Patent Description:
In medical image diagnosis and nondestructive inspection, a radiation imaging apparatus using a sensor which detects radiation has been broadly used. Such a radiation imaging apparatus is known to monitor radiation entering the radiation imaging apparatus and detect the start and end of radiation irradiation and the integrated irradiation amount of radiation. <CIT> describes a radiation imaging system in which a radiation control apparatus for controlling radiation irradiation controls the timing of stopping radiation irradiation based on arrival dose information including an arrival dose output from a radiation imaging apparatus and information of the time at which the arrival dose was acquired. <CIT> discloses an X-ray imaging system with an automatic exposure control module configured to calculate a corrected exposure dose based on an actual dose rate and a correction factor.

The time required for the radiation control apparatus to acquire the arrival dose information output from the radiation imaging apparatus can fluctuate due to a communication delay caused by external noise or the like. The fluctuation of the time required for the radiation control apparatus to acquire the arrival dose information can affect control of radiation irradiation.

Some embodiments of the present invention provide a technique advantageous in control of radiation irradiation.

According to one aspect, a radiation imaging system is provided as defined in claims <NUM> to <NUM>.

According to another aspect, a radiation control apparatus is provided as defined in claim <NUM>.

According to yet another aspect, a control method of a radiation control apparatus is provided as defined in claim <NUM>.

According to still another aspect, a program for causing a computer to execute a control method is provided as defined in claim <NUM>.

The radiation control apparatus may specify, based on the dose information, a threshold time at which an arrival dose entering the radiation imaging apparatus reaches the threshold dose. The radiation control apparatus may set the threshold dose based on a difference between a time included in one piece of dose information among a plurality of pieces of the dose information and a time at which the radiation control apparatus acquired the one piece of dose information. The radiation control apparatus may set the threshold dose based on differences between times included in two or more pieces of dose information among a plurality of pieces of the dose information and times at which the radiation control apparatus acquired the two or more pieces of dose information, respectively. If the difference exceeds a predetermined threshold, the radiation control apparatus may set the threshold dose. The radiation control apparatus may set the threshold dose based on dose information, among a plurality of pieces of the dose information, acquired at a preset timing. The radiation control apparatus may set the threshold dose based on dose information, among a plurality of pieces of the dose information, acquired at a timing at which a predetermined period has elapsed since the threshold dose was last changed. If the arrival dose reaches the threshold dose or if a time reaches the threshold time, the radiation control apparatus may control the radiation source to stop radiation irradiation. Based on the dose information and the threshold time, the radiation control apparatus may transmit a signal which causes
the radiation source to stop radiation irradiation. Based on a time from when the signal is transmitted to when the radiation source stops radiation irradiation, the radiation control apparatus may set at least one of the threshold dose or the threshold time.

The radiation control apparatus and the radiation source may be configured to capable of communication by wired communication. The radiation imaging apparatus and the radiation control apparatus may be configured to capable of communication by wireless communication.

The system may include a synchronizer configured to synchronize a time of the radiation imaging apparatus and a time of the radiation control apparatus. The synchronizer may be configured to synchronize the time of the radiation imaging apparatus and the time of the radiation control apparatus by wired communication or wireless communication. The synchronizer may synchronize the time of the radiation imaging apparatus and the time of the radiation control apparatus before radiation is emitted. The synchronizer may set the time of the radiation imaging apparatus based on the time of the radiation control apparatus.

Radiation in the present invention can include α-rays, β-rays, γ-rays, and the like, which are beams generated by particles (including photons) emitted by radiation decay, as well as beams having the similar or higher energy, for example, X-rays, particle beams, cosmic rays, and the like.

With reference to <FIG>, the configuration and operation of a radiation imaging system according to an embodiment will be described. <FIG> shows a configuration example of a radiation imaging system <NUM> according to this embodiment. The radiation imaging system <NUM> is used, for example, when capturing a radiation image in a hospital, and includes a radiation imaging apparatus <NUM>, a control apparatus <NUM>, a radiation source <NUM>, a radiation source control apparatus <NUM>, a LAN <NUM> (in-hospital LAN), and a radiation control apparatus <NUM> as its functional components.

The radiation imaging apparatus <NUM> detects radiation emitted from the radiation source <NUM> and transmitted through a subject. A radiation image is captured based on the radiation detected by the radiation imaging apparatus <NUM>. The control apparatus <NUM> includes, as functional components, a communication controller <NUM> that controls communication, and a controller <NUM> that controls an overall operation of the control apparatus <NUM>. For example, the controller <NUM> of the control apparatus <NUM> generates setting information for setting an image condition, setting operation control, and the like with respect to the radiation imaging apparatus <NUM>. And the communication controller <NUM> of the control apparatus <NUM> transmits, to the radiation imaging apparatus <NUM>, the setting information for setting the imaging condition, setting the operation control, and the like.

The radiation imaging apparatus <NUM> transmits, for example, information of an image captured based on the set imaging condition setting, operation control setting, and the like, the arrival dose, and the like to the control apparatus <NUM>. For example, the control apparatus <NUM> can use a mouse and a keyboard as input devices and can use a display <NUM> or the like as an output device to allow input and output of information, such as the imaging condition setting, operation control setting, and the like.

The radiation source <NUM> includes, for example, a rotor and a radiation tube that accelerates electrons by a high voltage and collides them against an anode to generate radiation. The radiation emitted from the radiation source <NUM> is applied to the subject. The radiation imaging apparatus <NUM> detects the radiation transmitted through the subject and generates a signal for forming a radiation image.

The radiation control apparatus <NUM> acquires dose information output from the radiation imaging apparatus <NUM>, which includes the dose of radiation entering the radiation imaging apparatus <NUM>, and information (timer information) of the time measured by a sensor timer <NUM> of the radiation imaging apparatus <NUM>. Although details will be described later, based on information such as the dose information, the radiation control apparatus <NUM> outputs, to the radiation source control apparatus <NUM>, an irradiation control signal for controlling radiation irradiation via the radiation source <NUM>.

<FIG> is a view showing an example of data communication between respective apparatuses of the radiation imaging system <NUM>. The radiation imaging apparatus <NUM> can include, for example, two communication units, such as a wireless communication unit and a wired communication unit. The radiation imaging apparatus <NUM> is configured to be capable of communication with the communication controller <NUM> of the control apparatus <NUM> and a communication controller <NUM> of the radiation control apparatus <NUM> by using the two communication units. In data communication <NUM> between the control apparatus <NUM> and the radiation imaging apparatus <NUM>, information, such as the imaging condition setting, the operation control setting, transfer of image information, and the arrival dose, are transmitted. In data communication <NUM> between the radiation control apparatus <NUM> and the radiation imaging apparatus <NUM>, the above-described dose information including information of the dose entering the radiation imaging apparatus <NUM> and information of the time at which the dose was detected, and the like, are transmitted. In the data communication <NUM>, the radiation imaging apparatus <NUM> may be configured to be capable of communication with the communication controller <NUM> of the radiation control apparatus <NUM> by using the wireless communication unit. The radiation control apparatus <NUM> outputs information, such as an irradiation control signal, to the radiation source control apparatus <NUM> based on the acquired dose information. That is, the irradiation control signal and the like are transmitted in data communication <NUM> between the radiation control apparatus <NUM> and the radiation source control apparatus <NUM>. In the data communication shown in <FIG>, the dose information indicates the dose which was emitted from the radiation source <NUM> to the radiation imaging apparatus <NUM> and arrived at the radiation imaging apparatus <NUM>.

The irradiation control signal transmitted from the radiation control apparatus <NUM> to the radiation source control apparatus <NUM> can include two signals of a stop signal (irradiation-stop signal) for stopping radiation irradiation, and an irradiation signal (non-irradiation-stop signal) for causing radiation irradiation. By controlling output of both or one of the stop signal and the irradiation signal, the radiation control apparatus <NUM> can control irradiation and the stopping of irradiation from the radiation source <NUM> via the radiation source control apparatus <NUM>.

For example, as an example of controlling the output of one of the stop signal and the irradiation signal, the radiation control apparatus <NUM> outputs the irradiation signal during radiation irradiation, and the radiation control apparatus <NUM> stops output of the irradiation signal when stopping the radiation irradiation. Also, for example, the radiation control apparatus <NUM> may stop output of the stop signal during radiation irradiation, and the radiation control apparatus <NUM> may output the stop signal when stopping the radiation irradiation. In this manner, by switching between outputting and stopping the outputting of the irradiation signal or the stop signal, the radiation control apparatus <NUM> can control irradiation of radiation or the stopping of irradiation of radiation in the radiation source control apparatus <NUM>.

As an example of controlling the output of both of the irradiation signal and the stop signal, the radiation control apparatus <NUM> outputs the irradiation signal and stops output of the stop signal to the radiation source control apparatus <NUM> during radiation irradiation. When stopping the radiation irradiation, the radiation control apparatus <NUM> stops the output of the irradiation signal and outputs the stop signal to the radiation source control apparatus <NUM>. In this manner, by switching output operations of both the irradiation signal and the stop signal, the radiation control apparatus <NUM> can control irradiation of radiation or control the stopping of irradiation of radiation in the radiation source <NUM> via the radiation source control apparatus <NUM>.

The wired communication unit, which is included in the radiation imaging apparatus <NUM> as a component for performing communication, is an information transmission path, and allows communication of information by, for example, a cable connection using a communication standard having a predetermined rule or a standard, such as RS232C, USB, or Ethernet®. The wireless communication unit, which is included in the radiation imaging apparatus <NUM> as a component for performing communication, is also an information transmission path, and includes, for example, a circuit board including a communication IC and the like. The wireless communication unit is electrically connected to an antenna (not shown), and performs communication using a radio wave. The circuit board including the communication IC and the like can perform protocol communication processing based on a wireless LAN via the antenna. The frequency band, standard, and method of the wireless communication are not particularly limited, and a short-range wireless method such as NFC (Near field radio communication) or Bluetooth®, or a method such as UWB (Ultra Wide band) may be used. In addition, the wireless communication unit may be configured to be capable of communication using a plurality of wireless communication methods, and an appropriate method may be selected, as appropriate, to perform communication.

The radiation imaging apparatus <NUM> may be, for example, a portable cassette flat panel detector (FPD). <FIG> is a view exemplarily showing the outer appearance of the portable radiation imaging apparatus <NUM>. The radiation imaging apparatus <NUM> can include a power button <NUM> for accepting power-on or power-off, a battery unit <NUM> for power supply, and a connector connection unit <NUM>. The battery unit <NUM> may be configured to be detachable. The battery main body included in the battery unit <NUM> is configured to be chargeable by a battery charger (charging device) or the like.

The radiation imaging apparatus <NUM> can be connected to the control apparatus <NUM> using a cable <NUM>, and the cable <NUM> can be connected to the radiation imaging apparatus <NUM> via the connector connection unit <NUM>. When the radiation imaging apparatus <NUM> and the control apparatus <NUM> are connected using the cable <NUM>, for example, the radiation imaging apparatus <NUM> is switched to communication using the wired communication unit. In accordance with this, information transmission between the radiation imaging apparatus <NUM> and the control apparatus <NUM> as shown in <FIG> is performed by wired communication. Further, the communication unit used in the radiation imaging apparatus <NUM> may be switchable from the control apparatus <NUM> by a user operation regardless of the connection form.

<FIG> is a view showing an arrangement example of the radiation imaging apparatus <NUM> according to this embodiment. The radiation imaging apparatus <NUM> includes a plurality of pixels arranged in an imaging region <NUM> so as to form a plurality of rows and a plurality of columns. The plurality of pixels include a plurality of pixels <NUM> used to acquire a radiation image based on detected radiation and include a dose detection pixel <NUM> (to also be referred to as a detection unit) that detects the dose of radiation emitted from the radiation source <NUM>. The pixel <NUM> includes a conversion element <NUM> that converts radiation into an electrical signal and includes a switch <NUM> arranged between a column signal line <NUM> and the conversion element <NUM>. Similar to the pixel <NUM>, the dose detection pixel <NUM> includes a conversion element <NUM> that converts radiation into an electrical signal and includes a switch <NUM> arranged between a detection signal line <NUM> and the conversion element <NUM>.

Each of the conversion element <NUM> and the conversion element <NUM> can include a scintillator that converts radiation into light and a photoelectric conversion element that converts light into an electrical signal. For example, the scintillator may be formed in a sheet shape so as to cover the imaging region <NUM>, and the scintillator may be shared by the plurality of pixels <NUM> and <NUM>. Each of the conversion element <NUM> and the conversion element <NUM> may be a conversion element that directly converts radiation into an electrical signal.

Each of the switch <NUM> and the switch <NUM> may be, for example, a thin film transistor (TFT) with an active region formed by a semiconductor, such as amorphous silicon or polysilicon. In this embodiment, a TFT using polysilicon is used as each of the switches <NUM> and <NUM>.

The radiation imaging apparatus <NUM> includes a plurality of the column signal lines <NUM> and a plurality of driving lines <NUM>. Each column signal line <NUM> can correspond to one of the plurality of columns in the imaging region <NUM>. Each driving line <NUM> corresponds to one of the plurality of rows in the imaging region <NUM>. Here, "column" indicates the vertical direction in <FIG>, and "row" indicates the horizontal direction in <FIG>. A driving signal is supplied to each driving line <NUM> by a driving unit <NUM>.

One electrode of the main electrodes of the conversion element <NUM> is connected to one electrode of the main electrodes of the switch <NUM>, and the other electrode of the conversion element <NUM> is connected to a bias line <NUM>. Here, each bias line <NUM> extends in the column direction, and is commonly connected to the other electrodes of the multiple conversion elements <NUM> arranged in the column direction. A bias voltage Vs is supplied to the bias line <NUM> from a power supply unit <NUM>. The other electrodes of the main electrodes of the switches <NUM> of the multiple pixels <NUM> forming one column are connected to one corresponding column signal line <NUM>. The control electrodes of the switches <NUM> of the multiple pixels <NUM> forming one row are connected to one corresponding driving line <NUM>.

The plurality of column signal lines <NUM> are connected to a readout unit <NUM>. Here, the readout unit <NUM> can include a plurality of detection units <NUM>, a multiplexer <NUM>, and an analog/digital (AD) converter <NUM>. Each of the plurality of column signal lines <NUM> is connected to a corresponding one of the plurality of detection units <NUM> of the readout unit <NUM>. One column signal line <NUM> corresponds to one detection unit <NUM>. The detection unit <NUM> includes, for example, a differential amplifier. The multiplexer <NUM> selects the plurality of detection units <NUM> in a predetermined order, and supplies, to the AD converter <NUM>, a signal output from the selected detection unit <NUM>. The AD converter <NUM> converts the supplied analog signal into a digital signal and outputs the digital signal.

One electrode of the main electrodes of the conversion element <NUM> is connected to one electrode of the main electrodes of the switch <NUM>, and the other electrode of the conversion element <NUM> is connected to the bias line <NUM>. The other main electrode of the main electrodes of the switch <NUM> is electrically connected to the detection signal line <NUM>. The control electrode of the switch <NUM> is electrically connected to a driving line <NUM>. The radiation imaging apparatus <NUM> can include a plurality of detection signal lines <NUM>. One detection signal line <NUM> can be connected to one or multiple dose detection pixels <NUM>. The driving line <NUM> is driven by a driving unit <NUM>. One driving line <NUM> can be connected to one or multiple dose detection pixels <NUM>.

Each detection signal line <NUM> is connected to a readout unit <NUM> (which may also be referred to as an AEC readout unit). The readout unit <NUM> can include a plurality of detection units <NUM>, a multiplexer <NUM>, and an AD converter <NUM>. Each of the plurality of detection signal lines <NUM> can be connected to a corresponding one of the plurality of detection units <NUM> of the readout unit <NUM>. One detection signal line <NUM> corresponds to one detection unit <NUM>. Each detection unit <NUM> includes, for example, a differential amplifier. The multiplexer <NUM> selects the plurality of detection units <NUM> in a predetermined order, and supplies, to the AD converter <NUM>, a signal output from the selected detection unit <NUM>. The AD converter <NUM> converts the supplied signal into a digital signal and outputs the digital signal.

The output of the AD convertor <NUM> of the readout unit <NUM> is supplied to a signal processing unit <NUM> and processed by the signal processing unit <NUM>. Based on the output of the AD convertor <NUM> of the readout unit <NUM>, the signal processing unit <NUM> outputs information of the radiation applied to the radiation imaging apparatus <NUM>.

Based on the electrical signal generated by the pixel <NUM> in accordance with the irradiated radiation, the signal processing unit <NUM> acquires information of the dose of radiation entering the pixel <NUM>. The signal processing unit <NUM> may generate a signal by performing digital signal processing to the detection result of the pixel <NUM>. For example, the signal processing unit <NUM> may be configured to, based on the generated signal, detect the start of radiation irradiation with respect to the radiation imaging apparatus <NUM>, or calculate the irradiation dose and integrated irradiation amount (arrival dose) of radiation. Also, the signal processing unit <NUM> may transmit, to the radiation control apparatus <NUM>, the acquired information of the dose of radiation entering the pixel <NUM>, and the radiation control apparatus <NUM> may acquire the irradiation dose and integrated irradiation amount (arrival dose) of radiation.

A controller <NUM> controls the operation of each of the driving unit <NUM>, the driving unit <NUM>, and the readout units <NUM> and <NUM>. Further, the controller <NUM> is provided with a sensor timer <NUM>. The sensor timer <NUM> measures the time at which the signal processing unit <NUM> detected the dose entering the pixel <NUM> of the radiation imaging apparatus <NUM>. The controller <NUM> acquires, from the signal processing unit <NUM>, the information of the dose of radiation entering the pixel <NUM>, and acquires the information of the time from the sensor timer <NUM>. Here, let Xi be the information of the dose, and let Ti be the information of the time. The information including a combination of the dose Xi and the time Ti is referred to as dose information Di. The controller <NUM> generates the dose information Di(Ti, Xi) including the dose Xi entering the pixel <NUM> of the radiation imaging apparatus <NUM> and the time Ti at which the dose Xi was detected.

The radiation imaging apparatus <NUM> includes a communication unit <NUM> used to communicate with the radiation control apparatus <NUM> and the control apparatus <NUM>. The communication unit <NUM> may include two communication units of a wired communication unit and a wireless communication unit. The communication unit <NUM> can transmit, to the radiation control apparatus <NUM> and the control apparatus <NUM>, the information output from the controller <NUM> by using the wired communication unit or the wireless communication unit. For example, the communication unit <NUM> outputs the dose information Di(Ti, Xi) generated by the controller <NUM> to the radiation control apparatus <NUM>. The controller <NUM> acquires, from the signal processing unit <NUM>, the information of the detected dose Xi at regular intervals, generates the dose information Di(Ti, Xi), and outputs the generated dose information Di to the radiation control apparatus <NUM> via the communication unit <NUM>.

A generation controller <NUM> of the radiation control apparatus <NUM> appends, to the received dose information Di(Ti, Xi), a time Ti' at which the radiation control apparatus acquired the dose information, thereby generating dose information Di'(Ti, Ti', Xi). In order to generates the dose information Di', the radiation control apparatus <NUM> includes a control timer <NUM>. The control timer <NUM> measures information of the time in the radiation control apparatus <NUM>. The radiation control apparatus <NUM> can also include a synchronizer <NUM> used to synchronize the information of the time of the control timer <NUM> and the information of the time of the sensor timer <NUM> of the radiation imaging apparatus <NUM>. The synchronizer <NUM> may set the time of the sensor timer <NUM> of the radiation imaging apparatus <NUM> based on the information of the time of the control timer <NUM> of the radiation control apparatus <NUM>. The synchronizer <NUM> may be configured to be capable of communication of the information of the time with the communication unit <NUM> of the radiation imaging apparatus <NUM> by wireless communication or wired communication. In this embodiment, the synchronizer <NUM> performs wireless communication with the communication unit <NUM> of the radiation imaging apparatus <NUM>.

The controller <NUM> of the radiation imaging apparatus <NUM> monitors the reception state of the communication <NUM> and, if the timer information is received, sets the time of the sensor timer <NUM> based on the received timer information. When the time of the sensor timer <NUM> is set based on the timer information, the time of the control timer <NUM> of the radiation control apparatus <NUM> and the time of the sensor timer <NUM> are synchronized with each other. The synchronizer <NUM> synchronizes the time of the control timer <NUM> of the radiation control apparatus <NUM> and the time of the sensor timer <NUM> of the radiation imaging apparatus <NUM> before radiation is emitted and radiation image capturing is started in the radiation imaging apparatus <NUM>. Here, synchronizing the times is not limited to setting the time of the control timer <NUM> and the time of the sensor timer <NUM> to the same time, and there may be a predetermined difference between the two times. As long as the delay between the above-described time Ti and time Ti' can be acquired, synchronization between the time of the control timer <NUM> and the time of the sensor timer <NUM> may take any form. By executing synchronization of the times prior to radiation image capturing in the radiation imaging apparatus <NUM>, it is possible to suppress a relative time shift between the time of the sensor timer <NUM> of the radiation imaging apparatus <NUM> and the time of the control timer <NUM> of the radiation control apparatus <NUM>.

The arrangement example has been described in <FIG> in which the radiation control apparatus <NUM> includes the synchronizer <NUM>, but the radiation imaging apparatus <NUM> may include a synchronizer. Also, the synchronizer <NUM> may be arranged in the radiation imaging system <NUM> while being independent of the radiation control apparatus <NUM> and the radiation imaging apparatus <NUM>. Any form can be employed as long as the time of the control timer <NUM> of the radiation control apparatus <NUM> and the time of the sensor timer <NUM> of the radiation imaging apparatus <NUM> can be synchronized with each other.

Based on the dose information Di(Ti, Xi) including the dose Xi of radiation entering the pixel <NUM> and the time Ti at which the dose Xi was detected, the generation controller <NUM> of the radiation control apparatus <NUM> specifies the threshold time at which the arrival dose entering the radiation imaging apparatus <NUM> (pixel <NUM>) reaches a preset threshold dose. More specifically, based on the dose Xi and time Ti included in the dose information Di(Ti, Xi) output from the communication unit <NUM> of the radiation imaging apparatus <NUM> and the time Ti' at which the radiation control apparatus <NUM> received the dose information Di, the generation controller <NUM> calculates a threshold time Te at which the arrival dose entering the radiation imaging apparatus <NUM> reaches a threshold dose Y. Then, the generation controller <NUM> of the radiation control apparatus <NUM> controls the radiation source control apparatus <NUM> to output an irradiation control signal such that the radiation source <NUM> emits radiation until the time obtained by the control timer <NUM> reaches the threshold time Te.

At this time, the communication between the radiation imaging apparatus <NUM> and the radiation control apparatus <NUM> may become unstable due to a change in environment of the wireless communication between the radiation imaging apparatus <NUM> and the radiation control apparatus <NUM>. For example, there is a case in which a shift occurs between the time Ti of the dose information Di output from the radiation imaging apparatus <NUM> and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di. In this case, the relationship between the threshold dose Y and the information of the arrival dose acquired from the actual dose information Di may become inappropriate. Therefore, the generation controller <NUM> of the radiation control apparatus <NUM> changes and corrects the threshold dose Y based on the difference between the time Ti included in the dose information Di and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di. With this, the generation controller <NUM> of the radiation control apparatus <NUM> can output the irradiation control signal to the radiation source control apparatus <NUM> at an appropriate timing. That is, the controllability of radiation irradiation can be improved in the radiation imaging system <NUM>.

Here, with reference to <FIG>, the procedure of synchronization processing of synchronizing the time of the control timer <NUM> of the radiation control apparatus <NUM> and the time of the sensor timer <NUM> of the radiation imaging apparatus <NUM> will be described as an operation procedure of the radiation imaging system <NUM>. When operation of the radiation control apparatus <NUM> is started by a user operation or the like (step S500), the control timer <NUM> of the radiation control apparatus <NUM> starts to measure the time (starts counting) in step S501. Then, in step S502, synchronization time waiting processing is performed. The synchronization time is a time at which a predetermined time has elapsed since the control timer <NUM> starts counting. The control timer <NUM> of the radiation control apparatus <NUM> measures the elapse time after the start of counting. If the elapse time has not reached the time (synchronization time) at which the predetermined time has elapsed after the start of counting (No in step S502), the radiation control apparatus <NUM> waits until the elapse time reaches the synchronization time. If the elapse time reaches the synchronization time (Yes in step S502), the radiation control apparatus <NUM> advances the process to step S503.

In step S503, the synchronizer <NUM> of the radiation control apparatus <NUM> acquires the timer information based on the time measured by the control timer <NUM>. The synchronizer <NUM> acquires information of the time measured by the control timer <NUM> and, in step S504, outputs the timer information (the information of the time of the control timer <NUM>) acquired from the control timer <NUM> to the radiation imaging apparatus <NUM> under the control of the communication controller <NUM>. Transmission processing of the timer information in step S504 is performed every time the synchronization time is reached, regardless of whether the timer information is received in the radiation imaging apparatus <NUM>.

Next, the operation in the radiation imaging apparatus <NUM> will be described. When operation of the radiation imaging apparatus <NUM> is started by a user operation or the like (step S505), the sensor timer <NUM> of the radiation imaging apparatus <NUM> starts to measure the time (starts counting) in step S506. Then, in step S507, the controller <NUM> of the radiation imaging apparatus <NUM> monitors whether the communication unit <NUM> receives the timer information, and waits in a state of waiting for reception of the timer information. If the timer information is not received (No in step S507), the controller <NUM> of the radiation imaging apparatus <NUM> continues the waiting state. If the timer information is received (Yes in step S507), the controller <NUM> advances the process to step S508. In step S508, the controller <NUM> acquires the timer information received by the communication unit <NUM>. When the timer information is acquired, in step S509, the controller <NUM> sets the time of the sensor timer <NUM> based on the acquired timer information. When the time of the sensor timer <NUM> is set based on the timer information, the time of the sensor timer <NUM> is synchronized with the time of the control timer <NUM> of the radiation control apparatus <NUM>.

When the time of the sensor timer <NUM> is synchronized with the time of the control timer <NUM> of the radiation control apparatus <NUM> in step S509, the process returns to step S507, and the controller <NUM> waits in the state of waiting for reception of the timer information. Thereafter, if the timer information is similarly received (Yes in step S507), the controller <NUM> of the radiation imaging apparatus <NUM> sets the time of the sensor timer <NUM> based on the timer information received by the communication unit <NUM> (step S509). With this, the time of the control timer <NUM> of the radiation control apparatus <NUM> and the time of the sensor timer <NUM> can be accurately synchronized with each other.

The control timer <NUM> of the radiation control apparatus <NUM> can start counting the operation time at the same time with power-on of the radiation control apparatus <NUM> and can measure the time. The synchronizer <NUM> acquires the timer information based on the time measured by the control timer <NUM>. The synchronizer <NUM> may transmit the timer information to the radiation imaging apparatus <NUM>, for example, every several µs, as the synchronization time under the control of the communication controller <NUM>. The timing (synchronization time) at which the synchronizer <NUM> transmits the timer information using the communication controller <NUM> can be arbitrarily set.

The controller <NUM> of the radiation imaging apparatus <NUM> transmits the dose information Di(Ti, Xi) to the radiation control apparatus <NUM> via the communication unit <NUM>, for example, every synchronization time. The generation controller <NUM> of the radiation control apparatus <NUM> can control output of an irradiation control signal to the radiation source control apparatus <NUM> based on the arrival dose information Di(Ti, Xi) transmitted from the radiation imaging apparatus <NUM>.

Next, with reference to <FIG>, a correction method and radiation irradiation control in a case in which a shift (difference) between the time Ti of the dose information Di and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di occurs in the radiation control apparatus <NUM> will be described.

The radiation imaging apparatus <NUM> sequentially outputs the dose information Di(Ti, Xi) at a predetermined timing (for example, every synchronization time as described above), and the generation controller <NUM> stores the dose information Di'(Ti, Ti', Xi) obtained by adding the acquirement time Ti' in a memory (not shown) in the radiation control apparatus <NUM>. The radiation imaging apparatus <NUM> can output the dose information Di to the radiation control apparatus <NUM> a plurality of times, and the radiation control apparatus <NUM> can store a plurality of pieces of the dose information Di' in the memory. <FIG> is a table showing examples of pieces of dose information Di'(Ti, Ti', Xi) stored in the memory of the radiation control apparatus <NUM>. Each dose information Di' is stored in a state in which the time Ti at which the dose Xi was detected in the radiation imaging apparatus <NUM> and the time Ti' at which the generation controller <NUM> of the radiation control apparatus <NUM> received the dose information Di are associated with the dose Xi (i = <NUM>, <NUM>,. The generation controller <NUM> of the radiation control apparatus <NUM> also stores the threshold dose Y of the arrival dose in the memory. The threshold dose Y for stopping radiation irradiation can be arbitrarily set by the user, and can be changed in accordance with the imaging method, imaging portion, imaging condition, and the like.

Based on the dose information Di including the dose Xi of radiation entering the radiation imaging apparatus <NUM> (pixel <NUM>) and the time Ti, the generation controller <NUM> of the radiation control apparatus <NUM> can specify the threshold time Te which is the predicted time at which the arrival dose entering the radiation imaging apparatus <NUM> reaches the preset threshold dose Y. As shown in <FIG>, straight-line approximation based on the least square method using a plurality of pieces of the dose information Di or the like can be used to specify the threshold time Te.

The generation controller <NUM> of the radiation control apparatus <NUM> can control radiation irradiation via the radiation source <NUM> based on a comparison between the threshold dose Y and the dose information Di acquired after the threshold time Te is specified, and the threshold time Te. That is, if the arrival dose obtained from the dose information Di reaches the threshold dose Y or if the time of the control timer <NUM> reaches the threshold time Te, the generation controller <NUM> of the radiation control apparatus <NUM> can control the radiation source <NUM> to stop radiation irradiation.

Next, with reference to <FIG>, a case will be described in which, for example, the communication between the radiation imaging apparatus <NUM> and the radiation control apparatus <NUM> becomes unstable due to a change in wireless environment or the like, and a shift occurs between the time Ti of the dose information Di output from the radiation imaging apparatus <NUM> and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di. If the difference between the time Ti of the dose information Di output from the radiation imaging apparatus <NUM> and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di exceeds a predetermined threshold value, the generation controller <NUM> of the radiation control apparatus <NUM> changes the threshold dose Y. More specifically, if the difference (delay time (Tm' - Tm)) between a time Tm of dose information Dm output from the radiation imaging apparatus <NUM> acquired after the threshold time Te is specified (for example, after the threshold time Te is first specified) and a time Tm' at which the radiation control apparatus <NUM> acquired the dose information Dm becomes equal to or larger than a predetermined time, a threshold change amount α(Tm' - Tm) is calculated from the delay time (Tm' - Tm) and a slope α of the approximate straight line used when calculating the threshold dose Y. Then, {Y - α(Tm' - Tm)} obtained by subtracting the threshold change amount α(Tm' - Tm) from the set threshold dose Y is set as a new threshold dose Y'. If the arrival dose obtained from the dose information Di reaches the threshold dose Y' or if the time of the control timer <NUM> reaches the threshold time Te, the generation controller <NUM> of the radiation control apparatus <NUM> changes a signal output to the radiation source control apparatus <NUM> so as to switch from the radiation irradiation state to the irradiation stop state.

A radiation image capturing method performed in the radiation imaging system <NUM> includes, for example, processing steps described below. First, the dose Xi of radiation emitted from the radiation source <NUM> is detected using the pixel <NUM> of the radiation imaging apparatus <NUM>. The dose information Di including the dose Xi and the time Ti at which the dose Xi was detected is transmitted to the radiation control apparatus <NUM>. The generation controller <NUM> of the radiation control apparatus <NUM> acquires, based on the transmitted dose information Di, the threshold time Te at which the arrival dose (integrated dose) entering the radiation imaging apparatus <NUM> reaches the threshold dose Y. Based on a comparison between the arrival dose entering the radiation imaging apparatus <NUM> and the threshold dose Y or a comparison between the time measured by the control timer <NUM> and the threshold time Te, the generation controller <NUM> controls the radiation emission from the radiation source <NUM>.

Here, the delay time is not limited to a delay caused by the communication between the radiation imaging apparatus <NUM> and the radiation control apparatus <NUM> as described above. For example, there is a possibility that when a delay occurs before the dose information Di is output, for example, a load is applied on the operation of the radiation imaging apparatus <NUM>, during a period after the dose information Di is generated in the radiation imaging apparatus <NUM> and before the dose information Di is output via the communication unit <NUM>. Similarly, there is a possibility that a delay occurs after the dose information Di is received in the radiation control apparatus <NUM> and before the dose information Di' is generated in the generation controller <NUM>. In consideration of the possibilities described above, the threshold value Y may be changed if the difference (delay time (Tm' - Tm)) between the time Tm of the dose information Dm output from the radiation imaging apparatus <NUM> and the time Tm' at which the radiation control apparatus <NUM> acquired the dose information Dm exceeds a predetermined threshold.

Each of the sensor timer <NUM> and the control timer <NUM> used in this embodiment is not limited to a counter that counts the time, and may be configured to measure the actual time. In addition, in this embodiment, it has been described that the radiation control apparatus <NUM> and the control apparatus <NUM> are independent apparatuses, but the radiation control apparatus <NUM> and the control apparatus <NUM> may be integrally formed.

Next, a modification of the method of changing the threshold dose Y will be described. In the description with reference to <FIG>, it has been described that the radiation control apparatus <NUM> changes the threshold dose Y based on the difference between the time Tm included in one piece of dose information Dm among the plurality of pieces of the dose information Di and the time Tm' at which the radiation control apparatus <NUM> acquired the one piece of dose information Dm. However, the radiation control apparatus <NUM> may change the threshold dose Y based on the differences between the times Ti included in two or more pieces of dose information Di among the plurality of pieces of the dose information Di and the times Ti' at which the radiation control apparatus <NUM> acquired the two or more pieces of dose information Di, respectively. That is, the threshold does Y may be corrected using the average time of the delay times of multiple pieces of dose information Di. With reference to <FIG>, a case of using the average time of delay times of multiple pieces of dose information Di' will be described.

Assume that a predetermined difference (delay time) or more occurs between the acquisition time Ti of the dose information Di output from the radiation imaging apparatus <NUM> and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di. In this case, the generation controller <NUM> of the radiation control apparatus <NUM> calculates an average delay time Tave from pieces of information of the times Ti included in the respective pieces of dose information Di and the times Ti' at which the radiation control apparatus <NUM> acquired the respective pieces of dose information Di. For example, Tave can be expressed as:<MAT>.

Further, the generation controller <NUM> calculates a threshold change amount αTave from the slope α of the approximate straight line and the average delay time Tave. Then, (Y - αTave) obtained by subtracting the threshold change amount from the set threshold dose Y is stored as the new threshold dose Y' in the memory.

In this embodiment, all pieces of information from the first dose information D1(T1, T1', X1) to the latest dose information Dm(Tm, Tm', Xm) are used to calculate the average delay time Tave, but the information to be used may be arbitrarily selected. That is, an arbitrary number of data before the timing at which the predetermined delay time or more occurs may be used. Also, a predetermined delay time for calculating the average delay time Tave is set, and only the information with which the predetermined delay time or more occurs may be used.

Still another example of the method of changing the threshold dose Y will be described. In the embodiment described above, the threshold dose Y is corrected if the predetermined delay time or more occurs, but the present invention is not limited to this. For example, the radiation control apparatus <NUM> may change the threshold dose Y every time the dose information Di is acquired. With reference to <FIG>, a case will be described in which the radiation control apparatus <NUM> changes the threshold dose Y every time the dose information Di is received.

As shown in <FIG>, after the first does information D1 from the radiation imaging apparatus <NUM> is acquired, the generation controller <NUM> of the radiation control apparatus <NUM> specifies the threshold dose Y using the dose X1, the time T1, and the time T1' at which the radiation control apparatus <NUM> acquired the dose information D1. Further, the generation controller <NUM> of the radiation control apparatus <NUM> calculates a threshold change amount α(T1' - T1) from the slope α of the approximate straight line used upon the specification and a delay time (T1' - T1). Then, {Y - α(T1' - T1)} obtained by subtracting the threshold change amount from the threshold dose Y is stored as a new threshold dose Y1 in the memory.

Then, as shown in <FIG>, after next dose information D2 from the radiation imaging apparatus <NUM> is acquired, the generation controller <NUM> of the radiation control apparatus <NUM> recorrects the threshold dose again using a dose X2, a time T2, and a time T2' at which the radiation control apparatus <NUM> acquired the dose information D2. More specifically, a threshold change amount α(T2' - T2) is calculated from the slope α of the approximate straight line and a delay time (T2' - T2). Then, {Y1 - α(T2' - T2)} obtained by subtracting the threshold change amount from the threshold dose Y1 is stored as a new threshold dose Y2 in the memory. That is, as shown in <FIG>, a threshold dose Yn at the time when nth dose information Dn was acquired is expressed as Yn = Ym - α(Tn' - Tn) (where m = n - <NUM>).

In this embodiment, the method of correcting the threshold dose Y every time the radiation control apparatus <NUM> acquires the dose information Di has been described. However, the correction timing may be an arbitrary timing. For example, the radiation control apparatus <NUM> may change the threshold dose Y based on the dose information Di, among the plurality of pieces of the dose information Di, acquired at a preset timing. Also, for example, the radiation control apparatus <NUM> may change the threshold dose Y based on the dose information Di, among the plurality of pieces of the dose information Di, acquired at the timing at which a predetermined period has elapsed since the threshold dose Y was last changed.

When changing the threshold dose Y, the period from when the generation controller <NUM> changes the irradiation control signal output to the generation source control apparatus <NUM> so as to switch from the radiation irradiation state to the irradiation stop state to when the radiation irradiation from the radiation source <NUM> is actually stopped may be taken into consideration. As shown in <FIG>, the radiation control apparatus <NUM>, the radiation source control apparatus <NUM>, and the radiation source <NUM> are wired-connected using a cable or the like, and transmit/receive signals. That is, the radiation control apparatus <NUM> and the radiation source <NUM> are configured to be capable of communication by wired communication. In this case, a time Tx from when the generation controller <NUM> transmits a signal to the radiation source control apparatus <NUM> so as to switch from the radiation irradiation state to the irradiation stop state to when the radiation source control apparatus <NUM> receives the signal can be a unique value for each radiation imaging system <NUM>. Further, a time Ty from when the radiation source control apparatus <NUM> receives the signal to when the radiation source <NUM> stops radiation irradiation can be a unique value for each radiation imaging system <NUM>, each imaging procedure, and each imaging condition. That is, a time (Tx + Ty) from when the radiation control apparatus <NUM> transmits the signal for causing the radiation source <NUM> to stop radiation irradiation based on the dose information Di and the threshold time Te as described above to when the radiation source <NUM> stops radiation irradiation can be a unique value according to the radiation imaging system <NUM>, the imaging procedure, and the imaging condition. Therefore, as shown in <FIG>, the radiation control apparatus <NUM> may change at least one of the threshold dose Y or the threshold time Te based on the time (Tx + Ty) from when the signal to stop radiation irradiation is transmitted to when the radiation source <NUM> stops radiation irradiation. By taking the time (Tx + Ty) into consideration when correcting the threshold dose Y, it is possible to further suppress excessive radiation irradiation.

More specifically, first, it is necessary to acquire, before imaging, the time (Tx + Ty) from when the generation controller <NUM> of the radiation control apparatus <NUM> changes the irradiation control signal transmitted to the radiation source control apparatus <NUM> to when the radiation irradiation from the radiation source <NUM> is actually stopped. The time (Tx + Ty) may be actually measured at the time of installation of the radiation imaging system <NUM>, or may be measured in advance before shipping from the factory or the like. Also, the time (Tx + Ty) may be registered in the control apparatus <NUM> or the like as a database in advance, and the database may be referred to.

Then, if the predetermined delay time or more occurs between the time Ti of the dose information Di output from the radiation imaging apparatus <NUM> and the time Ti' at which the radiation control apparatus <NUM> acquired the dose information Di, the generation controller <NUM> changes the threshold dose Y. As has been described above, a threshold change amount α(Tm' - Tm - Tx - Ty) is calculated from the delay time (Tm' - Tm) and the unique time (Tx - Ty) according to the radiation imaging system <NUM>, the imaging procedure, the imaging condition, and the like in addition to the slope α of the approximation straight line used when specifying the threshold dose Y. {Y - α(Tm' - Tm - Tx-Ty} obtained by subtracting the threshold change amount from the set threshold dose Y is stored as the new threshold dose Y' in the memory and set. Further, the generation controller <NUM> calculates a threshold time Te' (Te' = Te - Tx - Ty) as a predicted time. In this manner, by taking the time from when the radiation control apparatus <NUM> determines to stop radiation irradiation to when the radiation source <NUM> stops the radiation irradiation into consideration, the accuracy of radiation irradiation is further improved in the radiation imaging system <NUM>.

Claim 1:
A radiation imaging system (<NUM>) comprising a radiation imaging apparatus (<NUM>) configured to detect radiation emitted from a radiation source (<NUM>), and a radiation control apparatus (<NUM>) configured to control the radiation source (<NUM>), characterized in that
the radiation imaging apparatus (<NUM>) is configured to output, a plurality of times during a radiation irradiation, a piece of dose information (Di(Ti,Xi)), which includes a dose (Xi) of radiation entering the radiation imaging apparatus (<NUM>) and a time (Ti) at which the dose was detected, to the radiation control apparatus (<NUM>), and
the radiation control apparatus (<NUM>) is configured
to change a threshold dose (Y) based on a difference between the time (Ti) included in at least one of the pieces of dose information from the radiation imaging apparatus (<NUM>) and a time (Ti') at which the radiation control apparatus (<NUM>) received the at least one piece of dose information, and
to control the radiation source (<NUM>) to stop the radiation irradiation based on the at least one of the pieces of dose information and the threshold dose.