Radiographic image detecting apparatus and radiographic image capturing system
A radiographic image detecting apparatus and a radiographic image capturing system are provided. The radiographic image detecting apparatus includes photoelectric conversion elements for generating electric charge by emission of radiation, a bias line through which a bias voltage is supplied to the photoelectric conversion elements, a power supply for applying the bias voltage to the photoelectric conversion elements through the bias line, a current detector for detecting a bias current flowing through the bias line based on a voltage drop across a resistor inserted in the bias line, a first amplifying circuit, a second amplifying circuit connected to an output of the first amplifying circuit, and a controller for correcting the electric signal by increasing a gain of the second amplifying circuit depending on decrease in a sensitivity of the photoelectric conversion element, the decrease being caused by the voltage drop.
1. A radiographic image detecting apparatus comprising:
a plurality of photoelectric conversion elements for generating electric charge by emission of radiation;
a bias line through which a bias voltage is supplied to the photoelectric conversion elements;
a power supply for applying the bias voltage to the photoelectric conversion elements through the bias line;
a current detector for detecting a bias current flowing through the bias line based on a voltage drop across a resistor inserted in the bias line;
a first amplifying circuit having a gain, wherein in a case where an electric signal due to the electric charge is read out from the photoelectric conversion elements through a signal line, the gain at a time of reading out the electric signal is set based on a current value detected by the current detector at a time of emission of the radiation;
a second amplifying circuit connected to an output of the first amplifying circuit; and
a controller for correcting the electric signal by increasing a gain of the second amplifying circuit depending on decrease in a sensitivity of the photoelectric conversion element due to the voltage drop.
2. The radiographic image detecting apparatus according to claim 1 , wherein the second amplifying circuit comprises a non-inverting amplifying circuit which includes an operational amplifier having a non-inverting input connected to an output of the first amplifying circuit, a first resistor connected between an output of the operational amplifier and an inverting input of the operational amplifier, and a second resistor connected between the inverting input and a reference potential, and the controller changes a resistance value of at least one of the first and second resistors thereby to change the gain of the second amplifying circuit.
3. The radiographic image detecting apparatus according to claim 1 , wherein the first amplifying circuit comprises a charge amplifier which includes an operational amplifier and a capacitance-value varying unit connected in parallel to the operational amplifier.
4. The radiographic image detecting apparatus according to claim 1 , wherein the controller detects start and/or end of emission of the radiation based on increase and decrease in a current flowing through the bias line detected by the current detector.
5. The radiographic image capturing system comprising:
the radiographic image detecting apparatus according to claim 1 ; and
an image processor for forming a radiographic image based on electric signals which are read out from the photoelectric conversion elements and then amplified, the electric signals being output from the radiographic image detecting apparatus at the time of reading out the electric signal.
6. The radiographic image capturing system according to claim 5 , wherein the radiographic image detecting apparatus and the image processor are connected to each other by a wireless communication.
7. A radiographic image detecting apparatus comprising:
a plurality of photoelectric conversion elements for generating electric charge by emission of radiation;
a bias line through which a bias voltage is supplied to the photoelectric conversion elements;
a power supply for applying the bias voltage to the photoelectric conversion elements through the bias line;
a current detector for detecting a bias current flowing through the bias line based on a voltage drop across a resistor inserted in the bias line;
an amplifying circuit having a gain, wherein in a case where an electric signal due to the electric charge is read out from the photoelectric conversion elements through a signal line, the gain at a time of reading out the electric signal is set based on a current value detected by the current detector at a time of emission of the radiation; and
a controller for correcting the lowered electric signal depending on decrease in a sensitivity of the photoelectric conversion element due to the voltage drop.
8. The radiographic image detecting apparatus according to claim 7 , wherein the controller corrects the electric signal by changing the gain setting of the amplifying circuit.
9. The radiographic image detecting apparatus according to claim 7 , wherein the controller includes a digital processing unit for correcting a digital value which is obtained by A-D conversion of the electric signal amplified by the amplifying circuit, such that the digital value becomes larger as the voltage drop becomes larger.
10. The radiographic image detecting apparatus according to claim 7 , wherein the amplifying circuit comprises a charge amplifier which includes an operational amplifier and a capacitance-value varying unit connected in parallel to the operational amplifier.
11. The radiographic image detecting apparatus according to claim 7 , wherein the controller detects start and/or end of emission of the radiation based on increase and decrease in a current flowing through the bias line detected by the current detector.
12. The radiographic image capturing system comprising:
the radiographic image detecting apparatus according to claim 7 ; and
an image processor for forming a radiographic image based on electric signals which are read out from the photoelectric conversion elements and then amplified, the electric signals being output from the radiographic image detecting apparatus at the time of reading out the electric signal.
13. The radiographic image capturing system according to claim 12 , wherein the radiographic image detecting apparatus and the image processor are connected to each other by a wireless communication.
14. A radiographic image detecting apparatus comprising:
a plurality of photoelectric conversion elements for generating electric charge by emission of radiation;
bias lines through which a bias voltage is supplied to the photoelectric conversion elements;
a power supply for applying the bias voltage to the photoelectric conversion elements through the bias lines;
a current detector for detecting a bias current flowing through one of the bias lines, which is connected to one of the photoelectric conversion elements, based on a voltage drop across a resistor inserted in the one bias line;
a first amplifying circuit having a gain, the first amplifying circuit being connected through a signal line to the one photoelectric conversion element that is connected to the current detector connected to the one bias line, wherein in a case where an electric signal due to the electric charge is read out, through the signal line, from the one photoelectric conversion element, the gain at a time of reading out the electric signal is set based on a current value detected by the current detector at a time of emission of the radiation;
a second amplifying circuit having a gain, the second amplifying circuit being connected through another signal line to another of photoelectric conversion elements that is not connected to the current detector, wherein in a case where an electric signal due to the electric charge is read out, through the signal line, from the photoelectric conversion elements that are not connected to the current detector, the gain at a time of reading out the electric signal is set based on a current value detected by the current detector at the time of emission of the radiation; and
a controller for correcting the lowered electric signal of the first amplifying circuit depending on decrease in a sensitivity of the photoelectric conversion elements due to the voltage drop.
15. The radiographic image detecting apparatus according to claim 14 , wherein the controller corrects the electric signal by changing the gain setting of the first amplifying circuit.
16. The radiographic image detecting apparatus according to claim 14 , wherein the controller includes a digital processing unit for correcting a digital value which is obtained by A-D conversion of the electric signal of the first amplifying circuit, based on a digital value which is obtained by A-D conversion of the electric signal of the second amplifying circuit.
17. The radiographic image detecting apparatus according to claim 14 , wherein each of the first amplifying circuit and the second amplifying circuit comprises a charge amplifier which includes an operational amplifier and a capacitance-value varying unit connected in parallel to the operational amplifier.
18. The radiographic image detecting apparatus according to claim 14 , wherein the controller detects start and/or end of emission of the radiation based on increase and decrease in a current flowing through the bias line detected by the current detector.
19. The radiographic image capturing system comprising:
the radiographic image detecting apparatus according to claim 14 ; and
an image processor for forming a radiographic image based on electric signals which are read out from the photoelectric conversion elements and then amplified, the electric signals being output from the radiographic image detecting apparatus at the time of reading out the electric signal.
20. The radiographic image capturing system according to claim 19 , wherein the radiographic image detecting apparatus and the image processor are connected to each other by a wireless communication.