JP2008128725A - Radiographic image reading method and radiographic image detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image quality of a radioactive image by suppressing flow of an offset current from a charge pair generating electrode to a charge pair non-generating electrode in a radioactive image detector formed by laminating in the order of a photoconductive layer for recording for generating the charge by receiving irradiation of a radiation, a charge transport layer for accumulating the generated charge, a photoconductive layer for reading for generating the charge by irradiation of reading light, and an electrode layer wherein a large number of linear charge pair generating electrodes for generating charge pairs relative to irradiation of reading light and linear charge pair non-generating electrodes for not generating charge pairs relative to irradiation of the reading light are arranged alternately. <P>SOLUTION: This invention has a characteristic wherein a potential gradient is formed between the charge pair generating electrodes 5 and the charge pair non-generating electrodes 6 at the irradiation time of the reading light L1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation image reading method for reading a radiation image from a radiation image detector that receives a radiation image carrying the radiation image, records the radiation image, is scanned by reading light, and reads a signal corresponding to the radiation image. And the radiation image detector.

  2. Description of the Related Art Conventionally, in the medical field and the like, various radiological image detectors that generate a charge upon irradiation of radiation transmitted through a subject and record a radiation image related to the subject by accumulating the charge have been proposed and put into practical use.

  As a radiation image detector as described above, for example, Patent Document 1 discloses a first electrode layer that transmits radiation, a photoconductive layer for recording that generates charges when irradiated with radiation, and a latent image. A charge transport layer that acts as an insulator for charges and acts as a conductor for transport charges of the opposite polarity to the latent image charge, a photoconductive for reading that generates charges when irradiated with read light And a second electrode layer in which transparent linear electrodes extending linearly that transmit reading light and light-shielding linear electrodes extending linearly that block reading light are alternately arranged in parallel are stacked in this order. A radiation image detector is proposed.

  When a radiographic image is recorded by the radiographic image detector configured as described above, first, a negative high voltage is applied to the first electrode layer 51 as shown in FIG. Thus, the radiation transmitted through the subject is irradiated from the first electrode layer 51 side. The radiation irradiated as described above passes through the first electrode layer 51 and is irradiated to the recording photoconductive layer 52, and a charge pair is generated in the irradiated portion of the recording photoconductive layer 52. The positive charge of the charge pair moves toward the negatively charged first electrode layer 51 and is combined with the negative charge in the first electrode layer 51 and disappears. On the other hand, the negative charge of the charge pair generated as described above moves toward the positively charged transparent linear electrode 55 and the light shielding linear electrode 56. However, as described above, the charge transport layer 53 has a negative charge. Therefore, the negative charge is accumulated in the power storage unit 57, which is the interface between the recording photoconductive layer 52 and the charge transport layer 53, and the negative charge is stored in the power storage unit 57. Thus, a radiographic image is recorded (FIG. 7B).

  And when reading the radiographic image recorded as mentioned above from a radiographic image detector, as shown in FIG. 8, first in the state which grounded both the transparent linear electrode 55 and the light-shielding linear electrode 56, The reading light L1 is irradiated from the transparent linear electrode 55 and the light shielding linear electrode 56 side. The irradiated reading light L1 passes through the transparent linear electrode 55 and is irradiated to the reading photoconductive layer 54, and a charge pair is generated in the reading photoconductive layer 54. The positive charge generated in the reading photoconductive layer 54 by the irradiation of the reading light L1 is combined with the negative charge in the power storage unit 57, and the negative charge generated in the reading photoconductive layer 4 is combined with the charge pair generating electrode. 5 and the positive charge charged to the non-generating electrode 56 through the charge amplifier 35, and a current flows through the charge amplifier 35, and this current is integrated to form an image. The signal is detected as a signal, and an image signal corresponding to the radiation image is read.

  After the radiation image is read as described above, the erasing light is irradiated from the transparent linear electrode 55 and the light shielding linear electrode 56 side, the charge remaining in the power storage unit 57 is erased, and the radiation is again performed. Used for recording images.

JP 2000-284056 A

  Here, when the radiographic image is read as described above, the positive charge generated by the irradiation of the reading light not only moves toward the power storage unit 57 but also due to the action of the diffusion of the charge due to the photovoltaic force. As shown in FIG. 9, it moves toward the light-shielding linear electrode 56, which is detected as an offset current together with the image signal, resulting in degradation of image quality.

  Since the magnitude of the offset current changes depending on the change in the reading light and the irradiation history of the erasing light, the offset current cannot be appropriately removed by correcting the read image signal.

  In view of the above circumstances, an object of the present invention is to provide a radiation image detector that can suppress the offset current as described above and can improve the image quality of a read radiation image.

  The radiographic image reading method of the present invention generates charges by receiving irradiation of a recording electromagnetic wave carrying a radiographic image, accumulates the generated charges, and generates light by irradiating reading light. A large number of conductive layers, linear charge pair generating electrodes for generating charge pairs for irradiation of reading light, and linear charge pair non-generating electrodes for generating non-charge pairs for irradiation of reading light In a method of reading a radiation image by irradiating a radiographic image detector in which the arranged electrode layers are laminated in this order to read a radiographic image, a potential is generated between the charge pair generating electrode and the charge pair non-generating electrode when the reading light is irradiated. It is characterized by forming a gradient.

  In the radiation image detector of the present invention, a potential gradient can be formed by applying a voltage between the charge pair generating electrode and the charge pair non-generating electrode.

  Further, the potential gradient can be formed by forming the charge pair generating electrode and the charge pair non-generating electrode from different materials.

  The radiation image detector of the present invention generates a charge upon irradiation with a recording electromagnetic wave carrying a radiation image, and accumulates the generated charge, and light that generates a charge when irradiated with reading light. A large number of conductive layers, linear charge pair generating electrodes for generating charge pairs for irradiation of reading light, and linear charge pair non-generating electrodes for generating non-charge pairs for irradiation of reading light In the radiographic image detector in which the arranged electrode layers are laminated in this order, and the radiographic image is read out by reading light irradiation, the charge pair generating electrode and the charge pair non-generating at the time of reading light irradiation A potential gradient is formed between the electrode and the electrode.

  The radiological image detector of the present invention may further include voltage applying means for applying a voltage between the charge pair generating electrode and the charge pair non-generating electrode to form a potential gradient.

  Further, the charge pair generating electrode and the charge pair non-generating electrode can be formed of different materials so that a potential gradient is formed.

  According to the radiographic image reading method and radiographic image detector of the present invention, a potential gradient is formed between the charge pair generating electrode and the charge pair non-generating electrode when the reading light is irradiated. It is possible to suppress the above-described offset current from flowing between the charge pair generation electrode and the charge pair non-generation electrode, thereby improving the image quality of the read radiographic image.

  Hereinafter, a radiographic image recording / reading apparatus using an embodiment of the radiographic image detector of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the radiation image detector, and FIG. 2 is a cross-sectional view of the radiation image detector shown in FIG.

  As shown in FIGS. 1 and 2, the radiological image detector 10 is charged by receiving a first electrode layer 1 that transmits radiation carrying a radiographic image, and radiation irradiated through the first electrode layer 1. Of the charge generated in the recording photoconductive layer 2 and the recording photoconductive layer 2 acts as an insulator for the charge of one polarity and as a conductor for the charge of the other polarity The charge transport layer 3 that acts, the photoconductive layer 4 for reading that generates charges by receiving irradiation of reading light, and the linear charge pair generating electrode 5 and reading light for generating charge pairs in response to irradiation of reading light The second electrode layer 7 in which a large number of linear charge pair non-generating electrodes 6 for non-generation of charge pairs are alternately arranged with respect to the irradiation of the above is laminated in this order. Between the recording photoconductive layer 2 and the charge transport layer 3, a power storage unit 8 for accumulating charges generated in the recording photoconductive layer 2 is formed. In addition, although each said layer is formed in order from the 2nd electrode layer 7 on a glass substrate, the glass substrate is abbreviate | omitted in FIG. 1 and FIG. The recording photoconductive layer 2 and the charge transport layer 3 form a charge storage layer in the claims.

The first electrode layer 1 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 7 has the charge generation electrode 5 and the charge non-generation electrode 6 as described above.

  The charge generation electrode 5 is a transparent linear electrode, and may be formed of any material that is transparent and conductive. For example, as with the first electrode layer 1, ITO or IDIXO Can be used.

  The charge non-generating electrode 6 includes a transparent linear electrode 6a and a linear light shielding body 6b that shields reading light. The transparent linear electrode 6a may be formed of any material as long as it is transparent and conductive. For example, similar to the first electrode layer 1, ITO or IDIXO can be used. For example, when blue light having a wavelength of 400 nm to 480 nm is used as the reading light, the linear light shielding body 6b may be formed of a red resist or a yellow resist.

  The recording photoconductive layer 2 only needs to generate a charge when irradiated with radiation, and is excellent in that the quantum efficiency is relatively high with respect to radiation and the dark resistance is high. A material mainly composed of Se is used. A thickness of about 500 μm is appropriate.

As the charge transport layer 3, for example, the larger the difference between the mobility of charges charged in the first electrode layer 1 at the time of recording a radiographic image and the charge mobility of the opposite polarity, the better (for example, 10 ^2). or more, preferably 10 ³ or higher) poly N- vinylcarbazole (PVK), N, N'-diphenyl -N, N'-bis (3-methylphenyl) - [1,1'-biphenyl] -4,4 ' An organic compound such as diamine (TPD) or discotic liquid crystal, a TPD polymer (polycarbonate, polystyrene, PVK) dispersion, a semiconductor material such as a-Se doped with 10 to 200 ppm of Cl is suitable.

  The reading photoconductive layer 4 may be any material that exhibits conductivity when irradiated with reading light and erasing light. For example, a-Se, Se-Te, Se-As-Te, metal-free phthalocyanine, A photoconductive substance mainly containing at least one of metal phthalocyanine, MgPc (Magnesium phtalocyanine), VoPc (phase II of Vanadyl phthalocyanine), CuPc (Cupper phtalocyanine) and the like is preferable. A thickness of about 0.1 to 1 μm is appropriate.

  Further, the radiographic image detector 10 includes voltage applying means for forming a potential gradient between the charge pair generating electrode 5 and the charge pair non-generating electrode 6 at the time of reading the radiographic image. In FIG. 1 and FIG. 2, the voltage applying means is not shown.

  Next, the operation of recording and reading the radiation image on the radiation image detector by the radiation image recording / reading apparatus will be described.

  First, as shown in FIG. 3A, in a state where a negative voltage is applied to the first electrode layer 1 of the radiation image detector 10 by the high voltage source 20, radiation is emitted from the radiation source (not shown) toward the subject. Is irradiated from the first electrode layer 1 side of the radiation image detector 10 with radiation that carries the radiation image of the subject through the subject.

  The radiation applied to the radiation image detector 10 passes through the first electrode layer 1 and is applied to the recording photoconductive layer 2. Then, a charge pair is generated in the recording photoconductive layer 2 by the irradiation of the radiation, and the positive charge is combined with the negative charge charged in the first electrode layer 1 and disappears, and the negative charge is a latent image. A radiographic image is recorded by being accumulated in the power storage unit 8 formed at the interface between the recording photoconductive layer 2 and the charge transport layer 3 as charges (see FIG. 3B).

  Then, as shown in FIG. 4, a reading light source (not shown) is shown in a state where the first electrode layer 1 is grounded and a negative voltage is applied to the charge pair generating electrode 5 by the voltage applying means 25. The reading light L 1 is emitted from the second electrode layer 7, and the reading light L 1 is irradiated from the second electrode layer 7 side. The reading light L 1 passes through the charge generation electrode 5 and is irradiated to the reading photoconductive layer 4. The positive charge generated in the reading photoconductive layer 4 by the irradiation of the reading light L1 is combined with the latent image charge in the power storage unit 8, and the negative charge generated in the reading photoconductive layer 4 is applied to the charge pair generating electrode 5. When coupled with the charged positive charge and coupled with the positive charge charged on the non-generating electrode 6 via the charge amplifier 30, a current flows through the charge amplifier 30, and this current is integrated to form an image signal. Detection is performed, and an image signal corresponding to the radiation image is read.

  As described above, conventionally, an offset current flows from the charge pair generating electrode 5 to the charge pair non-generating electrode 6 by irradiation of the reading light, and this is detected as a noise signal together with the image signal. According to the image detector 10, since the negative voltage is applied to the charge pair generating electrode 5 by the voltage applying means 25, it is possible to suppress the offset current from flowing as described above.

  Here, FIG. 5 shows the result of measuring the offset by changing the bias voltage applied to the charge pair generating electrode 5 by the voltage applying means 25. FIG. 5 shows an offset detected by the charge amplifier 30 after reading without irradiating the radiation image detector. The black square graph in FIG. 5 shows the offset measured by the first reading, the black triangle graph shows the offset measured immediately after 1000 readings, and the white circle graph shows 10,000 times. The offset measured immediately after taking the reading is shown.

  From the measurement results shown in FIG. 5, it was found that the offset decreases with each reading. It was found that when the bias voltage was −0.13 (V), the offset was closest to 0 regardless of the number of readings. From the measurement results shown in FIG. 5, it was found that the bias voltage applied to the charge pair generating electrode 5 by the voltage applying means 25 is most preferably −0.13 (V). If a bias voltage of −0.13 ± 0.08 (V) is applied, a sufficient offset reduction effect can be obtained.

  That is, the bias voltage applied by the voltage applying means 25 is set to the bias voltage V1 ± 0.08 (V) at the point where the measurement results intersect when the relationship between the bias voltage and the offset is measured for various reading times. Is desirable, more preferably V1 (V).

FIG. 6 shows the result of measuring the offset by changing the bias voltage, as in FIG. The black square graph in FIG. 6 is an offset measured by reading with a reading light amount of 105 μW / mm ² , and the white circle graph is measured by reading with a reading light amount of 11 μW / mm ^2. Offset.

  From the measurement results shown in FIG. 6, it was found that the smaller the amount of reading light, the smaller the offset. It was found that when the bias voltage was −0.13 (V), the offset was closest to 0 regardless of the amount of reading light. Also from the measurement results shown in FIG. 6, it was found that the bias voltage applied to the charge pair generating electrode 5 by the voltage applying means 25 is most preferably −0.13 (V). In this case as well, a sufficient offset reduction effect can be obtained by applying a bias voltage of −0.13 ± 0.08 (V).

  In other words, the bias voltage applied by the voltage application means 25 is the bias voltage V2 ± 0.08 (V) at the point where the measurement results intersect when the relationship between the bias voltage and the offset is measured for various amounts of reading light. V2 (V) is more preferable.

  In the radiation image detector of the above embodiment, a voltage gradient is formed between the charge pair generating electrode and the charge pair non-generating electrode by applying a voltage to the charge pair generating electrode 5 by the voltage applying means 25. However, the present invention is not limited to this, and for example, the potential gradient may be formed by forming the charge pair generating electrode 5 and the charge pair non-generating electrode 6 from different materials. Specifically, the charge pair generating electrode may be formed of IZO, and the transparent linear electrode 6a as the charge non-generating electrode may be formed of ITO. Since the work function of IZO is 5.2 eV and the work function of ITO is 5.1 eV, a potential gradient of 0.1 V is formed between the charge pair generating electrode and the charge pair non-generating electrode. However, the present invention is not limited to this, and other materials that form a potential gradient may be selected.

  In the above-described embodiment, the present invention is applied to a so-called direct conversion type radiation oblique line image detector that records radiation images by receiving radiation irradiation and directly converting the radiation into electric charges. However, the present invention is not limited to this, and for example, the present invention is applied to a so-called indirect conversion type radiation image detector that records radiation images by once converting radiation into visible light and converting the visible light into electric charges. It may be.

  The layer configuration of the radiation image detector is not limited to the layer configuration as in the above embodiment, and other layers may be added.

Schematic configuration diagram of an embodiment of a radiation image detector of the present invention 2-2 sectional view of the radiation image detector shown in FIG. The figure for demonstrating the effect | action of recording of the radiographic image to the radiographic image detector shown in FIG. The figure for demonstrating the effect | action of reading of the radiographic image from the radiographic image detector shown in FIG. Results of measuring the relationship between bias voltage and offset for various readings Results of measuring the relationship between bias voltage and offset for various reading light quantities The figure for demonstrating the effect | action of recording of the radiographic image to the conventional radiographic image detector The figure for demonstrating the effect | action of reading of the radiographic image from the conventional radiographic image detector The figure for demonstrating the offset current which flows into the conventional radiographic image detector

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st electrode layer 2 Photoconductive layer for recording 3 Charge transport layer 4 Photoconductive layer for reading (photoconductive layer)
DESCRIPTION OF SYMBOLS 5 Charge pair generation electrode 6 Charge pair non-generation electrode 6a Transparent linear electrode 6b Linear light-shielding body 7 2nd electrode layer 8 Power storage part 10 Radiation image detector 25 Voltage application means 30 Charge amplifier

Claims (6)

A charge storage layer that generates a charge upon receiving irradiation of a recording electromagnetic wave carrying a radiation image, accumulates the generated charge, a photoconductive layer that generates a charge by irradiation of reading light, and irradiation of the reading light In contrast, a linear charge pair generating electrode for generating charge pairs and an electrode layer in which a large number of linear charge pair non-generating electrodes for generating charge pairs with respect to the irradiation of the reading light are alternately arranged. In the method of reading the radiation image by irradiating the reading light to the radiation image detectors laminated in this order,
A radiation image reading method, wherein a potential gradient is formed between the charge pair generating electrode and the charge pair non-generating electrode during irradiation of the reading light.   The radiation image reading method according to claim 1, wherein a voltage is applied between the charge pair generating electrode and the charge pair non-generating electrode to form the potential gradient.   2. The radiation image reading method according to claim 1, wherein the potential gradient is formed by forming the charge pair generating electrode and the charge pair non-generating electrode from different materials. A charge storage layer that generates a charge upon receiving irradiation of a recording electromagnetic wave carrying a radiation image, accumulates the generated charge, a photoconductive layer that generates a charge by irradiation of reading light, and irradiation of the reading light In contrast, a linear charge pair generating electrode for generating charge pairs and an electrode layer in which a large number of linear charge pair non-generating electrodes for generating charge pairs with respect to the irradiation of the reading light are alternately arranged. Radiation image detectors stacked in this order, wherein the radiation image is read out by irradiation of the reading light,
A radiation image detector, wherein a potential gradient is formed between the charge pair generating electrode and the charge pair non-generating electrode when the reading light is irradiated.   5. The radiation image detector according to claim 4, further comprising voltage applying means for applying a voltage between the charge pair generating electrode and the charge pair non-generating electrode to form the potential gradient.   5. The radiation image detector according to claim 4, wherein the charge pair generating electrode and the charge pair non-generating electrode are formed of different materials so as to form the potential gradient.

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