JP4746746B2 - Imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus and method for constructing an image by detecting light of a subject, and in particular, an imaging apparatus in which a large number of photoelectric conversion elements are arranged on a plane, for imaging a good X-ray digital image. The present invention relates to an X-ray imaging apparatus.
[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]
According to this method, when radiation such as X-rays transmitted through the subject enters the intensifying screen, the phosphor contained in the intensifying screen absorbs the X-ray energy and emits fluorescence.
[0004]
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.
[0005]
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 detection means comprising a combination of photoelectric conversion elements that are sensitive to light and output an electric signal corresponding to the intensity, the X-ray image is converted into an electric signal and digitally captured by A / D conversion. There are methods.
[0006]
Here, an X-ray imaging apparatus combining a phosphor and a photoelectric conversion element will be described as an example.
[0007]
FIG. 4 is a schematic block diagram showing an example of a conventional X-ray imaging apparatus.
In FIG. 4, 1 is an X-ray generator, 2 is a subject, 3 is a phosphor, 4 is a photoelectric conversion device having a large number of photoelectric conversion elements arranged on a plane, and 5 is an X-ray control device. X-rays irradiated from the X-ray generator 1 pass through the subject 2 and are converted by the phosphor 3 into light proportional to the incident X-ray dose. This light is converted into an electrical signal by the photoelectric conversion device 4, and an X-ray digital image is transferred to the X-ray control device 5. The transferred X-ray digital image is subjected to image processing by the X-ray control device 5, and the photographed X-ray digital image is displayed on a display device (not shown).
[0008]
FIG. 5 shows an equivalent circuit of the 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. 5, the configuration of one photoelectric conversion element 20 is composed of a photodetecting portion 21 and a switching TFT 22 for controlling charge accumulation and reading, and is generally amorphous silicon (α-Si) arranged on a glass substrate. ).
[0010]
In this example, 21C in the light detector 21 may be simply a photodiode having a parasitic capacitance, or a photodetector including an additional capacitor 21C in parallel so as to improve the dynamic range of the photodiode 21D and the detector. You may catch it.
[0011]
The anode A of the diode 21D is connected to the refresh control circuit 23, and the refresh control circuit 23 outputs a refresh signal to initialize the capacitor 21C. Normally, the refresh control circuit 23 outputs a bias voltage of the voltage Vs, and outputs the refresh voltage Vr when outputting it as a refresh signal.
[0012]
The cathode K is connected to a controllable switching TFT 22 for reading out the electric charge accumulated in the capacitor 21C. In this example, the switching TFT 22 is a thin film transistor connected between the cathode K of the diode 21D and the charge readout amplifier 25. A capacitor 19 is disposed between the switching TFT 22 and the amplifier 25. However, the capacitor 19 does not exist as an actual element, but is formed by the parasitic capacitance of the wiring.
[0013]
Further, a gate control circuit 24 is connected to the gate G of the TFT 22, and when the gate control circuit 24 outputs a gate signal, the charge accumulated in the capacitor 21C is transferred to the capacitor 19 and accumulated in the capacitor 21C. Read the charge.
[0014]
When the photoelectric conversion element 20 shown in FIG. 5 detects X-rays for the first time, the refresh control circuit 23 first outputs a refresh signal to initialize the light detection unit 21. At this time, no charge is accumulated in the capacitor 21C.
[0015]
Then, by irradiating X-rays, charges corresponding to the X-ray dose are generated in the photodiode 21D, and charges are accumulated in the capacitor 21C. Thereafter, the gate control circuit 24 outputs a gate signal to transfer the charge accumulated in the light detection unit 21 to the capacitor 19.
[0016]
At this time, if it is assumed that the charge of α is accumulated in the capacitor 21C by, for example, X-ray irradiation and the capacitances of the capacitor 19 and the capacitor 21C are equal, the charge transferred to the capacitor 19 is α / 2. Therefore, α / 2 charge remains in the capacitor 21C.
[0017]
The charge accumulated in the capacitor 19 is amplified by the amplifier 25, and the incident X-ray dose is detected by performing A / D conversion by the A / D conversion circuit 27 through the sample hold circuit 26.
[0018]
When the photoelectric conversion element detects X-rays again, the refresh control circuit 23 outputs a refresh signal to initialize the light detection unit 21 and repeats the same operation as the previous X-ray detection.
[0019]
[Problems to be solved by the invention]
However, in the above-described conventional example, α / 2 charges remain in the capacitor 21C during the second X-ray imaging. In this state, it takes a very long time for the refresh control circuit 23 to output a refresh signal and completely remove the charge remaining in the capacitor 21C. Therefore, normally, the refresh signal output from the refresh control circuit 23 is cut off in a certain amount of time, and a part of the electric charge accumulated during the previous X-ray imaging remains in the capacitor 21C.
[0020]
That is, in the conventional example, when the photoelectric conversion element 20 detects X-rays, charges corresponding to the X-ray dose are accumulated in the light detection unit 21, and the gate control circuit 24 outputs a gate signal to detect light. Although the charges accumulated in the unit 21 are read out, all the charges are not read out, and a part of the charges accumulated according to the X-ray dose remains in the light detection unit 21. If not all of the charges accumulated in the photodetection unit 21 are read out, the refresh control circuit 23 outputs a refresh signal and initializes the photodetection unit 21 without being completely initialized. Some charge remains.
[0021]
Therefore, when X-ray imaging is continuously performed, a part of the X-ray dose detected first is added to the X-ray dose detected the second time, and the X-ray digital image taken for the second time is the first time. There is a problem that an afterimage of the photographed X-ray digital image remains.
[0022]
Therefore, the present invention has been made in view of the above problems, and even if X-ray imaging is continuously performed by removing the charge remaining in the light detection unit, 1 is added to the X-ray digital image captured for the second time. It is an object of the present invention to provide a highly reliable image pickup apparatus and method that prevents an afterimage of an X-ray digital image taken at a second time from being left behind and enables high-accuracy image acquisition.
[0023]
[Means for Solving the Problems]
The imaging device according to the present invention includes a light detection unit, a first electric capacity connected in parallel with an anode and a cathode of the light detection unit, and a switching that is conductive and non-selective when connected to the cathode and selected. A photoelectric conversion element configured to include a TFT, an amplifier that amplifies a signal proportional to an electric charge read from the first electric capacity via the switching TFT, and the amplifier and the switching TFT A second electric capacity having one end connected and the other end connected to the ground, an A / D conversion circuit for A / D converting the output of the amplifier, a first for supplying power to the switching TFT and the amplifier 1 power supply, a second power supply that supplies power to the A / D conversion circuit, and a CPU that controls the switching TFT and the first power supply, Serial between a first state which is capable of capturing state switching TFT in the unselected state, the gate of said switching TFT in the state where the switching TFT is selected, the source and drain as a ground potential, the said anode cathode and And a second state in which the voltage is controlled to the ground potential, and after taking an X-ray digital image in the first state, the state is shifted to the second state for a predetermined time. .
[0026]
In one aspect of the imaging apparatus of the present invention, the time for the second state to be shifted after taking an X-ray digital image can be arbitrarily changed.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.
[0036]
FIG. 1 is a block diagram showing an example of an X-ray imaging apparatus according to the present invention.
In FIG. 1, reference numeral 6 denotes a CPU for reading an X-ray digital image from the photoelectric conversion device 4, to which a power supply 7, a refresh control circuit 8, a row address selection circuit 9, and a column address selection circuit 10 are connected. The CPU 6 can control each circuit. The CPU 6 is connected to the X-ray control device 5 and transfers the X-ray digital image read from the photoelectric conversion device 4 to the X-ray control device 5.
[0037]
Normally, the CPU 6 controls the power supply 7 to supply power to the refresh control circuit 8, the row address selection circuit 9, and the column address selection circuit 10. However, the CPU 6 and the A / D conversion circuit 27 are always supplied with power from a power source (not shown).
[0038]
In addition, the photoelectric conversion device 4 has a large number of photoelectric conversion elements 20 shown in FIG. 5 arranged on a plane. In FIG. 1, two photoelectric elements in the row direction and two photoelectric elements in the column direction are used for the sake of simplicity. The conversion element 20 is arranged on a plane.
[0039]
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 above-described light detection unit 21, and represent the cathode side of the light detection unit 21 as K and the anode side as A. Yes. 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.
[0040]
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.
[0041]
The drain electrode D of the TFT 22 in each column is connected to the column address circuit 10, and the column address circuit 10 includes an amplifier 25, a sample hold circuit 26, and switches SWc1-2.
[0042]
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. .
[0043]
In FIG. 1, the capacitor 19 shown in FIG. 5 is omitted for the sake of simplicity.
[0044]
Next, a procedure for capturing an X-ray digital line image from the photoelectric conversion device 4 by irradiating X-rays will be described with reference to a flowchart of FIG.
[0045]
First, the CPU 6 controls the power supply 7 to supply power to the refresh control circuit 8, the row address selection circuit 9, and the column address selection circuit 10 to enter a ready state (S1).
[0046]
As described above, the first state in which the power is supplied to the refresh control circuit 8, the row address selection circuit 9, and the column address selection circuit 10 and the CPU 6 can control the respective circuits is referred to as a ready state. Then, X-ray imaging can be performed in the ready state.
[0047]
Subsequently, in the ready state, the CPU 6 waits for a request for X-ray irradiation from the X-ray control device 5 (S2).
[0048]
When the CPU 6 receives the X-ray irradiation request, the CPU 6 controls the refresh control circuit (S3). Specifically, the refresh control circuit outputs a refresh signal and initializes the light detection units 21 (1, 1) to 21 (2, 2).
[0049]
When the initialization of the light detection unit 21 is completed, the X-ray generator 1 emits X-rays (S4). When X-rays are irradiated, charges corresponding to the X-ray dose are accumulated in the light detection units 21 (1, 1) to 21 (2, 2).
[0050]
Thereafter, the CPU 6 initializes the variable R to 1 and sets the variable Nr to 2 (S5). Here, Nr indicates the number of photoelectric conversion elements in the row direction of the photoelectric conversion device 4.
[0051]
Next, the CPU 6 controls the row address selection circuit to select the TFT 22 (R, 1) to TFT 22 (R, 2) in the R row (S6), and outputs a gate signal. For example, when R is 1, the switch SWr1 is turned on, and the gate control circuit 24 outputs a gate signal. Then, the TFT 22 (R, 1) to TFT 22 (R, 2) in the R-th row are selected, and the charges accumulated in the light detection units 21 (R, 1) to 21 (R, 2) can be read out.
[0052]
Next, the CPU 6 initializes the variable C to 1 and sets the variable Nc to 2 (S7). Here, Nc indicates the number of photoelectric conversion elements in the column direction of the photoelectric conversion device 4.
[0053]
Thereafter, the CPU 6 controls the column address selection circuit and amplifies the signals of the photodetection units 21 in all columns by the amplifier 25. Thereafter, the sample hold circuit 26 holds the amplified signal and turns on the switch SWc in the C-th row (S8). For example, when C is 1, if the SWc1 in the first column is turned on, the amplified signal of the light detection unit 21 (R, 1) in the first column is output to the A / D conversion circuit 27. Then, the signal is A / D converted by the A / D conversion circuit 27 (S9), and the digitized data is taken into the CPU 6 and transferred to the X-ray controller 5.
[0054]
Thereafter, the value of the variable C is increased by 1 (S10), and it is determined whether or not the value of C is Nc or less (S11). If the value of C is less than or equal to Nc, the process branches to S8, and the processes of S8 to S11 are repeated again. If the value of C is larger than Nc, the process exits the loop and proceeds to the next process.
[0055]
When exiting the loop, the value of the variable R is incremented by 1 (S12), and it is determined whether or not the value of R is Nr or less (S13). If the value of R is less than or equal to Nr, the process branches to S6, and the processes of S6 to S13 are repeated again. If the value of R is greater than Nr, the loop is exited.
[0056]
When exiting this loop, the charges accumulated in all the photoelectric conversion elements 20 are read out. However, as already described in the conventional example, a part of the accumulated charge remains in the photoelectric conversion element 20. Further, the operation of reading out the electric charge accumulated in the photoelectric conversion element 20 as in the processes from S6 to S13 is referred to as driving.
[0057]
Next, the CPU 6 controls the power supply 7 to stop the power supply to the refresh control circuit 8, the row address selection circuit 9, and the column address selection circuit 10, and enters a sleep state (S14). Thus, the second state in which the power supply to the refresh control circuit 8, the row address selection circuit 9, and the column address selection circuit 10 is stopped is called a sleep state. In the sleep state, since the power supply from the power supply 7 to each circuit is stopped, the anode electrode A and cathode electrode K of the light detection unit 21 and the source electrode S, gate electrode G, and drain electrode D of the TFT 22 are stopped. Becomes the ground potential. Therefore, the charge remaining in the light detection unit 21 is removed .
[0058]
And it waits for a predetermined time in a sleep state (S15), returns to S1 after that, becomes a ready state again, and waits for the request | requirement of the next X-ray irradiation. When the X-ray irradiation request comes again, the above-described processing is repeated.
[0059]
Generally, the waiting time in the sleep state is about 100 ms to 1 s, and normally, the charge remaining after driving the photoelectric conversion element in this time is completely eliminated. However, the waiting time in the sleep state varies depending on the characteristics of the photoelectric conversion element. If the waiting time is too short, the charge remains, and if the waiting time is long, it takes time until X-ray imaging can be performed next. Therefore, the waiting time in the sleep state can be changed by the X-ray control device 5, and an optimal time can be set according to the characteristics of the photoelectric conversion element.
[0060]
FIG. 3 is a timing chart showing a procedure for capturing an X-ray digital line image from the photoelectric conversion device 4.
[0061]
In FIG. 3, “A” indicates an X-ray irradiation state, and “H” indicates that the X-ray generator 1 has irradiated X-rays. B indicates a refresh state, and H indicates that the refresh control circuit 8 has output a refresh signal. C indicates the state of the switch SWr1, and D indicates the state of the switch SWr2. E indicates the state of the switch SWc1, and F indicates the state of the switch SWc2.
[0062]
G indicates a ready state and a sleep state. When H, the ready state is indicated.
[0063]
First, when in the ready state (G is H), the refresh control circuit 8 outputs a refresh signal (B is H), and initializes the light detection unit 21. When the refresh is completed, the X-ray generator 1 emits X-rays (A is H). When the X-rays are irradiated, charges corresponding to the X-ray dose are accumulated in the light detection unit 21.
[0064]
When the X-ray irradiation is finished, the switch SWr1 is turned ON (C is H), and the first row TFTs 22 (1,1) to TFT22 (1,2) are selected, and the first row light detection unit 21 (1, The charges accumulated in 1) to 21 (1, 2) can be read out. In this state, the switch SWc1 is turned on (E is H), the charge of the light detection unit 21 (1, 1) in the first row and first column is read, and when the reading is completed, the switch SWc1 is turned off (E is changed to E). L). Further, the switch SWr1 is turned on with the switch SWr1 being turned on (F is H), and the charge of the light detection unit 21 (1, 2) in the first row and second column is read out, and when the reading is finished, the switch SWr1 is turned on. SWc2 is turned off (F is L). Thereafter, the switch SWr1 is turned off (C is L).
[0065]
Next, the switch SWr2 is turned ON (D is H), the second row TFTs 22 (2, 1) to TFT 22 (2, 2) are selected, and the second row light detection units 21 (2, 1) to 21 are selected. The charge accumulated in (2, 2) can be read out. In this state, the switch SWc1 is turned on (E is H), and the electric charge of the light detection unit 21 (2, 1) in the second row and first column is read. When the reading is completed, the switch SWc1 is turned off (E is changed to E). L). Further, the switch SWr2 is turned on while the switch SWr2 is turned on (F is H), and the charge of the light detection unit 21 (2, 2) in the second row and the second column is read out. SWc2 is turned off (F is L). Thereafter, the switch SWr1 is turned off (C is L).
[0066]
When all the charges are read, the sleep state is entered (G is L), and the sleep state is maintained again for a predetermined time (G is H).
[0067]
In the present embodiment, the photoelectric conversion device 4 is described as having two rows and two columns of photoelectric conversion elements arranged in a plane. However, the present invention is not limited to this, and the row direction is actually 1000 to 4000. The column direction is often 1000 to 4000. However, the present invention is not limited to this, and may be smaller or larger.
[0068]
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.
[0069]
In the present 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. It only has to be selected.
[0070]
In FIG. 1, the power source 7 supplies power to the refresh control circuit 8, the row address selection circuit 9, and the column address selection circuit 10, and the A / D conversion circuit 12 is always supplied with power from a power source (not shown). However, the present invention is not limited to this, and the power supply 7 may supply power to the A / D conversion circuit 27.
[0071]
In the present embodiment, the standby time in the sleep state has been described as being about 100 ms to 1 s. However, the present invention is not limited to this, and it is sufficient that the slight charge remaining after driving the photoelectric conversion element is completely eliminated.
[0072]
Here, in order to realize each function of the image reading apparatus of the above-described embodiment, the function of the embodiment is realized for an apparatus connected to the various devices or a computer in the system so that the various devices are operated. The present invention includes a program implemented by supplying software program codes for performing the above operations and operating the various devices according to programs stored in a computer (CPU or MPU) of the system or apparatus.
[0073]
In this case, the program code of the software itself realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, the program code is stored. The storage medium constitutes the present invention. As a storage medium for storing the 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.
[0074]
Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) or other application software in which the program code is running on the computer, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized jointly.
[0075]
Further, after the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the CPU provided in the function expansion board or function expansion unit based on the instructions of the program, etc. However, the present invention also includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.
[0076]
【The invention's effect】
According to the present invention, after taking an X-ray digital image in the X-ray imaging apparatus in the first state, the state is shifted to the second state for a predetermined time, and the electric charge remaining in the light detection unit is removed, thereby continuously. Even when X-ray imaging is performed, an afterimage of the X-ray digital image captured at the first time is not left in the X-ray digital image captured at the second time so that high-accuracy image acquisition is possible. A high imaging device is realized.
[0077]
In addition, since the time in the second state can be changed, an optimum time can be set according to the characteristics of the image sensor.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of an X-ray imaging apparatus according to the present invention.
FIG. 2 is a flowchart for capturing an X-ray digital line image according to the present invention.
FIG. 3 is a timing chart for capturing an X-ray digital line image according to the present invention.
FIG. 4 is a schematic block diagram showing an example of a conventional X-ray imaging apparatus.
FIG. 5 is an equivalent circuit diagram of the photoelectric conversion element.
[Explanation of symbols]
1 X-ray generator 4 X-ray generator 5 X-ray controller 6 CPU
7 power supply 8 refresh circuit 9 row address selection circuit 10 column address selection circuit 20 photoelectric conversion element

Claims (2)

A photodetecting unit, a first electric capacity connected in parallel with the anode and cathode of the photodetecting unit, and a switching TFT that is conductive and non-selective when connected to the cathode and selected. A photoelectric conversion element,
An amplifier that amplifies a signal proportional to the electric charge read from the first electric capacity via the switching TFT;
A second electric capacitance having one end connected between the amplifier and the switching TFT and the other end connected to the ground;
An A / D conversion circuit for A / D converting the output of the amplifier;
A first power supply for supplying power to the switching TFT and the amplifier;
A second power source supplying power to the A / D converter circuit;
A CPU for controlling the switching TFT and the first power supply;
The CPU has a first state in which the switching TFT can be imaged in a non-selected state, and the gate, source and drain of the switching TFT with the switching TFT selected and the ground potential as the anode. And a second state in which the cathode is controlled to a ground potential, and after taking an X-ray digital image in the first state, shifting to the second state for a predetermined time. An imaging apparatus characterized by the above.   The imaging apparatus according to claim 1, wherein the time of the second state to be shifted after taking an X-ray digital image can be arbitrarily changed.

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