JP2014195480A - Radiation image detection device, and radiation image detection device control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to appropriately capture a moving image at an X-ray image detection device that is incapable of communicating with an X-ray source.SOLUTION: An X-ray image detection device includes an FPD (Flat Panel Display) that detects an X-ray image by means of a plurality of pixels arranged in a matrix manner and accumulating therein signal charges corresponding to X-ray incident amounts. A control part of the X-ray image detection device creates an irradiation profile which expresses an X-ray irradiation amount per unit time, and a detection profile, which expresses an X-ray integrated detection amount per unit time, based on an output voltage Vout of a short circuit pixel of the FPD. The control part compares a threshold value Ts set from the irradiation profile and a period Tf in which the integrated detection amount specified from the detection profile becomes almost constant, with each other. When the period Tf is shorter than the threshold value Ts, the control part determines that a falling part of a previously irradiated X-ray having a pulse shape and a rising part of the next irradiated X-ray overlap each other and sets an operation mode of the FPD to a continuous irradiation corresponding mode.

Description

  The present invention relates to a radiographic image detection apparatus that detects a radiographic image by receiving radiation that has passed through a subject, and a control method for the radiographic image detection apparatus.

  In the medical field, X-ray imaging systems using radiation, such as X-rays, are known. An X-ray imaging system includes an X-ray source having an X-ray tube that generates X-rays, and an X-ray image detection device that receives an X-ray irradiated through the subject and detects an X-ray image representing image information of the subject It consists of. The X-ray source is given a tube current that determines the X-ray dose per unit time and a tube voltage that determines the X-ray quality (energy spectrum) as imaging conditions. This is determined for each image according to the imaging region and age of the subject. The X-ray source emits X-rays corresponding to given imaging conditions.

  As an X-ray image detection apparatus, an apparatus using an X-ray image detector (FPD: Flat Panel Detector) instead of a conventional X-ray film or imaging plate (IP) has been put into practical use (see Patent Document 1). ). The FPD is a detection having an imaging region arranged in a matrix and provided with a plurality of pixels that accumulate signal charges according to the amount of incident X-rays and signal lines that are connected to each pixel and read out signal charges. A panel and a signal processing circuit that reads out signal charges accumulated in each pixel as a voltage signal and converts the read voltage signal into digital image data. Thereby, in the X-ray image detection apparatus using FPD, an X-ray image can be observed immediately after imaging.

  In the detection panel, each pixel in the imaging region is composed of a photodiode that is a photoelectric conversion element and a TFT (Thin Film Transistor), and a scintillator (phosphor) that converts X-rays into visible light is provided on the imaging region. Is provided. The TFT is a switching element that switches the operation of the pixel by turning on and off the electrical connection between the photodiode and the signal line. When the TFT is turned off, the photodiode and the signal line are brought into a non-conductive state, and an accumulation operation in which signal charges are accumulated in the photodiode is started. When the TFT is turned on, the photodiode and the signal line are brought into a conductive state. Then, a read operation for reading the signal charge from the photodiode through the TFT and the signal line is started.

  Unlike the X-ray film and the IP plate, the FPD requires synchronous control for starting the accumulation operation and the reading operation in synchronization with the X-ray irradiation timing. As a method of synchronization control, a method of communicating a synchronization signal between an X-ray source and an X-ray image detection device, an X-ray irradiation amount is measured by an X-ray image detection device, and the measured X-ray irradiation amount is measured. There is a method in which the X-ray image detection apparatus self-detects each timing of the start and end of X-ray irradiation by monitoring fluctuations.

  As described in Patent Document 1, in the X-ray image detection apparatus, moving images such as fluoroscopic imaging can be performed by causing the FPD to repeatedly perform accumulation and reading operations alternately at a predetermined frame rate. it can. Patent Document 1 also discloses that X-rays are continuously irradiated during moving image shooting, or that X-rays are pulse-irradiated at a predetermined interval. Moving image shooting by pulse irradiation has an advantage that the amount of exposure can be suppressed while increasing the amount of irradiation per unit time compared to continuous irradiation. Patent Document 2 describes that a radiation pulse is detected by a detection unit, a pulse width and a period of the radiation pulse are calculated based on a detection result of the detection unit, and an imaging unit is controlled based on the calculation result. Has been.

JP 2002-301053 A JP 2006-122667 A

  When taking a moving image by X-ray pulse irradiation, the X-ray source and the X-ray image detection apparatus are communicably connected so that the FPD can be controlled in synchronization with the X-ray pulse irradiation. It is desirable. However, when switching from an X-ray film or the like to an X-ray image detection device using FPD, it has been conventionally performed to purchase only the X-ray image detection device alone and incorporate it into an existing X-ray imaging system. However, in such an X-ray imaging system in which new and old devices are combined, communication between the X-ray image detection device and the X-ray source cannot be performed depending on the combination of the X-ray image detection device and the X-ray source. There are many cases.

  When communication between the X-ray image detection apparatus and the X-ray source cannot be performed, the X-ray image detection apparatus self-detects the start and end of X-ray irradiation, and performs video shooting in synchronization with the FPD. Can be considered. However, as shown in FIG. 10, the dose of X-rays emitted from a general X-ray tube consisting of a diode gradually rises from the start of X-ray irradiation and rises to a peak corresponding to the tube current. Therefore, the time until the X-ray irradiation amount becomes “0” from the end of the X-ray irradiation, that is, the wave tail becomes long. It is not suitable for moving image shooting performed by irradiating X-rays in pulses. When pulsed with X-rays having a long wave tail, depending on the frame rate at the time of moving image shooting, as shown in FIG. 11, the wave tail of the X-ray irradiated first and the rising portion of the X-ray irradiated later This is because the X-rays are nearly overlapped with each other and the X-ray irradiation start and end cannot be detected.

  The length of the wave tail of the X-ray irradiation dose varies depending on the capacity, tube current, and tube voltage when the X-ray tube is viewed as a resistance. For example, the tube current decreases or increases as the tube voltage increases. The larger or lower the tube voltage, the shorter. Therefore, even in the case of an X-ray tube made of a dipole tube, the wave tail is shortened depending on the combination of the type of X-ray tube, tube current and tube voltage. Synchronous control can be performed by self-detecting pulse irradiation. However, it is difficult for the user to determine whether or not moving image shooting by pulse irradiation is possible based on the type of X-ray tube, tube current, tube voltage, and frame rate.

  The above problem can be solved by using an X-ray tube having a function of immediately attenuating the wave tail, such as a triode tube or a tetrode tube. However, these X-ray tubes are expensive, and in terms of cost, they are X-rays. It is difficult to introduce these expensive X-ray sources into an X-ray imaging system in which only an image detection apparatus is introduced. Further, no means for solving such a problem is disclosed in Patent Documents 1 and 2.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to appropriately perform moving image shooting in an X-ray image detection apparatus that cannot communicate with an X-ray source.

  The radiological image detection apparatus of the present invention has an imaging region in which a plurality of pixels that accumulate signal charges corresponding to the amount of incident radiation upon receiving radiation from a radiation source are arranged in a matrix, and the radiation transmitted through the subject Detection means for detecting a radiation image upon receiving irradiation, radiation detection means for detecting radiation emitted from a radiation source and outputting a detection signal corresponding to the amount of radiation incident, and detection signal of the radiation detection means Based on this, the overlapping state of the falling portion of the pulsed radiation previously irradiated from the radiation source and the rising portion of the pulsed radiation irradiated next, based on this measurement result, The operation mode of the image detecting means is a pulse irradiation compatible mode in which signal charge accumulation and signal charge readout are alternately repeated in synchronization with radiation pulse irradiation, and continuous radiation. Is obtained by a control means for setting to one of the continuous irradiation corresponding mode are alternately repeated and reading of accumulation and the signal charges of the fixed time of the signal charge in Ichu.

  The control unit creates a detection profile representing the integrated detection amount of radiation per unit time based on the detection signal of the radiation detection unit, and according to the length of the period during which the integrated detection amount of the detection profile is substantially constant. Then, the operation mode of the image detecting means may be set.

  The control means may set the operation mode of the image detection means to the continuous irradiation mode when the period during which the integrated detection amount of the detection profile is substantially constant is shorter than the threshold.

  The threshold is preferably set based on the falling period of the pulsed radiation.

  The control means may cause the image detection means to perform a reset operation for discharging the signal charges accumulated in the pixels within a period in which the integrated detection amount of the detection profile is substantially constant during the continuous irradiation mode. Good.

  The control unit monitors the start of radiation irradiation by the radiation source based on the detection signal of the radiation detection unit in the pulse irradiation compatible mode, and detects the start of radiation irradiation by the radiation source. Alternatively, signal charge accumulation may be started.

  The control unit monitors the end of radiation irradiation by the radiation source based on the detection signal of the radiation detection unit in the pulse irradiation compatible mode, and detects the end of radiation irradiation by the radiation source, and then detects the image detection unit. Alternatively, signal charge accumulation may be terminated and signal charge readout may be started.

  The radiation detection means is a short-circuited pixel in which the pixel and a signal line for reading out the signal charge from the pixel are always short-circuited, and the short-circuited pixel transmits a signal charge corresponding to the amount of incident radiation to the signal line. It is preferable to always output.

  The method for controlling a radiological image detection apparatus according to the present invention includes an image detection unit in which a plurality of pixels that receive radiation from a radiation source and accumulate signal charges corresponding to the amount of incident radiation are arranged in a matrix. In the control method of the radiological image detection apparatus for detecting the radiographic image by receiving the radiation transmitted through the pulse, the pulse previously irradiated from the radiation source based on the detection signal of the radiation detection means for detecting the radiation dose Measuring the overlapping state between the falling portion of the radiation and the rising portion of the next pulsed radiation, and based on the measurement result, the operation mode of the image detecting means is changed to the pulse of radiation Pulse irradiation mode that alternately repeats signal charge accumulation and signal charge readout in synchronization with irradiation, and for a certain period of time during continuous radiation irradiation And setting a reading of No. charge accumulation and the signal charges in any of the continuous irradiation corresponding mode are alternately repeated, is intended to include.

  According to the present invention, the operation mode of the image detecting means is pulse-irradiated based on the overlapping state between the falling portion of the pulsed radiation irradiated first and the rising portion of the pulsed radiation irradiated next. Since either the corresponding mode or the continuous irradiation corresponding mode can be automatically set, a high-quality moving image can be taken even if an inexpensive radiation tube is used.

It is explanatory drawing which shows schematic structure of a X-ray imaging system. It is an external appearance perspective view which shows the structure of an X-ray image detection apparatus. It is explanatory drawing which shows the structure of FPD. It is explanatory drawing which shows the operation state of the irradiation profile in the pulse irradiation corresponding | compatible mode, a detection profile, and FPD. It is a graph of the irradiation profile and detection profile which show the state where the falling part and rising part of a pulse-shaped X-ray have overlapped. It is explanatory drawing which shows the operation state of the irradiation profile in the continuous irradiation corresponding | compatible mode, a detection profile, and FPD. It is a flowchart which shows the setting procedure of the operation mode of FPD. It is a flowchart which shows the control procedure of the pulse irradiation corresponding | compatible mode of FPD. It is a flowchart which shows the control procedure of the continuous irradiation corresponding | compatible mode of FPD. It is a graph for demonstrating the wave tail of the irradiation amount of a X-ray. It is a graph which shows the state which irradiated the X-ray with a long wave tail in the pulse form.

  In FIG. 1, an X-ray imaging system 10 includes an existing X-ray including an X-ray generator 11 that does not have a function of communicating with an external device, and an imaging table 22 to which a film cassette or an IP cassette can be attached. An X-ray imaging apparatus 12 including an X-ray image detection device 21, an imaging control device 23, and a console 24 is incorporated in the imaging system.

  The X-ray generator 11 includes an X-ray source 13, a radiation source controller 14 that controls 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 has 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 irradiation field limiter 13b has, for example, a plurality of lead plates that shield X-rays arranged in a cross pattern, and an irradiation opening that transmits X-rays is formed in the center, and moves the position of the lead plate. By changing the size of the irradiation aperture, the irradiation field is limited.

  The radiation source control device 14 includes a high voltage generator 14a that supplies a high voltage to the X-ray source 13, a tube voltage that determines the quality (energy spectrum) of the X-rays irradiated by the X-ray source 13, and per unit time. And a radiation source controller 14b for controlling the X-ray irradiation time. The high voltage generator 14a 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 14c. Imaging conditions such as tube voltage, tube current, X-ray irradiation time, and imaging purpose are manually set in the radiation source controller 14 b by an operator such as a radiologist through the operation panel of the radiation source controller 14. Note that the shooting purpose included in the shooting conditions is, for example, the type of shooting such as still image shooting and moving image shooting.

  The irradiation switch 15 is connected to the radiation source control device 14 by a signal cable. The irradiation switch 15 is a two-stage push switch that can be operated by a radiologist, generates a warm-up start signal for starting the warm-up of the X-ray source 13 by one-step push, and presses the X-ray source by two-stage push. 13 generates an irradiation start signal for starting irradiation. These signals are input to the radiation source controller 14 through a signal cable.

  The radiation source control unit 14 b controls the operation of the X-ray source 13 based on the control signal from the irradiation switch 15. When receiving the irradiation start signal from the irradiation switch 15, the radiation source control unit 14 b issues a start command to the X-ray source 13 to start power supply. Thereby, the X-ray source 13 starts irradiation. At the time of taking a still image, the radiation source control unit 14b starts measuring the X-ray irradiation time by starting a power supply and operating a timer. Then, when the irradiation time set in the imaging conditions has elapsed, the radiation source control unit 14b issues a stop command to the X-ray source 13 to stop power supply. When receiving the stop command, the X-ray source 13 stops the X-ray irradiation. Further, at the time of moving image shooting, for example, while the irradiation switch 15 is being operated, the radiation source control unit 14b causes the X-ray source 13 to irradiate X-rays in a pulse shape at a time interval corresponding to the set frame rate.

  The imaging table 22 has a slot in which a film cassette and an IP cassette are detachably attached, and is arranged so that an incident surface on which X-rays are incident faces the X-ray source 13. 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 standing position imaging stand which image | photographs the subject H with a standing posture may be sufficient.

  The X-ray imaging apparatus 12 includes an X-ray image detection apparatus 21, an imaging control apparatus 23, and a console 24. The X-ray image detection apparatus 21 includes an FPD 36 (see FIG. 3) and a portable housing that houses the FPD 36. The X-ray image detection apparatus 21 emits X-rays irradiated from the X-ray source 13 and transmitted through the subject (subject) H. It is a portable radiographic image detection device that receives and detects an X-ray image of the subject H. The X-ray image detection device 21 has a flat housing with a substantially rectangular planar shape, and the planar size is substantially the same size as a film cassette or an IP cassette, so that the X-ray image detection device 21 can be attached to the imaging table 22. is there.

  The imaging control device 23 communicates with the X-ray generation device 11, the X-ray image detection device 21 and the console 24 by a wired method or a wireless method, and imaging that controls the X-ray image detection device 21 via the communication unit. And a control unit. The imaging control device 23 transmits imaging conditions to the X-ray image detection device 21 to set the signal processing conditions of the FPD 36, that is, the operation mode. Further, the imaging control device 23 receives the image data output from the X-ray image detection device 21 and transmits it to the console 24.

  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 manually input by an operator such as a radiographer. The operator confirms the contents of the inspection order on the display, and inputs imaging conditions corresponding to the contents through the operation screen of the console 24.

  The console 24 transmits imaging conditions to the imaging control device 23 and performs various image processing such as gamma correction and frequency processing on the X-ray image data transmitted from the imaging control device 23. 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.

  As shown in FIG. 2, the X-ray image detection device 21 includes a housing 25 whose rectangular upper surface is a radiation irradiation surface. The case 25 includes a top plate 26 provided with an irradiation surface and a case main body 27 that constitutes other than the top plate 26. For example, the top plate 26 is made of carbon and the case main body 27 is made of metal. And resin. Thereby, the intensity | strength of the housing body 27 is ensured, suppressing the absorption of the X-ray by the top plate 26. FIG.

  On the upper surface of the housing 25, an indicator 28 is provided as a notification unit that notifies the operation state and the like of the X-ray image detection device 21. The indicator 28 includes, for example, a plurality of light emitting units, and displays the operation state of the X-ray image detection device 21, the remaining battery capacity, and the like depending on the combination of the light emitting states of the light emitting units. The operation state includes, for example, a “ready state” indicating a photographing standby state and “data transmitting” indicating that image data after photographing is being transmitted. A display device such as an LCD may be used for the indicator 28.

  In the housing 25 of the X-ray image detection device 21, an FPD 36 that is an image detection means for detecting an X-ray image is disposed so as to face the irradiation surface. The FPD 36 is an indirect conversion type that includes a scintillator 29 that converts X-rays into visible light and a detection panel 30 that photoelectrically converts visible light converted by the scintillator 29, and is detected on the X-ray irradiation surface side of the scintillator 29. It is a “surface reading method (ISS: Irradiation Side Sampling)” in which the panel 30 is arranged. The FPD 36 may be a “backside scanning method (PSS: Penetration Side Sampling)” in which the arrangement of the scintillator 29 and the detection panel 30 is reversed.

  Various electronic circuits 31, a battery 32, and a communication unit 33 are disposed inside the housing 25 on one end side along the short direction of the irradiation surface. The various electronic circuits 31 are electronic circuits for controlling the FPD 36, and are protected by materials having X-ray shielding properties so that various electronic components are not damaged by X-ray irradiation. The battery 32 is incorporated in the housing 25 so as to be rechargeable and detachable, and supplies power to the FPD 36, various electronic circuits 31, and the communication unit 33. The communication unit 33 communicates with the imaging control device 23 by a wired method or a wireless method.

  In FIG. 3, the FPD 36 has a TFT active matrix substrate, and a detection panel 30 having an imaging region 38 in which a plurality of pixels 37 for accumulating signal charges corresponding to the amount of incident X-rays are arranged on this substrate. , A gate driver 39 for driving the pixel 37 to control reading of the signal charge, a signal processing circuit 40 for converting the signal charge read from the pixel 37 into digital data and outputting it, a gate driver 39 and a signal processing circuit 40, and a control unit 41 that controls the operation of the FPD 36. The control unit 41 is connected to a communication unit 45 that communicates with the imaging control device 23 by a wired method or a wireless method. 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 (not shown) 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. The scintillator is made of a phosphor such as CsI (cesium iodide) or GOS (gadolinium oxysulfide). 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 semiconductor layer (for example, PIN type) such as a-Si (amorphous silicon), 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.

  A bias voltage is applied to the upper electrode of the photodiode 42 with respect to all the pixels 37 in the imaging region 38 through the bias line. By applying a bias voltage, an electric field is generated in the semiconductor layer of the photodiode 42, and the charge (electron-hole pair) generated in the semiconductor layer by photoelectric conversion is an upper electrode having a positive polarity on one side and a negative polarity on the other side. It moves to the lower electrode and charges are accumulated in the capacitor.

  The TFT 43 has a gate electrode connected to the scanning line 47, a source electrode connected to the signal line 48, and a drain electrode connected to the photodiode 42. The scanning lines 47 and the signal lines 48 are wired in a grid pattern. The scanning lines 47 are provided for the number of rows (n rows) of the pixels 37 in the imaging region 38, and each scanning line 47 is a common wiring connected to the plurality of pixels 37 in each row. The signal lines 48 are provided for the number of columns of the pixels 37 (m columns), and each signal line 48 is a common wiring connected to a plurality of pixels 37 in each column. Each scanning line 47 is connected to the gate driver 39, and each signal line 48 is connected to the signal processing circuit 40.

  The gate driver 39 drives the TFT 43 to accumulate a signal charge corresponding to the amount of incident X-rays in the pixel 37, a read operation for reading the signal charge from the pixel 37, and a charge accumulated in the pixel 37. And reset operation to reset. The control unit 41 controls the start timing of each of the operations executed by the gate driver 39.

  In the accumulation operation, the TFT 43 is turned off, and signal charges are accumulated in the pixel 37 during that time. In the reading 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 47 are sequentially activated one by one, and the TFTs 43 connected to the scanning lines 47 are supplied one by one. Turn on.

  When the TFTs 43 for one row are turned on, signal charges accumulated in the pixels 37 for one row are input to the signal processing circuit 40 through the signal lines 48. In the signal processing circuit 40, signal charges for one row are converted into voltages and output, and output voltages corresponding to the signal charges are read as voltage signals D1 to Dm. The analog voltage signals D1 to Dm are converted into digital data, and image data that is digital pixel values representing the density of each pixel for one row is generated. The image data is output to the memory 56 built in the housing of the X-ray image detection apparatus 21.

  A dark current is generated in the semiconductor layer of the photodiode 42 regardless of whether X-rays are incident. Dark charges, which are charges corresponding to the dark current, are accumulated in the capacitor because a bias voltage is applied. Since the dark charge becomes a noise component for the image data, a reset operation is performed to remove the dark charge. The reset operation is an operation of sweeping out dark charges generated in the pixel 37 from the pixel 37 through the signal line 48.

  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 47, and the TFTs 43 of the pixels 37 are turned on line by line. While the TFT 43 is on, dark charges are input from the pixel 37 to the signal processing circuit 40 through the signal line 48.

  In the reset operation, unlike the read operation, the signal processing circuit 40 does not read the output voltage corresponding to the dark charge. In the reset operation, the reset pulse RST is output from the control unit 41 to the signal processing circuit 40 in synchronization with the generation of the gate pulses G1 to Gn. When a reset pulse RST is input in the signal processing circuit 40, a reset switch 49a of an integration amplifier 49 described later is turned on, and the input dark charge is reset.

  Instead of the sequential reset method, multiple rows of array pixels are grouped as a group, and the reset is performed sequentially within the group, and the dark charge of the number of rows in the group is simultaneously discharged. An all-pixel reset method that simultaneously sweeps out the dark charges may be used. The reset operation can be speeded up by a parallel reset method or an all-pixel reset method.

  The signal processing circuit 40 includes an integrating amplifier 49, a MUX 50, an A / D converter 51, and the like. The integrating amplifier 49 is individually connected to each signal line 48. The integrating amplifier 49 includes an operational amplifier and a capacitor connected between the input and output terminals of the operational amplifier, and the signal line 48 is connected to one input terminal of the operational amplifier. The other input terminal (not shown) of the integrating amplifier 49 is connected to the ground (GND). The integrating amplifier 49 integrates the signal charges input from the signal line 48, converts them into voltage signals D1 to Dm, and outputs them.

  The output terminal of the integrating amplifier 49 in each column is connected to the MUX 50 via an amplifier (not shown) that amplifies the voltage signals D1 to Dm and a sample hold unit (not shown) that holds the voltage signals D1 to Dm. Has been. The MUX 50 selects one of a plurality of integrating amplifiers 49 connected in parallel, and inputs the voltage signals D1 to Dm output from the selected integrating amplifier 49 to the A / D converter 51 serially. The A / D converter 51 converts the analog voltage signals D1 to Dm into digital pixel values corresponding to the respective signal levels.

  In the readout operation for reading out the signal charges after the accumulation operation, the TFTs 43 are turned on row by row by the gate pulse, and the signal charges accumulated in the capacitors of the pixels 37 in each column in the row are integrated via the signal line 48. 49.

  When voltage signals D1 to Dm for one line are output from the integration amplifier 49, the control unit 41 outputs a reset pulse (reset signal) RST to the integration amplifier 49, and turns on the reset switch 49a of the integration amplifier 49. . As a result, the signal charge for one row accumulated in the integrating amplifier 49 is reset. When the integration amplifier 49 is reset, the gate pulse of the next row is output from the gate driver 39 to start reading the signal charge of the pixel 37 of the next row. These operations are sequentially repeated to read the signal charges of the pixels 37 in all rows.

  When the reading of all lines is completed, image data representing an X-ray image for one screen is recorded in the memory 56. For the image data recorded in the memory 56, offset correction for removing offset components, which are fixed pattern noises caused by individual differences in the FPD 36 and the environment, variations in sensitivity of the photodiodes 42 of the pixels 37, Image correction processing such as sensitivity correction for correcting variations in output characteristics of the signal processing circuit 40 is performed. The image data is read from the memory 56, output to the imaging control device 23, and transmitted to the console 24. Thus, an X-ray image of the subject H is detected.

  In addition, the FPD 36 can self-detect the irradiation timing of the X-ray source 13 without exchanging a synchronization signal with the X-ray source 13. As indicated by hatching in FIG. 3, a short-circuit pixel 62 is provided in the imaging region 38 of the FPD 36 as a detection element for detecting each timing of X-ray irradiation start and irradiation end. The pixel 37 is switched on / off of electrical connection with the signal line 48 by turning on / off the TFT 43, whereas the short-circuited pixel 62 is always short-circuited with the signal line 48.

  The short-circuited pixel 62 has substantially the same structure as the pixel 37, and includes a photodiode 42 and a TFT 43. The photodiode 42 generates a signal charge corresponding to the amount of incident X-rays. The short circuit pixel 62 has a structural difference from the pixel 37 in that the source and drain of the TFT 43 are short-circuited by connection, and the switching function of the TFT 43 of the short circuit pixel 62 is lost. As a result, the signal charge generated by the photodiode 42 of the short-circuited pixel 62 always flows out to the signal line 48 and is input to the integrating amplifier 49. Instead of connecting the source and drain of the TFT 43 of the short-circuited pixel 62, the photodiode 42 and the signal line 48 may be directly connected to the short-circuited pixel 62 without providing the TFT 43 itself.

  The control unit 41 measures the amount of X-ray irradiation irradiated from the X-ray source 13 to the FPD 36 based on the output of the short circuit pixel 62, and monitors the change in the amount of X-ray irradiation. The control unit 41 uses the MUX 50 to select the integration amplifier 49 to which the signal charge from the short circuit pixel 62 is input, and reads the voltage signal of the integration amplifier 49 as the output voltage Vout of the short circuit pixel 62. The controller 41 resets the integrating amplifier 49 when the output voltage Vout is read once. The controller 41 repeats the operation of reading out the output voltage Vout at a very short interval with respect to the X-ray irradiation time during the accumulation operation so that the intensity change of the X-ray during irradiation can be monitored.

  The control unit 41 converts the value of the output voltage Vout into digital data and records it in the memory 56. The control unit 41 monitors the change in the dose of X-rays emitted from the X-ray source 13 based on the change with time of the output voltage Vout recorded in the memory 56, and starts and ends the X-ray irradiation. To detect.

  The control unit 41 sets the operation mode of the FPD 36 to either the pulse irradiation corresponding mode or the continuous irradiation corresponding mode based on the detection result of the X-rays by the short pixel 62. The pulse irradiation compatible mode is a mode in which the FPD 36 is synchronously controlled by detecting the X-ray irradiation start and irradiation end based on the pulsed X-ray irradiation amount. The continuous irradiation compatible mode is a mode in which a storage operation and a reading operation for a fixed time during continuous radiation irradiation are alternately repeated.

  As shown in FIG. 10, the amount of X-ray irradiation irradiated from the X-ray tube 13a becomes longer from the end of irradiation to “0”, that is, the wave tail becomes longer, and depending on the frame rate at the time of moving image shooting. As shown in FIG. 11, the wave tail of the previously irradiated X-ray overlaps with the rising portion of the next irradiated X-ray so that the X-ray is substantially continuously irradiated, X-ray irradiation start and irradiation end cannot be detected.

  The irradiation amount of X-rays after the irradiation ends exponentially falls with a time constant τ determined according to the tube current and the tube voltage, and in order for the irradiation amount to become “0”, it is 3 to 5 times the time constant τ. It is known to take time. For example, when the X-ray tube is viewed as a resistance R, a relationship of R = V / I is established between the tube current I and the tube voltage V. Further, when the capacity of the X-ray tube is CTube [pF], the capacity of the high-voltage cable connecting the X-ray tube and the high voltage generator is Cline [pF / m], and the cable length is L, the X-ray tube The capacity C combined with the high voltage cable is obtained by C = CTube + Cline × L. Therefore, the time constant τ of the X-ray source can be obtained by τ = RC = V / I (CTube + Cline × L).

  From the above, the length of the wave tail of the X-ray varies depending on the capacitance C of the X-ray tube and the high-voltage cable, the tube current I and the tube voltage V. For example, the capacitance C is large, the tube current is small, or the tube The higher the voltage, the longer. Therefore, even with an inexpensive X-ray tube made of a diode, depending on the combination of the wave tail length and the frame rate, moving image shooting can be performed in the pulse irradiation compatible mode.

  As shown in FIG. 4, the control unit 41 represents an irradiation profile indicating an X-ray irradiation amount per unit time and an integrated X-ray detection amount per unit time based on the output voltage Vout of the short-circuited pixel 62. Create a detection profile. As shown in FIG. 7, the control unit 41 determines the falling time required for the pulsed X-ray dose to become “0” based on the irradiation profile, that is, the wave tail length of the X-ray dose. The threshold value Ts is set based on the above. Next, the control unit 41 specifies a period Tf in which the accumulated detection amount of pulsed X-rays is substantially constant based on the detection profile, and compares the threshold Ts with the period Tf. Note that “substantially constant” means, for example, a range of about 20% above and below a specific value.

  As shown in FIG. 4, when the period Tf is substantially the same as the threshold value Ts, the control unit 41 sets the operation mode of the FPD 36 to the pulse irradiation compatible mode. In this state, since the falling part of the pulsed X-ray previously irradiated and the rising part of the pulsed X-ray irradiated next do not overlap, the irradiation start and irradiation of the pulsed X-ray are not performed. This is because the end can be detected.

  In the pulse irradiation compatible mode, the control unit 41 measures the X-ray irradiation amount irradiated in a pulse form from the X-ray source 13 by the short-circuit pixel 62, monitors the change in the X-ray irradiation amount, and applies the X-ray irradiation. Detect start. While detecting the start of X-ray irradiation, the control unit 41 shifts the FPD 36 to a standby state and causes the FPD 36 to perform a reset operation.

  When the start of X-ray irradiation is detected, the control unit 41 turns off the TFT 43 of the pixel 37 to shift from the standby state to the accumulation operation. In addition, while the X-ray is being irradiated, the control unit 41 continues to monitor the fluctuation of the X-ray irradiation amount based on the output of the short-circuited pixel 62 flowing out to the signal line 48 and detects the end of the X-ray irradiation. When this happens, the accumulation operation of the FPD 36 is terminated, and the reading operation is started. The control unit 41 shoots a moving image through which the subject is seen through by repeating the above-described operation while the pulsed X-ray is irradiated.

  Further, as shown in FIG. 5, when the period Tf is shorter than the threshold value Ts, the control unit 41 sets the operation mode of the FPD 36 to the continuous irradiation compatible mode. In this state, since the falling part of the pulsed X-ray previously irradiated and the rising part of the pulsed X-ray irradiated next overlap, the irradiation start and irradiation of the pulsed X-ray are performed. This is because the end cannot be detected.

  As shown in FIG. 6, the control unit 41 causes the FPD 36 to perform an accumulation operation and a read operation for a certain time within the rising period of the integrated detection amount of the detection profile in the continuous irradiation mode. In addition, the control unit 41 causes the FPD 36 reset operation to be performed within a period Tf in which the integrated detection amount is substantially constant. In the continuous irradiation-supporting mode, a moving image in which the subject is seen through is photographed by repeating these operations.

  The operation of the X-ray image detection apparatus 21 will be described with reference to the flowchart of FIG. The imaging region of the subject H and the irradiation position of the X-ray source 13 are aligned with the imaging table 22 on which the X-ray image detection device 21 is set. The X-ray source 13 is set with imaging conditions such as tube voltage, tube current, and irradiation time. The console 24 has examination orders such as the patient's sex, age, imaging region, imaging purpose, and the like, and imaging conditions based on this. Are entered. The imaging conditions input to the console 24 are transmitted to the X-ray image detection device 21 via the imaging control device 23.

  When an imaging preparation instruction is input from the imaging control device 23 to the control unit 41 of the X-ray image detection device 21, the FPD 36 shifts to a standby state (S101). When the standby state is entered, the FPD 36 starts the reset operation and starts measuring the X-ray dose (S102).

  When an irradiation start command is input to the X-ray source 13 by pressing the irradiation switch 15, the X-ray source 13 starts irradiating pulsed X-rays toward the subject H. The control unit 41 compares the output voltage Vout with the threshold value Vth and monitors the change in the X-ray irradiation dose (S103). Then, it detects that the X-ray irradiation is started when the X-ray irradiation amount increases and the output voltage Vout exceeds the threshold value Vth (S104). When detecting the start of irradiation, the controller 41 sets the operation mode of the FPD 36 based on the output voltage Vout of the short-circuited pixel 62 (S105).

  When the operation mode of the FPD 36 is set to the pulse irradiation compatible mode, the control unit 41 starts measuring the irradiation amount of the next pulsed X-ray (S106), compares the output voltage Vout with the threshold value Vth, A change in the amount of radiation is monitored (S107). When the output voltage Vout exceeds the threshold value Vth, the start of X-ray irradiation is detected (S108), and the FPD 36 starts an accumulation operation in synchronization with the start of irradiation (S109). .

  The FPD 36 also compares the output voltage Vout with the threshold value Vth during the accumulation operation, and monitors the change in the X-ray dose (S110). A stop command is input to the X-ray source 13 when the irradiation time set as an imaging condition has elapsed, and the intensity of the X-ray starts to decrease. When the output voltage Vout becomes equal to or lower than the threshold value Vth, the control unit 41 determines that the X-ray intensity has started to decrease, and detects the end of irradiation (S111). The control unit 41 ends the accumulation operation of the FPD 36 together with the detection of the end of irradiation, and starts the reading operation (S112). The read X-ray image is recorded in the memory 56. The control unit 41 repeats the above steps S106 to S112 while the X-rays are irradiated in the form of pulses (S113), and captures a moving image through the subject. The captured moving image is transmitted from the memory 56 to the console 24.

  Next, the operation when the FPD 36 is set to the continuous irradiation compatible mode will be described with reference to the flowchart of FIG. As in the pulse irradiation compatible mode, the control unit 41 starts measuring the X-ray dose (S201), and causes the FPD 36 to perform a reset operation within a period Tf in which the X-ray integrated detection amount is substantially constant. (S202). After the reset operation, the control unit 41 causes the accumulation operation for a predetermined time (S203) and the read operation (S204) within the rising period of the X-ray integrated detection amount. The controller 41 repeats the steps S201 to S204 while the X-rays are being irradiated (S205), and captures a moving image through the subject. The captured moving image is transmitted from the memory 56 to the console 24.

  As described above, in the present embodiment, the operation of the FPD 36 is based on the overlapping state between the falling portion of the pulsed X-ray irradiated first and the rising portion of the pulsed X-ray irradiated next. Since the mode can be automatically set to either the pulse irradiation compatible mode or the continuous irradiation compatible mode, a high-quality moving image can be captured using an inexpensive X-ray tube.

  Note that the amount of X-ray irradiation is measured by the short-circuited pixel 62 provided in the imaging region 38, but the short-circuited pixel 62 has substantially the same structure as the normal pixel 37, and the sensitivity to X-rays is also substantially the same. Therefore, it is possible to accurately measure the intensity of X-rays, and it is possible to accurately detect the start and end of irradiation and the total irradiation amount. Moreover, since the structure is almost the same, it is easy to manufacture, and the increase in manufacturing cost is small.

  Moreover, you may measure the intensity | strength of X-rays by methods other than a short circuit pixel. For example, although a bias voltage is applied to a photodiode that constitutes a pixel, the bias current flowing through the bias line also changes according to the amount of signal charge generated in the photodiode. Such a bias current may be detected to measure the X-ray intensity. Even when the TFT of the pixel is turned off, a slight leak current flows through the signal line depending on the amount of signal charge generated in the photodiode. The leakage current may be detected to measure the X-ray intensity. In addition, an element dedicated to X-ray detection may be provided in the X-ray image detection apparatus, and this dedicated element may be provided in the imaging region or outside the imaging region.

  Further, the TFT type FPD in which the TFT matrix substrate is formed using the glass substrate has been described as an example, but an FPD using a CMOS image sensor or a CCD image sensor using a semiconductor substrate may be used. Of these, the use of a CMOS image sensor has the following advantages. In the case of a CMOS image sensor, so-called nondestructive reading is possible in which signal charges accumulated in a pixel are read as a voltage signal through an amplifier provided in each pixel without flowing out to a signal line for reading. According to this, even during the accumulation operation, it is possible to measure the X-ray intensity by selecting an arbitrary pixel in the imaging region and reading the signal charge from the pixel. Therefore, when a CMOS image sensor is used, one of ordinary pixels is used as a detection element for intensity measurement without using a dedicated detection element for X-ray intensity measurement like the short-circuited pixel. It is possible to use both.

  Further, the X-ray image detection apparatus according to the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.

  The X-ray image detection device is used in an X-ray imaging system installed in a hospital radiography room, or may be installed in a round-trip car that can take pictures while visiting a hospital room. The present invention may be applied to a portable system that can be carried to the site where medical care is required or the home of a patient receiving home medical care and can perform X-ray imaging.

  In the above example, the X-ray image detection apparatus and the imaging control apparatus have been described separately. However, the X-ray image detection apparatus includes a function of the imaging control apparatus built in the control unit of the X-ray image detection apparatus. And the imaging control device may be integrated.

  In the above-described embodiment, the 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 13a X-ray tube 14 Radiation source control apparatus 21 X-ray image detection apparatus 23 Imaging control apparatus 24 Console 28 Indicator 36 FPD
37 pixels 62 shorted pixels

Claims (9)

It has an imaging area in which a plurality of pixels that accumulate signal charges according to the amount of radiation incident upon receiving radiation from the radiation source are arranged in a matrix, and detect radiation images by receiving radiation that has passed through the subject. Image detecting means for
Radiation detecting means for detecting radiation emitted from the radiation source and outputting a detection signal corresponding to the amount of incident radiation;
Based on the detection signal of the radiation detection means, to measure the overlapping state of the falling portion of the pulsed radiation previously irradiated from the radiation source and the rising portion of the pulsed radiation irradiated next, Based on the measurement result, the operation mode of the image detecting means is a pulse irradiation compatible mode in which signal charge accumulation and signal charge readout are alternately repeated in synchronization with radiation pulse irradiation, and during continuous radiation irradiation. Control means for setting to one of the continuous irradiation corresponding mode that alternately repeats the accumulation of signal charge for a certain period of time and readout of the signal charge in
A radiological image detection apparatus comprising:   The control means creates a detection profile representing the integrated detection amount of radiation per unit time based on the detection signal of the radiation detection means, and sets the length of the period in which the integrated detection amount of the detection profile is substantially constant. The radiation image detection apparatus according to claim 1, wherein an operation mode of the image detection unit is set accordingly.   The control means sets the operation mode of the image detection means to the continuous irradiation corresponding mode when a period during which the integrated detection amount of the detection profile is substantially constant is shorter than a threshold value. 3. The radiological image detection apparatus according to 2.   The radiological image detection apparatus according to claim 3, wherein the threshold is set based on a falling period of pulsed radiation.   The control unit causes the image detection unit to perform a reset operation to discharge the signal charge accumulated in the pixel within a period in which the integrated detection amount of the detection profile is substantially constant in the continuous irradiation support mode. The radiographic image detection apparatus of Claim 3 or 4 characterized by these.   The control unit monitors the start of radiation irradiation by the radiation source based on the detection signal of the radiation detection unit in the pulse irradiation compatible mode, and detects the image detection when detecting the start of radiation irradiation by the radiation source. The radiological image detection apparatus according to claim 1, wherein accumulation of signal charges is started in the unit.   The control means monitors the end of radiation irradiation by the radiation source based on the detection signal of the radiation detection means in the pulse irradiation compatible mode, and detects the image detection when detecting the end of radiation irradiation by the radiation source. The radiological image detection apparatus according to claim 6, wherein the signal charge is accumulated in the unit and reading of the signal charge is started.   The radiation detection means is a short-circuited pixel in which the pixel and a signal line for reading out the signal charge from the pixel are always short-circuited, and the short-circuited pixel outputs a signal charge corresponding to the amount of incident radiation. The radiographic image detection apparatus according to claim 1, wherein the radiographic image detection apparatus always outputs to a line. A plurality of pixels that receive signal radiation corresponding to the amount of radiation incident upon receiving radiation from the radiation source have image detection means arranged in a matrix, and receive radiation radiation that has passed through the subject to generate a radiation image. In the control method of the radiation image detection device to detect,
Based on the detection signal of the radiation detection means for detecting the radiation dose, the falling portion of the pulsed radiation previously irradiated from the radiation source and the rising portion of the pulsed radiation irradiated next Measuring the overlap state;
Based on the measurement result, the operation mode of the image detecting means is a pulse irradiation compatible mode in which signal charge accumulation and signal charge readout are alternately repeated in synchronization with radiation pulse irradiation, and during continuous radiation irradiation. A step of setting to one of continuous irradiation corresponding modes in which accumulation of signal charge for a certain period of time and readout of signal charge are alternately repeated in
The control method of the radiographic image detection apparatus characterized by including this.

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