JP4810013B2 - X-ray imaging apparatus, X-ray imaging system, and control method of detector control apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray imaging technique.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in medical radiography, which is radiography for medical diagnosis, X-ray photography combining an intensifying screen and an X-ray photographic film is used for (spot) photography.
[0003]
When radiation such as X-rays transmitted through the subject enters the intensifying screen, the phosphor contained in the intensifying screen absorbs this X-ray energy and emits fluorescence. This light emission sensitizes the X-ray photographic film and forms a radiation image on the X-ray photographic film. An X-ray image can be visualized by developing and fixing the film.
[0004]
Recently, various techniques for digitally capturing radiation images have been developed. Visible with a photoelectric conversion element that has sensitivity to X-rays and converts / outputs detected X-rays into electrical signals according to the intensity, or a phosphor that absorbs X-ray energy and emits fluorescence with the corresponding intensity. Using an X-ray image detector comprising a combination of photoelectric conversion elements that are sensitive to light and output an electrical signal corresponding to the intensity, the X-ray image is converted into an electrical signal and digitally converted by A / D conversion. There are methods to capture.
[0005]
FIG. 7 is a schematic block diagram showing an example of an X-ray imaging system.
[0006]
In FIG. 7, 1 is an X-ray generator, 2 is a host computer, 3 is a phosphor, 4 is a flat detector in which a large number of photoelectric conversion elements made up of photodetectors and switching elements are arranged in a plane, and 5 is a flat detector. A flat detector control unit for controlling 4 and 6 represent a subject. The X-ray imaging apparatus includes a phosphor 3, a flat detector 4, and a flat detector control 5.
[0007]
The X-ray generator 1 has an X-ray irradiation switch (not shown), and when the X-ray irradiation switch is pressed, a signal indicating that an X-ray irradiation request has been generated reaches the host computer 2. Then, the host computer 2 notifies the flat detector control unit 5 that an X-ray irradiation request has occurred. The flat detector control unit 5 initializes the flat detector 4 when an X-ray irradiation request arrives, and transmits an X-ray irradiation permission signal to the host computer 2 when initialization of the flat detector 4 is completed. When the host computer 2 receives the X-ray irradiation permission signal, it transmits a signal indicating that X-ray irradiation is permitted to the X-ray generator 1. Then, the X-ray generator 1 performs X-ray irradiation. The irradiated X-rays pass through the subject 6 and are converted by the phosphor 3 into light proportional to the incident X-ray dose. This light is converted into an electric signal by the flat detector 4. At the same time when the flat detector control section 5 reads the electric signal, the X-ray digital image is transferred to the host computer 2. The transferred X-ray digital image is subjected to image processing by the host computer 2, and the captured X-ray digital image is displayed on a display device (not shown).
[0008]
FIG. 8 shows an equivalent circuit of one photoelectric conversion element. In the following example, an amorphous silicon sensor will be described as a photoelectric conversion element. However, the photoelectric conversion element is not particularly limited. For example, other solid-state imaging elements (charge-coupled elements, etc.) or elements such as photomultiplier tubes It may be.
[0009]
In FIG. 8, the configuration of one photoelectric conversion element 20 includes a photodetector 21 and a switching element 22 that controls charge accumulation and reading. Generally, amorphous silicon (α− Si).
[0010]
The capacitor 21C in the photodetector 21 may simply be a photodiode with parasitic capacitance in this example, or it may include an additional capacitor 21C in parallel to improve the dynamic range of the photodiode 21D and the detector. You may think of it as a vessel. When the photodetector 21 is irradiated with X-rays, charges corresponding to the X-ray dose are generated by the photodiode 21D, and the generated charges are accumulated in the capacitor 21C.
[0011]
The anode A of the diode 21D is connected to the refresh control circuit 23. The refresh control circuit 23 outputs a bias voltage of the normal voltage Vs, but can temporarily output the refresh voltage Vr to initialize the capacitor 21.
[0012]
The cathode K is connected to a controllable switching element 22 for reading out the electric charge accumulated in the capacitor 21C. In this example, the switching element 22 is a thin film transistor connected between the cathode K of the diode 21 </ b> D and the charge readout amplifier 25.
[0013]
A gate control circuit 24 is connected to the gate G of the switching element 22, and the gate control circuit 24 outputs a gate signal Vg to read out the electric charge accumulated in the capacitor 21C. The read charge is amplified by the amplifier 25, A / D conversion is performed by the A / D conversion circuit 27 through the sample hold circuit 26, and the charge accumulated in the capacitor 21C is digitized.
[0014]
Next, initialization processing of one photoelectric conversion element 20 will be described with reference to FIG.
[0015]
In FIG. 9, the refresh signal indicates the output signal of the refresh control circuit 23, the gate signal indicates the output signal of the gate control circuit 24, and the dark current indicates the current flowing through the capacitor 21C. Normally, the refresh signal voltage is bias voltage Vs, the gate signal voltage is 0 V, and dark current hardly flows.
[0016]
In order to initialize the capacitor 21C in this state, the refresh voltage Vr is output at time T1. When the refresh signal becomes the refresh voltage Vr, a negative dark current flows and the charge accumulated in the capacitor 21C is swept out. The time during which the refresh signal is at the refresh voltage Vr (the time from time T1 to time T2) is determined in advance so that the charge accumulated in the capacitor 21C is sufficiently small.
[0017]
Next, at time T2, the voltage of the refresh signal is set to the bias voltage Vs. Hereinafter, an operation in which the refresh control circuit 23 temporarily outputs a refresh signal, the voltage thereof becomes Vr, and the capacitor 21C is initialized is referred to as refresh. Immediately after switching to the bias voltage Vs, a large positive dark current is generated and accumulated as a charge in the capacitor 21C. It is known that the noise for the X-ray image is proportional to the square root of the charge accumulated by the dark current.
[0018]
Therefore, after performing the refresh process, the gate control circuit 24 temporarily outputs the gate signal Vg at time T3. As a result, the electric charge accumulated in the capacitor 21C is swept out.
[0019]
The time T3 is determined in advance so that the dark current is sufficiently small. Hereinafter, the operation in which the gate control circuit 24 temporarily outputs the gate signal Vg and sweeps out the electric charge accumulated in the capacitor 21C by dark current is referred to as idle reading. Next, when the charge accumulated in the capacitor 21C is sufficiently swept, the gate signal is set to 0 V at time T5. The time during which the gate signal is at the gate voltage Vg (the time from time T3 to time T5) is determined in advance so that the charge accumulated in the capacitor 21C is sufficiently small.
[0020]
However, even if the idle reading is performed, a slight dark current continues to flow, so that charge is gradually accumulated in the capacitor 21C. Therefore, the initialization process of the photoelectric conversion element 20 including the refresh process and the idle reading process is periodically repeated. For the same reason, the photoelectric conversion element 20 is initialized immediately before X-ray imaging.
[0021]
FIG. 10 is a block diagram illustrating an example of the flat detector 4 and the flat detector control unit 5.
[0022]
In FIG. 10, reference numeral 7 denotes a CPU for reading an X-ray digital image from the flat panel detector 4, to which a refresh control circuit 8, a row address selection circuit 9 and a column address selection circuit 10 are connected. The CPU 7 can control each circuit. The CPU 7 is connected to a host computer 2 (not shown), and can transfer an X-ray digital image read from the flat detector 4 to the host computer 2.
[0023]
The flat detector 4 has a large number of photoelectric conversion elements 20 shown in FIG. 8 arranged on a plane. In FIG. 10, two photoelectric conversion elements are arranged in the row direction and two photoelectric conversion elements in order to simplify the explanation. The element 20 is arranged in a planar shape.
[0024]
As described above, the one-pixel photoelectric conversion element 20 includes the light detection unit 21 and the switching TFT 22. The light detection units 21 (1, 1) to 21 (2, 2) correspond to the light detection unit 21 described above, where the cathode side of the light detection unit 21 is K and the anode side is A. Represents. The TFTs 22 (1, 1) to TFT 22 (2, 2) correspond to the switching TFTs 22, and the TFT has a source electrode S, a gate electrode G, and a drain electrode D.
[0025]
The gate electrode G of the TFT 22 in each row is connected to the row address selection circuit 9, and the row address selection circuit 9 includes the gate control circuit 24 and the switches SWr 1 and 2 described above.
[0026]
The drain electrode D of the TFT 22 in each column is connected to the column address selection circuit 10, and the column address selection circuit 10 includes an amplifier 25, a sample hold circuit 26, and switches SWc1-2.
[0027]
Further, the anode side of the light detection unit 21 is all connected to the refresh control circuit 8, and the normal refresh control circuit 8 outputs a bias voltage of the voltage Vs, and outputs the refresh voltage Vr when outputting it as a refresh signal. . The refresh control circuit 8 is the same as the refresh control circuit 23 shown in FIG.
[0028]
Next, initialization processing of the plurality of photoelectric conversion elements 20 illustrated in FIG. 11 in the configuration illustrated in FIG. 10 will be described.
[0029]
In FIG. 11, the refresh signal is the output signal of the refresh control circuit 8, the gate signal is the output signal of the gate control circuit 24, and SWr <b> 1-2 indicate the switches SWr <b> 1-2 in the row address selection circuit 9. Normally, the refresh signal voltage is the bias voltage Vs, the gate signal voltage is 0 V, and SWr 1 and SWr 1 are OFF. Accordingly, the anode side A of all the light detection units 21 (1, 1) to 21 (2, 2) is the bias voltage Vs, and the gate electrodes of all the TFTs 22 (1, 1) to TFT 22 (2, 2). G is 0V.
[0030]
In this state, the refresh voltage Vr is output at time T1 in order to initialize all the light detection units 21. When the refresh signal becomes the refresh voltage Vr, a negative dark current flows, and the charge accumulated in the capacitor 21C in the light detection unit 21 is swept out. Next, at time T2, the voltage of the refresh signal is set to the bias voltage Vs. Immediately after switching to the bias voltage Vs, a large amount of positive dark current is generated, and is accumulated as a charge in the capacitor 21 </ b> C in the light detection unit 21. Therefore, after performing the refresh process, the gate control circuit 24 temporarily outputs the gate signal Vg at time T3 and turns on the switch SWr1. Then, the voltage of the gate electrode G of the TFT 22 (1, 1) to TFT 22 (1, 2) in the first row becomes Vg, and the electric charge accumulated in the capacitor 21C in the photodetecting section 21 in the first row is swept out. It is. Next, at time T4, the switch SWr1 is turned off and the switch SWr2 is turned on. Then, the voltage of the gate electrode G of the TFT 22 (1, 1) to TFT 22 (1, 2) in the first row becomes 0 V, and the gate electrode G of the TFT 22 (2, 1) to TFT 22 (2, 2) in the second row. Since the voltage of V becomes Vg, the charge accumulated in the capacitor 21C in the photodetecting section 21 in the second row is swept out.
[0031]
Next, when the gate signal is set to 0V and the switch SWr2 is turned OFF at time T5, the gate electrodes G of all the TFTs 22 (1,1) to TFT22 (2,2) are set to 0V, and the initialization process ends. The initialization process is from time T1 to time T5.
[0032]
Next, the relationship between the initialization process of the photoelectric conversion element 20 and X-ray imaging is shown in FIG. As shown in FIG. 12, when X-ray imaging is not performed, refresh and idle reading (initialization processing) are periodically repeated at TI intervals. FIG. 12 shows that the X-ray irradiation switch of the X-ray generator 1 is pressed at time T1 (timing other than when refreshing and idle reading is performed), and an X-ray irradiation request is sent via the host computer 2. The case where it reaches the flat detector control unit 5 is shown. When an X-ray irradiation request is generated, the host computer 2 that has received this X-ray irradiation request sets the X-ray irradiation request signal to Low.
[0033]
When the X-ray irradiation request signal becomes Low, refresh and idle reading are performed again, and when this is finished, the flat panel detector control unit 5 outputs an X-ray irradiation permission signal at time T5. That is, the X-ray irradiation permission signal is set to Low. When the X-ray irradiation permission signal becomes Low, X-ray irradiation is permitted. Here, the time from when the X-ray irradiation request signal becomes Low until the X-ray irradiation permission signal becomes Low is called an exposure delay time, and is indicated by TD1 in FIG.
[0034]
When the X-ray irradiation permission signal reaches the X-ray generator 1 via the host computer 2, the X-ray generator 1 emits X-rays as shown in FIG. When the X-ray generator 1 emits X-rays, the irradiated X-rays pass through the subject 6 and are converted into light proportional to the incident X-ray amount by the phosphor 3, and the electric charge corresponding to the light is changed. Charge is accumulated in the capacitor 21C.
[0035]
When the X-ray irradiation is completed, the host computer 2 sets the X-ray irradiation permission signal to High at time T6 and outputs it to the X-ray generator 1. When the X-ray irradiation permission signal becomes High, the X-ray irradiation request signal becomes High.
[0036]
When the X-ray irradiation is completed, the gate signal is Vg and the switch SWr1 is turned ON at time T6. Then, the voltage of the gate electrode G of the TFT 22 (1, 1) to TFT 22 (1, 2) in the first row shown in FIG. 10 becomes Vg, and is accumulated in the capacitor 21C in the photodetecting section 21 in the first row. The charge read out is read and the signal read through the amplifier 25 and the sample hold circuit 26 is held. When the switch SWc1 is turned on at time T6, the signal held by the photodetection unit 21 in the first row and first column is digitized by the A / D conversion circuit 27 and the value is transferred to the host computer 2. At time T7, when the switch SWc1 is turned off and the switch SWc2 is turned on, the signal held by the photodetection unit 21 in the first row and second column is digitized by the A / D conversion circuit 27, and the value is converted to the host computer 2 Forwarded to
[0037]
Next, when the switch SWr1 is turned off and the switch SWr2 is turned on at time T8, the voltage of the gate electrode G of the TFTs 22 (2,1) to TFT22 (2,2) in the second row shown in FIG. 10 becomes Vg. The electric charge accumulated in the capacitor 21C in the light detection unit 21 in the second row is read, and the signal read through the amplifier 25 and the sample hold circuit 26 is held. Then, when the switch SWc1 is turned on at time T8, the signal held by the photodetection unit 21 in the second row and first column is digitized by the A / D conversion circuit 27 and the value is transferred to the host computer 2. At time T9, when the switch SWc1 is turned off and the switch SWc2 is turned on, the signal held by the light detection unit 21 in the second row and second column is digitized by the A / D conversion circuit 27, and the value is converted to the host computer. 2 is transferred.
[0038]
When all charges accumulated in the flat panel detector 4 are transferred to the host computer 2, the gate signal is set to 0V, SWr1 and SWr2 are turned off, and SWc1 and SWc2 are turned off at time T10. Hereinafter, reading the entire charges accumulated in the flat detector 4 by temporarily turning on the gate signals Vg, SWr1 and SWr2 and temporarily turning on SWc1 and SWc2 will be referred to as main reading.
[0039]
[Problems to be solved by the invention]
In the above-described conventional example, as shown in FIG. 12, when the X-ray irradiation switch is pressed at a time other than the initialization process and the X-ray irradiation request signal becomes Low, refresh processing and idle reading are immediately performed. .
[0040]
However, when the X-ray irradiation switch is pressed during the initialization process and the X-ray irradiation request signal becomes Low, the initialization process currently being performed is interrupted and the initialization process is performed again from the beginning. . If an initialization process is interrupted when an X-ray irradiation request is generated and refresh is performed immediately, a dark current flows. As a result, a large amount of charge is accumulated in the capacitor 21C, and a part of the charge remains even if the idle reading is performed thereafter. Since it is known that the noise for the X-ray image is proportional to the square root of the charge accumulated by the dark current, the X-ray image noise will increase when X-rays are irradiated in this state. There was a problem.
[0041]
The present invention has been made in view of the above problems, and an object thereof is not to increase noise in an X-ray image even when an X-ray irradiation request is received during initialization of a detector.
[0042]
In addition, it is desirable to shorten the time from receipt of an X-ray irradiation request to permission of X-ray imaging. Accordingly, an object of the present invention is to shorten the exposure delay time when an X-ray irradiation request is received during initialization of the detector.
[0043]
[Means for Solving the Problems]
In order to achieve the object of the present invention, for example, X-ray imaging of the present invention apparatus Has the following configuration.
[0044]
That is, a detector that detects X-rays emitted by the X-ray generator;
A signal requesting X-ray irradiation during the initialization process of the detector Recieved If The time from the start of the initialization process to the reception of the signal is End of the initialization process When Since Do Control means for emitting a signal permitting X-ray irradiation according to the circumstances;
It is characterized by having.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to the accompanying drawings.
[0048]
[First Embodiment]
In the present embodiment, an X-ray imaging system including an X-ray imaging apparatus in which a phosphor and a photoelectric conversion element are combined and processing thereof will be described below. The configuration of the X-ray imaging system of this embodiment is the same as the configuration shown in FIG. In addition, the flat detector 4 and the flat detector control unit 5 of the present embodiment are the same as the flat detector 4 and the flat detector control unit 5 shown in FIG.
[0049]
FIG. 13 shows the basic configuration of the host computer 2 used in this embodiment.
[0050]
A CPU 1301 controls the entire host computer 2 using programs and data stored in the RAM 1302 and the ROM 1303 and performs transmission / reception control of signals with the X-ray imaging apparatus 1 and the flat detector control unit 5.
[0051]
A RAM 1302 includes an area for temporarily storing programs and data loaded from the external storage device 1304 and the storage medium drive 1309, and also includes a work area used temporarily when the CPU 1301 executes each process. .
[0052]
A ROM 1303 stores a boot program and setting data of the host computer 2 and an overall control program and data.
[0053]
Reference numeral 1304 denotes an external storage device such as a hard disk, which stores programs and data installed from the storage medium drive 1309. Further, when the size of the work area exceeds the size of the RAM 1302, the excess area can be provided as a file.
[0054]
Reference numerals 1305 and 1306 denote a keyboard and a mouse, respectively, which function as pointing devices, and can input various instructions to the host computer 2.
[0055]
A display device 1307 includes a CRT, a liquid crystal screen, and the like, and can display, for example, a system message as character information and image information.
[0056]
Reference numeral 1308 denotes an interface (I / F) which can be connected to a network such as the Internet or a LAN, or an external device. Although the number of I / Fs is one in the figure, it is not limited to this, and a plurality of I / Fs can be provided. In this embodiment, each I / F is used to perform X-ray imaging apparatus and plane detection. Can be connected to the device controller 5 and can transmit / receive signals to / from each device.
[0057]
A storage medium drive 1309 includes a CD-ROM drive, a DVD drive, a floppy disk drive, and the like, and can load programs, data, and the like from a storage medium such as a CD-ROM or a DVD-ROM.
[0058]
A bus 1310 connects the above-described units.
[0059]
FIG. 1 shows the relationship between the initialization process and the X-ray imaging when an X-ray irradiation request is generated during the initialization process of the photoelectric conversion element 20. As shown in FIG. 1, when X-ray imaging is not performed, refresh and idle reading (initialization processing) are periodically repeated at TI intervals.
[0060]
FIG. 1 shows a case where the X-ray irradiation switch of the X-ray generator 1 is pressed at time TX during idle reading, and an X-ray irradiation request arrives at the flat detector control unit 5 via the host computer 2. ing. When an X-ray irradiation request is generated, the host computer 2 that has received this X-ray irradiation request sets the X-ray irradiation request signal to Low. When the X-ray irradiation request signal becomes Low, the flat panel detector control unit 5 receiving the X-ray irradiation request signal sets the time TW from the time T1 when the refresh process is started until the X-ray irradiation request signal becomes Low in the CPU 7. Is stored in a memory (see FIG. 14). The memory is not limited to being provided in the CPU 7 and may be provided outside the CPU 7.
[0061]
When the gate signal is set to 0 V at time T5 and the idle reading is completed, the stored time TW is waited. When waiting for the time TW ends, the flat panel detector control unit 5 sets the X-ray irradiation permission signal to Low at time T11.
[0062]
Here, after the initialization process is completed, the CPU 7 of the flat detector control unit 5 reads the TW stored in the memory and waits for the time TW (wait process). As a result, the time TD1 required for the initialization process is equal to the time TD1 from when the X-ray irradiation request signal becomes Low until the X-ray irradiation permission signal becomes Low. As a result, the exposure delay time is always a fixed time TD1.
[0063]
When the X-ray irradiation permission signal becomes Low, this signal reaches the X-ray generator 1 via the host computer 2, and the X-ray generator irradiates X-rays as shown in FIG. When the X-ray generator 1 irradiates X-rays, the irradiated X-rays are converted into light proportional to the X-ray dose that has passed through the subject 6 and entered by the phosphor 3, and the electric charge corresponding to the light is applied to the capacitor 21C. Charge is accumulated.
[0064]
When the X-ray irradiation ends, the flat panel detector control unit 5 sets the X-ray irradiation permission signal to High at time T6. When the X-ray irradiation permission signal becomes High, this signal reaches the X-ray generation device 1 via the host computer 2, and the X-ray generation device 1 sets the X-ray irradiation request signal to High.
[0065]
When the X-ray irradiation is completed, the gate signal is Vg and the switch SWr1 is turned ON at time T6. Then, the voltage of the gate electrode G of the TFT 22 (1, 1) to TFT 22 (1, 2) in the first row shown in FIG. 10 becomes Vg, and is accumulated in the capacitor 21C in the photodetecting section 21 in the first row. The charged charge is read out. The read charge is held through the amplifier 25 and the sample hold circuit 26. When the switch SWc1 is turned on at time T6, the signal held by the photodetecting unit 21 in the first row and first column is digitized by the A / D conversion circuit 27, and the value is transferred to the host computer. At time T7, when the switch SWc1 is turned off and the switch SWc2 is turned on, the signal held by the light detection unit 21 in the first row and the second column is digitized by the A / D conversion circuit 27, and the value is converted to the host computer. 2 is transferred.
[0066]
Next, when the switch SWr1 is turned off and the switch SWr2 is turned on at time T8, the voltage of the gate electrode G of the TFTs 22 (2,1) to TFT22 (2,2) in the second row shown in FIG. 10 becomes Vg. The electric charge accumulated in the capacitor 21C in the light detection unit 21 in the second row is read out. The read charge is held through the amplifier 25 and the sample hold circuit 26. When the switch SWc1 is turned on at time T8, the signal held by the photodetection unit 21 in the second row and first column is digitized by the A / D conversion circuit 27 and the value is transferred to the host computer 2. At time T9, when the switch SWc1 is turned off and the switch SWc2 is turned on, the signal held by the light detection unit 21 in the second row and second column is digitized by the A / D conversion circuit 27, and the value is converted to the host computer. 2 is transferred.
[0067]
When all charges accumulated in the flat panel detector 4 are transferred to the host computer 2, the gate signal is set to 0V, SWr1 and SWr2 are turned off, and SWc1 and SWc2 are turned off at time T10.
[0068]
When an X-ray irradiation request is generated at a time other than the initialization process of the photoelectric conversion element 20, the same process as the process illustrated in FIG. Therefore, the description when an X-ray irradiation request occurs at a time other than the initialization process of the photoelectric conversion element 20 is omitted.
[0069]
Next, flowcharts of the X-ray imaging method of this embodiment are shown in FIGS. FIG. 2 is a main routine of the X-ray imaging method, and FIG. 3 is a subroutine of initialization processing.
[0070]
In FIG. 2, the timer (TM) value is initialized to 0 (step S201). This timer is a hardware timer. For example, a hardware timer built in the CPU 7 may be used, or a hardware timer may be provided outside the CPU. This timer automatically counts up every fixed time (for example, every 1 ms).
[0071]
And the initialization process of the photoelectric conversion element 20 is performed (step S202). The initialization process is a subroutine. The subroutine for the initialization process will be described later in detail.
[0072]
Next, it is determined whether XFLG is 1 (step S203). XFLG is 1 when the X-ray irradiation request signal becomes Low during the initialization process of Step S202, and is 0 when the X-ray irradiation request signal does not become Low during the initialization process of Step S202. If XFLG is not 1 in step S203, the process proceeds to step S204, and it is determined whether or not the fall of the X-ray irradiation request signal is detected (step S204). In step S204, if the falling of the X-ray irradiation request signal is detected (X-ray irradiation request signal becomes Low), the process proceeds to step S206. If the falling of the X-ray irradiation request signal is not detected, a timer ( The value of TM) is compared with the initialization processing interval TI (step S205). As a result of the comparison processing, when TM is smaller than the initialization processing interval TI, step S204 and step S205 are repeated. Here, TI indicates the interval of the initialization process shown in FIG. In step S205, if TM is equal to or greater than TI, the process proceeds to step S201, and the processes from step S201 to step S205 are repeated.
[0073]
If XFLG is 1 in step S203, the timer (TT) value is initialized to 0 (step S211). This timer is a hardware timer. For example, a hardware timer built in the CPU 7 may be used, or a hardware timer may be provided outside the CPU. This timer automatically counts up every fixed time (for example, every 1 ms). Then, the value of the timer (TT) is compared with the value of TW (step S212), and if TT is smaller, the process of step S212 is repeated. If TT is equal to or greater than TW in step S212, the process proceeds to step S207. Here, TW is set in the initialization process subroutine in step S202, and is the time from the start of the initialization process until the X-ray irradiation request signal becomes Low.
[0074]
Next, in step S204, when the X-ray irradiation request signal becomes low, the photoelectric conversion element 20 is immediately initialized (step S206). When the initialization process ends, the X-ray irradiation permission signal is set to Low (step S207). Then, the X-ray generator irradiates X-rays and performs X-ray imaging (Step S208). Thereafter, the X-ray irradiation permission signal is set to High (step S209), and the main reading is performed to read the photographed X-ray image (step S210). When the main reading is finished, the process proceeds to step S201, and the above-described process is repeated. When the actual reading is performed, the photographed X-ray digital image is transferred to the host computer, and the X-ray digital image is displayed on the display device through image processing and the like.
[0075]
Next, the initialization subroutine in step S202 will be described with reference to FIG.
[0076]
First, the timer (TS) value and the XFLG value are initialized to 0 (step S301). This timer is a hardware timer. For example, a hardware timer built in the CPU 7 may be used, or a hardware timer may be provided outside the CPU. This timer automatically counts up every fixed time (for example, every 1 ms). XFLG is a flag indicating whether or not the fall of the X-ray irradiation request signal (X-ray irradiation request signal becomes Low) is detected during the initialization process.
[0077]
Thereafter, the refresh signal is set to Vr (step S302), and it is determined whether or not the fall of the X-ray irradiation request signal is detected (step S303). When the falling edge of the X-ray irradiation request signal is not detected, the value of the timer (TS) is compared with the refresh time T2 (S4), and when TS is smaller than the refresh time T2, step S303 and step S304 are repeated. Here, in FIG. 1, when the time of T1 is 0, T2 is the time during which the refresh signal is set to Vr. If the falling edge of the X-ray irradiation request signal is detected in step S303, the process proceeds to step S317, the value of the timer (TS) is stored in the variable TW, and XFLG is set to 1. Therefore, TW indicates the time from when the initialization process is started until the falling edge of the X-ray irradiation request signal is detected.
[0078]
Next, in step S304, if TS is equal to or greater than T2, the process proceeds to step S305, and the refresh signal is set to Vs (step S305).
[0079]
Thereafter, it is determined whether or not the falling edge of the X-ray irradiation request signal has been detected (step S306). If the falling edge of the X-ray irradiation request signal is detected, the process proceeds to step S318. On the other hand, when the fall of the X-ray irradiation request signal is not detected, the value of the timer (TS) is compared with the idle reading start time T3 (step S307), and when TS is smaller than the idle reading start time T3. Step S306 and step S307 are repeated. Here, T3 is the time when idle reading is started as shown in FIG. If the falling edge of the X-ray irradiation request signal is detected in step S306, the process proceeds to step S318, the timer (TS) value is stored in the variable TW, and XFLG is set to 1.
[0080]
In step S307, if TS is equal to or greater than T3, the gate signal is set to Vg (step S308), and the value of variable n is set to 1 (step S309). Next, since n = 1, the switch SWr1 is turned on (step S310), and it is determined whether or not the falling of the X-ray irradiation request signal is detected (step S311). If the falling edge of the X-ray irradiation request signal is detected, the process proceeds to step S319. On the other hand, when the falling edge of the X-ray irradiation request signal is not detected, the value of the timer (TS) is compared with time T4 because n = 1 (step S312). When TS is smaller than T4, step S311 is compared. Step S312 is repeated. Here, T4 is the time when the SWr1 that is turned on is turned off as shown in FIG. If the falling edge of the X-ray irradiation request signal is detected in step S311, the process proceeds to step S319, the timer (TS) value is stored in TW, and XFLG is set to 1.
[0081]
In step S312, if TS is equal to or greater than T4, the process proceeds to step S313, and the switch SWr1 is turned OFF (step S313). Thereafter, the value of the variable n is incremented by 1 (step S314), and it is determined whether or not the variable n is 2 or less (step S315). In this embodiment, as shown in FIG. 10, since two photoelectric conversion elements are provided in the row direction and two in the column direction, whether or not the variable n is 2 or less is determined in step S315. If three such elements are provided in the row direction and the column direction, it is determined in step S315 whether or not the variable n is 3 or less.
[0082]
If the variable n is 2 or less, the process proceeds to step S310. Since n = 2 this time, the switch SWr2 is turned on, and the processes from step S310 to step S315 are repeated. If the variable n is larger than 2 in step S315, the gate signal is set to 0 V in step S316, and the subroutine is terminated.
[0083]
Thus, in the initialization processing subroutine, when the falling edge of the X-ray irradiation request signal is detected, the value of the timer (TS) is stored in TW and XFLG is set to 1.
[0084]
[Second Embodiment]
In the present embodiment, an X-ray imaging system for shortening the exposure delay time and its processing will be described below. FIG. 4 shows the relationship between the initialization process and the X-ray imaging when an X-ray irradiation request is generated during the initialization process of the photoelectric conversion element 20.
[0085]
As shown in FIG. 4, when X-ray imaging is not performed, refresh and idle reading are periodically repeated at TI intervals.
[0086]
In FIG. 4, the X-ray irradiation switch of the X-ray generator 1 is pushed at time TX during idle reading as in the case shown in FIG. 1, and the X-ray irradiation request passes through the host computer 2. In this case, it reaches the flat detector control unit 5. When an X-ray irradiation request is generated, the host computer 2 that has received this X-ray irradiation request signal sets the X-ray irradiation request signal to Low.
[0087]
Then, when the gate signal is set to 0 V at time T5 and the idle reading is completed, the flat detector control unit 5 immediately sets the X-ray irradiation permission signal to Low.
[0088]
As a result, after the initialization process is finished, the flat panel detector control unit 5 immediately sets the X-ray irradiation permission signal to Low, so that the X-ray irradiation permission signal becomes Low after the X-ray irradiation request signal becomes Low. The time until exposure (exposure delay time) TD2 can be made shorter than the method shown in the first embodiment, for example.
[0089]
When the X-ray irradiation permission signal becomes Low, this signal reaches the X-ray generator 1 via the host computer 2, and the X-ray generator 1 emits X-rays as shown in FIG. When the X-ray generator 1 irradiates X-rays, the irradiated X-rays pass through the subject 6 and are converted into light proportional to the incident X-ray dose by the phosphor 3, and the electric charge corresponding to the light is converted into the capacitor 21C. The charge is accumulated in the.
[0090]
When the X-ray irradiation ends, the flat panel detector control unit 5 sets the X-ray irradiation permission signal to High at time T6. When the X-ray irradiation permission signal becomes High, this signal reaches the X-ray generator 1 via the host computer 2. The X-ray generator 1 sets the X-ray irradiation request signal to High.
[0091]
When the X-ray irradiation is completed, the gate signal is Vg and the switch SWr1 is turned ON at time T6. Then, the voltage of the gate electrode G of the TFT 22 (1, 1) to TFT 22 (1, 2) in the first row shown in FIG. 10 becomes Vg, and is accumulated in the capacitor 21C in the photodetecting section 21 in the first row. The charged charge is read out. The read charge is held through the amplifier 25 and the sample hold circuit 26. When the switch SWc1 is turned on at time T6, the signal held by the photodetecting unit 21 in the first row and first column is digitized by the A / D conversion circuit 27, and the value is transferred to the host computer. At time T7, when the switch SWc1 is turned off and the switch SWc2 is turned on, the signal held by the light detection unit 21 in the first row and the second column is digitized by the A / D conversion circuit 27, and the value is converted to the host computer. 2 is transferred.
[0092]
Next, when the switch SWr1 is turned off and the switch SWr2 is turned on at time T8, the voltage of the gate electrode G of the TFTs 22 (2,1) to TFT22 (2,2) in the second row shown in FIG. 10 becomes Vg. The electric charge accumulated in the capacitor 21C in the light detection unit 21 in the second row is read out. The read charge is held through the amplifier 25 and the sample hold circuit 26. When the switch SWc1 is turned on at time T8, the signal held by the photodetection unit 21 in the second row and first column is digitized by the A / D conversion circuit 27 and the value is transferred to the host computer 2. At time T9, when the switch SWc1 is turned off and the switch SWc2 is turned on, the signal held by the light detection unit 21 in the second row and second column is digitized by the A / D conversion circuit 27, and the value is converted to the host computer. 2 is transferred.
[0093]
When all charges accumulated in the flat panel detector 4 are transferred to the host computer 2, the gate signal is set to 0V, SWr1 and SWr2 are turned off, and SWc1 and SWc2 are turned off at time T10.
[0094]
When an X-ray irradiation request is generated at a time other than the initialization process of the photoelectric conversion element 20, the same process as the process illustrated in FIG. Therefore, the description when an X-ray irradiation request occurs at a time other than the initialization process of the photoelectric conversion element 20 is omitted.
[0095]
Therefore, according to the present embodiment, the exposure delay when the X-ray irradiation request is generated at a time other than the initialization process is TD1, and the exposure delay when the X-ray irradiation request is generated during the initialization process is TD2. Since TD2 is equal to or less than TD1, the exposure delay is TD1 at the maximum. As a result, when an X-ray irradiation request is generated during the initialization process, the exposure delay time can be made shorter than that in the first embodiment, for example.
[0096]
Next, flowcharts of the X-ray imaging method of this embodiment are shown in FIGS. FIG. 5 is a main routine of the X-ray imaging method, and FIG. 6 is a subroutine of initialization processing.
[0097]
In FIG. 5, the value of the timer (TM) is initialized to 0 (step S501). This timer is a hardware timer. For example, a hardware timer built in the CPU 7 may be used, or a hardware timer may be provided outside the CPU. This timer automatically counts up every fixed time (for example, every 1 ms).
[0098]
And the initialization process of the photoelectric conversion element 20 is performed (step S502). The initialization process is a subroutine. The subroutine for the initialization process will be described later in detail.
[0099]
Next, it is determined whether XFLG is 1 (step S503). XFLG is 1 when the X-ray irradiation request signal is Low during the initialization process in Step S502, and is 0 if the X-ray irradiation request signal is not Low during the initialization process of Step S502. If XFLG is not 1 in step S503, it is determined whether or not the fall of the X-ray irradiation request signal has been detected (step S504). If the falling edge of the X-ray irradiation request signal is detected in step S504, the process proceeds to step S506. On the other hand, when the falling edge of the X-ray irradiation request signal is not detected, the value of the timer (TM) is compared with the initialization processing interval TI (step S505). If TM is smaller than TI, step S504 and step S505 are repeated. Here, TI indicates the interval of the initialization process shown in FIG. If TM is equal to or greater than TI in step S505, the process proceeds to step S501, and the processes from step S501 to step S505 are repeated.
[0100]
If XFLG is 1 in step S503, the process proceeds to step S507, and the X-ray irradiation permission signal is set to low (step S507). Therefore, if the X-ray irradiation request signal becomes Low during the initialization process in step S502, the initialization process in step S506 is not performed.
[0101]
Next, when the X-ray irradiation request signal becomes Low in step S504, the process proceeds to step S506, and the photoelectric conversion element 20 is immediately initialized (step S506). When the initialization process is completed, the X-ray irradiation permission signal is set to Low (step S507). Then, the X-ray generator 1 performs X-ray imaging by irradiating X-rays (step S508). Thereafter, the X-ray irradiation permission signal is set to High (step S509), and the main reading is performed to read the photographed X-ray image (step S510). When the main reading is performed, the process proceeds to step S501, and the above-described process is repeated. When the actual reading is performed, the photographed X-ray digital image is transferred to the host computer 2, and the X-ray digital image is displayed on the display device through image processing and the like.
[0102]
Next, the initialization subroutine in step S502 will be described with reference to FIG.
[0103]
First, the timer (TS) value and the XFLG value are initialized to 0 (step S601). This timer is a hardware timer. For example, a hardware timer built in the CPU 7 may be used, or a hardware timer may be provided outside the CPU. This timer automatically counts up every fixed time (for example, every 1 ms). XFLG is a flag indicating whether or not the fall of the X-ray irradiation request signal is detected during the initialization process.
[0104]
Thereafter, the refresh signal is set to Vr (step S602), and it is determined whether or not the fall of the X-ray irradiation request signal is detected (step S603). When the fall of the X-ray irradiation request signal is not detected, the value of the timer (TS) is compared with the refresh time T2 (step S604), and when TS is smaller than the refresh time T2, steps S603 and S604 are repeated. . Here, in FIG. 1, when the time of T1 is 0, T2 is the time during which the refresh signal is set to Vr. If the falling edge of the X-ray irradiation request signal is detected in step S603, the process proceeds to step S617, and XFLG is set to 1. Next, in step S604, if TS is equal to or greater than T2, the process proceeds to step S605, and the refresh signal is set to Vs (step S605).
[0105]
Thereafter, it is determined whether or not the falling edge of the X-ray irradiation request signal has been detected (step S606). If the falling edge of the X-ray irradiation request signal is detected, the process proceeds to step S618. On the other hand, when the falling of the X-ray irradiation request signal is not detected, the value of the timer (TS) is compared with the idle reading start time T3 (step S607), and when TS is smaller than the idle reading start time T3. Steps S606 and S607 are repeated. Here, T3 is the time when idle reading is started as shown in FIG. If the falling edge of the X-ray irradiation request signal is detected in step S606, the process proceeds to step S618, and XFLG is set to 1.
[0106]
In step S607, when TS becomes T3 or more, the gate signal is set to Vg (step S608), and the value of the variable n is set to 1 (step S609). Next, since n = 1, the switch SWr1 is turned on (step S610), and it is determined whether or not the falling edge of the X-ray irradiation request signal is detected (step S611). If the falling edge of the X-ray irradiation request signal is detected, the process proceeds to step S619. On the other hand, when the falling edge of the X-ray irradiation request signal is not detected, the value of the timer (TS) is compared with time T4 because n = 1 (step S612). When TS is smaller than T4, step S611 is executed. Step S612 is repeated. Here, T4 is the time to turn off SWr1, which is turned on as shown in FIG. If the falling edge of the X-ray irradiation request signal is detected in step S611, the process proceeds to step S619, and XFLG is set to 1.
[0107]
In step S612, if TS is equal to or greater than T4, the process proceeds to step S613, and the switch SWr1 is turned OFF (step S613). Thereafter, the value of the variable n is increased by 1 (step S614), and it is determined whether or not the variable n is 2 or less (step S615). In this embodiment, as shown in FIG. 10, since two photoelectric conversion elements are provided in the row direction and two in the column direction, whether or not the variable n is 2 or less is determined in step S615. If three such elements are provided in the row direction and the column direction, respectively, in step S615, it is determined whether or not the variable n is 3 or less.
[0108]
If the variable n is 2 or less, the process proceeds to step S610. Since n = 2 at this time, the switch SWr2 is turned on and the processes from step S610 to step S615 are repeated. If the variable n is larger than 2 in step S615, the gate signal is set to 0 V in step S616, and the subroutine is terminated.
[0109]
Thus, in the initialization subroutine, XFLG is set to 1 when the falling edge of the X-ray irradiation request signal is detected.
[0110]
In the present embodiment, the initialization process includes one refresh and one idle reading. However, the initialization process is not limited to this. For example, the initialization process may include one refresh and a plurality of idle readings.
[0111]
In addition, the photoelectric conversion device 4 has been described as having two rows and two columns of photoelectric conversion elements arranged in a plane, but the present invention is not limited to this, and the row direction is actually 1000 to 4000 and the column direction is It is often composed of 1000 to 4000. However, the present invention is not limited to this, and may be smaller or larger.
[0112]
In the present embodiment, the row address selection circuit 9 includes the gate control circuit 24 and the switches SWr1 and SWr1-2. However, the present invention is not limited to this, and it is sufficient that the photoelectric conversion element 20 in the row direction can be selected.
[0113]
In this embodiment, the column address selection circuit 10 is composed of the amplifier 25, the sample hold circuit 26, and the switches SWc1 and SWc1-2. However, the present invention is not limited to this, and if the photoelectric conversion element 20 in the column direction can be selected. Good.
[0114]
[Other Embodiments]
Further, the present invention is not limited to only the apparatus and method for realizing the above-described embodiment, and a software program for realizing the above-described embodiment on a computer (CPU or MPU) in the system or apparatus. A case where the embodiment is realized by supplying a code and causing the computer of the system or apparatus to operate the various devices according to the program code is also included in the scope of the present invention.
[0115]
In this case, the software program code itself realizes the functions of the above embodiment, and the program code itself and means for supplying the program code to the computer, specifically, the program code is stored. The storage medium is included in the category of the present invention.
[0116]
As a storage medium for storing such a program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
[0117]
The computer controls various devices according to only the supplied program code, so that not only the functions of the above embodiments are realized, but also the OS (operating system) on which the program code is running on the computer. In the case where the above embodiment is realized in cooperation with other application software or the like, such program code is also included in the scope of the present invention.
[0118]
Further, after the supplied program code is stored in the memory of the function expansion board of the computer or the function expansion unit connected to the computer, the program code is stored in the function expansion board or function storage unit based on the instruction of the program code. A case in which the CPU or the like provided performs part or all of the actual processing and the above-described embodiment is realized by the processing is also included in the scope of the present invention.
[0119]
【The invention's effect】
As described above, according to the present invention, even if an X-ray irradiation request is received during initialization of the detector, noise in the X-ray image can be suppressed. Further, when an X-ray irradiation request is received during the initialization of the detector, the exposure delay time can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between initialization processing and X-ray imaging when an X-ray irradiation request is generated during initialization processing of a photoelectric conversion element 20 in the first embodiment of the present invention.
FIG. 2 is a flowchart of a main routine of the X-ray imaging method in the first embodiment of the present invention.
FIG. 3 is a flowchart of an initialization process subroutine in the X-ray imaging method according to the second embodiment of the present invention;
FIG. 4 is a diagram illustrating a relationship between initialization processing and X-ray imaging when an X-ray irradiation request is generated during initialization processing of the photoelectric conversion element 20 in the second embodiment of the present invention.
FIG. 5 is a flowchart of a main routine of an X-ray imaging method according to a second embodiment of the present invention.
FIG. 6 is a flowchart of an initialization process subroutine in the X-ray imaging method according to the second embodiment of the present invention;
FIG. 7 is a schematic block diagram showing an example of a conventional X imaging system.
FIG. 8 is a diagram showing an equivalent circuit of one photoelectric conversion element.
FIG. 9 is a diagram illustrating an initialization process for one photoelectric conversion element 20;
10 is a block diagram showing an example of a flat detector 4 and a flat detector control unit 5. FIG.
FIG. 11 is a diagram illustrating an initialization process for a plurality of photoelectric conversion elements 20;
12 is a diagram showing a relationship between the initialization process of the photoelectric conversion element 20 and X-ray imaging. FIG.
13 is a diagram showing a basic configuration of a host computer 2. FIG.
FIG. 14 is a diagram for explaining a memory provided in a CPU 7;

Claims (11)

A detector for detecting X-rays emitted by the X-ray generator;
When receiving a signal for requesting the X-ray irradiation during initialization of the detectors, the time to receive the signal from the start of the initialization process, elapsed from the ending point in time of the initialization processing An X-ray imaging apparatus comprising: control means for emitting a signal for permitting X-ray irradiation according to   When the control means receives a signal requesting X-ray irradiation when the detector is not performing initialization processing, the control means causes the detector to perform initialization processing in response to the reception and performs the initialization. 2. The X-ray imaging apparatus according to claim 1, wherein a signal for permitting X-ray irradiation is issued in response to completion of the processing. Furthermore,
When a signal requesting X-ray irradiation is received during the initialization process of the detector, the time from when the detector starts the initialization process until receiving the signal requesting X-ray irradiation is stored. Having storage means;
3. The X according to claim 1, wherein the control unit issues a signal for permitting X-ray irradiation in accordance with elapse of a time stored in the storage unit since the end of the initialization process. X-ray equipment. 4. The control unit according to claim 1, wherein the control unit periodically causes the detector to execute the initialization process while the signal requesting the X-ray irradiation is not received. 5. X-ray imaging apparatus described in 1.   5. The X-ray imaging apparatus according to claim 1, wherein the control unit issues a signal permitting the X-ray irradiation to the X-ray generation apparatus. 6. A detector for detecting X-rays emitted by the X-ray generator;
An X-ray imaging apparatus having control means for causing the detector to periodically perform initialization processing of the detector,
The control means includes
When the detector is not performing the initialization process, when receiving a first signal emitted in response to an instruction of X-ray irradiation, the detector is caused to perform the initialization process in response to the reception, In response to the completion of the initialization process, a second signal that permits X-ray irradiation is issued,
When the first signal is received during the initialization process of the detector, the detector emits the second signal in response to elapse of time required for the initialization process from the reception timing. A featured X-ray imaging apparatus.   An X-ray imaging system comprising: the X-ray imaging apparatus according to claim 1; and the X-ray generation apparatus. An X-ray imaging system comprising a detector that detects X-rays emitted by an X-ray generator, and a detector control device that controls the detector,
The detector control device comprises:
When receiving a signal for requesting the X-ray irradiation during initialization of the detectors, the time to receive the signal from the start of the initialization process, elapsed from the ending point in time of the initialization processing In response to this, an X-ray imaging system that emits a signal that permits X-ray irradiation to the X-ray generator. A control method of a detector control device that controls a detector that detects X-rays emitted by an X-ray generator,
When receiving a signal for requesting the X-ray irradiation during initialization of the detector, or the time it takes to receive the signal from the start of the initialization process, it has elapsed from the ending point in time of the initialization processing A determination step of determining whether or not,
And a step of issuing a signal permitting X-ray irradiation in response to the determination that the time has elapsed in the determination step. A control method for a detector control device that causes a detector that detects X-rays emitted by an X-ray generator to periodically perform initialization processing,
When the detector is not performing the initialization process, when receiving a first signal emitted in response to an instruction of X-ray irradiation, the detector is caused to perform the initialization process in response to the reception, In response to the completion of the initialization process, a second signal that permits X-ray irradiation is issued,
When the first signal is received during the initialization process of the detector, the detector emits the second signal in response to elapse of time required for the initialization process from the reception timing. A control method for a detector control device.   The program for making a computer perform the control method of Claim 9 or 10.

Images