermined value. However, whether the radiation irradiation period tends to be earlier or later than the accumulation period is known in advance from the characteristics of the crystal oscillators of the radiation control device 1 and the FPD cassette 3 and the radiation output characteristics of the radiation source 2. often

Therefore, for example, when it is known that the radiation irradiation period tends to be delayed with respect to the accumulation period, the control unit 22 performs accumulation for generation of the next frame image as shown in FIG. 4(b). The period is extended or a waiting time is provided before the accumulation start timing for the next frame image to adjust the synchronization deviation between the irradiation period and the accumulation period. The reading start time for each frame image that has not yet been captured is delayed from the time notified from the radiation control apparatus 1 by the extension of the accumulation time or the waiting time.
Also, for example, if it is known that the radiation irradiation period tends to be shorter than the accumulation period, the control unit 22 shortens the accumulation period for the next frame image. The readout start time for each frame image that has not yet been captured is advanced from the time notified from the radiation control apparatus 1 by the shortened accumulation time.
The control unit 22 repeatedly executes the above-described accumulation and readout processing for all frame images, and generates a plurality of frame images that constitute the moving image of the subject H. FIG.

In this manner, when the read start time transmitted from the radiation control apparatus 1 arrives, the control unit 22 of the FPD cassette 3 causes the gate driver 15b to sequentially apply the ON voltage to the lines L0 to Lx of the scanning lines 5, thereby Image data is read out as described above. When the readout process for the line Lx is completed, the control unit 22 rereads the charges of the radiation detection elements 7 for one line, and determines the radiation irradiation period and accumulation period based on the charge amount of the reread line. A determination is made as to whether or not there is a synchronization deviation, and if there is a synchronization deviation, the synchronization deviation is adjusted. Therefore, it is possible to suppress deterioration in image quality due to the synchronization deviation between the radiation irradiation period and the accumulation period.

<Second embodiment>
Next, a second embodiment will be described.
Since the configuration of the radiation imaging system according to the second embodiment is the same as that of the radiation imaging system 100 described in the first embodiment, the description is cited and the operation of the second embodiment will be described.

In the first embodiment, every time the readout of the charges from the radiation detection elements 7 for generating each frame image is completed, the charges of the radiation detection elements 7 for one line are read out again, and the charges are read out again. A case has been described in which synchronization deviation between the radiation irradiation period and the accumulation period is adjusted based on the charge amount of the radiation detection element 7 for one line. In the second embodiment, every time the readout of charges from the radiation detection elements 7 for generating each frame image is completed, the charge amounts of the radiation detection elements 7 for a plurality of lines are read out again. A case will be described in which synchronization deviation is adjusted based on the amount of charge of the radiation detection elements 7 of a plurality of lines obtained. The operation of the radiation imaging system 100 until the reading start time transmitted from the radiation control apparatus 1 arrives in the FPD cassette 3 is the same as that described in the first embodiment, so the description will be used.

In the FPD cassette 3, when the readout start time transmitted from the radiation control apparatus 1 arrives, the control unit 22 causes the gate driver 15b to sequentially apply the ON voltage to each line L0 to Lx of the scanning lines 5, as described above. Read processing of the image data of the frame image is performed. When the readout process for the line Lx is completed, the control unit 22 rereads the charges from the radiation detection elements 7 of the plurality of lines, and determines whether or not the reread charge amount of each line is equal to or greater than a predetermined threshold value. do. Note that a representative value (for example, an average value) of the charge amounts of a plurality of pixels on the line on which rereading is performed may be compared with a predetermined threshold value, or the charge amount of one pixel may be compared with a predetermined threshold value. may

FIG. 5(a) shows the operation of the FPD cassette 3, the amount of read charge, and the radiation tube voltage when the second embodiment is normal (that is, when there is no synchronization deviation between the irradiation period and the accumulation period). . FIG. 5B shows the operation and readout of the FPD cassette 3 when there is a synchronization deviation between the radiation irradiation period and the accumulation period (when the radiation irradiation period is earlier than the accumulation time) in the second embodiment. It indicates the amount of electric charge and the radiation tube voltage. 5(a) and 5(b) show an example in which charges are read again from the radiation detection elements 7 of lines L0 and L1 (Line0, Line1) after the completion of readout of each line L0 to Lx. showing.

As shown in FIG. 5A, when there is no synchronization deviation between the radiation irradiation period and the accumulation period, the charge amount of the radiation detection elements 7 of the re-read lines L0 and L1 is approximately zero. However, as shown in FIG. 5B, for example, when the time measured by the radiation control apparatus 1 is earlier than the time measured by the FPD cassette 3, or when the radiation output of the radiation source 2 fluctuates If the start of the radiation irradiation period is delayed, such as when this occurs, charges are already accumulated in the radiation detecting element 7 at the start of the accumulation time for generating the next frame image. Further, as shown in FIG. 4B, when the radiation irradiation period is shifted behind the accumulation period and overlaps with the readout period, the charges corresponding to the radiation irradiated during the readout period are stored in the radiation detection elements. 7 is accumulated. Therefore, by rereading charges from the radiation detection elements 7 of a plurality of lines, for example, lines L0 and L1, charges equal to or greater than a predetermined threshold value are detected.

If it is determined that the re-read charge amounts of the multiple lines are not equal to or greater than the predetermined threshold value, the control unit 22 determines that there is no synchronization deviation between the radiation irradiation period and the accumulation period, and continues the imaging sequence.
If the control unit 22 determines that the re-read charge amounts of the multiple lines are equal to or greater than the predetermined threshold value, the control unit 22 delays the radiation irradiation period from the accumulation period based on the re-read charge amounts of the multiple lines. Based on the result of the determination, the synchronization of the irradiation period and the accumulation period is adjusted, and after the adjustment, the imaging sequence is continued.

Specifically, when the charge amount of a line read later than the line read earlier is larger than the charge amount of a plurality of re-read lines (for example, the case shown in FIG. 5B), the control unit 22 By judging that the radiation irradiation period is earlier than the accumulation period, and shortening the accumulation period for generating the next frame image, the synchronization deviation between the radiation irradiation period and the accumulation period is adjusted. The readout start time for each frame image that has not yet been captured is advanced from the time notified from the radiation control apparatus 1 by the shortened accumulation time.
When the charge amount of the line read later than the line read earlier is smaller than the charge amount of the lines read out again, the control unit 22 determines that the radiation irradiation period is delayed with respect to the accumulation period, Either the accumulation period for generating the next frame image is extended, or a waiting time is provided before the accumulation start timing for generating the next frame image to adjust the synchronization deviation between the irradiation period and the accumulation period. The reading start time for each frame image that has not yet been captured is delayed from the time notified from the radiation control apparatus 1 by the extension of the accumulation time or the waiting time.
The control unit 22 repeatedly performs accumulation and readout processing for all frame images, and generates a plurality of frame images that form a moving image of the subject H. FIG.

In this way, when the readout start time transmitted from the radiation control apparatus 1 arrives, the control unit 22 of the FPD cassette 3 causes the gate driver 15b to sequentially apply the on-voltage to the lines L0 to Lx of the scanning lines 5, thereby performing a frame operation. Read processing of the image data of the image is performed. When the readout process for the line Lx is completed, the control unit 22 rereads the radiation detection elements 7 of the multiple lines, and determines the synchronization deviation between the radiation irradiation period and the accumulation period based on the re-read charge amounts of the multiple lines. is occurring. If it is determined that synchronization deviation has occurred, the control unit 22 determines whether the accumulation period is delayed or accelerated with respect to the radiation irradiation period, based on the re-read electric charge amounts of the multiple lines. , based on the determination result, adjust the synchronization deviation.
Therefore, in the second embodiment, it is possible to determine whether the accumulation period is delayed or advanced with respect to the radiation irradiation period for each frame, and to adjust the synchronization deviation. Even if the direction is not constant, it is possible to suppress deterioration in image quality due to the synchronization deviation between the irradiation period and the accumulation period.

<Third Embodiment>
Next, a third embodiment of the invention will be described.
FIG. 6 is a block diagram showing an equivalent circuit of the FPD cassette 3A in the third embodiment. As shown in FIG. 6, the FPD cassette 3A in the third embodiment has, in addition to the configuration of the FPD cassette 3 described in the first embodiment, a temperature sensor for detecting the temperature inside the housing of the FPD cassette 3A. and an A/D converter 32 that converts the voltage output from the temperature sensor 31 into a digital voltage value and outputs the digital voltage value to the control unit 22 .

The storage unit 23 also stores a clock adjustment table 231 .
The frequency characteristic of the oscillation of the crystal oscillator 25 with respect to temperature is represented by an upward convex quadratic curve with 25.degree. Based on the frequency characteristics of the crystal oscillator 25, the clock adjustment table 231 sets a reference temperature of 25° C. at which the operating frequency of the crystal oscillator 25 is the highest, a difference temperature from the reference temperature, and a temperature difference at the difference temperature. It is a table in which the number of oscillations of the crystal oscillator 25 corresponding to one unit time (for example, one second) is associated with each other.

Other configurations of the FPD cassette 3A are the same as those of the FPD cassette 3 described in the first embodiment, so the description is incorporated.

Next, operation of the third embodiment will be described.
FIG. 7 is a block diagram showing the flow of information relating to time measurement and adjustment by the control unit 22. As shown in FIG.
As shown in FIG. 7, the number of oscillations of the crystal oscillator 25 is input to a timer 222 within the CPU 221 of the control section 22 . A register in the timer 222 is set with the number of oscillations (count setting value 222a) of the crystal oscillator 25 corresponding to one unit time (for example, one second), and the timer 222 counts the set number of oscillations. A clock is output to the CPU core 223 each time. The CPU core 223 measures time based on the clock from the timer 222 . It should be noted that, when the facility is introduced, the clock is calibrated at a predetermined temperature (that is, 25° C.) at which the operating frequency of the crystal oscillator 25 is maximized. The same applies to time measurement and calibration of the radiation control apparatus 1 .

However, the FPD cassette 3A is often used in an environment where the temperature is likely to rise, such as between a patient lying on a bed and a sheet, and there are cases where sufficient heat dissipation cannot be ensured. On the other hand, the radiation control apparatus 1 naturally dissipates enough heat for its own heat generation even during operation, and the influence of heat generation can be ignored. Therefore, even if the times of the radiation control apparatus 1 and the FPD cassette 3A are synchronized in advance, the times of the two may deviate due to the influence of fluctuations in the operating frequency of the crystal oscillator 25 due to the temperature rise of the FPD cassette 3A. There are cases.

Therefore, in the third embodiment, the control unit 22 executes clock adjustment processing (see FIG. 8) immediately before shooting. For example, when depression of the first stage switch of the exposure switch 102a is detected in the radiation control apparatus 1 and an activation signal is transmitted to the FPD cassette 3A via the antenna 108 (when the wireless communication unit 30 receives the activation signal) , the control unit 22 of the FPD cassette 3A performs the reset process and the clock adjustment process shown in FIG.

In the clock adjustment process, the control unit 22 first acquires a temperature value from the temperature sensor 31, and determines whether the acquired temperature is equal to the reference temperature (here, 25° C., which is a predetermined temperature at which the operating frequency is the highest). (step S1).
When determining that the temperature obtained from the temperature sensor 34 is equal to the reference temperature (step S1; YES), the control unit 22 executes photographing (step S3).
When it is determined that the temperature acquired from the temperature sensor 31 is not equal to the reference temperature (step S1; NO), the control unit 22 determines the number of oscillations according to the temperature difference between the acquired temperature and the reference temperature from the clock adjustment table 231. is read, and the count set value 222a of the timer 222 is updated with the read value, thereby adjusting the timer 222 (step S2). After the adjustment, shooting is executed (step S3).

In step S3, the control unit 22 waits for the end of the reset process, and when the reset process ends, the control unit 22 causes the gate driver 15b to apply an off voltage to each of the lines L1 to Lx of the scanning lines 5 to accumulate charges. transition to state. At the same time, the wireless communication unit 30 transmits an interlock release signal to the radiation control apparatus 1 . When the time to start reading by the FPD cassette 3A is received from the radiation control apparatus 1, and when the reading start time arrives, the control unit 22 causes the gate driver 15b to sequentially apply an ON voltage to each line L0 to Lx of the scanning lines 5. Then, the image data is read out as described above. When the readout of the line Lx is completed, the control unit 22 shifts to the accumulation state for generating the next frame image, accumulates charges according to the radiation emitted from the radiation source 2, and when the readout start time arrives. , the control unit 22 causes the gate driver 15b to sequentially apply an on-voltage to each of the lines L0 to Lx of the scanning lines 5 to read out the image data as described above. The control unit 22 repeats accumulation and readout processing for all frame images to generate a radiographic image of the subject.

In this way, the control unit 22 of the FPD cassette 3A acquires the temperature from the temperature sensor 34 immediately before the start of imaging, and if the acquired temperature is not equal to the reference temperature, adjusts the clock of the timer 222, and shifts to imaging after the adjustment. do. Therefore, it is possible to suppress deterioration in image quality due to synchronization deviation between the radiation irradiation period and the accumulation period due to clock deviation due to the influence of temperature.

As described above, according to the control unit 22 of the FPD cassette 3 in the radiation imaging system 100, the waveform of the radiation irradiated by the radiation source 3 obtained by reading out the charges from at least some of the plurality of radiation detection elements 7 is is used to adjust the synchronous timing of the radiation source 3 and the FPD cassette 3 . For example, after the charges are read out from the plurality of radiation detection elements 7 to generate one frame image of a moving image, the charges are read out again from some of the plurality of radiation detection elements 7, and the charges are read out again. Based on the charge amount of the radiation detection element 7 obtained, it is determined whether or not the radiation was irradiated outside the charge accumulation period of the radiation detection element 7, and it was judged that the radiation was irradiated outside the charge accumulation period of the radiation detection element 7. In this case, the charge accumulation period is adjusted so that the radiation is emitted during the charge accumulation period in the generation of the next frame image. Therefore, it is possible to suppress deterioration in image quality due to the synchronization deviation between the radiation irradiation period in the radiation source 2 and the charge accumulation period in the FPD cassette 3 .

For example, the control unit 22 of the FPD cassette 3 re-reads charges from the radiation detection elements 7 of a plurality of lines. If the charge amount of the line re-read out after is larger than the charge amount of , it is determined that the radiation exposure period is earlier than the charge accumulation period, and the charge accumulation period for generating the next frame image is shortened. Therefore, when the radiation irradiation period is earlier than the charge accumulation period, it can be detected and adjusted so that the radiation is irradiated within the charge accumulation period when the next frame image is generated.
Further, the controller 22 of the FPD cassette 3 determines that the charge amount of the re-read line is equal to or greater than a predetermined value, and that the charge amount of the line re-read after the line re-read is greater than the charge amount of the line re-read first. If it is less, it is determined that the radiation irradiation period is delayed with respect to the charge accumulation period, and the charge accumulation period when generating the next frame image is extended or a waiting time is provided before the start of the charge accumulation period. Therefore, when the radiation irradiation period is delayed with respect to the charge accumulation period, it can be detected and adjusted so that the radiation is irradiated within the charge accumulation period when the next frame image is generated.

It should be noted that the description in the above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Further, the detailed configuration and detailed operation of each device that constitutes the radiation imaging system can be changed as appropriate without departing from the scope of the present invention.

100 Radiation imaging system 1 Radiation control device 101 Control unit 102 Operation unit 102a Exposure switch 103 Display unit 104 Storage unit 105 Drive unit 106 Wireless communication unit 107 Crystal oscillator 108 Antenna 2 Radiation source 3 FPD cassette 5 Scanning line 6 Signal line 7 Radiation detection element 8 TFT
9 bias line 10 connection 14 bias power supply 15 scan driver 16 readout IC
17 readout circuit 18 amplifier circuit 19 correlated double sampling circuit 20 A/D converter 21 analog multiplexer 22 control unit 23 storage unit 24 built-in power supply 25 crystal oscillator 29 antenna 30 wireless communication unit

Claims (7)

a detection portion including a plurality of radiation detection elements that accumulate charge upon irradiation by a radiation source;
a control unit configured to generate a plurality of frame images by repeatedly performing accumulation by the radiation detection elements and reading out of the accumulated charges from the radiation detection elements,
The control unit performs a first process for synchronizing a radiation irradiation period during which the radiation source emits radiation and an accumulation period during which the radiation detecting element accumulates the radiation, before the irradiation with the radiation source. A radiation imaging apparatus, wherein second processing for adjusting the synchronization deviation is performed based on the amount of charge accumulated in at least a part of a radiation detection element. 2. The radiographic imaging apparatus according to claim 1, wherein in the first process, the control unit synchronizes based on a time when the radiation source emits radiation and a time when the reading is started. 3. The radiation imaging apparatus according to claim 1, further comprising a wireless communication unit that wirelessly communicates information about a time when the radiation source emits radiation and a time when the reading is started. 4. The radiographic imaging apparatus according to claim 1, further comprising an interlock releasing section that releases an interlock before irradiation with the radiation source. 5. The radiation imaging apparatus according to claim 1, wherein said control unit adjusts a clock of a timer used for said synchronization before irradiation with said radiation source. Equipped with a temperature sensor to measure the temperature,
6. The radiation imaging apparatus according to claim 5, wherein the control unit adjusts the clock based on the temperature obtained from the temperature sensor. 7. The radiographic imaging apparatus according to claim 1, wherein said control unit repeatedly executes reading from said radiation detection elements based on said synchronization.

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