JP2012115306A - Radiographic image detecting apparatus and radiation irradiation start detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably prevent erroneous detection of start of radiation irradiation without forcing a subject to be unnecessarily exposed to radiation.SOLUTION: The irradiation detecting section 53 has a first comparing circuit 61, a second comparing circuit 62 and a determining circuit 63. The first comparing circuit 61 compares a voltage signal Dave which has been offset with a first threshold value Dref. The second comparing circuit 62 compares the voltage signal Dave to a second threshold value Dref'. The second threshold value Dref' is obtained by superimposing a noise component Δ generated by transmitting receiving operations of a communication section 34 on the first threshold value Dref. A control circuit 41 switches switching elements 64, 65 to the first comparing circuit 61, if the communication section 34 does not perform the transmitting receiving operations, and to the second comparing circuit 62, if the transmitting receiving operations are performed. The determining circuit 63 monitors voltage values of output terminals of the respective comparing circuits 61, 62 and determines whether or not the irradiation of X-ray is started. When the determining circuit 63 determines that X-ray irradiation is started, the control circuit 41 immediately allows an FPD 36 to shift to an accumulating operation.

Description

  The present invention relates to a radiation image detection apparatus that receives radiation and detects a radiation image, and a radiation irradiation start detection method.

  A radiation imaging system, for example, an X-ray imaging system includes an X-ray generation apparatus that generates X-rays and an X-ray imaging apparatus that receives an X-ray and captures an X-ray image. The X-ray generator has an X-ray source that irradiates X-rays toward a subject, a radiation source control device that controls driving of the X-ray source, and an irradiation switch for inputting an X-ray irradiation start instruction. ing. The X-ray imaging apparatus has an X-ray image detection apparatus that receives an X-ray transmitted through a subject and detects an X-ray image, and an imaging control apparatus that controls driving of the X-ray image detection apparatus.

  As an X-ray image detection apparatus, an apparatus using a flat panel detector (FPD) as a detector in place of an X-ray film or an imaging plate (IP) has recently become widespread. In the FPD, pixels that accumulate signal charges corresponding to the amount of incident X-rays are arranged in a matrix. The FPD accumulates signal charges for each pixel to detect an X-ray image representing the image information of the subject and outputs it as digital image data.

  A portable X-ray image detection apparatus (hereinafter referred to as an electronic cassette) in which an FPD is built in a rectangular parallelepiped housing has also been put into practical use. The electronic cassette is used by being attached to an imaging table for a film cassette or an IP cassette, and is used by holding the subject itself in order to image a portion that is difficult to image with the stationary type. In addition, in order to take pictures of elderly people who are being treated at home or those who are suddenly ill due to accidents, disasters, etc., they may be taken out of hospitals where there is no equipment for taking pictures.

  Conventionally, in order to synchronize the timing at which X-rays are emitted from an X-ray source by pressing an irradiation switch and the timing at which the X-ray image detection device starts a signal charge accumulation operation, ) And the X-ray imaging apparatus (imaging control apparatus) exchanged an operation signal generated by the irradiation switch as a synchronization signal indicating the start of X-ray irradiation. However, it is necessary to electrically connect the X-ray generator and the X-ray imaging apparatus for exchanging the synchronization signal. The manufacturers of the X-ray generator and the X-ray imaging apparatus are different, and the connection interfaces (cables and If the connector standard, sync signal format, etc. are not compatible, a new interface must be prepared.

  In order to solve this problem, the X-ray image detection apparatus itself detects the start of X-ray irradiation without exchanging the synchronization signal (without electrically connecting the X-ray generator and the X-ray imaging apparatus) A technique for synchronizing with an X-ray generator has been proposed (see Patent Document 1).

  In general, the output of an electrical component is affected by noise due to internal factors of the component itself or external factors such as the surrounding environment. An X-ray image detection apparatus on which many electrical components are mounted is no exception, and noise is generated during communication with the imaging control apparatus. If this noise is placed on a signal for detecting the start of X-ray irradiation, it may be erroneously detected that X-rays have been irradiated even though X-rays are not actually being irradiated. If erroneous detection is performed, the X-ray image detection apparatus is caused to perform an unnecessary operation, which increases power consumption. In addition, since shooting cannot be performed during the above operation, there is a risk of missing a shooting opportunity.

  Furthermore, the shooting control device and the device for setting shooting conditions (a so-called console) behave as if shooting has been performed, and as a result, troublesome operations such as resetting the shooting conditions are required. In addition, when it is erroneously detected that X-rays have been irradiated, the X-ray image detection apparatus operates and the output image is treated like a regular image, leading to a medical error such as being transferred to a doctor. There is also a risk that will occur.

  Therefore, in Patent Document 1, erroneous detection due to noise is prevented by detecting, as the start timing of the accumulation operation, the timing when a predetermined period has elapsed since the start of X-ray irradiation was detected. If the signal for detecting the start of X-ray irradiation is due to a single noise, the signal disappears after a predetermined period of time, and in this case, the storage operation is not erroneously shifted.

JP 2006-246961 A

  In Patent Document 1, since there is a gap between the start of true X-ray irradiation and the start timing of the accumulation operation, the X-rays irradiated during that time are wasted, and there has been a problem in that unnecessary exposure is imposed on the subject.

  The present invention has been made in view of the above problems, and an object of the present invention is to reliably prevent erroneous detection of the start of radiation irradiation without forcing unnecessary exposure to the subject.

  The radiological image detection apparatus of the present invention includes a radiological image detector in which a plurality of pixels that receive radiation irradiated from a radiation source and accumulates signal charges, an accumulation operation that accumulates signal charges in the pixels, and signal charges. A control unit that causes the radiation image detector to perform an irradiation start detection operation that repeats a read operation that is converted into an electrical signal and output a predetermined number of times, and radiation based on a comparison result between the electrical signal output in the irradiation start detection operation and a threshold An irradiation detection unit that detects the start of irradiation, an offset correction unit that removes dark charge noise components from the electrical signal using offset correction data, and a communication unit that exchanges information with an external device, the irradiation detection unit When the communication unit does not perform a communication operation during the irradiation start detection operation, the first threshold value is compared with the electric signal offset-corrected by the first offset correction data. When the detection operation is performed based on the result and the communication operation is performed, the comparison result of the second threshold value obtained by adding the electrical noise corrected by the first offset correction data and the communication noise component due to the communication operation to the first threshold value, or Detection is performed based on a comparison result between an electrical signal offset-corrected by second offset correction data obtained by adding a communication noise component to the first offset correction data and a first threshold value.

  The said irradiation detection part outputs the signal showing the irradiation start of a radiation to the said control part, when an electrical signal becomes more than a threshold value. The control unit causes the radiological image detector to perform an accumulation operation as soon as a signal is input from the irradiation detection unit.

  The irradiation detection unit preferably performs detection based on an electric signal obtained by converting a signal charge of a pixel arranged near the center of the radiation image detector.

  The electronic cassette is preferably housed in a portable housing.

  The radiation irradiation start detection method of the present invention performs an irradiation start detection operation for a radiographic image detector by repeating a storage operation for accumulating signal charges in a pixel and a read operation for converting the signal charges into an electrical signal and outputting the signal a predetermined number of times. When the communication unit does not perform communication operation with the external device during the irradiation start detection operation, the irradiation start is started based on the comparison result between the electric signal offset-corrected with the first offset correction data and the first threshold value. When the communication operation is detected and detected, the comparison result of the second threshold value obtained by adding the electric signal offset-corrected by the first offset correction data and the communication noise component due to the communication operation to the first threshold value, or the communication noise component is obtained. Detection can be performed based on the comparison result of the first threshold value and the electrical signal offset-corrected by the second offset correction data added to the first offset correction data. The features.

  Since the present invention detects the start of radiation irradiation based on the comparison result between the threshold value added with the communication noise component and the electric signal or the comparison result between the electric signal corrected with the offset correction data added with the communication noise component and the threshold value. Further, it is possible to prevent erroneous detection of the start of radiation irradiation due to the communication noise component, and it is possible to perform photographing without leaving a gap between the start of true radiation irradiation and the start timing of the accumulation operation. Therefore, it is possible to reliably prevent erroneous detection of the start of radiation irradiation without forcing unnecessary exposure to the subject.

It is the schematic which shows the structure of a X-ray imaging system. It is a figure which shows the electrical structure of FPD. It is a figure which shows the outline | summary of the irradiation detection part of 1st embodiment. It is a timing chart which shows the operation | movement procedure of an electronic cassette. It is a flowchart which shows the operation | movement procedure of an electronic cassette. It is a figure which shows the outline | summary of the offset correction part and irradiation detection part of 2nd embodiment.

[First embodiment]
In FIG. 1, the X-ray imaging system 10 includes an X-ray generation device 11 and an X-ray imaging device 12. The X-ray generator 11 includes an X-ray source 13, a radiation source controller 14 that controls driving of the X-ray source 13, and an irradiation switch 15. The X-ray source 13 includes an X-ray tube 13a that emits X-rays, and an irradiation field limiter (collimator) 13b that limits an X-ray irradiation field emitted by the X-ray tube 13a.

  The X-ray tube 13a includes a cathode made of a filament that emits thermoelectrons, and an anode (target) that emits X-rays when the thermoelectrons emitted from the cathode collide. The target has a disk shape, and is a rotating anode in which the focal point moves on a circular orbit by rotation, and the heat generated at the focal point where thermal electrons collide is dispersed. The irradiation field limiter 13b has a plurality of lead plates that shield X-rays arranged in a cross-beam shape, and an irradiation opening that transmits X-rays is formed in the center. By moving the position of the lead plate, The irradiation field is limited by changing the size of the irradiation opening.

  The radiation source control device 14 determines a high voltage generator that supplies a high voltage to the X-ray source 13, a tube voltage that determines the energy spectrum of the X-rays that the X-ray source 13 irradiates, and an irradiation amount per unit time. It consists of a controller that controls the tube current and the X-ray irradiation time. The high voltage generator boosts the input voltage with a transformer to generate a high voltage tube voltage, and supplies driving power to the X-ray source 13 through the high voltage cable 16. The X-ray generation apparatus 11 of this example does not have a communication function with the X-ray imaging apparatus 12, and radiographers can set imaging conditions such as tube voltage, tube current, and irradiation time through the operation panel of the radiation source control apparatus 14. Set manually.

  The irradiation switch 15 is operated by a radiologist and is connected to the radiation source control device 14 by a signal cable 17. The irradiation switch 15 is a two-stage push switch, which generates a warm-up start signal for starting the warm-up of the X-ray source 13 by pressing the single stage, and for starting the irradiation of the X-ray source 13 by pressing the two-stage. The irradiation start signal is generated. These signals are input to the radiation source controller 14 through the signal cable 17.

  The radiation source control device 14 controls the operation of the X-ray source 13 based on a control signal from the irradiation switch 15. When the warm-up start signal is received, the radiation source control device 14 activates the heater to preheat the filament, and also starts the rotation of the target to reach the target rotational speed. The time required for warm-up is about 200 msec to 1500 msec. The radiologist inputs a warm-up start instruction by pressing the irradiation switch 15 in one stage, and then inputs the irradiation start instruction by pressing in two stages after a necessary interval for warm-up.

  When receiving the irradiation start signal, the radiation source control device 14 starts supplying power to the X-ray source 13 and activates a timer to start measuring the X-ray irradiation time. Then, when the irradiation time set in the imaging conditions has elapsed, X-ray irradiation is stopped. Although the X-ray irradiation time varies depending on the imaging conditions, in the case of still image shooting, the maximum X-ray irradiation time is often set to a range of about 500 msec to about 2 s, and the irradiation time Is set with this maximum irradiation time as the upper limit.

  The X-ray imaging apparatus 12 includes an electronic cassette 21, an imaging table 22, an imaging control apparatus 23, and a console 24. The electronic cassette 21 includes an FPD 36 (see FIG. 2) and a portable housing that houses the FPD 36, and is normally used without a cable. The electronic cassette 21 receives an X-ray irradiated from the X-ray source 13 and transmitted through the subject H, and outputs an X-ray image. The electronic cassette 21 has a flat shape with a substantially rectangular planar shape, and the planar size is substantially the same as a film cassette or an IP cassette.

  The imaging table 22 has a slot to which the electronic cassette 21 can be detachably attached, and holds the electronic cassette 21 with an incident surface on which X-rays are incident facing the X-ray source 13. The electronic cassette 21 can be attached to a film cassette or an IP cassette photographing stand because the size of the casing is substantially the same as that of the film cassette or the IP cassette. In addition, although the standing position imaging stand which image | photographs the subject H with a standing posture is illustrated as the imaging stand 22, the supine position imaging stand which image | photographs the subject H with a standing posture may be sufficient.

  In FIG. 2, a battery 31 and an antenna 32 are built in the electronic cassette 21, and wireless communication with the imaging control device 23 is possible. The battery 31 supplies power for operating each part of the electronic cassette 21. The battery 31 is a relatively small battery that can be accommodated in the thin electronic cassette 21. The battery 31 can be taken out from the electronic cassette 21 and charged. The antenna 32 transmits and receives radio waves for wireless communication to and from the imaging control device 23.

  In addition to the antenna 32, the electronic cassette 21 is provided with a socket 33. The socket 33 is provided for wired connection with the imaging control device 23, and a connector of a communication cable 25 (see FIG. 1) connected to the imaging control device 23 is inserted into the socket 33. The communication cable 25 is used when wireless communication between the electronic cassette 21 and the imaging control device 23 becomes impossible due to the remaining amount of the battery 31 being insufficient. When the communication cable 25 is used, wired communication with the imaging control device 23 becomes possible and power can be supplied from the imaging control device 23 to the electronic cassette 21. Although not shown, the electronic cassette 21 is provided with an indicator for displaying a power switch and other operation switches, power on / off, the remaining amount of the battery 31, an operation error, a wireless communication status, and the like.

  An antenna 32 and a socket 33 are connected to the communication unit 34. The communication unit 34 mediates transmission / reception of various information and signals including image data between the antenna 32 or the socket 33 and the control circuit 41 and the memory 51.

  The communication unit 34 periodically communicates with the imaging control device 23 in order to report irregularity of image data, indicator display control signals, and the like, and transmission / reception of signals, as well as the quality of wireless or wired communication status. A communication confirmation signal is exchanged. The communication confirmation signal is first transmitted from the photographing control device 23 first, and is transmitted and received between the electronic cassette 21 and the photographing control device 23 in a format that the communication unit 34 receives.

  The communication unit 34 sequentially transmits information and signal transmission / reception states with the imaging control device 23 via the antenna 32 or the socket 33 to the control circuit 41. Thereby, the control circuit 41 can always grasp the communication state with the imaging control device 23.

  The FPD 36 includes a TFT active matrix substrate, and an imaging region 38 in which a plurality of pixels 37 that accumulate signal charges corresponding to the amount of incident X-rays is arranged on this substrate, and the pixels 37 are driven to drive the signal charges. Operation of the FPD 36 by controlling the gate driver 39 for controlling the reading of the signal, the signal processing circuit 40 for converting the signal charge read from the pixel 37 into digital data and outputting it, and the gate driver 39 and the signal processing circuit 40. And a control circuit 41 for controlling. The plurality of pixels 37 are two-dimensionally arranged in a matrix of n rows (x direction) × m columns (y direction) at a predetermined pitch.

  The FPD 36 has a scintillator (phosphor) that converts X-rays into visible light, and is an indirect conversion type in which visible light converted by the scintillator is photoelectrically converted by the pixels 37. The scintillator is disposed so as to face the entire surface of the imaging region 38 in which the pixels 37 are arranged. Note that a direct conversion type FPD using a conversion layer (such as amorphous selenium) that directly converts X-rays into electric charges may be used.

  The pixel 37 includes a photodiode 42 that is a photoelectric conversion element that generates charges (electron-hole pairs) upon incidence of visible light, a capacitor (not shown) that accumulates charges generated by the photodiode 42, and a switching element. A thin film transistor (TFT) 43 is provided.

  The photodiode 42 has a structure in which a semiconductor layer (for example, PIN type) that generates electric charges and an upper electrode and a lower electrode are arranged above and below the semiconductor layer. In the photodiode 42, the TFT 43 is connected to the lower electrode, and a bias line (not shown) is connected to the upper electrode, and a bias voltage is applied through the bias line. An electric field is generated in the semiconductor layer by applying a bias voltage, and charges (electron-hole pairs) generated in the semiconductor layer by photoelectric conversion move to the upper and lower electrodes, one having a positive polarity and the other having a negative polarity. As a result, charge is accumulated in the capacitor.

  The TFT 43 has a gate electrode connected to the scanning line 44, a source electrode connected to the signal line 46, and a drain electrode connected to the photodiode 42. The scanning lines 44 and the signal lines 46 are wired in a grid pattern. The scanning lines 44 are the number of rows of the pixels 37 in the imaging region 38 (n rows), and the signal lines 46 are the number of columns of the pixels 37 (m columns). Min) each is provided. The scanning line 44 is connected to the gate driver 39, and the signal line 46 is connected to the signal processing circuit 40.

  The gate driver 39 drives the TFT 43, thereby accumulating signal charges corresponding to the amount of incident X-rays in the pixel 37, reading (main reading) operation for reading signal charges from the pixel 37, and reset (empty reading). ) Operation and irradiation start detection operation. The control circuit 41 controls the start timing of each operation executed by the gate driver 39 based on the control signal from the imaging control device 23 input through the communication unit 34.

  In the accumulation operation, the TFT 43 is turned off, and signal charges are accumulated in the pixel 37 during that time. In the read operation, gate pulses G1 to Gn for simultaneously driving the TFTs 43 in the same row are generated in sequence from the gate driver 39, the scanning lines 44 are sequentially activated one by one, and the TFTs 43 connected to the scanning lines 44 are provided for each row. Turn on. The charge accumulated in the capacitor of the pixel 37 is read out to the signal line 46 and input to the signal processing circuit 40 when the TFT 43 is turned on.

  Dark charges are generated in the semiconductor layer of the photodiode 42 regardless of whether X-rays are incident. This dark charge is accumulated in the capacitor because the bias voltage is applied. Since the dark charge generated in the pixel 37 becomes a noise component for the image data, a reset operation is performed to remove this. The reset operation is an operation of sweeping out dark charges generated in the pixel 37 through the signal line 46.

  The reset operation is performed by, for example, a sequential reset method in which the pixels 37 are reset row by row. In the sequential reset method, similarly to the signal charge reading operation, gate pulses G1 to Gn are sequentially generated from the gate driver 39 to the scanning line 44, and the TFTs 43 of the pixels 37 are turned on line by line. While the TFT 43 is on, dark charge flows from the pixel 37 to the integrating amplifier 47 through the signal line 46. In the reset operation, unlike the read operation, the charge accumulated in the integrating amplifier 47 is not read by the multiplexer (MUX) 48, and the reset pulse RST is generated from the control circuit 41 in synchronization with the generation of the gate pulses G1 to Gn. Is output, and the integrating amplifier 47 is reset. Since the charge is not read, the time required for the reset operation is shorter than the time required for the read operation.

  The signal processing circuit 40 includes an integrating amplifier 47, a MUX 48, and an A / D converter 49. The integrating amplifier 47 is individually connected to each signal line 46. The integrating amplifier 47 includes an operational amplifier and a capacitor connected between the input and output terminals of the operational amplifier, and the signal line 46 is connected to one input terminal of the operational amplifier. The other input terminal of the integrating amplifier 47 is connected to the ground (GND). The integrating amplifier 47 integrates the charges input from the signal line 46, converts them into voltage signals D1 to Dm, and outputs them. The MUX 48 is connected to the output terminal of the integrating amplifier 47 in each column via an amplifier and a sample hold unit (both not shown). An A / D converter 49 is connected to the output side of the MUX 48.

  The MUX 48 selects one integration amplifier 47 in order from a plurality of integration amplifiers 47 connected in parallel, and serially inputs voltage signals D1 to Dm output from the selected integration amplifier 47 to the A / D converter 49. . The A / D converter 49 converts the input voltage signals D1 to Dm into digital data, and outputs the digital data to the memory 51 built in the casing of the electronic cassette 21.

  When the voltage signal D1 to Dm for one row is read from the integrating amplifier 47 by the MUX 48, the control circuit 41 outputs a reset pulse RST to the integrating amplifier 47 and turns on the reset switch 47a of the integrating amplifier 47. As a result, the signal charge for one row accumulated in the integrating amplifier 47 is reset. When the integration amplifier 47 is reset, the gate pulse of the next row is output from the gate driver 39, and the readout of the signal charge of the pixel 37 of the next row is started. These operations are sequentially repeated to read the signal charges of the pixels 37 in all rows.

  When the reading of all rows is completed, image data representing an X-ray image for one screen is recorded in the memory 51. This image data is read from the memory 51 and output to the imaging control device 23 through the communication unit 34. Thus, an X-ray image of the subject H is detected.

  The offset correction unit 52 receives image data from the memory 51, and executes offset correction by subtracting noise caused by dark charges from the image data. Specifically, the offset correction unit 52 subtracts dark image data (offset correction data) obtained by performing a reading operation when X-rays are not irradiated from the image data (see also FIG. 6). The offset correction unit 52 records the image data after the offset correction in the memory 51 again. It should be noted that the reading operation during non-irradiation of X-rays for obtaining dark image data may be performed before the start of a day's work, or may be performed every time X-ray imaging is performed. In addition, in order to remove the influence of noise other than dark charges, the surrounding environment (temperature), the operation mode of the electronic cassette 21, etc., the readout operation when X-rays are not irradiated is continuously performed a plurality of times and obtained each time. The average value of the dark image data may be used for offset correction.

  In the irradiation start detection operation, the time required for the accumulation operation is set to be much shorter than the maximum X-ray irradiation time and long enough to detect the X-ray irradiation, and the accumulation operation and the read operation are determined in advance. Repeat a number of times. In FIG. 3, in the irradiation start detection operation, at least one of the pixels 37 is used as the detection pixel 37 a, and the irradiation detection unit 53 detects that X-rays have been irradiated from the X-ray source 13.

  As the detection pixel 37a, for example, a plurality of pixels 37 near the center of the imaging region 38 are used. If the pixel 37 near the center of the imaging region 38 is used as the detection pixel 37a, even if the X-ray irradiation range is set smaller than the imaging region 38 according to the size of the imaging region, the vicinity of the center of the imaging region 38 is irradiated. Since it does not deviate from the range, the irradiation start can be reliably detected regardless of the size of the X-ray irradiation range. Note that all the pixels 37 may be used as the detection pixels 37a.

  The irradiation detection unit 53 includes a first comparison circuit 61, a second comparison circuit 62, and a determination circuit 63. Each comparison circuit 61, 62 has two input terminals and one output terminal. The average value Dave of the offset corrected digital voltage signals of the plurality of detection pixels 37 a is input to one input terminal of each of the comparison circuits 61 and 62 via the first switching element 64. The first threshold value Dref is input to the other input terminal of the first comparison circuit 61, and the second threshold value Dref ′ (= Dref + Δ) is input to the second comparison circuit 62. The average value Dave is obtained by extracting signals corresponding to the detection pixels 37a from the offset-corrected digital voltage signals recorded in the memory 51, adding them, and dividing by the number of detection pixels 37a. The output terminals of the comparison circuits 61 and 62 are connected to the determination circuit 63 via the second switching element 65. Each switching element 64, 65 is interlocked under the control of the control circuit 41.

  Δ is a noise component generated in the transmission / reception (communication) operation of the communication unit 34 such as exchange of a communication confirmation signal. Therefore, the second threshold value Dref ′ is obtained by adding a noise component generated in the transmission / reception operation of the communication unit 34 to the first threshold value Dref. Δ is acquired in advance from dark image data obtained in a state where the communication unit 34 is operated at the time of shipment of the electronic cassette 21 or the like.

  When the communication unit 34 is not performing transmission / reception operations, the control circuit 41 switches the switching elements 64 and 65 to the first comparison circuit 61 side illustrated. The voltage signal Dave is input to the first comparison circuit 61, and the output of the first comparison circuit 61 is input to the determination circuit 63. On the other hand, when the transmission / reception operation is performed by the communication unit 34, the switching elements 64 and 65 are switched to the second comparison circuit 62 side. The voltage signal Dave is input to the second comparison circuit 62, and the output of the second comparison circuit 62 is input to the determination circuit 63.

  The first comparison circuit 61 compares the voltage signal Dave with the first threshold value Dref, and the voltage value V1a that differs between when the voltage signal Dave is below the first threshold value Dref and when the voltage signal Dave is greater than or equal to the first threshold value Dref. , V1b is output. Similarly, the second comparison circuit 62 outputs different voltage values V2a and V2b depending on whether the voltage signal Dave is lower than the second threshold value Dref 'or more than the second threshold value Dref'.

  The determination circuit 63 monitors the voltage value of the output terminal of each of the comparison circuits 61 and 62, and when the voltage value changes from V1a1 to V1b or V2a to V2b, that is, the voltage signal Dave is the first threshold value Dref or the first threshold value Dref. When the threshold value Dref ′ is exceeded, it is determined that X-ray irradiation from the X-ray source 13 has started. Then, an irradiation start detection signal indicating this is output to the control circuit 41.

  In the state where X-rays are not irradiated, only dark charges are accumulated in the pixel 37. Since this dark charge is removed by offset correction, the voltage signal Dave of the detection pixel 37a input to either of the comparison circuits 61 and 62 becomes substantially zero, and is lower than the first threshold value Dref or the second threshold value Dref ′. Become. On the other hand, when X-rays are irradiated, signal charges corresponding to the X-rays are accumulated in the pixels 37. Since the signal charge is much larger than the dark charge, the voltage signal Dave becomes equal to or higher than the first threshold value Dref or the second threshold value Dref ′ immediately after the X-ray irradiation. The irradiation detection unit 53 monitors the change of the voltage signal Dave before and after the start of X-ray irradiation and detects the start of X-ray irradiation.

  The communication unit 34 transmits and receives a communication confirmation signal and other information and signals even during the irradiation start detection operation. Such a transmission / reception operation of the communication unit 34 generates noise, and this noise component is added to the voltage signal. If a noise component is added to the voltage signal, the voltage signal Dave output during the irradiation start detection operation is naturally raised accordingly. The voltage signal Dave becomes equal to or greater than the threshold value Dref due to a noise component, and there is a possibility that the irradiation detection unit 53 erroneously detects that X-ray irradiation has started even though X-ray irradiation has not actually been performed.

  In this example, when the communication unit 34 is performing a transmission / reception operation, the switching elements 64 and 65 are switched to the second comparison circuit 62 side, and the noise component generated by the transmission / reception operation of the communication unit 34 is set to the first threshold value Dref. The X-ray irradiation start is detected based on the comparison result between the added second threshold value Dref ′ and the voltage signal Dave. For this reason, even if a noise component is added to the voltage signal Dave, the voltage signal Dave does not exceed the second threshold value Dref ′, so that no irradiation start detection signal is input to the control circuit 41. Therefore, the electronic cassette 21 does not erroneously shift to the accumulation operation after the X-ray irradiation start detection, and continues to perform the irradiation start detection operation. Then, only when the X-ray irradiation is truly started, the irradiation start detection signal is input to the control circuit 41, and the operation proceeds to the accumulation operation.

  The control circuit 41 causes the FPD 36 to perform a reset operation until the imaging condition is transmitted from the imaging control device 23 after the electronic cassette 21 is turned on. When the imaging condition is transmitted from the imaging controller 23, the operation of the FPD 36 is shifted from the reset operation to the irradiation start detection operation. When receiving the irradiation start detection signal from the irradiation detection unit 53 during the irradiation start detection operation, the control circuit 41 shifts the operation of the FPD 36 from the irradiation start detection operation to the accumulation operation. At this time, the reset operation is performed once before shifting to the accumulation operation. The control circuit 41 measures the elapsed time from the start of the accumulation operation with a timer. When the elapsed time reaches the time set in the shooting conditions, the FPD 36 is shifted from the accumulation operation to the read operation.

  The imaging control device 23 is communicably connected to the electronic cassette 21 by a wireless method using the antenna 32 or a wired method using the communication cable 25, and controls the electronic cassette 21. Specifically, the imaging conditions are transmitted to the electronic cassette 21 to set the signal processing conditions (amplifier gain, etc.) of the FPD 36, and the respective operations of the FPD 36 are indirectly controlled. The image data from the cassette 21 is transmitted to the console 24.

  In FIG. 1, the imaging control device 23 communicates with the CPU 23 a that controls the device centrally, the electronic cassette 21 by a wireless method or a wired method, and communicates with the console 24 via the communication cable 26, And a memory 23c. The communication unit 23b and the memory 23c are connected to the CPU 23a. The memory 23c stores a control program executed by the CPU 23a, and stores various information such as a first threshold value Dref, a second threshold value Dref ', or Δ. The first threshold value Dref and the second threshold value Dref 'of the memory 23c are transmitted to the electronic cassette 21 after the electronic cassette 21 is turned on, and are set to the inputs of the comparison circuits 61 and 62, respectively.

  The console 24 is connected to the imaging control device 23 via a communication cable 26 and transmits imaging conditions to the imaging control device 23 and various images for X-ray image data transmitted from the imaging control device 23. Apply processing. In addition to being displayed on the display of the console 24, the processed X-ray image is stored in a data storage device such as a hard disk or memory in the console 24 or an image storage server connected to the console 24 via a network.

  The console 24 receives an input of an examination order including information such as the patient's sex, age, imaging region, and imaging purpose, and displays the examination order on the display. The examination order is input from an external system that manages patient information such as HIS (Hospital Information System) and RIS (Radiation Information System) and examination information related to radiation examination, or is manually input by a radiographer. The radiologist confirms the contents of the examination order on the display, and inputs imaging conditions corresponding to the contents through the operation screen of the console 24.

  Hereinafter, the operation of the above configuration will be described with reference to the timing chart of FIG. 4 and the flowchart of FIG. The notations such as S10 in FIGS. 4 and 5 correspond to each other.

  When imaging with the X-ray imaging system 10, first, the height of the electronic cassette 21 set on the imaging table 22 is adjusted to align the imaging site of the subject H with the position. Further, the height of the X-ray source 13 and the size of the irradiation field are adjusted according to the height of the electronic cassette 21 and the size of the imaging region.

  Next, as shown in step 10 (S10) of FIG. 5, the electronic cassette 21 is powered on. At this time, a bias voltage is supplied from the power supply circuit to the pixel 37 of the FPD 36, the gate driver 39 and the signal processing circuit 40 operate, and the FPD 36 starts a reset operation by the control circuit 41 (S11). Subsequently, shooting conditions are input from the console 24, and shooting conditions are set in the electronic cassette 21 via the shooting control device 23. The imaging conditions are also set in the radiation source control device 14. When the imaging condition is received from the imaging controller 23 (YES in S12), the FPD 36 shifts from the reset operation to the irradiation start detection operation by the control circuit 41 (S13).

  When the above preparation for photographing is completed, the radiation switch 15 is pushed one step by the radiologist. As a result, a warm-up start signal is transmitted to the radiation source control device 14 and the warm-up of the X-ray source 13 is started. After a predetermined time has elapsed, the irradiation switch 15 is pushed in two steps, an irradiation start signal is transmitted to the radiation source control device 14, and X-ray irradiation is started.

  In the FPD 36, the accumulation operation and the readout operation of the irradiation start detection operation are repeatedly performed a predetermined number of times, and the irradiation signal detection unit 53 compares the average value Dave of the voltage signal of the detection pixel 37a with the first threshold value Dref or the second threshold value Dref ′. Then, the start of X-ray irradiation is detected (S13). Note that if the start of X-ray irradiation is not detected during the predetermined number of accumulation and readout operations, the control circuit 41 returns the FPD 36 to the reset operation.

  During the irradiation start detection operation, when the communication unit 34 performs a transmission / reception operation by exchanging a communication confirmation signal with the imaging control device 23 (YES in S14), the switching elements 64 and 65 are switched by the control circuit 41, The second comparison circuit 62 is selected (S15). Then, based on the result of comparing the voltage signal Dave and the second threshold value Dref ′ by the second comparison circuit 62, that is, based on the voltages V2a and V2b from the second comparison circuit 62, the determination circuit 63 detects the start of X-ray irradiation. .

  On the other hand, when the communication unit 34 is not performing the transmission / reception operation (NO in S14), the first comparison circuit 61 is selected (S16), and the voltage signal Dave and the first threshold value Dref are compared by the first comparison circuit 61 and output. X-ray irradiation start is detected based on the applied voltages V1a and V1b. Note that FIG. 4 illustrates a case where the X-ray irradiation start and the transmission / reception operation of the communication unit 34 just overlap, and the second comparison circuit 62 is selected to detect the X-ray irradiation start.

  The X-ray source 13 irradiates the X-ray and the voltage signal Dave becomes equal to or higher than the first threshold value Dref or the second threshold value Dref ′, and the output of the first comparison circuit 61 is V1b or the output of the second comparison circuit 62 is V2b. When the change is detected by the determination circuit 63 (X-ray irradiation start is detected) (YES in S17), the control circuit 41 causes the FPD 36 to perform a reset operation once (in FIGS. 4 and 5). The TFTs 43 of all the pixels 37 are turned off and the storage operation is shifted to (S18). During the accumulation operation, X-rays that have passed through the subject H enter the imaging region 38 of the FPD 36, and signal charges corresponding to the amount of incident X-rays are accumulated in the pixels 37.

  The radiation source control device 14 stops the X-ray irradiation when the irradiation time set in the imaging conditions has elapsed. The FPD 36 also ends the accumulation operation after a predetermined time corresponding to the irradiation time set in the imaging conditions (YES in S19) and shifts to the reading operation (S20). In the read operation, the signal charges accumulated in the pixels 37 are read one by one in order from the first row, and are recorded in the memory 51 as X-ray image data for one screen. This image data is transmitted to the console 24 through the imaging control device 23 after offset correction. When the readout operation is completed, the FPD 36 returns to the state of the reset operation in S11 immediately after the power is turned on when the next imaging condition is not set, and returns to S13 and restarts the irradiation start detection operation when it is set.

  Note that the communication unit 34 is not limited to the regular transmission / reception operation illustrated in FIG. 4, and may occasionally transmit / receive an indicator display control signal or the like to / from the imaging control device 23 irregularly. In this case, the second comparison circuit 62 is selected each time to prevent erroneous detection of X-ray irradiation start due to noise components.

  As described above, the present invention detects the start of X-ray irradiation by adding the noise component generated in the transmission / reception operation to the first threshold value Dref when the communication unit 34 performs the transmission / reception operation. It is possible to reliably prevent erroneous detection of the start of irradiation of the line. For this reason, the electronic cassette 21 is not caused to perform an unnecessary operation due to erroneous detection, and there is no possibility of missing an imaging opportunity due to the unnecessary operation, so that high efficiency and power saving of X-ray imaging can be achieved.

  Since the FPD 36 shifts to the accumulation operation at the same time as the start of X-ray irradiation is detected, the irradiated X-rays can be used for the generation of X-ray images without any excess, and unnecessary exposure to the subject H is avoided. be able to.

[Second Embodiment]
In the first embodiment, the influence of the noise component is removed by adding the noise component generated in the transmission / reception operation of the communication unit 34 to the first threshold value Dref. On the other hand, in the present embodiment, a noise component is added to dark image data to be subtracted from image data at the time of offset correction.

  In FIG. 6, the first dark image data q0 or the second dark image data q0 ′ (= q0 + Δ) is input to the subtractor 72 of the offset correction unit 71 via the switching element 73. The first dark image data q0 is the same default value as the dark image data described in the first embodiment. The second dark image data q0 'is obtained by adding a noise component generated in the transmission / reception operation of the communication unit 34 to the first dark image data q0.

  When the communication unit 34 is not performing transmission / reception operations, the control circuit 41 switches the switching element 73 to the first dark image data q0 side shown in the figure. The subtracter 72 subtracts the first dark image data q0 from the image data read from the memory 51. On the other hand, when the transmission / reception operation is performed by the communication unit 34, the switching element 73 is switched to the second dark image data q0 'side. In this case, the second dark image data q0 'is subtracted from the image data by the subtractor 72.

  The irradiation detection unit 74 of this embodiment is different from the irradiation detection unit 53 of the first embodiment in that the second comparison circuit 62 and the switching elements 64 and 65 are not provided. It is the same. The comparison circuit 75 has the same configuration and operation as the first comparison circuit 61 of the first embodiment. The comparison circuit 75 compares the offset-corrected voltage signal Dave from the offset correction unit 71 with the first threshold value Dref, and outputs the voltage V1a or V1b as in the first embodiment. Similarly to the determination circuit 63 of the first embodiment, the determination circuit 76 monitors the voltage output of the comparison circuit 75 to determine whether or not X-ray irradiation has started. Subsequent processing is the same as that of the first embodiment, and thus description thereof is omitted.

  In the present embodiment, the noise component generated in the transmission / reception operation of the communication unit 34 is added to the first dark image data q0 to perform the offset correction, so the data after the offset correction is a noise component generated in the transmission / reception operation of the communication unit 34. Will be removed. Even if a noise component exceeding the first threshold value Dref is generated, it is removed from the voltage signal Dave by offset correction, so that the X-ray irradiation start is not erroneously detected as in the first embodiment. Further, the configuration of the irradiation detection unit can be simplified as compared with the first embodiment.

  It should be noted that the X-ray imaging system according to the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

  The X-ray imaging system 10 is not limited to the type installed in the imaging room of the hospital, but the type installed in the round-trip car, the X-ray source 13, the source control device 14, the electronic cassette 21, the imaging control device 23, etc. The present invention may be applied to a portable system capable of carrying out X-ray imaging by carrying it to a site requiring emergency medical treatment such as a disaster or the home of a patient receiving home medical care.

  In each of the above embodiments, irradiation detection is performed by comparing the threshold value with the digitized voltage signal after A / D conversion. However, the analog voltage signal output from the integrating amplifier may be compared with the threshold value.

  Instead of the sequential reset method in each of the above embodiments, a parallel reset method in which a plurality of rows of array pixels are sequentially reset within a group and dark charges in rows corresponding to the number of groups are simultaneously discharged, or a gate pulse is applied to all rows. An all-pixel reset method in which dark charges of all the pixels are simultaneously swept out may be used. The reset operation can be speeded up by a parallel reset method or an all-pixel reset method.

  Some X-ray sources do not require warm-up, such as a fixed anode type in which the anode does not rotate and a cold cathode type source that does not require preheating. For this reason, the irradiation switch may have only a function of generating an irradiation start signal. Even in the case of an X-ray source that requires warm-up, an irradiation start signal is input from the irradiation switch to the radiation source controller, and the radiation source controller starts warm-up based on the irradiation start signal. If irradiation is started after completion, it is not necessary to provide a function for generating a warm-up start signal in the irradiation switch.

  In each of the above-described embodiments, the electronic cassette 21 and the imaging control device 23 are described as separate examples. However, the electronic cassette and the imaging control device are integrated, for example, the function of the imaging control device 23 is built in the control circuit 41. May be. Further, although image processing is performed by the console 24, it may be performed by the photographing control device 23.

  In each of the above embodiments, the electronic cassette which is a portable X-ray image detection apparatus has been described as an example. However, the present invention may be applied to a stationary X-ray image detection apparatus.

  The present invention can be applied not only to X-rays but also to imaging systems that use other radiation such as gamma rays.

DESCRIPTION OF SYMBOLS 10 X-ray imaging system 11 X-ray generator 12 X-ray imaging apparatus 13 X-ray source 14 Radiation source control apparatus 21 Electronic cassette 23 Imaging control apparatus 23a CPU
24 console 34 communication section 36 FPD
37 pixel 37a detection pixel 40 signal processing circuit 41 control circuit 52, 71 offset correction unit 53, 74 irradiation detection unit 61, 62 first and second comparison circuit 63, 76 determination circuit 75 comparison circuit

Claims (5)

A radiation image detector in which a plurality of pixels that receive radiation emitted from a radiation source and accumulate signal charges are arranged;
A control unit that causes the radiation image detector to perform an irradiation start detection operation that repeats a predetermined number of times of an accumulation operation for accumulating signal charges in pixels and a read operation for converting the signal charges into an electrical signal and outputting the electrical signals;
An irradiation detection unit that detects the start of radiation irradiation based on the comparison result of the electrical signal and threshold value output in the irradiation start detection operation;
An offset correction unit that removes dark charge noise components from the electrical signal using the offset correction data; and
A communication unit for exchanging information with an external device;
When the communication unit is not performing a communication operation during the irradiation start detection operation, the irradiation detection unit performs detection based on a comparison result between the electric signal corrected with the first offset correction data and the first threshold value,
When the communication operation is performed, the comparison result of the second threshold value obtained by adding the electrical signal offset-corrected by the first offset correction data and the communication noise component due to the communication operation to the first threshold value, or the communication noise component is the first offset. A radiological image detection apparatus that performs detection based on a comparison result between an electrical signal offset-corrected by second offset correction data added to correction data and a first threshold value. The irradiation detection unit outputs a signal indicating the start of radiation irradiation to the control unit when the electrical signal is equal to or greater than a threshold value,
The radiological image detection apparatus according to claim 1, wherein the control unit causes the radiological image detector to perform an accumulation operation as soon as a signal is input from the irradiation detection unit.   The radiation image detection apparatus according to claim 1, wherein the irradiation detection unit performs detection based on an electric signal obtained by converting a signal charge of a pixel arranged near the center of the radiation image detector.   The radiographic image detection apparatus according to claim 1, wherein the radiographic image detection apparatus is an electronic cassette housed in a portable housing. Causing the radiation image detector to perform an irradiation start detection operation that repeats a predetermined number of times an accumulation operation for accumulating signal charges in pixels and a readout operation for converting the signal charges into an electrical signal and outputting them,
When the communication unit is not communicating with an external device during the irradiation start detection operation, the irradiation start is detected based on the comparison result between the electrical signal offset-corrected with the first offset correction data and the first threshold value. ,
When the communication operation is performed, the comparison result of the second threshold value obtained by adding the electrical signal offset-corrected by the first offset correction data and the communication noise component due to the communication operation to the first threshold value, or the communication noise component is the first offset. A radiation irradiation start detection method, wherein detection is performed based on a comparison result between an electrical signal offset-corrected by second offset correction data added to correction data and a first threshold value.

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