JP7077719B2 - Radiation imaging device - Google Patents

Description

The present invention relates to a radiographic imaging apparatus.

In recent years, various radiographic imaging devices have been developed, and there is one called an FPD (Flat Panel Detector). Conventionally, this type of radiation imaging device has been configured as a so-called dedicated machine type (also called a fixed type) integrally formed with a support base or the like, but in recent years, a radiation detection element or the like is housed in a housing. However, a portable type (also called a cassette type) that can be carried is also being developed.

Further, in recent years, the radiation imaging device has a function of automatically detecting that radiation has been irradiated even if an interface with the radiation generator is not constructed (hereinafter, automatic radiation detection function: AED: Auto Exposure Detection). ) Is provided.

In an environment where radiographic imaging equipment is used, various medical devices may be used. Therefore, the radiation imaging apparatus may detect the electromagnetic wave noise emitted from the medical device and erroneously detect that the radiation has been emitted even though the radiation is not irradiated during the AED operation. Conventionally, a radiation imaging apparatus capable of preventing erroneous detection of the start of irradiation of radiation has been provided even in a noise environment affected by external noise (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-22851

However, in Patent Document 1, the threshold value of the detection sensitivity at the start of irradiation of radiation is changed based on the variation in the noise level. Therefore, in Patent Document 1, for example, when the detection sensitivity of the start of radiation irradiation is increased, there is a possibility that the start of radiation irradiation is detected even though the radiation is not irradiated.

Therefore, an object of the present invention is to provide a technique for appropriately detecting the start of radiation irradiation without changing the detection sensitivity of the start of radiation irradiation.

The radiographic imaging apparatus of the present invention is
A radiation detection unit that receives the radiation emitted from the radiation generator and outputs a signal corresponding to the radiation.
A charging / discharging unit that charges and discharges the signal, and
An irradiation start determination unit that determines the start of irradiation of the radiation based on the signal charged by the charge / discharge unit, and an irradiation start determination unit.
A noise detection unit that detects disturbance noise that affects the signal charged by the charging / discharging unit, and a noise detection unit.
A change unit that changes the charge / discharge cycle of the charge / discharge unit based on the detected disturbance noise, and a change unit.
Have.

According to the present invention, the start of radiation irradiation can be appropriately detected without changing the detection sensitivity of the start of radiation irradiation.

It is a figure which showed an example of the X-ray image taking system which concerns on 1st Embodiment. It is a figure explaining the operation example of the X-ray image taking system. It is a figure explaining the reset operation of a TFT sensor. It is a figure explaining the relationship between a gate drive cycle and a sampling cycle. It is a figure which showed the circuit block example of the X-ray image taking apparatus. It is a figure explaining the influence of the disturbance noise of the X-ray detection circuit. It is a figure explaining the principle which suppresses the influence of disturbance noise. It is the 1 of the figure explaining the operation example of the sampling cycle change part. Part 2 of the figure illustrating an operation example of the sampling cycle changing unit. It is a figure explaining the charge period and the reset period of an integrator. It is a flowchart which showed the operation example of the X-ray image taking apparatus. It is a figure which showed the circuit block example of the X-ray image taking apparatus which concerns on 2nd Embodiment. It is a figure explaining the example of the disturbance noise signal of the electromagnetic wave sensor stored in the storage device. It is a figure explaining the selection of the sampling period of the integrator of the X-ray detection circuit. It is a flowchart which showed the operation example of the sampling cycle change part. It is a flowchart which showed the operation example of the X-ray image taking apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, an example in which the radiographic imaging apparatus is applied to the X-ray imaging apparatus will be described.

(First Embodiment)
FIG. 1 is a diagram showing an example of an X-ray imaging system according to the first embodiment. As shown in FIG. 1, the X-ray imaging system includes an X-ray imaging device 1, an X-ray generator 2, a round-trip car 3, a control device 4, and a display 5. Further, FIG. 1 shows a bed 6 and a patient 7 in addition to the X-ray imaging system.

The X-ray imaging apparatus 1 is, for example, an FPD. The X-ray imaging apparatus 1 includes, for example, a two-dimensional TFT (Thin Film Transistor) sensor, and captures X-rays emitted from the X-ray generator 2 in two dimensions. The X-rays captured by the TFT sensor (radiation detection unit) are converted into electrical signals (image signals) from the TFT sensor and output. The X-ray imaging apparatus 1 transmits the electric signal output from the TFT sensor to the control device 4 of the round-trip vehicle 3 by, for example, wirelessly or by wire.

The X-ray generator 2 outputs X-rays according to the control of the control device 4 mounted on the round-trip vehicle 3. The X-ray generator 2 emits, for example, X-rays of a dose specified by the control device 4 for a time specified by the control device 4.

The round-trip vehicle 3 is equipped with an X-ray generator 2, a control device 4, and a display 5. The round-trip car 3 has wheels and can be carried to a hospital room together with, for example, an X-ray imaging apparatus 1 to take an X-ray image of a patient 7.

The control device 4 controls the entire X-ray imaging system. For example, the control device 4 communicates with the X-ray image capturing device 1, the X-ray generator 2, and the display 5 wirelessly or by wire, and controls them. The control device 4 generates an X-ray image based on the image signal transmitted from the X-ray image capturing device 1, and displays the generated X-ray image on the display 5.

The display 5 is, for example, a touch panel type display. The display 5 displays a screen for taking an X-ray image, for example, under the control of the control device 4. Further, the display 5 accepts an operation of an operator such as a radiologist, and outputs a signal (information) corresponding to the accepted operation to the control device 4.

Bed 6 is the bed on which the patient 7 undergoing radiography lies. The X-ray imaging apparatus 1 is inserted, for example, between the bed 6 and the patient 7.

FIG. 1 shows an example of an X-ray imaging system using the round-trip car 3, but the present invention is not limited to this. The X-ray imaging system may be applied to, for example, an X-ray imaging room. For example, the X-ray imaging apparatus 1 may be attached to the examination table in the X-ray imaging room.

FIG. 2 is a diagram illustrating an operation example of the X-ray imaging system. The control device 4 displays, for example, a standby button on the display 5. When the standby button displayed on the display 5 is pressed by the operator, the control device 4 shifts the X-ray image capturing device 1 to the standby state.

When the control device 4 instructs the X-ray imaging apparatus 1 to be in a standby state, the X-ray imaging apparatus 1 performs a reset operation and an operation of detecting the start of X-ray irradiation. For example, in the TFT sensor of the X-ray imaging apparatus 1, a weak dark current flows and charges are accumulated even if the X-ray generator 2 does not irradiate X-rays. When the control device 4 instructs the X-ray imaging apparatus 1 to be in the standby state, the X-ray imaging apparatus 1 resets (discharges) the charge accumulation due to the dark current at a predetermined cycle. Further, the X-ray imaging apparatus 1 starts sampling of a signal output from the TFT sensor (periodic reading of the signal output from the TFT sensor) in order to detect the start of X-ray irradiation by the AED.

The control device 4 displays, for example, an X-ray photographing button on the display 5. The control device 4 controls the X-ray generator 2 so as to irradiate X-rays when the photographing button displayed on the display 5 is pressed by the operator.

The X-ray generator 2 irradiates X-rays when instructed by the control device 4 to irradiate X-rays. When X-rays are irradiated, the amplitude of the signal output from the TFT sensor of the X-ray imaging apparatus 1 becomes large. When the amplitude of the signal output from the TFT sensor exceeds a predetermined value, the X-ray imaging apparatus 1 determines that X-rays have been emitted from the X-ray generator 2 and stops the reset operation.

As a result, charges corresponding to the X-ray irradiation are accumulated in the TFT sensor of the X-ray imaging apparatus 1. That is, the X-ray image capturing device 1 autonomously determines that the X-ray generator 2 has irradiated X-rays without receiving an instruction or the like from the control device 4, and performs X-ray imaging.

When the X-ray irradiation (X-ray imaging) is completed, the X-ray imaging apparatus 1 may return to the state before the standby state (the state in which the reset operation is not performed and the signal sampling operation is not performed). Further, when the X-ray imaging is continuously performed, the X-ray image capturing apparatus 1 may return to the standby state again after the end of the X-ray imaging.

FIG. 3 is a diagram illustrating a reset operation of the TFT sensor. As described with reference to FIG. 2, in the TFT sensor of the X-ray imaging apparatus 1, the charge is periodically reset in the standby state. The reset circuit (not shown) of the X-ray imaging apparatus 1 turns the TFT of the TFT sensor on and off in row units via a gate wiring extending in the row direction.

For example, G1, G2, ... Shown in FIG. 3 indicate gate wiring extending in the row direction of the TFT. The TFT sensor is turned on and off for each G1, G2, ... By the reset circuit, and the charge is reset.

The on / off cycle of the TFT in each row of the gate wiring is called the gate drive cycle or the gate drive frequency. The gate drive cycle and the signal reading cycle in the AED (hereinafter referred to as sampling cycle or sampling frequency) generally have a relationship represented by the following equation (1). Note that n in the equation (1) is a positive integer (1, 2, 3, ...).

Sampling cycle = (1 / n) x gate drive cycle ... (1)

FIG. 4 is a diagram illustrating the relationship between the gate drive period and the sampling period. G1, G2, ... Shown in FIG. 4 indicate the row of the TFT. Each row of the TFT is reset in the gate drive cycle _TG in the standby state.

As described with reference to FIG. 2, the X-ray imaging apparatus 1 detects that X-rays have been emitted from the X-ray generator 2 in the standby state (to detect the start of X-ray irradiation), so that the TFT is used. The signal output from the sensor is read periodically. The arrow A1 shown in FIG. 4 indicates the sampling period of the signal output from the TFT sensor.

The sampling period and the gate drive period have the relationship shown in the above equation (1). The arrow A1 in FIG. 4 indicates the case where “n” in the equation (1) is “n = 1”. That is, the arrow A1 in FIG. 4 shows an example of “sampling cycle = gate drive cycle”.

The arrow A2 in FIG. 4 indicates the case where “n” in the above equation (1) is “n = 2”. That is, the arrow A2 in FIG. 4 shows an example of “sampling cycle = (1/2) × gate drive cycle”.

FIG. 5 is a diagram showing an example of a circuit block of the X-ray imaging apparatus 1. As shown in FIG. 5, the X-ray imaging apparatus 1 includes a TFT sensor 11, an integrator (charge / discharge unit) 12, an LPF (Low Pass Filter) 13, and an A / D (Analog / Digital) converter 14. , 17, an irradiation start determination unit 15, a BPF (Band Pass Filter) 16, and a sampling cycle changing unit (changing unit) 18.

The TFT sensor 11 has TFTs arranged in two dimensions. The TFT sensor 11 receives the X-rays emitted from the X-ray generator 2 and outputs a signal corresponding to the X-rays.

The input of the integrator 12 is connected to the bias line included in the TFT sensor 11. The bias line is a line that supplies a bias voltage to the photodiode included in the TFT sensor 11. When the photodiode is irradiated with X-rays, a current flows through the bias lines. Therefore, the X-ray imaging apparatus 1 can determine whether or not the X-ray is irradiated from the X-ray generator 2 by monitoring the current flowing through the bias line. In addition to monitoring the current of the bias line, the X-ray imaging apparatus 1 may monitor the current of the signal line or the gate line.

The integrator 12 charges and discharges the current (current flowing through the bias line) output from the TFT sensor 11. The integrator 12 has a switch SW1, a capacitor C1, and an operational amplifier OP1.

The electric charge of the current flowing through the bias line of the TFT sensor 11 is accumulated (charged) in the capacitor C1 when the switch SW1 is open. The electric charge charged in the capacitor C1 is discharged when the switch SW1 is closed. The switch SW1 is controlled to be turned on and off by the sampling cycle changing unit 18. The on / off cycle of the switch SW1 is the signal reading cycle (sampling cycle or sampling frequency) of the TFT sensor 11.

The voltage of the electric charge charged by the integrator 12 is input to the LPF 13. That is, the signal of the TFT sensor 11 read by the integrator 12 is input to the LPF 13. The LPF 13 passes the low frequency component of the input signal. The cutoff frequency of the LPF 13 is, for example, several tens of Hz to several kHz.

The A / D converter 14 converts the analog signal output from the LPF 13 into a digital signal. The sampling period of the A / D converter 14 is, for example, twice the cutoff frequency of the LPF 13.

A digital signal output from the A / D converter 14 is input to the irradiation start determination unit 15. That is, the signal (digital value) output from the TFT sensor 11 that has passed through the LPF 13 is input to the irradiation start determination unit 15.

The irradiation start determination unit 15 determines whether or not X-rays have been emitted from the X-ray generator 2 based on the digital signal output from the A / D converter 14. For example, the irradiation start determination unit 15 determines that X-rays have been emitted from the X-ray generator 2 when the value (absolute value) of the digital signal output from the A / D converter 14 exceeds a predetermined threshold value. .. The irradiation start determination unit 15 may be configured by, for example, a CPU (Central Processing Unit).

The voltage of the electric charge charged by the integrator 12 is input to the BPF 16. That is, the signal of the TFT sensor 11 read by the integrator 12 is input to the BPF 16. The BPF 16 passes a frequency component of a predetermined bandwidth of the input signal. The low frequency side cutoff frequency of the BPF 16 is, for example, several kHz, and the high frequency side cutoff frequency is, for example, several MHz.

The A / D converter 17 converts the analog signal output from the BPF 16 into a digital signal. The sampling period of the A / D converter 17 is, for example, twice the high frequency side cutoff frequency of the BPF 16.

A digital signal output from the A / D converter 17 is input to the sampling cycle changing unit 18. That is, the signal (digital value) output from the TFT sensor 11 that has passed through the BPF 16 is input to the sampling cycle changing unit 18.

The sampling cycle changing unit 18 changes the on / off cycle of the switch SW1 of the integrator 12 based on the digital signal output from the A / D converter 17. For example, the sampling cycle changing unit 18 changes the on / off cycle of the switch SW1 of the integrator 12 when the value (absolute value) of the digital signal output from the A / D converter 17 exceeds a predetermined threshold value. .. As described below, the digital signal output from the A / D converter 17 can be said to be an index of disturbance noise. That is, the sampling cycle changing unit 18 changes the on / off cycle of the switch SW1 of the integrator 12 based on the disturbance noise. The sampling cycle changing unit 18 may be configured by, for example, a CPU.

The reset circuit for resetting the electric charge of the TFT sensor 11 adjusts the reset cycle to the sampling cycle changed by the sampling cycle changing unit 18.

Hereinafter, a circuit including a TFT sensor 11, an integrator 12, an LPF 13, an A / D converter 14, and an irradiation start determination unit 15 may be referred to as an X-ray detection circuit. Further, the TFT sensor 11, the integrator 12, the BPF 16, the A / D converter 17, and the sampling cycle changing unit 18 may be referred to as a noise detection circuit.

When a disturbance noise that is a multiple of the sampling frequency is input to the TFT sensor 11, the output of the A / D converter 14 of the X-ray detection circuit looks as if a DC level disturbance noise is applied (effect of aliasing). ). Therefore, the X-ray detection circuit is susceptible to noise at multiples of the sampling frequency.

In the integrator 12 of FIG. 5, the switch SW1 may be used as a fixed resistance for discharging and used as a transimpedance amplifier. In this case, the sampling cycle changing unit 18 changes the sampling cycle of the A / D converter 14 based on the digital signal output from the A / D converter 17, and changes the gate drive cycle of the TFT sensor 11. By using the integrator 12 as a transimpedance amplifier, the fixed resistance plays the role of constant discharge, so that the control of the switch SW1 becomes unnecessary, and there is an advantage that the circuit configuration becomes simple. The gate drive cycle of the TFT sensor 11 and the sampling cycle of the A / D converter 14 do not necessarily have to be synchronized, but in the case of synchronization, the relationship of (gate drive cycle) = N × (sampling cycle) is established. It is desirable to control to.

FIG. 6 is a diagram illustrating the influence of disturbance noise in the X-ray detection circuit. The horizontal axis of FIG. 6 indicates the frequency of disturbance noise. The vertical axis shows the susceptibility to disturbance noise of the X-ray detection circuit. On the vertical axis, the smaller the value, the less susceptible the X-ray detection circuit is to disturbance noise. The waveform W1 shown in FIG. 6 shows the influence of the X-ray detection circuit on the disturbance noise when the sampling period is 200 μs. The waveform W2 shows the influence of the X-ray detection circuit on the disturbance noise when the sampling period is 250 μs.

The waveforms W1 and W2 have peaks at positive integer multiples of the sampling frequency. That is, the X-ray detection circuit is susceptible to disturbance noise at a frequency that is a positive integral multiple of the sampling frequency. Therefore, the X-ray detection circuit may malfunction if there is an electronic device or the like that emits disturbance noise having a frequency that is an integral multiple of the sampling frequency in the surroundings. For example, the X-ray detection circuit may erroneously determine that the X-ray irradiation has started even though the X-ray generator 2 has not irradiated the X-rays.

As shown in the waveforms W1 and W2, the X-ray detection circuit changes the frequency affected by the disturbance noise when the sampling period changes. For example, it is assumed that disturbance noise (10 kHz) having a frequency shown by arrow A11 in FIG. 6 is generated. In this case, it can be seen that the X-ray detection circuit is easily affected by disturbance noise when the sampling period is 200 μs (waveform W1), but is not easily affected by disturbance noise when the sampling period is 250 μs (waveform W2). ..

That is, the X-ray detection circuit can suppress the influence of disturbance noise by changing the sampling frequency. For example, it is assumed that the X-ray detection circuit reads a signal with a sampling cycle of 200 μs in a standby state. Then, it is assumed that the disturbance noise of the frequency shown by the arrow A11 in FIG. 6 is generated. In this case, the X-ray detection circuit can suppress the influence of disturbance noise by changing the sampling period from 200 μs to 250 μs.

If the output signal of the X-ray detection circuit is subjected to integration processing, moving average processing, or the like in order to improve the SN ratio of the X-ray detection circuit, the size of the above-mentioned peak becomes large. That is, the X detection circuit is susceptible to disturbance noise.

FIG. 7 is a diagram illustrating a principle of suppressing the influence of disturbance noise. The arrow A21 shown in FIG. 7 indicates a gate drive cycle. The TFT sensor 11 resets the charge accumulation due to the dark current of each gate in the cycle of the arrow A21 shown in FIG. 7 in the standby state.

The arrow A22 shown in FIG. 7 indicates the sampling period of the X-ray detection circuit. The sampling period indicated by the arrow A22 is the same as the gate drive period.

The waveform W11 shown in FIG. 7 shows disturbance noise. The frequency of the disturbance noise is a positive integer multiple (twice) of the sampling frequency indicated by the arrow A22. The TFT sensor 11 picks up the disturbance noise shown in the waveform W11, and the signal output from the integrator 12 includes the disturbance noise.

As described with reference to FIG. 6, when the frequency of the disturbance noise is a positive integer multiple of the sampling frequency, the X-ray detection circuit is susceptible to the disturbance noise. For example, when the integrator 12 reads the signal output from the TFT sensor 11 in the sampling period indicated by the arrow A22, the integrator 12 reads the signal of the mountain portion of the disturbance noise. For example, the signal is read at the black circle portion of the waveform W1. Therefore, the signal input to the irradiation start determination unit 15 exceeds a predetermined threshold value, for example, and the irradiation start determination unit 15 erroneously determines that X-rays have been emitted from the X-ray generator 2.

However, the X-ray imaging apparatus 1 shown in FIG. 5 monitors the signal output from the integrator 12 by the sampling cycle changing unit 18, and changes the sampling cycle. For example, the sampling cycle changing unit 18 changes the sampling cycle when the signal output from the integrator 12 (absolute value of the signal output from the A / D converter 17) exceeds a predetermined threshold value.

The arrow A23 shown in FIG. 7 indicates a changed sampling period of the X-ray imaging apparatus 1. When the integrator 12 is changed to the sampling period shown by the arrow A23, for example, the integrator 12 reads a signal at the triangular portion of the waveform W1. The integrator 12 reads the disturbance noise shown in the waveform W1 with a value smaller than the peak value indicated by the triangle, instead of the peak value indicated by the black circle. As a result, the X-ray detection circuit can suppress the influence of erroneous determination due to disturbance noise.

Disturbance noise is generated, for example, from electronic devices used around X-ray imaging systems. The frequency of disturbance noise varies from several kHz to several MHz, for example. On the other hand, the frequency of the signal based on X-ray irradiation is several kHz or less.

Therefore, the pass band of the BPF 16 of the noise detection circuit shown in FIG. 5 is higher than the pass band of the LPF 13 of the X-ray detection circuit. Further, the sampling frequency of the noise A / D converter 17 of the noise detection circuit is higher than the sampling frequency of the A / D converter 14 of the X-ray detection circuit.

In FIG. 5, an example in which the LPF 13 and the BPF 16 are formed by an analog circuit is shown, but after the output signal of the integrator 12 is converted into a digital signal by the high-speed A / D converter, the LPF for the X-ray detection circuit and noise It may be processed separately for the detection circuit BPF. In this case, it is desirable to provide an analog LPF for antialiasing in front of the high-speed A / D converter.

FIG. 8 is Part 1 of a diagram illustrating an operation example of the sampling cycle changing unit 18. The waveform W21 in FIG. 8 shows a signal waveform input to the sampling cycle changing unit 18. In other words, the waveform W21 indicates a signal waveform output from the A / D converter 17.

The sampling cycle changing unit 18 determines whether or not the absolute value of the signal output from the A / D converter 17 exceeds a predetermined threshold value. The sampling cycle changing unit 18 changes the sampling frequency of the integrator 12 when the absolute value of the signal output from the A / D converter 17 exceeds a predetermined threshold value. For example, the dotted line shown in FIG. 8 indicates a predetermined threshold value. The sampling cycle changing unit 18 changes the sampling frequency of the integrator 12 when the waveform W21 exceeds a predetermined threshold value.

FIG. 9 is Part 2 of the figure illustrating an operation example of the sampling cycle changing unit 18. The waveform W31 shown in FIG. 9 shows a signal waveform input to the sampling cycle changing unit 18 that has changed due to the change of the sampling frequency. The dotted line waveform W32 shows the waveform W21 shown in FIG.

The sampling cycle changing unit 18 changes the sampling frequency until the absolute value of the signal output from the A / D converter 17 does not exceed a predetermined threshold value. For example, the sampling cycle changing unit 18 changes the sampling frequency until the waveform W32 that has exceeded the threshold value does not exceed a predetermined threshold value, as shown in the waveform W31. That is, when the absolute value of the signal output from the A / D converter 17 does not exceed a predetermined threshold value, the sampling cycle changing unit 18 stops and fixes the sampling frequency change. In addition to using the absolute value, the sampling cycle changing unit 18 sets a threshold value for the data subjected to processing such as differentiation, higher-order differentiation, integration, and moving average, and determines the change in sampling frequency. good. By using a higher-order differential waveform, there is an advantage that the disturbance noise component to be detected can be separated from the DC component and the trend component generated in a circuit or the like. By using the integrated value or the moving average value, it is possible to suppress the influence of the disturbance noise component to be detected and the random noise generated in the circuit or the like.

The sampling cycle changing unit 18 may change the sampling frequency within a constant frequency width. For example, the sampling cycle changing unit 18 may reduce the sampling frequency within a constant frequency width. Alternatively, the sampling cycle changing unit 18 may increase the sampling frequency within a constant frequency width.

The sampling cycle changing unit 18 may set the threshold value for starting the change of the sampling frequency and the threshold value for stopping the change of the sampling frequency to different values. For example, the threshold value for starting the change of the sampling frequency is set as the first threshold value. The threshold value for stopping the change of the sampling frequency is set as the second threshold value. It is assumed that the second threshold value is smaller than the first threshold value. In this case, when the absolute value of the signal output from the A / D converter 17 exceeds the first threshold value, the sampling cycle changing unit 18 changes the sampling frequency and outputs the sampling frequency from the A / D converter 17. The change in sampling frequency may be stopped when the absolute value of the signal falls below the second threshold.

The irradiation start determination unit 15 does not perform the irradiation start determination while the sampling cycle changing unit 18 changes the sampling frequency. Since the influence of the disturbance noise is large while the sampling cycle changing unit 18 changes the sampling frequency, the irradiation start determination unit 15 does not perform the irradiation start determination so as not to determine the start of X-ray irradiation by the disturbance noise.

One sampling cycle includes a charging period (integration period) for charging the electric charge and a reset period for discharging the electric charge. When the sampling cycle changing unit 18 changes the sampling cycle to be short, the sampling cycle changing unit 18 shortens the reset period.

FIG. 10 is a diagram illustrating a charging period and a reset period of the integrator 12. Ts1 shown in FIG. 10 indicates the charge / discharge cycle of the integrator 12 shown in FIG. That is, Ts1 indicates the sampling period of the signal output from the TFT sensor 11.

Tc1 shown in FIG. 10 indicates the charging period (integration period) of the capacitor C1 of the integrator 12 shown in FIG. That is, Tc1 indicates a period during which the switch SW1 is turned off.

Tr1 shown in FIG. 10 indicates the reset period of the capacitor C1 of the integrator 12 shown in FIG. That is, Tr1 indicates a period during which the switch SW1 is turned on.

As described above, the sampling cycle changing unit 18 changes the sampling cycle according to the disturbance noise. For example, the sampling cycle changing unit 18 changes the sampling cycle from Ts1 to Ts2 as shown in FIG. In the example of FIG. 10, "Ts2 <Ts1".

When changing the sampling cycle, the sampling cycle changing unit 18 changes the reset period without changing the charging period. For example, the sampling cycle changing unit 18 changes the reset period from Tr1 to Tr2 (Tr2 <Tr1) as shown in FIG. The charging period Tc2 has not changed (Tc2 = Tc1).

The integrator 12 repeats charging and resetting of the capacitor C1. The longer the charging time, the better the X-ray detection sensitivity of the X-ray detection circuit. Therefore, when the sampling frequency is changed, the sampling cycle changing unit 18 does not change the charging period but changes the reset period as described above. As a result, the X-ray imaging apparatus 1 can maintain the X-ray detection sensitivity.

Shortening the reset period of the integrator 12 corresponds to shortening the reset period (discharging time of dark current) of the TFT sensor 11. Therefore, even if the reset period of the integrator 12 is shortened, a reset period is secured at the design stage so that the dark current of the TFT sensor 11 can be sufficiently discharged.

FIG. 11 is a flowchart showing an operation example of the X-ray image capturing apparatus 1. The X-ray image capturing apparatus 1 executes the flowchart shown in FIG. 11 when the standby button is pressed on the display 5, for example. The X-ray imaging apparatus 1 repeatedly executes the flowchart shown in FIG. 11 at a predetermined cycle until the X-ray detection circuit determines the start of X-ray irradiation.

When the standby button is pressed, the A / D converters 14 and 17 of the X-ray imaging apparatus 1 digitally convert the input analog signal at a predetermined sampling cycle. Further, the integrator 12 charges and discharges the capacitor C1 at the sampling frequency of the initial value. Hereinafter, a case where the threshold value for starting the change of the sampling frequency and the threshold value for stopping the change of the sampling frequency are different will be described.

The sampling cycle changing unit 18 determines whether or not the absolute value of the signal output from the A / D converter 17 exceeds the first threshold value (step S1). That is, the sampling cycle changing unit 18 determines whether or not disturbance noise has occurred around the X-ray image capturing apparatus 1. When the sampling cycle changing unit 18 determines that the absolute value of the signal output from the A / D converter 17 does not exceed the first threshold value (“No” in S1), the process proceeds to step S4. ..

On the other hand, when the sampling cycle changing unit 18 determines that the absolute value of the signal output from the A / D converter 17 exceeds the first threshold value (“Yes” in S1), the sampling of the integrator 12 is performed. The frequency is changed (step S2). For example, the sampling cycle changing unit 18 increases the sampling frequency by a predetermined value.

After changing the sampling frequency, the sampling cycle changing unit 18 determines whether or not the absolute value of the signal output from the A / D converter 17 is below the second threshold value (second threshold value <first threshold value). Is determined (step S3). That is, the sampling cycle changing unit 18 determines whether or not the influence of the disturbance noise of the X-ray image capturing apparatus 1 is reduced by changing the sampling frequency. When the sampling cycle changing unit 18 determines that the absolute value of the signal output from the A / D converter 17 does not fall below the second threshold value (“No” in S3), the process proceeds to step S2. .. That is, the sampling cycle changing unit 18 further changes the sampling frequency.

On the other hand, when the sampling cycle changing unit 18 determines that the absolute value of the signal output from the A / D converter 17 is below the second threshold value (“Yes” in S3), the irradiation start determination unit 15 determines. It is determined whether or not the absolute value of the signal output from the A / D converter 14 exceeds a predetermined threshold value (step S4). That is, the irradiation start determination unit 15 determines the start of X-ray irradiation of the X-ray generator 2 in a state where the influence of disturbance noise is suppressed. When the irradiation start determination unit 15 determines that the absolute value of the signal output from the A / D converter 14 exceeds a predetermined threshold value (“Yes” in S4), the irradiation of the X-ray of the X-ray generator 2 The start is determined (step S5).

On the other hand, when the irradiation start determination unit 15 determines that the absolute value of the signal output from the A / D converter 14 does not exceed a predetermined threshold value (“No” in S4), the X-ray generator 2 The process of the flowchart is terminated without determining the start of X-ray irradiation.

The TFT sensor 11 starts the charge reset operation by the dark current when the standby button is pressed on the display 5. When the irradiation start determination unit 15 determines the start of X-ray irradiation of the X-ray generator 2, the TFT sensor 11 stops the reset operation. That is, the TFT sensor 11 enters the X-ray imaging state.

As described above, the X-ray imaging apparatus 1 charges the TFT sensor 11 that receives the X-rays emitted from the X-ray generator 2 and outputs the signal corresponding to the X-rays, and the signal of the TFT sensor 11. And an integrator 12 that discharges, an irradiation start determination unit 15 that determines the start of X-ray irradiation of the X-ray generator 2 based on the signal charged by the integrator 12, and a noise detection circuit that detects disturbance noise. It has a sampling cycle changing unit 18 that changes the sampling cycle of the integrator 12 based on the disturbance noise.

As a result, the X-ray imaging apparatus 1 can appropriately detect the start of X-ray irradiation. For example, the X-ray imaging apparatus 1 does not change the detection sensitivity of the start of X-ray irradiation, but changes the sampling period of the integrator 12, and suppresses the influence of disturbance noise on the apparatus. Can be detected properly.

The X-ray imaging apparatus 1 may include a plurality of BPFs whose pass bands do not overlap, and may select one BPF from the plurality of BPFs. For example, the X-ray imaging apparatus 1 may select a BPF according to the frequency of disturbance noise generated by an electronic device used in the surroundings.

Further, in the above, the sampling cycle changing unit 18 changes the sampling frequency within a constant frequency width, but it may be changed randomly.

(Second embodiment)
In the first embodiment, the presence or absence of disturbance noise is determined from the signal output from the integrator 12. In the second embodiment, a sensor for detecting disturbance noise is provided, and the presence or absence of disturbance noise is determined from the signal output from the sensor.

FIG. 12 is a diagram showing an example of a circuit block of the X-ray imaging apparatus 21 according to the second embodiment. In FIG. 12, the same components as those in FIG. 5 are designated by the same reference numerals. Hereinafter, the parts different from those in FIG. 5 will be described.

As shown in FIG. 12, the X-ray imaging apparatus 21 includes an electromagnetic wave sensor (sensor) 31, an integrator (noise charging / discharging unit) 32, a BPF 33, an A / D converter 34, and a sampling cycle changing unit (sampling cycle changing unit). It has a cycle changing unit) 35 and.

The electromagnetic wave sensor 31 detects electromagnetic wave noise generated around the X-ray imaging apparatus 21. The electromagnetic noise is generated from, for example, an electronic device used around the X-ray imaging apparatus 21. The electromagnetic wave sensor 31 is, for example, a hall sensor, a magnetoresistive sensor, a giant magnetoresistive sensor, a magnetic impedance element, or the like.

The integrator 32 charges and discharges the signal output from the electromagnetic wave sensor 31. The integrator 32 has a switch SW11, a capacitor C11, and an operational amplifier OP11. The integrator 32 has the same configuration as the integrator 12, and the description thereof will be omitted.

The voltage of the electric charge charged by the integrator 32 is input to the BPF 33. That is, the signal of the electromagnetic wave sensor 31 read by the integrator 32 is input to the BPF 33. The BPF 33 passes the frequency component of the input signal in a predetermined bandwidth. The passband frequency of the BPF 33 is the same as (including substantially the same) the passband frequency of the BPF 16.

The A / D converter 34 converts the analog signal output from the BPF 33 into a digital signal. The sampling period of the A / D converter 34 is, for example, twice the high frequency side cutoff frequency of the BPF 33.

A digital signal output from the A / D converter 34 is input to the sampling cycle changing unit 35. That is, a signal (digital value) output from the electromagnetic wave sensor 31 that has passed through the BPF 33 is input to the sampling cycle changing unit 35. The sampling cycle changing unit 35 may be configured by, for example, a CPU.

The sampling cycle changing unit 35 changes the sampling cycle (sampling frequency) of the integrator 32 during the standby state. The sampling cycle changing unit 35 stores the signal for each changed sampling cycle in a storage device (not shown) such as a memory. The sampling cycle changing unit 35 selects (determines) the sampling frequency of the integrator 12 in the next standby state based on the signal stored in the storage device. That is, the sampling cycle changing unit 35 selects the sampling frequency of the integrator 12 from the disturbance noise signal of the electromagnetic wave sensor 31 with respect to the past sampling cycle.

Hereinafter, a circuit including a TFT sensor 11, an integrator 12, an LPF 13, an A / D converter 14, and an irradiation start determination unit 15 may be referred to as an X-ray detection circuit. The electromagnetic wave sensor 31, the integrator 32, the BPF 33, the A / D converter 34, and the sampling cycle changing unit 35 may be referred to as a noise detection circuit.

FIG. 13 is a diagram illustrating an example of a disturbance noise signal of an electromagnetic wave sensor stored in a storage device. The sampling cycle changing unit 35 changes the sampling cycle of the integrator 32 during the standby state. Then, the sampling cycle changing unit 35 stores the disturbance noise signal (digital value) of the electromagnetic wave sensor 31 in each sampling cycle.

For example, the sampling cycle changing unit 35 switches the sampling cycle of the integrator 32 between “200 μs”, “205 μs”, and “210 μs”. As shown in FIG. 13, the sampling cycle changing unit 35 stores (stores) disturbance noise signals in each of the three sampling cycles “200 μs”, “205 μs”, and “210 μs” in the storage device. The sampling cycle changing unit 35 may store a disturbance noise signal for a certain period (for example, several days) in a FIFO (First In First Out).

The sampling cycle changing unit 35 selects the sampling cycle of the integrator 12 of the X-ray detection circuit from the signal of the past electromagnetic wave sensor 31 stored in the storage device.

FIG. 14 is a diagram illustrating selection of a sampling period of the integrator 12 of the X-ray detection circuit. The sampling cycle changing unit 35 generates a histogram of the frequency of occurrence of the disturbance noise signal stored in the storage device. For example, as shown in FIG. 14, the sampling cycle changing unit 35 calculates the frequency of occurrence of the disturbance noise signal in each of the sampling cycles “200 μs”, “205 μs”, and “210 μs” with respect to the noise intensity.

Based on the generated histogram, the sampling cycle changing unit 35 selects the sampling frequency having the lowest noise intensity index among the sampling cycles “200 μs”, “205 μs”, and “210 μs”.

For example, the sampling cycle changing unit 35 extracts the frequency with respect to the noise intensity of 10% from the one with the larger noise intensity in each sampling cycle. Then, the sampling cycle changing unit 35 averages the extraction frequencies. More specifically, in the case of the sampling cycle of 210 μs in FIG. 14, the sampling cycle changing unit 35 extracts the frequency of the noise intensity “20” and the frequency of the noise intensity “19”. Then, the sampling cycle changing unit 35 calculates the average value of the frequency of the noise intensity “20” and the frequency of the noise intensity “19”.

The sampling cycle changing unit 35 similarly calculates the average value of the noise frequency for the other sampling cycles “200 μs” and “205 μs”. The sampling cycle changing unit 35 selects the sampling cycle having the lowest average noise frequency as the sampling cycle of the integrator 12.

FIG. 15 is a flowchart showing an operation example of the sampling cycle changing unit 35. The sampling cycle changing unit 35 executes the flowchart shown in FIG. 15 when the standby button is pressed on the display 5, for example. The sampling cycle changing unit 35 repeatedly executes the flowchart shown in FIG. 15 at a predetermined cycle until the X-ray detection circuit detects the start of X-ray irradiation. That is, the sampling cycle changing unit 35 executes the processing of the flowchart shown in FIG. 15 at a fixed cycle in the standby state.

When the standby button is pressed, the A / D converter 34 digitally converts the input analog signal at a predetermined sampling cycle. Further, the integrator 32 charges and discharges the capacitor C11 at the sampling frequency of the initial value.

The sampling cycle changing unit 35 stores the signal output from the A / D converter 34 in the storage device (step S11). That is, the sampling cycle changing unit 35 stores the disturbance noise signal (digital value) output from the electromagnetic wave sensor 31 in the storage device.

The sampling cycle changing unit 35 determines whether or not a certain time has elapsed (step S12). If the sampling cycle changing unit 35 does not elapse for a certain period of time (“No” in S12), the processing of the flowchart ends.

On the other hand, if the sampling cycle changing unit 35 has elapsed for a certain period of time (“Yes” in S12), the sampling cycle of the integrator 32 is changed (step S13). For example, the sampling cycle changing unit 35 selects (selects in order) one of the three sampling cycles “200 μs”, “205 μs”, and “210 μs” to change the sampling cycle of the integrator 32. Thereby, for example, as described with reference to FIG. 13, the storage device stores the disturbance noise signal in each sampling period.

The fixed time in step S12 is set to be shorter than the expected standby time, for example. Further, for a certain period of time, disturbance noise is set to be sampled at a plurality of sampling frequencies during one standby state. For example, for a certain period of time, the disturbance noise signals in the three sampling cycles “200 μs”, “205 μs”, and “210 μs” are set to be stored during one standby state.

FIG. 16 is a flowchart showing an operation example of the X-ray imaging apparatus 21. The X-ray image capturing apparatus 21 executes the flowchart shown in FIG. 16 when the standby button is pressed on the display 5, for example. The X-ray imaging apparatus 21 repeatedly executes the flowchart shown in FIG. 16 at a predetermined cycle until the X-ray detection circuit determines the start of X-ray irradiation. When the standby button is pressed, the A / D converter 14 of the X-ray imaging apparatus 21 digitally converts the input analog signal at a predetermined sampling cycle.

The sampling cycle changing unit 35 determines whether or not the processing of the flowchart is the first execution after the standby button is pressed (step S21).

When the sampling cycle changing unit 35 determines that the processing of the flowchart is the first execution after the standby button is pressed (“Yes” in S21), the past disturbance noise signal stored in the storage device. The sampling period of the integrator 12 is selected based on (step S22). For example, the sampling cycle changing unit 35 selects the sampling cycle of the integrator 12 based on the statistical processing described with reference to FIG.

The storage device stores the past disturbance noise signal by the processing of the flowchart described with reference to FIG. Further, since the process of step S22 is executed via the process of step S21, the sampling period of the integrator 12 is not changed after being selected once until the X-ray imaging is performed.

On the other hand, when the sampling cycle changing unit 35 determines that the processing of the flowchart is not the first execution after the standby button is pressed (“No” in S21), the irradiation start determination unit 15 performs A / D conversion. It is determined whether or not the signal output from the device 14 exceeds a predetermined threshold value (step S23). That is, the irradiation start determination unit 15 determines the start of X-ray irradiation of the X-ray generator 2. When the irradiation start determination unit 15 determines that the absolute value of the signal output from the A / D converter 14 exceeds a predetermined threshold value (“Yes” in S23), the irradiation of the X-ray of the X-ray generator 2 The start is determined (step S24).

On the other hand, when the irradiation start determination unit 15 determines that the absolute value of the signal output from the A / D converter 14 does not exceed a predetermined threshold value (“No” in S23), the X-ray generator 2 The process of the flowchart is terminated without determining the start of X-ray irradiation.

As described above, the X-ray imaging apparatus 21 includes an electromagnetic wave sensor 31 that outputs a disturbance noise signal, an integrator 32 that charges and discharges the disturbance noise signal, and sampling that changes the disturbance noise sampling cycle of the integrator 32. A cycle changing unit 35 and a storage device for storing a disturbance noise signal in each changed disturbance noise sampling cycle are provided. Then, the sampling cycle changing unit 35 changes the sampling cycle of the integrator 12 based on the disturbance noise signal in each disturbance noise sampling cycle stored in the storage device. For example, the sampling cycle changing unit 35 calculates the occurrence frequency of the disturbance noise signal in each changed disturbance noise sampling cycle stored in the storage device, and sets the integrator 12 to the disturbance noise sampling cycle in which the occurrence frequency is low. Change the sampling period of.

As a result, the X-ray imaging apparatus 21 can appropriately detect the start of X-ray irradiation. For example, the X-ray imaging apparatus 21 does not change the detection sensitivity of the start of X-ray irradiation, but changes the sampling period of the integrator 12, and suppresses the influence of disturbance noise on the apparatus. Can be detected properly.

In the above, the sampling cycle changing unit 35 calculates the frequency of occurrence of the disturbance noise signal in each disturbance noise sampling cycle stored in the storage device, but the frequency is not limited to this. For example, the sampling cycle changing unit 35 may calculate the frequency of occurrence of the disturbance noise signal in a cycle other than the disturbance noise sampling cycle stored in the storage device by interpolation processing. Then, the sampling cycle changing unit 35 may change the sampling cycle of the integrator 12 to the disturbance noise sampling cycle having the lowest occurrence frequency among the calculated occurrence frequencies.

Further, in the above, the X-ray imaging apparatus 21 is provided with an electromagnetic wave sensor 31 dedicated to outputting a disturbance noise signal, but in a configuration in which the disturbance noise signal is measured from the output of one integrator 12 shown in FIG. It is also possible to store the disturbance noise data when the sampling period of the integrator 12 is changed in the storage device. For example, the sampling cycle changing unit 18 in FIG. 5 stores the signal output from the A / D converter 17 in the storage device for each sampling cycle. Then, the sampling frequency changing unit 18 executes the same processing as the flowchart shown in FIG.

Each of the above embodiments is merely an example of the embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

1,21 X-ray imaging device 2 X-ray generator 3 round-trip car 4 control device 5 display 6 bed 7 patient 11 TFT sensor 12, 32 integrator 13 LPF
14,17,34 A / D converter 15 Irradiation start determination unit 16,33 BPF
18,35 Sampling cycle changer 31 Electromagnetic wave sensor SW1, SW11 Switch C1, C11 Capacitor OP1, OP11 Operational amplifier

Claims (8)

A radiation detection unit that receives the radiation emitted from the radiation generator and outputs a signal corresponding to the radiation.
A charging / discharging unit that charges and discharges the signal, and
An irradiation start determination unit that determines the start of irradiation of the radiation based on the signal charged by the charge / discharge unit, and an irradiation start determination unit.
A noise detection unit that detects disturbance noise that affects the signal charged by the charging / discharging unit, and a noise detection unit.
A change unit that changes the charge / discharge cycle of the charge / discharge unit based on the detected disturbance noise, and a change unit.
Radiation imaging device with. The noise detection unit detects the disturbance noise from the signal charged by the charge / discharge unit.
The radiographic imaging apparatus according to claim 1. The changing unit changes the charging / discharging cycle when the magnitude of the disturbance noise exceeds the threshold value.
The radiographic imaging apparatus according to claim 2. The irradiation start determination unit does not determine the start of irradiation of the radiation while the change unit changes the charge / discharge cycle.
The radiographic imaging apparatus according to claim 3. A storage unit for storing a signal separated and extracted from the signal charged by the charge / discharge unit as the disturbance noise for each changed charge / discharge cycle is further provided.
The changing unit changes the charging / discharging cycle based on the disturbance noise in each charging / discharging cycle stored in the storage unit.
The radiographic imaging apparatus according to claim 2. The noise detection unit
A sensor that outputs a noise signal corresponding to the disturbance noise,
A noise charging / discharging unit that charges and discharges the noise signal,
A cycle changing unit that changes the noise charging / discharging cycle of the noise charging / discharging unit,
A storage unit for storing the noise signal in each changed noise charge / discharge cycle is provided.
The cycle changing unit changes the charging / discharging cycle based on the noise signal in each noise charging / discharging cycle stored in the storage unit.
The radiographic imaging apparatus according to claim 1. The cycle changing unit calculates the generation frequency of the noise signal for each noise charging / discharging cycle stored in the storage unit, and changes the charging / discharging cycle to the noise charging / discharging cycle having the lowest generation frequency.
The radiographic imaging apparatus according to claim 6. Further, it has a reset unit for resetting the accumulated charge accumulated in the radiation detection unit.
The reset unit adjusts the reset cycle for resetting the accumulated charge to the charge / discharge cycle.
The radiographic imaging apparatus according to any one of claims 1 to 7.

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