JP5509228B2 - Radiation image recording / reading apparatus - Google Patents

Description

  The present invention records image information upon receiving irradiation of recording light carrying image information, and outputs an image signal representing the recorded image information, and detects a signal output from the radiation solid detector The present invention relates to protection of signal detection means in a radiographic image recording / reading apparatus comprising signal detection means and the like.

  Today, in X-ray (radiation) imaging for the purpose of medical diagnosis and the like, a solid-state radiation detector (having a semiconductor as a main part) is used as an X-ray image information recording means, and the subject is transmitted through the solid-state detector. Various X-ray image recording / reading apparatuses that detect X-rays and obtain an image signal representing an X-ray image related to a subject have been proposed and put into practical use.

  Various types of solid state detectors used in this apparatus have been proposed. For example, from the aspect of the charge generation process that converts X-rays into electric charges, the signal charge obtained by detecting the fluorescence emitted from the phosphor by the photoconductive layer when irradiated with X-rays is temporarily stored in the power storage unit. Then, the photoelectric conversion type solid state detector that converts the latent image charge into an image signal (electrical signal) and outputs it, or the signal charge generated in the photoconductive layer by irradiating the X-ray with the charge collecting electrode. There is a direct conversion type solid state detector that collects and temporarily accumulates in a power storage unit, converts the accumulated charge into an electric signal, and outputs the electric signal. The solid state detector in this system has a photoconductive layer and a charge collecting electrode as main parts.

  From the aspect of the charge reading process for reading out the accumulated charges to the outside, a light reading method of reading light by irradiating a detector with reading light (reading electromagnetic waves), or as described in Patent Document 1 In addition, there is a TFT reading type that scans and reads out a TFT (thin film transistor) connected to the power storage unit.

  The applicant of the present application has proposed an improved direct conversion type solid state detector in Patent Document 2 and the like. The improved direct conversion type solid state detector is a direct conversion type and optical readout type, and exhibits photoconductivity by receiving recording light (X-ray or fluorescence generated by X-ray irradiation). Photoconductive layer for recording, a charge transport layer that acts as an insulator for charges having the same polarity as the latent image charge, and acts as a conductor for transport charges having a polarity opposite to that of the latent image charge A photoconductive layer for reading that exhibits photoconductivity by receiving irradiation of an electromagnetic wave for reading is laminated in this order, and is formed at the interface (electric storage unit) between the photoconductive layer for recording and the charge transport layer. A signal charge (latent image charge) carrying image information is accumulated. Electrodes (first conductor layer and second conductor layer) are laminated on both sides of these three layers. Further, the solid state detector in this system has a recording photoconductive layer, a charge transport layer, and a reading photoconductive layer as main parts.

JP 2000-244824 A JP 2000-105297 A

  In the above solid state detector, a high voltage is applied at the time of photographing and a voltage is not applied at the time of signal reading, and a different voltage is applied at each process, but at a timing when the voltage applied to the solid state detector changes. There is a transient overcurrent inflow / outflow in the solid state detector. This may shorten the life of the signal detection means such as a charge amplifier connected to the solid state detector. Many devices for overcurrent countermeasures have already been proposed, but solid-state detectors usually use LSIs as signal detection means, so it is necessary to secure a space for incorporating overcurrent countermeasure devices. It is very difficult to do.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a radiation solid detector that receives image light recording image information, records image information, and outputs an image signal representing the recorded image information. In a radiographic image recording / reading apparatus composed of signal detection means for detecting a signal output from a detector, a transient inflow / outflow in the radiation solid detector at a timing when a voltage applied to the radiation solid detector changes. It is an object of the present invention to provide a radiographic image recording / reading apparatus capable of protecting a signal detection means from excessive overcurrent.

  The radiation image recording / reading apparatus according to the present invention includes an electrostatic recording unit including a photoconductive layer that exhibits conductivity when irradiated with recording light, and receives image information received by recording light carrying image information. A radiation solid state detector that outputs an image signal representing the recorded image information, a voltage applying means for applying a voltage to the photoconductive layer of the radiation solid state detector, and a signal output from the radiation solid state detector In the radiographic image recording / reading apparatus comprising the signal detecting means, the signal detecting means is inactivated when the voltage applying means changes the voltage applied to the radiation solid state detector. is there.

  In the above, the “radiation solid state detector” is a detector that detects radiation carrying image information of a subject and outputs an image signal representing a radiation image related to the subject, and directly or once converts incident radiation into light. Then, the charge is converted into electric charge, and the electric charge is temporarily stored in the power storage unit, and then the electric charge is output to the outside, whereby an image signal representing a radiographic image related to the subject can be obtained.

  There are various types of radiation solid state detectors. For example, from the aspect of the charge generation process that converts radiation into electric charges, the fluorescence emitted from the phosphors when irradiated with radiation is converted into photoelectric conversion elements. The signal charge obtained by the detection is temporarily stored in the power storage unit of the photoelectric conversion element, and the light conversion type radiation solid state detector that outputs the stored charge converted into an image signal (electric signal) or radiation is irradiated. The signal charge generated in the radiation conductor is collected by the charge collecting electrode, temporarily stored in the power storage unit, and the stored charge is converted into an electrical signal and output. From the aspect of the charge reading process for reading out the charge to the outside, a TFT reading type that reads out the TFT (thin film transistor) connected to the power storage unit by scanning and reading light (reading power) And the like, which are proposed by the applicant of the present application combining the direct conversion method and the optical readout method. There is a type direct conversion method.

  Further, the “non-operating state” of the signal detection means means a state in which the signal detection operation is not performed in the signal detection means, for example, a state where the power of the signal detection means is turned off, a power supply of the signal detection means Even if the signal is present, the detection operation is not performed, or even when the signal detection unit is capable of detecting the signal, the signal detection unit is not input with any signal.

  The radiation image recording / reading apparatus according to the present invention includes an electrostatic recording unit including a photoconductive layer that exhibits conductivity when irradiated with recording light, and receives image information received by recording light carrying image information. A radiation solid state detector that outputs an image signal representing the recorded image information, a voltage applying means for applying a voltage to the photoconductive layer of the radiation solid state detector, and a signal output from the radiation solid state detector In the radiographic image recording / reading apparatus comprising the signal detecting means, the voltage applying means changes the voltage applied to the radiation solid state detector, that is, at the timing when a transient overcurrent flows in / out of the solid state detector. Since the signal detection means is set in a non-operating state, the signal detection means can be protected from an overcurrent.

1 is a schematic configuration diagram of a radiation image recording / reading apparatus according to a first embodiment of the present invention. Configuration diagram of a charge amplifier circuit of the radiation image recording / reading apparatus Timing chart for explaining the operation of the radiation image recording / reading apparatus Timing chart for explaining the operation of the radiation image recording / reading apparatus according to the second embodiment of the present invention.

  A radiation image recording / reading apparatus according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a radiographic image recording / reading apparatus according to a first embodiment of the present invention, and FIG. 2 is a configuration diagram of a charge amplifier circuit of the radiographic image recording / reading apparatus.

  As shown in FIG. 1, the radiation image recording / reading apparatus 1 includes a radiation source 5 that emits radiation, and a radiation solid detection that detects a radiation image of a subject by irradiation of radiation emitted from the radiation source 5 and transmitted through the subject 6. In the radiation solid detector 10, the surface light source 20 for irradiating the radiation solid detector 10 with the reading light for reading the radiation image recorded in the radiation solid detector 10, and the irradiation of the reading light of the surface light source 20. A signal detector 30 provided with a large number of charge amplifier circuits 31 for detecting generated signals (currents), a voltage source 40 for applying a voltage to the radiation solid detector 10 when a radiation image is recorded by the radiation solid detector 10; When a radiation image is read from the radiation solid detector 10 as a signal, a first electrode layer 11 and a second electrode layer 15 (to be described later) of the radiation solid detector 10 are shortened. The short-circuit means 50 for controlling the reading light control means 60 and the erasing light control means 70 for controlling the operation of the planar light source 20, the voltage control means 80 for controlling the operation of the voltage source 40, and the operation of the short-circuit means 50. Switch control means 90 is provided.

  The radiation solid detector 10 includes a first electrode layer 11 that transmits radiation carrying a radiation image of the subject 6, and a photoconductive device for recording that generates charges when irradiated with radiation transmitted through the first electrode layer 11. A charge transport layer 13 that acts as an insulator for the latent image charges generated in the layer 12 and the recording photoconductive layer 12, and acts as a conductor for transport charges having a polarity opposite to that of the latent image charges; A reading photoconductive layer 14 that generates an electric charge when irradiated with reading light and a second electrode layer 15 that transmits the reading light are laminated in this order. Between the recording photoconductive layer 12 and the charge transport layer 13, a power storage unit 19 that accumulates latent image charges generated in the recording photoconductive layer 12 is formed.

The first electrode layer 11 may be any material that can transmit radiation. For example, Nesa film (SnO ₂ ), ITO (Indium Tin Oxide), IDIXO (Idemitsu Indium X- metal Oxide (Idemitsu Kosan Co., Ltd.) can be used with a thickness of 50 to 200 nm, and Al or Au with a thickness of 100 nm can also be used.

  The second electrode layer 15 includes a large number of linear electrodes 15a arranged in parallel.

  The recording photoconductive layer 12 only needs to generate a charge when irradiated with radiation, and is excellent in that it has a relatively high quantum efficiency with respect to radiation and a high dark resistance. A material mainly composed of Se is used. A thickness of about 500 μm is appropriate.

Charge as the transport layer 13, for example, the mobility of the charge charged on the first electrode layer 11 may greater the difference in mobility of the charge and vice versa polarity (e.g. 10 ² or more, preferably 10 ³ or more ) Poly N-vinylcarbazole (PVK), N, N′-diphenyl-N, N′-bis (3-methylphenyl)-[1,1′-biphenyl] -4,4′-diamine (TPD) and disco An organic compound such as a tick liquid crystal, a TPD polymer (polycarbonate, polystyrene, PVK) dispersion, or a semiconductor material such as a-Se doped with 10 to 200 ppm of Cl is suitable.

  The reading photoconductive layer 14 may be any material that exhibits conductivity when irradiated with reading light. For example, a-Se, Se-Te, Se-As-Te, metal-free phthalocyanine, metal phthalocyanine, A photoconductive substance containing at least one of MgPc (Magnesium phtalocyanine), VoPc (phase II of Vanadyl phthalocyanine), CuPc (Cupper phtalocyanine) and the like as a main component is preferable. A thickness of about 10 μm is appropriate.

  The layer configuration of the radiation solid state detector 10 is not limited to the layer configuration as described above, and may include other layers. The material of each layer may have the same function as the function of each layer. For example, materials other than those described above may be used.

  And in the radiation solid detector 10 comprised as mentioned above, the planar light source 20 is provided in the 2nd electrode layer 15 side, as shown in FIG. The planar light source 20 is an EL light emitter composed of a first conductive layer 21, an EL layer 22, and a second conductive layer 23. Note that an insulating layer 24 is provided between the second electrode layer 15 and the first conductive layer 21 of the radiation solid state detector 10.

  The first conductive layer 21 in the planar light source 20 is composed of a large number of linear electrodes 21 a arranged in parallel. The linear electrode 21 a is a line of the second electrode layer 15 of the radiation solid state detector 10. Are arranged so as to be orthogonal to the electrode 15a. In other words, each linear electrode 21 a, EL layer 22, and second conductive layer 23 has a configuration in which a number of substantially linear light sources are arranged in the length direction of the linear electrode 15 a of the second electrode layer 15. It becomes equivalent. As the EL layer 22, a material that emits EL light having a wavelength of about 470 nm may be used in consideration of matching with a-Se that is the main component of the reading photoconductive layer 14 of the radiation solid-state detector 10. . The linear electrode 21a of the first conductive layer 21 is made of a material that transmits EL light. The linear electrodes 21a may be formed of a material that transmits EL light or may be formed of a material that blocks EL light as long as the linear electrodes 21a are insulated from each other. .

  The linear electrode 21a of the planar light source 20 is connected to the reading light control means 60. The reading light control means 60 includes the first conductive layer 21a of the planar light source 20 and the second conductive layer facing it. A predetermined voltage is applied between the first and second electrodes 23 to control irradiation of reading light. For example, when the reading light control means 60 applies a predetermined DC voltage between the respective linear electrodes 21a and the second conductive layer 23 while sequentially switching the linear electrodes 21a, the linear electrodes 21a and the second electrodes EL light is emitted from the EL layer 22 sandwiched between the conductive layers 23, and the EL light transmitted through the linear electrode 21a is used as line-shaped reading light. Then, the line electrode 21a is sequentially switched over the entire length from one end to the other end of the linear electrode 15a of the second electrode layer 15 to emit EL light, so that the second electrode layer is emitted with line light. The entire surface of 15 is scanned. The longitudinal direction of the linear electrode 15a of the second electrode layer 15 corresponds to the sub-scanning direction, and the direction in which the line light extends corresponds to the main scanning direction.

  In the present embodiment, the linear electrode 21 a of the planar light source 20 is also connected to the erasing light control means 70, and the electric charge remaining in the radiation solid state detector 10 is erased by the control of the erasing light control means 70. It is also used as an erasing light source. For example, when the erasing light source control means 70 applies a voltage to a plurality or all of the linear electrodes 21a simultaneously, the application of this voltage causes the EL light to be emitted substantially uniformly over the entire surface of the EL layer 22, and this EL light. Is used as erasing light for erasing residual charges.

  The signal detection unit 30 includes a large number of charge amplifier circuits 31 connected to each linear electrode 15 a of the second electrode layer 15.

  As shown in FIG. 2, the charge amplifier circuit 31 which is a signal detection means is composed of an operational amplifier 31a, a reset switch 31b, and the like. When the reset switch 31b is in an OFF state, the operational amplifier 31a flows into the charge amplifier circuit 31. When the current detection operation is performed (enable state) and the reset switch 31b is in the ON state, the input / output terminal of the operational amplifier 31a is short-circuited and no current flows into the operational amplifier 31a, that is, the signal detection operation is not performed (disable) State). The ON / OFF operation of the reset switch 31b is controlled by control means (not shown).

  The voltage source 40 is used not only for recording a radiographic image but also for erasing charges remaining in the radiation solid state detector 10. The voltage ON / OFF and the magnitude of the voltage are voltages. Controlled by voltage control means 80 connected to the source 40.

  The short-circuit means 50 is a switch. As shown in FIG. 1, the positive terminal of the voltage source 40 is connected to the a terminal of the switch, and the first electrode layer in the radiation solid detector 10 is connected to the b terminal. 11 is connected, and the charge amplifier circuit 31 of the signal detector 30 is connected to the c terminal. The short-circuit means 50 is switched when the radiation solid-state detector 10 records and reads the radiation image, but is also switched when the charge remaining in the radiation solid-state detector 10 is erased. The switching of the short-circuit means 50 is controlled by a switch control means 90 connected to the short-circuit means 50.

  Next, the operation of the radiation image recording / reading apparatus of the first embodiment will be described. FIG. 3 is a timing chart for explaining the operation of the radiation image recording / reading apparatus.

  First, an operation when a radiation image is recorded on the radiation solid detector 10 will be described. At the time of recording a radiation image, the voltage source 80 is controlled by the voltage control means 80, and a recording voltage is applied between the first electrode layer 11 and the second electrode layer 15 of the radiation solid detector 10. After the recording voltage is applied, radiation is emitted from the radiation source 5, and the radiation that has passed through the subject 6 is irradiated to the radiation solid detector 10. Then, positive and negative charges are generated in the recording photoconductive layer 12 of the radiation solid-state detector 10, and the negative charges of the second electrode are formed along the electric field distribution formed by the application of the recording voltage. It is concentrated on each linear electrode 15 a of the layer 15 and accumulated as a latent image charge in the power storage unit 19, which is an interface between the recording photoconductive layer 12 and the charge transport layer 13. The amount of latent image charge is substantially proportional to the amount of irradiation radiation, and this amount of latent image charge indicates a radiation image of the subject 6. On the other hand, the positive charge generated in the recording photoconductive layer 12 is attracted to the first electrode layer 11 and is combined with the negative charge injected from the voltage source 40 and disappears.

  After the emission of radiation from the radiation source 5 is stopped, the voltage source 80 is controlled by the voltage control means 80, and the application of the voltage to the radiation solid detector 10 is stopped.

  As shown in FIG. 3, there is a transient inflow / outflow of transient overcurrent in the radiation solid detector 10 at the timing when the voltage is applied to the radiation solid detector 10 and when the voltage application is stopped.

  Therefore, in the present embodiment, the reset of each charge amplifier circuit 31 of the signal detection unit 30 is performed in a period from before the timing at which the voltage is applied to the radiation solid state detector 10 to after the timing at which the voltage application is stopped. The switch 31b is turned on (disabled) so that no signal is input to the operational amplifier 31a. As a result, the operational amplifier 31a can be protected from overcurrent flowing in / out of the radiation solid state detector 10.

  The timing at which the reset switch 31b of the charge amplifier circuit 31 is switched from the ON state (disable state) to the OFF state (enable state) is after the overcurrent flowing in / out of the radiation solid state detector 10 is settled (for example, overcurrent) It is preferable that the value is after 10% or less of the maximum amplitude.

  Next, the operation when the radiation image recorded in the radiation solid detector 10 as described above is read will be described. In the radiation image recording / reading apparatus 1, when reading a radiation image from the radiation solid detector 10, the switch control means 90 connects the b terminal and the c terminal of the short-circuit means 50, and the first electrode layer 11 and the second electrode layer 11 are connected. A positive charge corresponding to the negative charge accumulated in the power storage unit 19 is charged to the linear electrode 15 a of the electrode layer 15. Then, while the reading light control means 60 sequentially switches the linear electrodes 21a of the planar light source 20, a predetermined DC voltage is applied between the respective linear electrodes 21a and the second conductive layer 23, and the EL layer. The whole surface of the radiation solid detector 10 is scanned with the line light emitted from the line 22.

  By irradiating this line light, positive and negative charges are generated in the reading photoconductive layer 14, and the positive charge in the charge transport layer 13 is attracted to the negative charge accumulated in the power storage unit 19. It moves rapidly and combines with the latent image charge in the power storage unit 19 and disappears. On the other hand, the negative charge generated in the reading photoconductive layer 14 flows from the first electrode layer 11 through the charge amplifier circuit 31 and the positive charge charged in the linear electrode 15 a of the second electrode layer 15. Combines with the positive charge and disappears. As described above, the negative charge generated in the reading photoconductive layer 14 is combined with the positive charge flowing from the first electrode layer 11 to the second electrode layer 15 via the charge amplifier circuit 31. A current corresponding to the amount of latent image charge is detected by the charge amplifier circuit 31, and a radiation image can be acquired as an electric signal.

  Next, a radiation image recording / reading apparatus according to a second embodiment of the present invention will be described. The radiographic image recording / reading apparatus of the present embodiment is a modification of the operation of the radiographic image recording / reading apparatus of the first embodiment, which is performed at the time of radiographic image recording. The description of the portion is omitted unless particularly necessary. FIG. 4 is a timing chart for explaining the operation of the radiation image recording / reading apparatus of the present embodiment.

  As described above, during the radiographic image recording, transient overcurrent inflow / outflow occurs in the radiation solid detector 10 at the timing when the voltage is applied to the radiation solid detector 10 and when the voltage application is stopped.

  Therefore, as shown in FIG. 4, in the present embodiment, each charge of the signal detection unit 30 is divided between a period in which the voltage application timing is applied to the radiation solid state detector 10 and a period in which the voltage application is stopped. The reset switch 31b of the amplifier circuit 31 is in an ON state (disable state), and the reset switch 31b of each charge amplifier circuit 31 is in an OFF state (enable state) while the radiation solid state detector 10 is irradiated with radiation.

  By detecting the amount of radiation applied to the radiation solid state detector 10 at the time of recording, control when performing image processing and control when erasing residual charges accumulated in the radiation solid state detector 10 are performed. Although it is possible to optimize, by adopting the configuration as in the present embodiment, the amount of radiation irradiated to the radiation solid detector 10 at the time of recording is detected and the inflow / It is possible to protect the operational amplifier 31a from the overcurrent that flows out.

  The timing at which the reset switch 31b of the charge amplifier circuit 31 is switched from the ON state (disable state) to the OFF state (enable state) is after the overcurrent flowing in / out of the radiation solid state detector 10 is settled (for example, overcurrent) It is preferable that the value is after 10% or less of the maximum amplitude.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to those using the above-described optical readout type radiation solid state detector, and includes various TFT readout type radiation solid state detectors. It is possible to use a solid-state radiation detector.

  Moreover, the radiation image is not limited to a direct conversion type radiation solid state detector that directly converts radiation into a charge pair in the photoconductive layer, but radiation that has been irradiated through a scintillator is once converted into fluorescence, and this fluorescence is detected to produce a radiographic image. The present invention can also be applied to a light-conversion radiation solid state detector that detects light.

DESCRIPTION OF SYMBOLS 1 Radiation image recording / reading apparatus 5 Radiation source 6 Subject 10 Radiation solid state detector 11 First electrode layer 12 Recording photoconductive layer 13 Charge transport layer 14 Reading photoconductive layer 15 Second electrode layer 20 Planar light source 30 Signal Detection unit 31 Charge amplifier circuit 40 Voltage source 50 Short-circuit means 60 Reading light control means 70 Erase light control means 80 Voltage control means 90 Switch control means

Claims (5)

A recording light that includes an electrostatic recording portion including a photoconductive layer that exhibits conductivity when irradiated with recording light, and a TFT switch portion that reads charges generated in the photoconductive layer, and carries image information. A radiation solid state detector that records the image information in response to irradiation and outputs an image signal representing the recorded image information;
Voltage application means for applying a recording voltage to the photoconductive layer of the radiation solid detector;
In a radiation image recording / reading apparatus that is normally in an operating state and includes a signal detection unit that detects a signal output from the TFT switch unit,
The signal detection means includes an operational amplifier, a capacitor disposed between the inverting input terminal and the output terminal of the operational amplifier, a charge amplifier circuit including a reset switch connected in parallel with the capacitor,
When the reset switch is turned on and the input / output terminal of the operational amplifier is short-circuited, the signal detection unit is configured to be in an inoperative state,
At the time of recording a radiographic image, when the voltage application unit applies the recording voltage to the radiation solid state detector, the signal detection unit is operated by changing the reset switch from an OFF state to an ON state. A radiation image recording / reading apparatus, wherein the radiation image recording / reading apparatus is in a non-operating state . The radiographic image recording / reading apparatus according to claim 1, wherein the voltage application unit receives the recording light while applying the recording voltage to the radiation solid state detector. At the time of radiographic image recording, before the recording voltage is applied to the photoconductive layer of the radiation solid detector by the voltage application means, the reset switch is changed from an OFF state to an ON state, and the voltage application means 3. The radiographic image recording / reading apparatus according to claim 1 , wherein the reset switch is changed from an ON state to an OFF state after the application of the recording voltage is stopped. 4. The radiographic image recording / reading apparatus according to claim 3 , wherein the reset switch is turned off during a period in which the radiation solid detector is irradiated with radiation. Claims wherein the solid-state radiation detector, the radiation irradiated as the recording light is converted once into fluorescence by a scintillator, and characterized in that the light conversion method for recording the image information by detecting the fluorescence Item 5. The radiation image recording / reading apparatus according to any one of Items 1 to 4 .

Images