WO2013015351A1 - Radiograph detection device and method for controlling same - Google Patents

Abstract

Provided is a radiograph detection device capable of appropriate operation control that is in accordance with the radiation profile of a radiation generation device while suppressing an increase in cost and greater task complexity, even when performing video capture in combination with a radiation generation device that is not capable of communication. On the basis of the output voltage (Vout) of a short circuit pixel (62), an FPD (36) that detects an x-ray image determines whether or not it is possible to detect the fall of a radiation pulse radiated first and the rise of a radiation pulse radiated second in a plurality of radiation pulses that an x-ray generation device (11) sequentially generates. On the basis of the determination result, a control unit (41) sets either: a pulse radiation response mode that detects the rise and fall of an x-ray pulse and synchronizes the timing of an accumulation operation to the detected timing; or a continuous radiation response mode for executing the accumulation operation in a predetermined time interval without detecting the rise or fall of an x-ray pulse.

Description

Radiation image detection apparatus and control method thereof

The present invention relates to a radiological image detection apparatus that detects a radiographic image of a subject and a control method thereof.

In the medical field, X-ray imaging systems using radiation, for example, X-rays, are known. An X-ray imaging system includes an X-ray generation apparatus having an X-ray tube that generates X-rays, and X-ray image detection that detects an X-ray image representing image information of a subject when irradiated with X-rays transmitted through the subject Device. The X-ray generator is given a tube current that determines the dose per unit time of X-rays and a tube voltage that determines the X-ray quality (energy spectrum) as imaging conditions. It is determined for each imaging according to the imaging region and age of the examinee. The X-ray generator irradiates X-rays according 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 for accumulating signal charges according to the amount of X-ray irradiation and a signal line connected to each pixel for reading 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, which is a photoelectric conversion element, and a TFT (Thin Film Transistor). In the indirect conversion type FPD, a scintillator (phosphor) that converts X-rays into visible light is provided so as to be positioned on the imaging region. 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 out of conduction, and an accumulation operation in which signal charges are accumulated in the photodiode is started. On the other hand, when the TFT is turned on, the photodiode and the signal line become conductive, and a read operation for reading signal charges 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 that starts the accumulation operation and the readout operation in synchronization with the X-ray irradiation timing. As a method of synchronization control, a method of communicating a synchronization signal between the X-ray generation device and the X-ray image detection device, an X-ray irradiation amount measured by the X-ray image detection device, and the measured X-ray irradiation amount 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 the fluctuation of the X-ray.

As described in Patent Document 1, an X-ray image detection apparatus can perform moving image shooting such as fluoroscopic shooting by causing an FPD to alternately perform a storage operation and a read operation at a predetermined frame rate. it can. When performing moving image shooting, the X-ray generator continuously irradiates X-rays with a substantially constant X-ray intensity (irradiation amount per unit time) during moving image shooting, or as described in Patent Document 2. As shown, X-rays are pulse-irradiated at a predetermined cycle.

When moving image shooting is performed by pulse irradiation, X-rays are emitted intermittently. Therefore, compared to continuous irradiation, the X-ray pulse intensity is reduced by the amount of X-ray irradiation during moving image shooting. Therefore, it is possible to improve the image quality while suppressing the exposure amount of the subject. However, when performing moving image capturing by pulse irradiation, the X-ray image detection apparatus needs to detect the irradiation timing of the X-ray pulse and synchronize the detected irradiation timing with the FPD accumulation operation. In the X-ray image detection apparatus, the synchronization control is generally a communication system that receives a synchronization signal from the X-ray generation apparatus. If the X-ray generation apparatus does not have a communication function, the synchronization control by the communication system is performed. Can not do.

The X-ray image detection apparatus described in Patent Document 2 monitors a change in the intensity of an X-ray pulse and detects the rise and fall of the X-ray pulse, thereby self-detecting the irradiation timing of the X-ray pulse. Detection means is provided, and the X-ray image detection apparatus performs self-detection type synchronous control that synchronizes the operation of the FPD with the irradiation timing detected by the pulse detection means. With such an X-ray image detection apparatus having a self-detection type synchronization control function, even when communication with the X-ray generation apparatus is not possible, moving image shooting by pulse irradiation can be performed.

JP 2002-301053 A JP 2006-122667 A

However, there is a limit to the self-detection type synchronous control described in Patent Document 2, and there are cases where the self-detection type synchronous control cannot be performed depending on the period of the X-ray pulse, the length of the tail of the X-ray pulse, or the like. is there. FIG. 11 and FIG. 12 show irradiation profiles representing changes with time in the intensity of X-rays when moving images are shot by pulse irradiation. As shown in FIG. 11, when an X-ray tube receives a start command, voltage application is started, and when voltage application is started, the intensity of X-rays rises. Then, the intensity of the X-ray rises to a peak corresponding to the tube current and maintains a substantially steady state. When a stop command is received, the voltage application is stopped and falls. Thereby, one X-ray pulse is generated, and a plurality of X-ray pulses are irradiated with a constant pulse period by repeating this at a constant interval. The rise (irradiation start) and fall (irradiation end) of one X-ray pulse is detected by comparing a voltage signal representing the X-ray intensity with a threshold voltage Vth. When using an X-ray tube composed of a general diode, the response speed of the X-ray tube to the stop command is relatively slow, so the X-ray intensity becomes “0” after receiving the stop command. The time, that is, the length Ts of the wave tail of the X-ray pulse becomes long.

As shown in FIG. 11, when the pulse period PP is relatively long (PP1), even if the wave tail of the X-ray pulse is long, the wave tail of the previously irradiated X-ray pulse and the next irradiated X-ray pulse The rising parts of the line pulses do not overlap. Therefore, the boundary between the two X-ray pulses that are generated sequentially is clear, and the X-ray intensity falls below the threshold voltage Vth in the valley between the two X-ray pulses. The rise and fall of the X-ray pulse can be reliably detected.

On the other hand, as shown in FIG. 12, when the pulse period PP is relatively short (PP2), if the wave tail of the X-ray pulse is long, the wave tail of the previously irradiated X-ray pulse and the next The X-ray pulse rising portion of the X-ray pulse is overlapped, and the valley between the peak of the X-ray pulse and the X-ray pulse becomes unclear. In FIG. 12, hatched portions indicate a portion where two X-ray pulses overlap and an increase in X-ray intensity caused by the overlap. In the irradiation profile of FIG. 12, the X-ray intensity changes in a state exceeding the threshold voltage Vth due to the overlap of X-ray pulses, so that the X-ray intensity is substantially close to a state where X-rays are continuously irradiated. In such a case, since the rise and fall of the X-ray pulse cannot be detected by the pulse detection means described in Patent Document 2, synchronization control by the self-detection method cannot be performed.

As a solution to such a problem, for example, by using an X-ray tube having a function of quickly attenuating the wave tail of an X-ray pulse, such as a triode tube or a tetrode tube, a plurality of X-rays generated sequentially A method for eliminating the overlap of pulses is conceivable. If there is no overlap, the rise and fall of the X-ray pulse can be detected, so that synchronous control by the self-detection method is possible.

However, an X-ray tube having a high response speed is very expensive, and there is a problem that the replacement cost of the X-ray tube increases. Moreover, even if it is replaced with an X-ray tube with a fast response speed, self-detection may not be possible if the frame rate at the time of video recording is extremely short. not.

As another countermeasure, there is a method in which the operator obtains the overlapping state of two X-ray pulses that are sequentially generated by calculation to determine whether or not the self-detection type synchronous control is possible. The length of the wave tail of the X-ray pulse varies depending on the capacity when the X-ray tube is viewed as a resistance, and the tube current and tube voltage set for each imaging. Therefore, if the specification information corresponding to the type of the X-ray tube and the tube current and tube voltage set for each imaging are known, it can be obtained by calculation. If the pulse period set in accordance with the calculated wave tail length of the X-ray pulse and the frame rate of moving image capturing is known, the overlapping state of two X-ray pulses that are sequentially generated can be calculated.

However, the method of calculating the overlap state of X-ray pulses by the operator, even when the same X-ray tube is used, must be calculated according to the tube current and tube voltage that change at each imaging. The work becomes very complicated and is not realistic.

In addition, even if a method using an X-ray tube with a high response speed or a method in which an operator obtains an overlap state of X-ray pulses by calculation, it is necessary to take some measures when the self-detection type synchronous control is impossible. .

Neither Patent Document 1 nor 2 discloses or suggests such problems and solutions.

The present invention enables proper operation control according to the irradiation profile of the radiation generation device while suppressing an increase in cost and complication of work even when performing moving image shooting in combination with a radiation generation device that cannot communicate. It is an object of the present invention to provide a possible radiological image detection apparatus and a control method thereof.

In order to achieve the above object, the radiological image detection apparatus of the present invention is a radiological image detection apparatus used in combination with a radiation generation apparatus that sequentially generates pulsed radiation and performs pulse irradiation of radiation for moving image capturing. The apparatus includes an image detection unit, a radiation detection unit, a determination unit, a mode setting unit, and a control unit. The image detection unit has an imaging region in which a plurality of pixels that receive irradiation of radiation and accumulate signal charges corresponding to the amount of radiation irradiation are arranged in a matrix, and detect a radiation image of the subject. The radiation detection unit detects radiation and outputs a detection signal corresponding to the radiation dose. The determination unit determines whether it is possible to detect rising and falling of a plurality of radiation pulses sequentially generated by the radiation generation device based on the detection signal. The mode setting unit is a mode setting unit that sets the operation mode of the image detection unit based on the determination result of the determination unit, and rises and falls of the radiation pulse based on the detection signal while the pulse irradiation is performed. And the start timing of the accumulation operation for accumulating the signal charge is determined based on the timing at which the rise is detected, and the start timing of the signal charge read operation is determined based on the timing at which the fall is detected. Either a pulse irradiation compatible mode or a continuous irradiation compatible mode in which the accumulation operation and the readout operation are alternately repeated at a predetermined time interval without detecting the rising and falling of the radiation pulse is set. The control unit controls the operation of the image detection unit according to the set mode.

For the radiation irradiated in pulses from the radiation generating device, the determination unit is configured to indicate an irradiation profile representing a change over time in radiation intensity, which is an irradiation amount per unit time, based on a detection signal of the radiation detection unit, and an irradiation amount per unit time It is preferable to make a determination by creating at least one detection profile that represents a change over time in the integrated detection amount obtained by integrating.

It is preferable that the determination unit performs the determination by examining the overlapping state of the rising and falling portions of two X-ray pulses that are sequentially generated based on at least one of the irradiation profile and the detection profile.

It is preferable that the determination unit examines the overlap state by measuring the length of the period in which the integrated detection amount is constant in the detection profile.

When the length of the period during which the integrated detection amount is constant is shorter than a preset threshold, the determination unit determines that the rising and rising of the radiation pulse cannot be detected, and sets the operation mode of the image detection unit. When the continuous irradiation mode is set and the length of the period is equal to or greater than the threshold, it is determined that the rising and falling of the radiation pulse can be detected, and the operation mode of the image detection unit is set to the pulse irradiation mode. It is preferable.

It is preferable that the mode setting unit calculates the accumulation operation time in the continuous irradiation mode.

It is preferable that the mode setting unit measures the pulse period of the radiation pulse based on at least one of the irradiation profile and the detection profile, and calculates the accumulation operation time based on the measured pulse period.

The mode setting unit may calculate the accumulation operation time so that the three operations of the accumulation operation, the subsequent readout operation, and the reset operation for discharging the signal charge accumulated in the pixel are within the pulse period. preferable.

It is preferable that the control unit determines the start timing of the accumulation operation so that the reset operation is executed between the two radiation pulses in the irradiation profile.

It is preferable that the control unit starts the accumulation operation at the timing when the rising edge of the radiation pulse is detected.

It is preferable that the control unit specifies a section where the radiation intensity is maximum in the radiation pulse based on at least one of the irradiation profile and the detection profile, and determines the valley of the radiation pulse based on the specified section.

It is preferable that the controller starts the accumulation operation at the timing when the rising edge of the radiation pulse is detected in the pulse irradiation compatible mode.

It is preferable that the control unit terminates the accumulation operation and starts the reading operation at the timing when the falling edge of the radiation pulse is detected in the pulse irradiation compatible mode.

The radiation detection unit is a short-circuited pixel in which a pixel and a signal line for reading out signal charges from the pixel are always short-circuited, and the short-circuited pixel can always output a signal charge corresponding to the radiation dose to the signal line. preferable.

The method for controlling a radiological image detection apparatus of the present invention is a radiological image detection apparatus that is used in combination with a radiation generation apparatus that sequentially generates pulsed radiation and performs pulse irradiation of radiation in order to perform moving image shooting. In a control method of a radiological image detection apparatus for detecting a radiographic image of a subject, the image detection unit having an image detection unit in which a plurality of pixels that accumulate signal charges according to the amount of radiation irradiated by the generator is arranged in a matrix, a determination step; , Including a mode setting step and a control step. In the determination step, it is determined whether or not the rising and falling of a plurality of radiation pulses sequentially generated by the radiation generating device can be detected based on the detection signal of the radiation detecting unit that detects the radiation dose. The mode setting step is a mode setting step for setting the operation mode of the image detection unit based on the determination result of the determination unit. During the pulse irradiation, the rising and falling of the radiation pulse are detected based on the detection signal. And the start timing of the accumulation operation for accumulating the signal charge is determined based on the timing at which the rise is detected, and the start timing of the signal charge read operation is determined based on the timing at which the fall is detected. A mode setting step for setting to either a pulse irradiation compatible mode or a continuous irradiation compatible mode in which accumulation operation and readout operation are alternately repeated at a predetermined time interval without detecting rising and falling of the radiation pulse. is there. The control step controls the operation of the image detection unit in accordance with the set mode.

According to the present invention, even when a moving image is taken in combination with a radiation generating apparatus that cannot communicate, an appropriate operation according to the irradiation profile of the radiation generating apparatus is achieved while suppressing an increase in cost and complication of work. It is possible to provide a radiological image detection apparatus that can be controlled and a control method therefor.

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 of an irradiation profile and a detection profile when there is no overlap in an X-ray pulse. It is explanatory drawing of an irradiation profile in case an X-ray pulse has an overlap, and a detection profile. It is a flowchart which shows a mode setting procedure. It is a flowchart which shows the control procedure in the pulse irradiation corresponding | compatible mode of FPD. It is operation | movement explanatory drawing of FPD in the pulse irradiation corresponding | compatible mode. It is a flowchart which shows the control procedure in the continuous irradiation corresponding | compatible mode of FPD. It is operation | movement explanatory drawing of FPD in the continuous irradiation corresponding | compatible mode. It is explanatory drawing of an irradiation profile when there is no overlap in an X-ray pulse. It is explanatory drawing of an irradiation profile in case an X-ray pulse has an overlap.

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 is an existing X-ray generator used in, for example, a film cassette or an IP cassette, and does not have a communication function with the X-ray imaging apparatus 12. 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, four lead plates that shield X-rays, and a rectangular irradiation opening that transmits X-rays is formed by the four lead plates. By moving the position, the size of the irradiation aperture is changed to limit the irradiation field. Four lead plates are made into one set, and each set of lead plates is arranged opposite to each other. By arranging each set in two orthogonal directions, a rectangular irradiation opening is formed.

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 a control signal from the irradiation switch 15. When receiving the irradiation start signal generated by pressing the irradiation switch 15 in two steps, the radiation source control unit 14b issues a start command to the X-ray source 13 and starts supplying power. 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, when the radiation source control unit 14b receives an irradiation start signal generated by pressing the irradiation switch 15 in two steps, it starts and stops the X-ray source 13 with a set pulse cycle. By alternately issuing commands, the X-ray source 13 is sequentially irradiated with a plurality of X-ray pulses at a constant pulse period.

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 device 21 includes an FPD 36 (see FIG. 3) and a portable housing that accommodates the FPD 36. The X-ray image detection device 21 emits X-rays that are irradiated from the X-ray source 13 and pass 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 controls the X-ray image detection device 21 via the communication unit that 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 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. Further, the imaging control device 23 sets an operation mode of the X-ray image detection device 21 such as still image shooting or moving image shooting. 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 apparatus 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 which is a notification means for notifying the operation state of the X-ray image detection device 21 and the like is provided. 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 apparatus 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.

Inside the housing 25, various electronic circuits 31, a battery 32, and a communication unit 33 are arranged on one end side along the short side 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 X-ray irradiation are arranged on the 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. An electric field is generated in the semiconductor layer of the photodiode 42 by application of the bias voltage, 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 X-ray irradiation amount 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 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 47 are sequentially activated one by one, and the TFTs 43 connected to the scanning lines 47 are provided for each row. Turn on.

When the TFTs 43 for one row are turned on, the 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 integration amplifiers 49 connected in parallel, and inputs the voltage signals D1 to Dm output from the selected integration 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 the voltage signals D1 to Dm for one row 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.

Further, the FPD 36 self-detects the irradiation timing of the X-ray source 13 without exchanging a synchronization signal with the X-ray generator 11 and synchronizes the operation of the FPD 36 with the detected irradiation timing. It has a synchronization control function. 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, and the photodiode 42 generates a signal charge corresponding to the amount of X-ray irradiation. 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 intensity of X-rays (irradiation amount per unit time) emitted from the X-ray source 13 to the FPD 36 based on the output of the short-circuited pixel 62, and monitors changes in the intensity of X-rays. 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 (detection signal) 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 intensity change of the 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. When performing the synchronous control by the self-detection method, the control unit 41 detects the rise and fall of the X-ray based on the change with time of the output voltage Vout, thereby starting and stopping the X-ray irradiation. Detect timing. In the case of still image shooting, the FPD 36 executes synchronization control by the self-detection method, starts the accumulation operation in accordance with the irradiation start timing, ends the accumulation operation in accordance with the irradiation end timing, and reads out. Migrate to

The FPD 36 has a pulse irradiation mode corresponding to the case where the X-ray source 13 irradiates X-rays as a mode when performing moving image shooting, and the case where the X-ray source 13 continuously irradiates X-rays with substantially constant intensity. There are two operation modes of continuous irradiation corresponding mode. In the pulse irradiation compatible mode, the FPD 36 self-detects the timing of the start and end of X-ray irradiation by self-detecting the rising and falling edges of a plurality of sequentially generated X-ray pulses, as in the case of still image shooting. Synchronous control based on the detection method is executed. Although the pulse irradiation by the X-ray source 13 is performed at a constant pulse cycle, there may be a slight deviation in the rise and fall timings of sequentially generated X-ray pulses, resulting in fluctuations in the pulse cycle. By performing the synchronous control by the self-detection method, the operation of the FPD 36 can accurately correspond to the X-ray pulse irradiation even when the pulse period varies.

The continuous irradiation support mode is a mode corresponding to continuous irradiation of X-rays that are continuously irradiated with a substantially constant X-ray intensity, and is a mode in which an accumulation operation and a reading operation are alternately repeated at predetermined time intervals. In the case of continuous irradiation, since the intensity of X-rays is substantially constant, the FPD 36 may repeat the accumulation operation and the read operation alternately at predetermined time intervals without considering synchronization.

The pulse irradiation compatible mode and the continuous irradiation compatible mode are basically set according to whether the X-ray source 13 performs pulse irradiation or continuous irradiation. As described above, as shown in FIGS. As shown, in the case of pulse irradiation, there are cases where synchronous control by the self-detection method is possible and impossible depending on the X-ray irradiation profile. In the irradiation profiles shown in FIGS. 11 and 12, the width of the X-ray pulse and the length Ts of the wave tail of the X-ray pulse are the same, and only the pulse period is different. When the pulse cycle PP of the X-ray pulse is long (PP1) as in the irradiation profile shown in FIG. 11, there is no overlap between the two X-ray pulses that are sequentially generated, and the valley between the two X-ray pulses is clear. Therefore, synchronous control by the self-detection method is possible.

On the other hand, when the pulse cycle PP of the X-ray pulse is short (PP2) as in the irradiation profile shown in FIG. 12, the two X-ray pulses that are sequentially generated overlap, and the valley between the two X-ray pulses is not good. In a clear case, synchronous control by the self-detection method is impossible. Specifically, in the irradiation profile, when the X-ray intensity does not fall below the threshold voltage Vth in the valley between the two X-ray pulses, the rise and fall of the X-ray pulse cannot be detected. Synchronous control is not possible.

When the X-ray source 13 performs pulse irradiation, the FPD 36 automatically determines whether synchronization control by the self-detection method is possible based on the irradiation profile of the X-ray source 13 and sets the mode according to the determination result. It has a mode setting function. The FPD 36 is set to the pulse irradiation compatible mode when synchronous control by the self detection method is possible, and is set to the continuous irradiation compatible mode when synchronous control by the self detection method is impossible. In the case of the irradiation profile as shown in FIG. 11, the X-ray source is close to the irradiation profile of continuous irradiation in which the X-ray intensity is irradiated in a substantially constant state due to the overlap of two X-ray pulses that are sequentially generated. Even if 13 performs pulse irradiation, it can be operated in the continuous irradiation mode.

The mode setting process of the FPD 36 will be described with reference to FIGS. The FPD 36 determines whether or not synchronization control by the self-detection method is possible in a state where the X-ray source 13 is performing pulse irradiation, and performs mode setting according to the determination result. In the mode setting process, the control unit 41 performs a dose sampling operation, samples the output voltage Vout of the shorted pixel 62 at predetermined time intervals, and records a digitized value of the sampled output voltage Vout in the memory 56. To do. Since the output voltage Vout of the short-circuited pixel 62 represents the X-ray intensity that is the irradiation amount per unit time, an irradiation profile that represents the temporal change in the X-ray intensity is created by sequentially recording the sampled output voltage Vout. The And the control part 41 produces the detection profile showing the time-dependent change of the integrated detection amount which is an integrated value of the irradiation amount per unit time based on an irradiation profile.

In FIG. 4, the irradiation profile is an irradiation profile in the case of the same pulse period PP1 as the irradiation profile shown in FIG. In the detection profile in this case, the integrated detection amount gradually increases as the X-ray pulse rises. When the intensity becomes maximum in one X-ray pulse, the intensity becomes substantially constant in the irradiation profile until a stop command is received. In the detection profile of section C, the increase rate of the integrated detection amount is also maximized, and the integrated detection amount increases almost linearly at the maximum increase rate. In the irradiation profile, when the stop command is received, the intensity of the X-ray pulse starts to decrease. However, when the response speed of the X-ray source 13 is slow, the X-ray intensity does not instantaneously become “0”. Since the irradiation of the X-ray source 13 is continued while the line intensity is attenuated, a wave tail is generated in the X-ray pulse.

In the detection profile shown in FIG. 4, during the wave tail period of the X-ray pulse, the integrated detection amount continues to increase although the increase rate gradually decreases. Then, when the intensity of the X-ray pulse becomes substantially “0”, the increase rate becomes “0”, and the integrated detection amount becomes substantially constant. The period Tf in which the integrated detection amount is substantially constant continues until the next rise of the X-ray pulse. Note that “substantially constant” means, for example, a case where a state where the fluctuation amount of the integrated detection amount is in the range of about 20% in the upper and lower directions continues.

On the other hand, in FIG. 5, the irradiation profile is an irradiation profile in the case of the same pulse period PP2 as the irradiation profile shown in FIG. In the detection profile in this case, as in the case of FIG. 4, the integrated detection amount gradually increases at the rising edge of the first X-ray pulse, and the increase rate becomes maximum in the section C, and the integrated detection amount is the increase rate. Increases almost linearly. In the irradiation profile, the X-ray intensity starts decreasing after the stop command, but the next X-ray pulse rises before the intensity of the first X-ray pulse falls below the threshold voltage Vth. It overlaps the wave tail of the X-ray pulse and the rising portion of the second X-ray pulse.

In the irradiation profile shown in FIG. 5, the X-ray intensity increases in the valley between two X-ray pulses that are sequentially generated in accordance with the amount of overlap of the X-ray pulses. There is little decrease. Therefore, the integrated detection amount continues to increase in the valleys although the rate of increase is lower than that in the section C. Then, when entering the section X of the next X-ray pulse, the integrated detection amount increases linearly again at the maximum increase rate. The control unit 41 measures the period Tf from the detection profile. In the case of the irradiation profile shown in FIG. 5, the period Tf in which the integrated detection amount is substantially constant is “0”. In this way, by measuring the period Tf in which the integrated detection amount is substantially constant, it is possible to investigate the overlapping state of two X-ray pulses that are sequentially generated.

The control unit 41 measures the period Tf from the detection profile, and then compares the period Tf with a predetermined threshold Th. As in the example of FIG. 4, when the period Tf is equal to or greater than the threshold Th, the control unit 41 determines that the synchronous control by the self-detection method is possible and sets the pulse irradiation compatible mode. . On the other hand, when the period Tf is smaller than the threshold Th, it is determined that the synchronous control by the self-detection method is impossible, and the continuous irradiation mode is set.

The control unit 41 further measures the pulse period PP from the detection profile when the continuous irradiation mode is set. The measurement of the pulse period PP is performed by the following procedure, for example. From the detection profile, the control unit 41 specifies a section C in which the increase rate of the integrated detection amount is the maximum and the integrated detection amount increases linearly at the increase rate. Then, the start time interval of each section C of two X-ray pulses that are sequentially generated is calculated as a pulse period PP. Of course, the end time interval may be obtained instead of the start time of the section C. Further, the control unit 41 calculates the accumulation operation time based on the measured pulse period PP. Since it is preferable that a series of operations of accumulation operation, read operation, and reset operation is performed during the pulse period PP, the FPD 36 requires the time for the accumulation operation from, for example, the pulse period PP to the reset operation and the read operation. The remaining time obtained by subtracting this time is calculated as the accumulation operation time.

As described above, the control unit 41 determines whether the rising and falling of the X-ray pulse can be determined. Based on the determination result, either the pulse irradiation compatible mode or the continuous irradiation compatible mode. Functions as a mode setting unit for setting to

When performing moving image shooting by pulse irradiation, the above mode setting process is executed, and either the pulse irradiation compatible mode or the continuous irradiation compatible mode is set. After the mode setting process is executed, the main shooting of moving image shooting is started. When the FPD 36 operates in the pulse irradiation compatible mode, the FPD 36 performs self-detection type synchronous control that self-detects the rising (irradiation start) and falling (irradiation end) of X-ray pulses sequentially generated from the X-ray source 13. . When the FPD 36 operates in the continuous irradiation-compatible mode, the time accumulation operation and the read operation calculated according to the pulse cycle PP of the X-ray source 13 are repeatedly executed in the pulse cycle PP.

Hereinafter, the operation of the above configuration will be described with reference to the flowcharts of FIGS. 6, 7, and 9, and the timing charts of FIGS. When performing video imaging with the X-ray imaging system 10, first, the position of the imaging region of the subject H and the irradiation position of the X-ray source 13 with respect to the imaging table 22 on which the X-ray image detection device 21 is set. Matching is done. The console 24 is input with an examination order such as a patient's sex, age, imaging region, imaging purpose, and imaging conditions such as tube current and tube voltage. In the case of moving image shooting, the shooting conditions include the irradiation method (pulse irradiation or continuous irradiation) of the X-ray source 13. The imaging conditions input to the console 24 are transmitted to the X-ray image detection device 21 via the imaging control device 23. Further, the imaging conditions are set for the X-ray source 13 by the operator based on the imaging conditions input to the console 24.

When the irradiation method of the X-ray source 13 is continuous irradiation, an imaging preparation instruction is input from the console 24 to the X-ray image detection device 21 to place the FPD 36 in a standby state. In the standby state, the FPD 36 repeatedly executes the reset operation. In the standby state, the FPD 36 also starts monitoring the output voltage Vout of the shorted pixel 65 and waits for the start of X-ray irradiation. When the irradiation switch 15 is operated and X-ray irradiation is started from the X-ray source 13, the FPD 36 detects that X-ray irradiation has started when the output voltage Vout of the short-circuited pixel exceeds the threshold voltage Vth. . When the start of irradiation is detected, moving image shooting is started. In the case of continuous irradiation, X-rays are continuously emitted from the X-ray source 13 at a constant X-ray intensity. Therefore, the FPD 36 performs a storage operation for a predetermined time in accordance with a predetermined frame rate and subsequent readout. Repeat the operation and the reset operation. The read images are sequentially transmitted to the console 24 and displayed.

When the irradiation method of the X-ray source 13 is pulse irradiation, the mode setting process of the X-ray image detection device 21 is executed before moving image shooting. When a mode setting instruction is input from the console 24 to the X-ray image detection apparatus 21, the FPD 36 starts the mode setting process shown in the flowchart of FIG. An X-ray irradiation start signal is input to the X-ray source 13 by operating the irradiation switch 15, and pulse irradiation of the X-ray source 13 is started. In the mode setting process, as shown in FIGS. 4 and 5, the FPD 36 performs an irradiation amount sampling operation for sampling the output voltage Vout of the short-circuited pixel 65, and the irradiation profile and detection based on the sampled output voltage Vout. A profile is created (S001).

Then, the FPD 36 measures a period Tf in which the integrated detection amount is constant from the detection profile (S002). As shown in FIG. 4, when the measured period Tf is equal to or greater than the threshold Th (N in S003), the FPD 36 determines that synchronization control by the self-detection method is possible and sets the pulse irradiation compatible mode ( S004).

On the other hand, as shown in FIG. 5, when the measured period Tf is smaller than the threshold value Th (Y in S003), the FPD 36 determines that the synchronous control by the self-detection method is impossible, and the continuous irradiation corresponding mode. (S005). When the FPD 36 is set to the continuous irradiation compatible mode, the section C in which the integrated detection amount is constant is specified from the detection profile, and the time interval between the start or end of the section C of the two X-ray pulses is determined. The pulse period PP is measured (S006). Based on the measured pulse period PP, the accumulation operation time is calculated (S007).

After the mode setting process is completed, the pulse irradiation of the X-ray source 13 and the irradiation amount sampling operation of the FPD 36 are temporarily stopped. Then, moving image shooting by pulse irradiation is started in the set operation mode.

In the pulse irradiation compatible mode, the FPD 36 executes moving image shooting according to the procedure shown in the flowchart of FIG. 7 and the timing chart of FIG. The FPD 36 is shifted from the stop state to the standby state by the input of the shooting preparation instruction, and the reset operation is started (S101). Simultaneously with the reset operation, measurement of the X-ray intensity by monitoring the output voltage Vout of the short-circuited pixel 65 is started (S102).

When an irradiation start signal is input to the X-ray source 13 by pressing the irradiation switch 15, as shown in FIG. 8, the X-ray source 13 generates an X-ray pulse in response to an input of a start command and a stop command. Then, pulse irradiation for irradiating the subject H with a plurality of X-ray pulses at regular intervals is started. The control unit 41 compares the output voltage Vout and the threshold voltage Vth and monitors the change in the X-ray intensity (S103). As shown in FIG. 8, it is detected that X-ray irradiation has started when the X-ray intensity increases and the output voltage Vout exceeds the threshold voltage Vth (S104). When detecting the start of irradiation, the control unit 41 starts an accumulation operation (S105).

The FPD 36 compares the output voltage Vout and the threshold voltage Vth during the accumulation operation, and monitors the X-ray intensity change (S106). As shown in FIG. 8, when the X-ray intensity of the X-ray pulse starts to decrease and the FPD 36 detects the end of irradiation when the output voltage Vout becomes equal to or lower than the threshold voltage Vth (S107). The FPD 36 ends the accumulation operation in synchronization with the detection of the end of irradiation (S108). The FPD 36 executes a read operation when the accumulation operation is completed. When the read operation is completed, a reset operation is performed until the next irradiation start is detected (S109). The read X-ray image is recorded in the memory 56. While the pulse irradiation from the X-ray source 13 continues, the FPD 36 repeats the above steps S103 to S109 (S110) and executes moving image shooting of the subject. A plurality of images taken for each X-ray pulse are sequentially transmitted from the memory 56 to the console 24 and displayed on the console 24.

On the other hand, in the continuous irradiation compatible mode, the FPD 36 performs moving image shooting according to the procedure shown in the flowchart of FIG. 9 and the timing chart of FIG. When the imaging preparation instruction is input, the FPD 36 shifts from the stop state to the standby state and starts a reset operation (S201). Simultaneously with the reset operation, measurement of the X-ray intensity by monitoring the output voltage Vout of the shorted pixel 65 is started (S202).

When an irradiation start signal is input to the X-ray source 13 by pressing the irradiation switch 15, as shown in FIG. 10, the X-ray source 13 generates an X-ray pulse in response to an input of a start command and a stop command. Then, pulse irradiation for irradiating the subject H with a plurality of X-ray pulses at regular intervals is started. The control unit 41 compares the output voltage Vout with the threshold voltage Vth and monitors the change in the X-ray intensity (S203). As shown in FIG. 10, when the X-ray intensity increases and the output voltage Vout exceeds the threshold voltage Vth, it is detected that X-ray irradiation has started (Y in S203). The operation so far is the same as in the pulse irradiation compatible mode.

In the continuous irradiation compatible mode, when the FPD 36 detects the start of irradiation, the FPD 36 starts an accumulation operation for the time calculated in the mode setting process described in FIG. 5 (S204). After a predetermined time has elapsed, the FPD 36 ends the accumulation operation, and executes a read operation and a reset operation (S205). When the reset operation is completed, the FPD 36 repeats the accumulation operation, the read operation, and the reset operation at predetermined time intervals. The FPD 36 repeats the above steps S204 and S205 while the X-ray irradiation from the X-ray source 13 continues and the pulse irradiation continues (S206).

In the continuous irradiation mode, the accumulation operation time is a time calculated based on the pulse period PP measured in the mode setting process (see FIGS. 5 and 6). Even in such a case, moving image shooting can be performed at a frame rate synchronized with the pulse period PP.

In this example, the accumulation operation is started in accordance with the detection timing of the first X-ray pulse irradiation start, and thereafter, the accumulation operation is repeated in accordance with the pulse period PP. The timing of the operation and the reset operation can be adjusted to a valley between two X-ray pulses in which the X-ray intensity decreases.

As described above, according to the X-ray image detection device 21 of the present invention, when performing moving image shooting by pulse irradiation, an appropriate operation mode is determined based on the irradiation profile of the X-ray generation device 11, and the self- When the synchronous control of the detection method is possible, it operates in the pulse irradiation compatible mode, and when the synchronous control of the self-detection method is impossible, it operates in the continuous irradiation compatible mode. Appropriate operation control can be performed.

In the case of an X-ray image detection device that can only perform self-detection type synchronous control, such as the device described in the conventional patent document 2, there may be cases where moving image shooting cannot be performed depending on the irradiation profile of the X-ray source 13. Therefore, in order to use the X-ray image detection apparatus described in Patent Document 2, it is necessary to use an expensive X-ray tube having a fast response speed of the falling edge of the X-ray pulse. On the other hand, according to the X-ray image detection apparatus 21 of the present invention, the pulse irradiation compatible mode and the continuous irradiation compatible mode are selectively used according to the irradiation profile, and the synchronous control of the self-detection method is impossible. Since it corresponds by the continuous irradiation corresponding | compatible mode, it can image | video using a general X-ray tube, without using an expensive X-ray tube. Therefore, there is no increase in cost such as the replacement cost of the X-ray tube. The X-ray image detection apparatus 21 of the present invention capable of such a flexible response is highly useful when used in combination with an existing X-ray generation apparatus.

In addition, since the mode setting of the pulse irradiation compatible mode and the continuous irradiation compatible mode is automatically performed according to the irradiation profile, even when the X-ray image detection device 21 is used in combination with the X-ray generation device 11 that cannot communicate. No complicated setting work is required.

Whether or not synchronization control by the self-detection method is possible depends on the overlapping state of the X-ray pulses in the irradiation profile, but whether or not the X-ray pulses overlap is determined by various factors as described below. The Therefore, the effect of the present invention by automatically determining whether or not the synchronous control by the self-detection method is possible according to the irradiation profile is particularly useful.

In this example, as in the irradiation profiles shown in FIG. 4 and FIG. 5, using two examples in which the width of the X-ray pulse and the length Ts of the wave tail of the X-ray pulse are the same and only the pulse period is different. Although the case where X-ray pulses are overlapped and the case where there is no overlap has been described, there are two cases in which the length of the wave tail Ts of the X-ray pulse changes depending on the tube current or tube voltage even if the pulse period is the same. X-ray pulse overlap may occur.

That is, the intensity of the X-ray pulse after the stop command falls exponentially with a time constant τ determined according to the tube current and the tube voltage, and 3 to 5 times the time constant τ for the intensity to become “0”. It is known to take a long 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 tube can be obtained by τ = RC = V / I (CTube + Cline × L).

Specific values of the parameters for obtaining the time constant τ are, for example, the capacitance C _Tube of the X-ray tube 13a is 500 to 1000 [pF], and the capacitance C _Line of the high voltage cable 14c is 100 to 200 [p. pF / m], the cable length L of the high voltage cable 14c is 10 to 20 [m], the tube voltage V is 50 to 150 [kV], and the tube current I is 0.5 to 20 [mA]. It is. The value of the time constant τ obtained from these parameter values is about several ms to several tens of ms.

From the above, the length of the wave tail Ts of the X-ray pulse 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 or the tube current is small. Or it becomes long, so that a tube voltage becomes high. Thus, even when pulse irradiation is performed with the same X-ray tube at the same pulse period, the length of the wave tail Ts of the X-ray pulse changes according to the tube current and tube voltage set for each imaging. Depending on the length of the wave tail Ts, there may or may not be overlap of X-ray pulses.

Furthermore, even if there are overlapping X-ray pulses, if there are few overlapping parts, synchronous control by the self-detection method may be possible. As described above, in pulse irradiation, whether or not the self-detection type synchronous control in the X-ray image detection apparatus is possible depends on the performance of the X-ray tube, the pulse cycle (the frame rate of the corresponding moving image capturing), and the X-ray pulse. It is determined by various factors such as imaging conditions (tube current and tube voltage) that determine the wave tail length Ts. The present invention examines the overlapping state of X-ray pulses based on the irradiation profile taking these factors into account, and determines whether or not the self-detection type synchronous control is possible, thereby greatly reducing complicated setting work. It becomes possible to do.

In the above example, after performing the mode setting process shown in FIGS. 4 and 5, the X-ray irradiation is once stopped and then the moving image shooting shown in FIGS. 8 and 10 is started. The mode setting process may be shifted to video shooting without stopping.

However, in this case, it is necessary to determine the timing for starting the accumulation time by a method different from the above example in the continuous irradiation mode. This is because in the above example, in the continuous irradiation mode, the timing for starting the accumulation operation is synchronized with the rising edge of the first X-ray pulse. When shifting to imaging, the X-ray intensity does not fall below the threshold voltage Vth in the irradiation profile, so the method of the above example cannot be adopted. Therefore, for example, the start timing of the accumulation operation is determined by the following method. In the mode setting process, since the section C in which the intensity of the X-ray pulse is maximum is specified from the detection profile, information on the section C is used. If the end of section C is known, the valley of the X-ray pulse can be specified, and the start timing of the accumulation operation is determined so that the read operation and the reset operation are accommodated there.

In the above example, the pulse period PP is measured from the start or end of the section C specified from the detection profile, but an irradiation profile may be used instead of or in addition to the detection profile. By examining the section where the X-ray intensity becomes the maximum in the irradiation profile, the section C can be specified.

In the above example, whether or not the rising and falling of the two X-ray pulses can be detected by measuring the overlapping state of two X-ray pulses that are sequentially generated based on the detection profile, that is, self Although it is determined whether or not the synchronous control by the detection method is possible, the determination may be made based on the irradiation profile instead of or in addition to the detection profile. For example, as shown in FIG. 5, also in the irradiation profile, the X-ray intensity between the valleys of two overlapping X-ray pulses is lower than the maximum intensity of the X-ray pulse. By comparing the X-ray intensity between the valleys of the X-ray pulse and the threshold voltage Vth, if the X-ray intensity between the valleys is lower than the threshold voltage Vth, it is determined whether the rising and falling of two X-ray pulses can be detected. Can be determined.

In addition, when the threshold voltage Vth changes, even when the irradiation profile is substantially the same (even if the overlapping state of the two X-ray pulses is the same), the rise and fall of the X-ray pulse may or may not be detected. As a result, the determination result of whether or not the pulse irradiation mode can be set also changes. For example, even in the irradiation profiles shown in FIGS. 5 and 10, when the threshold voltage Vth is higher than the minimum value of the X-ray intensity in the valley between two X-ray pulses, the rise and fall of the X-ray pulse Can be detected.

Therefore, when the threshold voltage Vth is changed, the control unit 41 determines whether or not the self-detection type synchronous control is possible based on the changed threshold voltage Vth, and the pulse irradiation compatible mode. It is preferable to determine whether or not setting is possible. As a factor for changing the threshold voltage Vth, for example, there is a material of a target (anode) of the X-ray tube 13a. As a target material of the X-ray tube 13a, tungsten (W), molybdenum (Mo), or the like is used. For example, the threshold voltage Vth is set to about 15 kV in the case of tungsten, and about 5 kV in the case of molybdenum. When the threshold voltage Vth and the target material of the X-ray tube 13a have a one-to-one correspondence, the control unit 41 is based on information on the type of the X-ray tube 13a representing the target material of the X-ray tube 13a. Thus, the threshold voltage Vth may be specified. Information regarding the type of the X-ray tube 13a is input through the console 24, for example. The control unit 41 changes the set value to the specified threshold voltage Vth and makes a determination based on the changed set value.

In the irradiation profile, when the drop in the X-ray intensity between the valleys of the X-ray pulse is very small, the X-ray source 13 may be regarded as equivalent to the irradiation profile in the case of continuously irradiating X-rays with a constant intensity. is there. In that case, the FPD 36 may start the accumulation operation at an arbitrary timing without performing the process of determining the start timing of the accumulation operation in the continuous irradiation mode.

Further, the control unit 41 may determine whether or not it is necessary to determine the start timing of the accumulation operation by examining the degree of X-ray intensity drop in the valley of the X-ray pulse based on the irradiation profile. .

In the above example, in the pulse irradiation compatible mode, the accumulation operation is started at the timing when the rising edge of the X-ray pulse is detected, and the reading operation is started at the timing when the falling edge of the X-ray pulse is detected. The accumulation operation and the read operation may be started after a predetermined time has elapsed from the detection of the rise or fall. In other words, the timing at which rising or falling is detected does not have to coincide completely with the timing at which accumulation or reading operation starts, and the timing at which accumulation or reading operation starts is based on the timing at which rising or falling is detected. It only has to be decided.

The X-ray intensity is measured by the short-circuited pixel 62 provided in the imaging region 38. However, 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 X-ray intensity, 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.

Further, the form of the radiation detection unit for measuring the X-ray intensity is not limited to the short-circuited pixel, and there are various forms. 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. This leakage current may be detected to measure the X-ray intensity.

In the method of detecting the bias current and the leak current, the radiation detecting unit is configured by the wiring through which the bias current and the leak current are disposed and the ammeter that detects the current flowing through the wiring, which are provided in the FPD 36. If the method detects a bias current or a leak current, the function of the radiation detection unit can be added to the FPD 36 without greatly modifying the structure of the imaging region of the FPD 36. In the case of the method for detecting the leakage current, the image reading circuit of the FPD 36 can be used as the current detection unit. In addition, in the method of detecting the bias current and the leakage current, the signal charge accumulation state representing the image is maintained even if radiation detection is performed during irradiation. Therefore, pixel defects (point defects or line defects) are detected in the read image. ) Does not occur.

Further, instead of providing the short-circuited pixel, a part of the plurality of pixels 37 in the FPD 36 may be used as a detection element constituting the radiation detection unit. For example, for a pixel that also serves as a detection element, a radiation detection TFT and a dedicated detection wiring are provided separately from the image readout TFT. Then, when reading an image, the image reading TFT is turned on to read the charge from the signal line, and when used as a detection element, the radiation detection TFT gate is turned on to read the charge from the dedicated detection wiring. Thus, two TFTs are selectively used. Of course, the leakage current leaking from the TFT to the dedicated wiring may be read with the TFT turned off. Alternatively, when a part of the pixel 37 is used as a detection element, the structure of the pixel 37 is a structure in which the photodiode is divided into two, such as an image detection photodiode and a detection element photodiode. In the above, each photodiode may be provided with a TFT so that each can be selectively used.

In addition, when a dedicated detection element constituting the radiation detection unit is provided separately from the pixel 37, it may be disposed between the plurality of pixels 37. The detection element may be provided outside the imaging area. Moreover, you may use well-known radiation detection parts, such as an ion chamber, as a radiation detection part.

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, any one of the normal pixels is used as the radiation for measuring the X-ray intensity without using a dedicated radiation detection unit for measuring the X-ray intensity as in the case of the short-circuited pixel. It can also be used as a detection unit.

Furthermore, the X-ray image detection apparatus according to the present invention is not limited to the above-described embodiment, but can of course have various configurations 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 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 γ 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 (15)

1. In a radiological image detection apparatus used in combination with a radiation generation apparatus that sequentially generates pulsed radiation and performs pulse irradiation of radiation to perform moving image shooting,
   An image detection unit that has an imaging region in which a plurality of pixels that accumulates signal charges corresponding to the radiation dose upon receiving the radiation is arranged in a matrix, and detects a radiographic image of the subject;
   A radiation detector that detects the radiation and outputs a detection signal corresponding to the radiation dose;
   A determination unit that determines whether it is possible to detect the rising and falling of a plurality of radiation pulses that are sequentially generated by the radiation generating device based on the detection signal;
   A mode setting unit configured to set an operation mode of the image detection unit based on a determination result of the determination unit, and during the pulse irradiation, rise and fall of the radiation pulse based on the detection signal Detecting and determining the start timing of the accumulation operation for accumulating the signal charge based on the timing when the rising edge is detected, and determining the start timing of the signal charge reading operation based on the timing when the falling edge is detected A mode setting unit configured to set one of a corresponding mode and a continuous irradiation corresponding mode in which the accumulation operation and the reading operation are alternately repeated at a predetermined time interval without detecting the rising and falling of the radiation pulse; ,
   A control unit for controlling the operation of the image detection unit according to the set mode;
   A radiological image detection apparatus comprising:
2. The determination unit includes an irradiation profile representing a change over time in radiation intensity, which is an irradiation amount per unit time, based on a detection signal of the radiation detection unit, and per unit time for the radiation irradiated by the radiation from the radiation generation apparatus. The radiological image detection apparatus according to claim 1, wherein the determination is performed by creating at least one detection profile representing a change over time in the integrated detection amount obtained by integrating the irradiation amounts of the two.
3. The determination unit performs the determination by examining an overlapping state of rising portions and falling portions of two X-ray pulses that are sequentially generated based on at least one of the irradiation profile and the detection profile. 3. A radiological image detection apparatus according to item 2.
4. The radiological image detection apparatus according to claim 3, wherein the determination unit examines the overlapping state by measuring a length of a period in which the integrated detection amount is constant in the detection profile.
5. The determination unit determines that the rising and rising of the radiation pulse cannot be detected when the length of the period during which the integrated detection amount is constant is shorter than a preset threshold, and the image detection unit When the operation mode is set to the continuous irradiation mode and the length of the period is equal to or greater than the threshold, it is determined that the rising and falling of the radiation pulse can be detected, and the operation of the image detection unit The radiographic image detection apparatus according to claim 4, wherein the mode is set to the pulse irradiation compatible mode.
6. The radiological image detection device according to any one of claims 2 to 5, wherein the mode setting unit calculates a time of the accumulation operation in the continuous irradiation-supporting mode.
7. The mode setting unit measures a pulse period of the radiation pulse based on at least one of the irradiation profile and the detection profile, and calculates a time of the accumulation operation based on the measured pulse period. 7. A radiological image detection apparatus according to item 6.
8. The mode setting unit performs the accumulation operation so that the three operations of the accumulation operation, the subsequent readout operation, and the reset operation for discharging the signal charge accumulated in the pixel are accommodated within the pulse period. The radiological image detection apparatus according to claim 7, wherein the time is calculated.
9. The radiological image detection apparatus according to claim 8, wherein the control unit determines a start timing of the accumulation operation so that the reset operation is executed between two radiation pulse valleys in the irradiation profile.
10. The radiological image detection apparatus according to claim 9, wherein the control unit starts the accumulation operation at a timing when the rising of the radiation pulse is detected.
11. The control unit identifies a section where the radiation intensity is maximum in the radiation pulse based on at least one of the irradiation profile and the detection profile, and determines a valley of the radiation pulse based on the identified section. The radiographic image detection apparatus according to claim 9.
12. The radiological image detection according to any one of claims 1 to 11, wherein the control unit starts the accumulation operation at a timing when a rising edge of the radiation pulse is detected in the pulse irradiation compatible mode. apparatus.
13. 13. The radiological image detection apparatus according to claim 12, wherein the control unit ends the accumulation operation and starts the reading operation at a timing when the falling of the radiation pulse is detected in the pulse irradiation compatible mode. .
14. The radiation detection unit 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 radiation dose to the signal. The radiological image detection apparatus according to any one of claims 1 to 13, wherein the radiation image detection apparatus constantly outputs to a line.
15. A radiographic image detection apparatus used in combination with a radiation generation apparatus that sequentially generates pulsed radiation and performs pulse irradiation of radiation in order to perform movie shooting, and a signal corresponding to the radiation dose by the radiation generation apparatus In a control method of a radiological image detection apparatus that has an image detection unit in which a plurality of pixels that accumulate electric charges are arranged in a matrix and detects a radiographic image of a subject,
    A determination step for determining whether or not it is possible to detect the rising and falling of a plurality of radiation pulses sequentially generated by the radiation generating device, based on a detection signal of a radiation detecting unit that detects an irradiation amount of radiation;
    A mode setting step for setting an operation mode of the image detection unit based on a determination result of the determination unit, and during the pulse irradiation, rising and falling of the radiation pulse are performed based on the detection signal. Detecting and determining the start timing of the accumulation operation for accumulating the signal charge based on the timing when the rising edge is detected, and determining the start timing of the signal charge reading operation based on the timing when the falling edge is detected A mode setting step for setting one of a corresponding mode and a continuous irradiation corresponding mode in which the accumulation operation and the readout operation are alternately repeated at predetermined time intervals without detecting the rising and falling of the radiation pulse; ,
    A control step for controlling the operation of the image detection unit according to a set mode;
    The control method of the radiographic image detection apparatus characterized by including this.

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