JP2010107198A - Radiation image detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the amount of radiation to a detector of visible light converted by a wavelength conversion layer without absorbing any radiation in a radiation image detector, where a support, the wavelength conversion layer, and the detector for detecting visible light converted by the wavelength conversion layer are laminated in this order. <P>SOLUTION: The support 33 is formed by an organic matter containing a number of bubbles 33a and is allowed not to contain any inorganic matters, and visible light converted by the wavelength conversion layer 32 is reflected toward the detector 31. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiation image detector that detects light converted by a wavelength conversion layer and converts it into an image signal representing a radiation image.

  2. Description of the Related Art Conventionally, in the medical field and the like, various radiological image detectors that record a radiographic image related to a subject by irradiation with radiation that has passed through the subject have been proposed and put into practical use.

  As the radiation image detector as described above, for example, a radiation image detector using a semiconductor that generates a charge upon irradiation of radiation has been proposed. An electric reading type using a thin film transistor (TFT), a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS) sensor, or the like has been proposed.

  The electric reading type radiological image detector may be a direct conversion type that directly converts radiation into a charge in a semiconductor layer and accumulates it, or radiation is once converted into light by a phosphor, and the converted light is converted into light. There has been proposed an indirect conversion method in which a charge is converted and accumulated by a photodiode or the like.

  For example, Patent Document 1 proposes an indirect conversion radiation image detector in which a phosphor layer and a detection substrate on which a large number of detection elements are arranged are stacked.

  And in patent document 1, the reflective layer which consists of a metal thin film which reflects the light converted by the fluorescent substance layer to the detection board | substrate side between the fluorescent substance layer and the support body which supports the fluorescent substance layer is provided, This describes increasing the amount of light incident on the detection substrate.

  Patent Document 2 proposes a radiation intensifying screen in which a light reflecting layer, a phosphor layer, and a surface protective layer are provided in this order on a support. Also in this radiation intensifying screen, a light reflecting layer made of titanium dioxide is provided in order to increase the amount of light emitted from the screen.

Patent Document 3 proposes a radiation conversion panel in which a reflective layer, a photostimulable phosphor layer, and a protective layer are provided in this order on a support plate. And in patent document 3, forming a support plate from the polyethylene terephthalate containing a bubble and giving a reflective function to a support plate is proposed.
JP 2006-258618 A Japanese Patent Laid-Open No. 9-21899 JP 2002-131495 A

  However, when a reflective layer is provided as in the radiation image detector described in Patent Document 1 and radiation is irradiated from the phosphor layer side, the radiation passes through the reflective layer before reaching the phosphor layer. As a result, the radiation is absorbed and attenuated, and as a result, the amount of light emitted by the phosphor layer is reduced, resulting in a problem of image quality degradation.

  Furthermore, since the reflection layer in the radiation image detector described in Patent Document 1 is a specular reflection surface, the final reflectivity is obtained by multiplying the reflectivity of one time to the nth power, and sufficient reflected light. Can't get.

  Also, in the radiation intensifying screen described in Patent Document 2, when radiation is irradiated from the support side, the radiation is absorbed and attenuated by the light reflecting layer also made of titanium dioxide, and the amount of light emitted by the phosphor layer decreases. Problems arise.

  Further, in Patent Document 3, it is proposed that the support plate has a reflection function by forming the support plate from polyethylene terephthalate containing bubbles, but in the support plate described in Patent Document 3, Inorganic materials such as barium sulfate are used as the firing core to contain bubbles, and when radiation is irradiated from the support side, the radiation is absorbed and attenuated by the support plate containing the inorganic material, and the amount of light emitted by the phosphor layer This causes a problem of lowering.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radiation image detector that can increase the amount of irradiation of visible light converted by a phosphor layer without absorbing radiation. And

  The radiation image detector according to the present invention detects a radiation image by detecting a support, a wavelength conversion layer that receives radiation and converts the radiation into light having a longer wavelength, and light converted by the wavelength conversion layer. In the radiation image detector in which detectors for converting into image signals are stacked in this order, the support is formed from an organic substance containing a large number of bubbles, does not contain an inorganic substance, and is converted by a wavelength conversion layer. It is characterized in that the reflected light is reflected toward the detector.

  Here, the above-mentioned “containing no inorganic material” includes not only one containing no inorganic material but also one containing a certain amount of inorganic material within an allowable range in which radiation absorption does not affect the image quality. For example, when the inorganic content is 1% by weight or less, the image quality is not affected.

  The “wavelength conversion layer” converts radiation into light having a longer wavelength, and preferably converts near-infrared light, visible light, and near-infrared light. More preferably, the light is converted into visible light.

  In addition, a support having a reflectance of 85% or more with respect to the main emission wavelength of the light converted by the wavelength conversion layer can be used.

  Moreover, what is formed from resin can be used as a support body.

  Moreover, what is formed from a polyethylene terephthalate can be used as a support body.

A wavelength conversion layer containing GOS (Gd ₂ O ₂ S: Tb) particles can be used.

  A wavelength conversion layer including at least one of CsI: Na and CsI: Tl can be used.

  According to the radiographic image detector of the present invention, the support is formed from an organic substance containing a large number of bubbles, does not contain an inorganic substance, and the reflection is reflected toward the detector by the light converted by the wavelength conversion layer. Since it has a function, the radiation amount is not absorbed by the support, and the irradiation amount of the light converted by the wavelength conversion layer to the detector can be increased.

  In addition, when a support having a reflectance of 85% or more with respect to the main emission wavelength of the light converted by the wavelength conversion layer is used, a sufficient amount of light irradiation to the detector is set. Obtainable.

  A radiographic imaging apparatus using an embodiment of the radiographic image detector of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of the radiographic image capturing apparatus.

  The radiation imaging apparatus is a radiation source 1 that emits radiation toward a subject 2 and radiation that is irradiated with radiation that has passed through the subject 2 and that outputs an image signal representing a radiation image of the subject 2 carried by the radiation. An image detector 3, a signal processing unit 4 that performs predetermined signal processing on the image signal output from the radiation image detector 3, and a radiographic image is reproduced based on the image signal that has undergone signal processing in the signal processing unit 4 And a reproducing unit 5 for performing the above operation.

  FIG. 2 is a cross-sectional view showing a configuration of the radiographic image detector 3 in the radiographic image capturing apparatus.

  As shown in FIG. 2, the radiation image detector 3 detects a phosphor layer 32 that receives radiation that has passed through a subject and converts the radiation into visible light, and visible light converted by the phosphor layer 32. Thus, a solid state detector 31 that converts the image signal into a radiographic image and a support 33 that supports the phosphor layer 32 are provided.

  In the present embodiment, the radiation image detector 3 includes the support 33, the phosphor layer 32, and the solid detector 31 arranged in this order from the radiation source 1 side, and the radiation from the support 33 side. It is intended to receive irradiation.

  FIG. 3 is a plan view showing the configuration of the solid state detector 31. As shown in FIG. 3, the solid-state detector 31 includes a plurality of photodiode portions 36 and TFT switches 37 that are two-dimensionally arranged in the XY direction, and a row of photodiode portions 36 and TFT switches 37 that are aligned in the X direction. Provided for each column of the scanning line 31b to which the scanning signal input to each TFT switch 37 of the row is applied, and the photodiode portion 36 and the TFT switch 37 arranged in the Y direction. And a data line 31c from which a pixel signal detected by the photodiode portion 36 flows out.

  The scanning line 31b and the data line 31c are provided so as to be orthogonal to each other, and a photodiode portion 36 and a TFT switch 37 are provided corresponding to the intersection of the scanning line 31b and the data line 31c.

  A gate driver 40 that outputs a scanning signal to each scanning line 31b is connected to one end of each scanning line 31b, and an integrating amplifier 50 that detects a pixel signal flowing out to each signal line is connected to one end of each data line 31c. It is connected. 1 and 2, the gate driver 40 and the integrating amplifier 50 are not shown.

  FIG. 4 is a diagram showing a schematic configuration of each photodiode unit 36 and TFT switch 37 in the solid state detector 31. The photodiode unit 36 photoelectrically converts visible light converted by the phosphor layer 32. The TFT switch 37 is for reading out a charge signal photoelectrically converted in the photodiode section 36 as a pixel signal.

  As shown in FIG. 4, the photodiode portion 36 and the TFT switch 37 are provided on an insulating substrate 31d made of non-alkali glass or the like. The photodiode portion 36 includes a transparent electrode 36a that transmits visible light converted by the phosphor layer 32, a semiconductor layer 36b that functions as a photodiode, and a lower electrode 36c. As the semiconductor layer 36b, for example, a PIN structure can be used. Note that a MIS (Metal Insulator Semiconductor) structure may be used as the photodiode portion. The lower electrode 36c is connected to a drain electrode 37b of a TFT switch 37 described later. In FIG. 4, the photodiode portion 36 and the TFT switch 37 are arranged side by side. However, it is preferable that the photodiode area is increased by overlapping the photodiode portion 36 and the TFT switch 37.

  The TFT switch 37 includes a gate electrode 37a, a drain electrode 37b, a source electrode 37c, a semiconductor layer 37d, and a gate insulating film 37e. The gate electrode 37a is connected to the scanning line 31b, the drain electrode 37b is connected to the lower electrode 36c of the photodiode portion 36 as described above, and the source electrode 37c is connected to the data line 31c. Is. The semiconductor layer 37d is a channel portion of the TFT switch 37, and is a current path connecting the data line 31c and the drain electrode 37b which are turned ON / OFF by the gate voltage.

As described above, the phosphor layer 32 receives radiation and converts the radiation into visible light. The phosphor layer 32 includes a phosphor that converts radiation into visible light. Examples of the phosphor include GOS (Gd ₂ O ₂ S: Tb) particles and CsI: Na and CsI made of columnar crystals. : At least one of Tl can be used. In addition, the formation method of the fluorescent substance layer 32 is demonstrated in detail in the Example mentioned later.

  The support 33 has a phosphor layer 32 formed thereon and supports the phosphor layer 32.

  The support 33 is formed from an organic material containing a large number of bubbles 33 a and reflects visible light converted by the phosphor layer 32 toward the solid state detector 31.

  Specifically, a film formed from a member in which a large number of bubbles are contained in a resin such as polyethylene terephthalate can be used. As such a film, for example, E6SL of white low specific gravity film manufactured by Toray Industries, Inc. can be used.

  The support 33 may be made of an organic substance other than polyethylene terephthalate, for example, cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, etc. Use. In addition, what does not contain an inorganic substance shall include not only what does not contain an inorganic substance at all, but also what contains some inorganic substances with a certain amount of radiation absorption within an allowable range.

  The support 33 preferably has a reflectance of 85% or more with respect to the main emission wavelength of visible light converted by the phosphor layer 32. In addition, the measurement of a reflectance measures the reflectance with respect to a standard white board (210-0740) using a 150phi integrating sphere (150-0901) for Hitachi Ltd. U-3210 type self-recording spectrophotometer. A method to do is available. The measurement wavelength for the reflectance measurement is determined in consideration of the wavelength of the emitted light of the phosphor constituting the radiation intensifying screen. When the emitted light has a plurality of wavelength peaks or when the peaks are broad, measurement is performed at each wavelength and the weighted average is calculated in consideration of the emission intensity.

  In addition, the thickness of the support is preferably 0.07 mm or more and 0.5 mm or less.

  Next, the operation of the radiographic imaging apparatus using the radiographic image detector of this embodiment will be described.

  First, radiation is emitted from the radiation source 1 toward the subject 2. Then, radiation that passes through the subject 2 and carries a radiographic image of the subject is irradiated from the support 33 side of the radiographic image detector 3.

  The radiation applied to the radiation image detector 3 passes through the support 33 and is applied to the phosphor layer 32.

  Here, the radiation that has passed through the subject 2 passes through the support 33 as described above. However, since the support 33 according to the present embodiment is formed of an organic material, the radiation absorption is small and the radiation on the support 33 is large. No attenuation occurs.

  And the fluorescent substance layer 32 which received irradiation of the radiation converts the radiation into visible light.

  Here, the visible light converted by the phosphor layer 32 is directed not only to the solid state detector 31 side but also to the opposite side of the solid state detector 31 side, but such light is also reflected by the support 33. It can lead to the solid detector 31 side.

  The visible light converted by the phosphor layer 32 is irradiated on the solid state detector 31 and is incident on each photodiode portion 36 of the solid state detector 31.

  The visible light incident on the photodiode portion 36 is irradiated onto the semiconductor layer 36b of the photodiode portion 36, and charges are generated in the semiconductor layer 36b.

  At the time of image reading, each scanning line 31b connected to the row of TFT switches 37 arranged in the X direction is sequentially selected in the Y direction by the gate driver 40, and each scanning line 31b is selected from the gate driver 40 with respect to the selected scanning line 31b. An ON signal for turning on the TFT switch 37 is sequentially output.

  When an ON signal is added to the scanning line 31b, a gate voltage is applied to the gate electrode 37a of each TFT switch 37 connected to the scanning line 31b, and a semiconductor between the drain electrode 37b and the source electrode 37c of the TFT switch 37 is applied. Conduction is performed through the layer 37d, and the TFT switch 37 is turned on.

  As a result, the charge signal generated in the photodiode portion 36 is read out via the TFT switch 37 and flows out to the data line 31c. The charge signal flowing out to each data line 31c is detected as an image signal by the integrating amplifier 50 connected to each data line 31c, and the image signal is output from the integrating amplifier 50 every time the scanning line 31b is selected.

  Then, the image signal output from the radiation image detector 3 is output to the signal processing unit 4, subjected to predetermined signal processing in the signal processing unit 4, and then the processed image signal is output to the reproduction unit 5. .

  Then, in the reproduction unit 5, for example, a radiographic image of the subject 2 is reproduced and displayed on a monitor or a radiographic image is reproduced and recorded on a predetermined recording medium based on the processed image signal.

  Hereinafter, examples of the radiation image detector of the above-described embodiment will be described.

1) Formation of phosphor sheet Dissolve 20% by weight of a mixture of polyvinyl butyral resin, urethane resin fat and plasticizer in 80% by weight of a mixed solvent of toluene, 2-butanol and xylene, and stir well to obtain a binder solution. Created.

Then, this binder solution and a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 5 μm were mixed as a solid component in a weight ratio of 15:85, and dispersed by a ball mill to prepare a phosphor coating solution. .

  Then, this phosphor coating solution was applied to the surface of a polyethylene terephthalate sheet (temporary support, thickness: 190 μm) coated with a silicone release agent using a doctor blade in a width of 430 mm, dried, and then temporarily supported. The phosphor sheet was peeled from the body to obtain a phosphor sheet (thickness: 300 μm).

2) Formation of support A material having the following composition was added to 5 g of MEK (methyl ethyl ketone) and mixed and dispersed to prepare a coating solution. This coating solution is applied to the surface of a plastic film (E6SL, a white low specific gravity film manufactured by Toray Industries, Inc.) using a doctor blade, dried and cured, and an adhesive layer (film thickness: 5 μm) on the phosphor layer side is applied. Formed.

Resin: ME of saturated polyester resin (Byron 300 (registered trademark), manufactured by Toyobo Co., Ltd.)
K solution (solid content 30% by weight)
Curing agent: Polyisocyanate (Olestar NP38-70S (registered trademark) (solid content 7
0%), manufactured by Mitsui Toatsu Corporation
Conductive agent: MEK dispersion of SnO ₂ (Sb dope) needle-shaped fine particles (solid content 30% by weight)
3) Formation of phosphor layer The phosphor sheet prepared in 1) is superimposed on the surface of the adhesive layer on the support so that the back surface (temporary support side) at the time of coating and formation is in contact with the surface, using a calendar machine. Heat compression was performed at a total load of 2300 kg, an upper roll of 45 ° C., a lower roll of 45 ° C., and a feed rate of 0.3 m / min. Thereby, the phosphor sheet was completely fused on the support.

4) Formation of radiation image detector A double-sided adhesive tape (adhesive layer; thickness 25 μm, CS9621 manufactured by Nitto Denko Corporation) was applied to the surface of the phosphor layer on the support, and then a solid state detector using a laminator. A radiographic image detector was prepared by attaching a phosphor layer to the surface of the film with a double-sided adhesive tape.

  On the other hand, the following radiographic image detector was created as a comparative example. As shown in FIG. 5, the radiation image detector 100 of the comparative example receives a radiation that has passed through a subject and converts the radiation into visible light, and the visible light converted by the phosphor layer 102. A solid-state detector 101 that detects light and converts it into an image signal representing a radiographic image, and a support 104 that supports the phosphor layer 102, are provided between the support 104 and the phosphor layer 102. A reflective layer 103 is provided.

  The support 104 of the radiation image detector 100 of the comparative example does not contain bubbles like the support of the example, and does not function as a reflection of the light converted by the phosphor layer 102. In the radiation image detector 100 of the comparative example, the light converted by the phosphor layer 102 by the reflection layer 103 is reflected toward the solid state detector 101 side.

  The radiation image detector 100 of the comparative example was created as follows.

1) Production of phosphor sheet The phosphor sheet was produced in the same manner as in the above example.

2) Formation of Reflective Layer A material having the following composition was added to 5 g of MEK (methyl ethyl ketone) and mixed and dispersed to prepare a coating solution. This coating solution was applied to the surface of PET (polyethylene terephthalate) (support, thickness: 200 μm) using a doctor blade, dried and cured to form an adhesive layer (film thickness: 5 μm) on the reflective layer side.

Resin: MEK solution of saturated polyester resin (Byron 300, manufactured by Toyobo Co., Ltd.) “Solid content 30% by weight”
Curing agent: Polyisocyanate (Olestar NP38-70S “Solid content 70%”, manufactured by Mitsui Toatsu Co., Ltd.)
Conductive agent: MEO dispersion of SnO ₂ (Sb dope) needle-shaped fine particles “solid content 30% by weight”
Subsequently, a material having the following composition was added to 387 g of MEK and mixed and dispersed to prepare a coating solution. This coating solution was applied to the surface of the adhesive layer on the support made of PET using a doctor blade and dried to form a reflective layer (layer thickness, about 100 μm).

Light reflecting material: rutile type titanium dioxide powder (average particle size: 0.28 μm) (Ishihara Sangyo)
CR95)
Binder: Soft acrylic resin (Chriscoat P-1018GS “20% toluene solution”, manufactured by Dainippon Ink & Chemicals, Inc.)
3) Formation of phosphor layer The phosphor sheet prepared in 1) is overlapped with the surface of the reflective layer on the support so that the back surface (temporary support side) at the time of coating and formation is in contact with the surface, and this is used with a calendar machine. Thermal compression was performed at a total load of 2300 kg, an upper roll of 45 ° C., a lower roll of 45 ° C., and a feed rate of 0.3 m / min. As a result, the phosphor layer was completely fused to the reflective layer. The thickness of the phosphor layer after heat compression was 200 μm.

4) Formation of radiographic image detector After a double-sided adhesive tape (adhesive layer; thickness 25 μm, CS9621 manufactured by Nitto Denko Corporation) was applied to the surface of the phosphor layer, the surface of the solid detector was used using a laminator. The phosphor layer was bonded through a double-sided adhesive tape.

  Then, the reflectance of the support in the radiographic image detectors of [Example 1] and [Comparative Example 1] prepared as described above was evaluated, and the sensitivity was evaluated. The evaluation results are shown in Table 1 below.

  The measurement of the reflectance is a method of measuring the reflectance with respect to a standard white plate (210-0740) using a 150φ integrating sphere (150-0901) in a U-3210 self-recording spectrophotometer manufactured by Hitachi, Ltd. Used. The measurement wavelength for reflectance measurement was set to 545 nm in consideration of the wavelength of the emitted light of the phosphor constituting the phosphor layer.

  The sensitivity was evaluated by irradiating X-rays with a tube voltage of 50 kVp from the support side of the radiation image detector and obtaining the relative sensitivity from the average signal value of the image data detected by the solid state detector.

  As shown in Table 1 below, the radiation image detector of Example 1 has a reflectance of 98% with respect to light having a measurement wavelength of 545 nm, and it was found that sufficient reflectance can be obtained. In addition, almost the same results were obtained for the radiographic image detector of Comparative Example 1.

On the other hand, with respect to the sensitivity, sufficient sensitivity was obtained in Example 1, whereas in Comparative Example 1, the relative sensitivity was 90 as a result of X-ray absorption and attenuation by the inorganic substance (the relative sensitivity of the Example was set to 100). The sensitivity was clearly reduced.

  In the above example, a phosphor sheet was prepared, and the phosphor sheet adhered on a support was attached to a solid detector. However, as a phosphor of the phosphor layer, a columnar crystal was used as the phosphor. When at least one of CsI: Na and CsI: Tl is used, a phosphor layer is formed by depositing CsI: Tl or the like after providing a layer such as parylene on the solid state detector. And you may make it affix a support body on the fluorescent substance layer.

  Moreover, in the radiographic imaging apparatus of the said embodiment, although radiation was irradiated from the support body side of a radiographic image detector, you may make it irradiate a radiation from the solid state detector side of a radiographic image detector. That is, the radiation image detector may be configured such that the solid detector 31, the phosphor layer 32, and the support 33 are arranged in this order from the radiation source 1 side. By irradiating radiation from the solid-state detector side as described above, the light converted by the phosphor layer is prevented from being absorbed by the phosphor layer itself, or light is scattered in the phosphor layer. Can be prevented.

  In the above-described embodiments and examples, the radiation image detector using the electric reading type solid state detector has been described. However, the radiation image detector of the present invention uses an optical reading type solid state detector. Also good. Specifically, as an optical reading type solid state detector, for example, the first electrode layer that transmits visible light converted into the wavelength conversion layer, and the irradiation of visible light transmitted through the first electrode layer are received. Acts as an insulator for the charge of one polarity of the charges generated in the photoconductive layer for recording, and as a conductor for the charge of the other polarity. A second layer comprising an acting charge transport layer, a reading photoconductive layer that generates charges when irradiated with reading light, and a transparent linear electrode that transmits the reading light and a light shielding linear electrode that blocks the reading light. What laminated | stacked an electrode layer in this order can be used. Then, the phosphor layer and the support described above may be provided on the first electrode layer of the radiation image detector so that the phosphor layer is disposed on the first electrode layer side.

Schematic configuration diagram of a radiographic imaging apparatus using an embodiment of a radiographic image detector of the present invention Sectional drawing which shows schematic structure of one Embodiment of the radiographic image detector of this invention The figure which shows the top view of the solid state detector The figure which shows the composition of the photodiode section and TFT switch in the solid state detector Sectional drawing which shows schematic structure of the radiographic image detector of a comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation source 2 Subject 3 Radiation image detector 4 Signal processing part 5 Reproducing part 31 Solid state detector 31b Scan line 31c Data line 31d Substrate 32 Phosphor layer 33 Support body 36 Photodiode part 37 TFT switch 40 Gate driver 50 Integrating amplifier 100 Radiation image detector 101 Solid state detector 102 Phosphor layer 103 Reflective layer 104 Support

Claims (6)

A support, a wavelength conversion layer that receives radiation and converts the radiation into light having a longer wavelength, and a detector that detects the light converted by the wavelength conversion layer and converts the light into an image signal representing a radiation image In the radiological image detector in which and are stacked in this order,
The support is formed from an organic substance containing a large number of bubbles, does not contain an inorganic substance, and reflects the light converted by the wavelength conversion layer toward the detector. Radiation image detector.   The radiation image detector according to claim 1, wherein the support has a reflectance of 85% or more with respect to a main emission wavelength of light converted by the wavelength conversion layer.   The radiation image detector according to claim 1, wherein the support is made of a resin.   The radiation image detector according to claim 3, wherein the support is formed of polyethylene terephthalate. The radiation image detector according to claim 1, wherein the wavelength conversion layer includes GOS (Gd ₂ O ₂ S: Tb) particles.   The radiation image detector according to any one of claims 1 to 4, wherein the wavelength conversion layer includes at least one of CsI: Na and CsI: Tl.

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