JP5136661B2 - Radiation image detector - Google Patents

Description

  The present invention relates to a radiation image detector.

  Conventionally, radiation images represented by X-ray images have been widely used for diagnosis of medical conditions in the medical field. In recent years, digital radiation image detectors represented by flat panel radiation detectors (FPD (Flat Panel Detector)) and the like have also appeared, and a radiation image can be acquired as digital information and freely processed. It is possible to transmit image information instantly.

  In the FPD, a scintillator panel that receives radiation transmitted through a subject and instantaneously emits fluorescence with an intensity corresponding to the dose is used. The light emission efficiency of the scintillator panel increases as the thickness of the phosphor layer increases. However, if the phosphor layer is too thick, scattered light is generated in the phosphor layer and the contrast is lowered. In order to improve diagnosis, it is necessary to obtain an image with high contrast.

  When a phosphor having a columnar crystal structure such as cesium iodide (CsI) is used, there is little generation of scattered light in the crystal due to the light guide effect, and the phosphor layer is thickened to maintain the contrast. It is possible to increase luminous efficiency. Furthermore, it is possible to improve luminous efficiency by adding thallium (Tl) or the like as an activator to cesium iodide (CsI) (see, for example, Patent Document 1).

  Usually, a protective cover for protecting the scintillator panel from an external impact or the like is provided on the radiation incident side of the scintillator panel. A light receiving element that receives light emitted from the scintillator panel is provided on the side opposite to the protective cover via the scintillator panel. In addition, a cushion member is provided between the protective cover and the scintillator panel so that the scintillator panel is appropriately pressed against the planar light receiving element, and the scintillator panel is compressed by the pressure of the cushion member compressed when the protective cover is attached. The light receiving element is brought into pressure contact with an appropriate pressure.

  When assembling the radiation image detector, the scintillator panel and the cushion member are sequentially placed on the light receiving element arranged in the casing, and then the protective cover is fixed to the casing with screws or the like.

  At this time, if the pressure of the cushion member is too strong, the tip of the phosphor crystal having a columnar crystal structure is crushed and the contrast of the radiation image is lowered. On the contrary, even when the pressure of the cushion member is weak, when the FPD is directed downward, the scintillator panel and the planar light receiving element are incompletely adhered, and the contrast of the radiation image is lowered. In addition, defects between the planar light receiving element and the phosphor layer easily occur due to friction between the scintillator panel and the planar light receiving element due to movement or vibration of the FPD device.

  In general, a phosphor layer needs to have a thickness of 400 μm or more in order to obtain a radiographic image with high graininess. However, the increase in the mass of the scintillator panel and the increase in the size of the scintillator panel due to the increase in film thickness make this problem more serious To.

  In order to solve such a problem, a method of fixing the scintillator panel and the planar light receiving element with an adhesive (for example, refer to Patent Document 2), a method of bonding with a matching oil (for example, refer to Patent Document 3), etc. is proposed. However, there are problems such as the occurrence of unevenness in the adhesive and matching oil and an increase in the number of work steps.

JP 2002-116258 A JP 2006-189377 A JP 2000-9845 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a radiographic image detector that is easy to assemble a radiographic image detector and excellent in graininess and contrast.

  The above object of the present invention can be achieved by the following configuration.

1. A scintillator panel having a radiation transparent substrate and a CsI phosphor layer formed in a columnar shape by a vapor phase method;
A protective cover disposed on the radiation incident side of the scintillator panel on the side opposite to the phosphor layer through the radiation transmissive substrate;
A planar light-receiving element that is provided on the opposite side of the protective cover via the scintillator panel and in which a plurality of light-receiving pixels are arranged in a two-dimensional manner to photoelectrically convert light from the scintillator panel;
A radiation image detector comprising:
The radiation transmissive substrate has a thickness of 50 to 500 μm and has a flexibility selected from a polyimide film, a cellulose acetate film, a polyester film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyamide film, a triacetate film, and a polycarbonate film. The mass W (g) of the scintillator panel satisfies the relationship of the following formula (1) with respect to the area S (cm ² ) of the radiation transmissive substrate,
Furthermore, the scintillator panel is pressed against the planar light receiving element at a pressure of 1 kPa or more and 20 kPa or less by a cushion member or a cushioning mechanism using air pressure arranged between the scintillator panel side surface of the protective cover and the scintillator panel. A radiation image detector.
Equation (1) W (g) < 0.31 (g / cm 2) × S (cm 2)

2. 2. The radiation image detector according to 1 above, wherein the phosphor layer has a thickness of 400 to 1000 μm.

3. 3. The radiation image detector according to 1 or 2 above , wherein the cushion member is made of a silicon-based or urethane-based foam material.

4). 4. The radiological image detector according to any one of 1 to 3 , wherein the protective cover is made of a material containing aluminum or carbon.

  According to the present invention, the mass of the scintillator panel and the pressure by the cushion member are optimized, and high sharpness can be obtained regardless of the direction of the radiation incident surface of the FPD. In addition, since no adhesive or oil is required to bond the scintillator panel and the planar light receiving element, when the radiation image detector is assembled, only the scintillator panel and the cushion member are placed on the light receiving element and a protective cover is attached. Because it is good, it can be assembled easily with high accuracy.

It is a block diagram of a radiographic image detector. It is a block diagram at the time of using a film as a protective layer. It is a figure which shows schematic structure of a vapor deposition apparatus.

  Hereinafter, although this embodiment is described with reference to an accompanying drawing, it is an example and is not limited to this embodiment.

  FIG. 1 is a configuration diagram of a radiation image detector 1 according to the present embodiment. The radiation image detector 1 is provided in a housing 11 so as to be in pressure contact with the scintillator panel 12 that receives radiation transmitted through a subject and instantaneously emits fluorescence at an intensity corresponding to the dose. A planar light receiving element 13 in which a plurality of light receiving pixels that photoelectrically convert light from the panel 12 are two-dimensionally arranged and a protective cover 14 that protects the scintillator panel 12 are provided.

  The scintillator panel 12 is configured to be covered with a protective film 124 together with the substrate 122 on which the phosphor layer 121 is formed. A cushion layer 15 as a cushion member is disposed on the side of the scintillator panel opposite to the phosphor layer, and the scintillator panel and the planar light receiving element are in pressure contact with each other.

  The substrate 122 is made of a material that transmits radiation. The substrate 122 is provided with a metal reflection layer containing at least one substance selected from the group consisting of Al, Ag, Cr, Cu, Ni, Mg, Pt, and Au, and a phosphor and a substrate with a film. It is preferable that an undercoat layer is formed. The substrate 122 is a resin film having flexibility so that the scintillator panel 12 can be brought into uniform contact with the mass and the surface of the light receiving element 13. The resin film having flexibility is any one selected from polyimide film, cellulose acetate film, polyester film, polyethylene terephthalate film, polyethylene naphthalate film, polyamide film, triacetate film, and polycarbonate film. As thickness, it is 50-500 micrometers.

  The phosphor layer 121 is composed of a phosphor layer having a columnar crystal structure having a light guide effect and high luminous efficiency. For example, a phosphor layer having a columnar crystal structure can be formed on the substrate 122 by vacuum-depositing cesium iodide (CsI) to which thallium (Tl) is added as an activator as a phosphor material. In addition to cesium iodide (CsI), cesium bromide (CsBr) or the like can be used. As the activator, europium, indium, lithium, potassium, rubidium, sodium, copper, cerium, zinc, titanium, gadolinium, terbium and the like can be used in addition to thallium (Tl).

  The cushion layer 15 is for bringing the scintillator panel 12 into pressure contact with the light receiving element 13 with an appropriate pressure. Any material can be used as long as it absorbs less X-rays and has a buffering effect. Examples thereof include commercially available silicon-based and urethane-based foam materials, latex sponges, polyethylene sponges, rubber-based sponges, and air bags using air pressure. In particular, a silicon-based or urethane-based foam material is preferable because the scintillator panel 12 can be pressed against the light receiving element 13 with an appropriate pressure.

  The protective film 124 is for moisture-proofing the phosphor layer 121 and suppressing deterioration of the phosphor layer 121, and is made of a resin or film having a low moisture permeability. For example, the polyparaxylylene film 124 is formed in the gap and the surface of the scintillator 12 by the CVD method (vapor phase chemical growth method). A polyethylene terephthalate film (PET) can be used as the film. Besides PET, a polyester film, a polymethacrylate film, a nitrocellulose film, a cellulose acetate film, a polypropylene film, a polyethylene naphthalate film, or the like can be used.

  FIG. 2 is a configuration diagram when a film is used as a protective layer. On the surfaces of the first protective film 1241 and the second protective film 1242 facing each other, a fusion layer for fusing and sealing each other is formed. For example, a casting polypropylene (CPP) layer is formed. By sandwiching the substrate 122 and the phosphor layer 121 between the first protective film 1241 and the second protective film 1242 and fusing the end portions where the first protective film 124 and the second protective film 125 are contacted in a reduced-pressure atmosphere. It can be sealed.

  The light receiving element 13 is composed of a plurality of light receiving pixels arranged two-dimensionally. For example, it can be constituted by a photodiode + a thin film transistor (TFT). The signal charge photoelectrically converted by the photodiode is read out using the TFT. In addition, a CMOS, a CCD, or the like can be used as the light receiving element 13.

  The protective cover 14 protects the scintillator panel 12 from external impacts and the like, and also serves to compress the cushion layer 15 and press the scintillator panel 12 to the light receiving element 13 with an appropriate pressure. The protective cover 14 is preferably made of a material that has high radiation transparency, low radiation scattering, and can physically withstand a certain degree of impact. Specifically, a carbon plate, an aluminum plate, fiber reinforced plastic (FRP), etc. can be mentioned. As the protective cover 14 of the present invention, a carbon plate or an aluminum plate is particularly preferable.

  Although the cushion layer 15 can be omitted, if the cushion layer 15 does not exist, the scintillator panel 12 cannot be pressed against the light receiving element 13 with an appropriate pressure. For this reason, the adhesion between the scintillator panel 12 and the light receiving element 13 is deteriorated, and the sharpness is lowered.

  As the phosphor layer 121 according to the present invention, a crystal is formed on the basis of Cs, and CsI is preferable. It is preferable to add an activator to the phosphor layer 121. This activator should just contain 0.01 mol% or more with respect to CsI used as a base. Here, if the additive is less than 0.01 mol% with respect to CsI, the target light emission luminance cannot be obtained without much difference from the light emission luminance obtained by using CsI alone. In addition, the content rate of the activator prescribed | regulated as mentioned above has pointed out the ratio in the material at the time of forming the fluorescent substance layer 121. FIG. In the present invention, since the phosphor layer 121 is formed by vapor deposition, the material for forming the phosphor layer 121 refers to a raw material that becomes a supply source (vapor deposition source) for vapor deposition.

  Hereinafter, a method for forming the phosphor layer 121 on the substrate 122 will be described.

  The phosphor layer 121 is formed by a vapor deposition method.

In the vapor deposition method, the substrate 122 is set in a known vapor deposition apparatus, and the raw material of the phosphor layer containing the activator specified as described above in the vapor deposition source and gold or gold compound are filled in different boats. At the same time as exhausting the inside of the apparatus, an inert gas such as nitrogen was introduced from the inlet to create a vacuum of about 1.33 Pa to 1.33 × 10 ⁻³ Pa, and then the phosphor containing the activator was filled. The boat is heated and evaporated by a resistance heating method or the like to deposit the phosphor on the surface of the substrate 122 to a desired thickness, and the phosphor layer 121 is formed on the substrate 122. Note that the phosphor layer 121 can be formed by performing this vapor deposition step in a plurality of times.

  For example, a plurality of vapor deposition sources having the same configuration are prepared, and after vapor deposition by one vapor deposition source is completed, vapor deposition by the next vapor deposition source is started, and this is repeated until the phosphor layer 121 having a desired thickness is obtained. Note that, during vapor deposition, the substrate 122 may be cooled or heated as necessary. Further, after the vapor deposition, the phosphor layer 121 may be heat-treated together with the substrate 122.

  Here, with reference to FIG. 3, the vapor deposition apparatus 61 is demonstrated as an example of the vapor deposition apparatus used when performing a vapor deposition method.

  The vapor deposition apparatus 61 includes a vacuum pump 66 and a vacuum container 62 that is evacuated by the operation of the vacuum pump 66. Inside the vacuum vessel 62, a resistance heating crucible 63 is provided as a vapor deposition source, and a substrate 122 configured to be rotatable by a rotation mechanism 65 is installed above the resistance heating crucible 63 via a substrate holder 64. Has been. A slit for adjusting the vapor flow of the phosphor evaporating from the resistance heating crucible 63 is provided between the resistance heating crucible 63 and the substrate 122 as necessary. The substrate 122 is installed on the substrate holder 64 when the vapor deposition apparatus 61 is used.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, the embodiment of this invention is not limited to this.

Example 1
(Production of radiation transmissive substrate)
Prepare the following radiation transmissive substrates (hereinafter also simply referred to as substrates) 1 to 4 (also described in the substrate type column in Tables 1 and 2). A layer was formed. Each of the substrate sizes was 13 cm × 13 cm, 25 cm × 20 cm, and 40 cm × 30 cm.

1: 125 μm thick polyimide film 2: 500 μm thick amorphous carbon plate 3: 500 μm thick aluminum plate 4: 1000 μm thick amorphous carbon plate (Preparation of undercoat layer)
Byron 20SS (Toyobo Co., Ltd .: polymer polyester resin) 300 parts by weight Methyl ethyl ketone (MEK) 200 parts by weight Toluene 300 parts by weight Cyclohexanone 150 parts by weight The above formulation is mixed and dispersed in a bead mill for 15 hours, for undercoating coating. A coating solution was obtained. This coating solution was applied on the vapor deposition surface side of the substrates 1 to 4 with a spin coater so that the dry film thickness was 1.0 μm, and then dried at 100 ° C. for 8 hours to prepare an undercoat layer.

(Formation of scintillator layer)
A scintillator phosphor (CsI: 0.03 Tlmol%) was vapor-deposited on the undercoat layer side of the substrate using the vapor deposition apparatus shown in FIG. 3 to form a phosphor layer on the entire surface of the substrate.

  That is, first, the resistance heating crucible was filled with the phosphor raw material as an evaporation material, and the substrate was placed on a rotating support holder, and the distance between the substrate and the evaporation source was adjusted to 400 mm.

  Subsequently, the inside of the vapor deposition apparatus was once evacuated, Ar gas was introduced and the degree of vacuum was adjusted to 0.5 Pa, and then the substrate temperature was maintained at 200 ° C. while rotating the substrate at a speed of 10 rpm. Next, the resistance heating crucible was heated to deposit the phosphor, and when the thickness of the phosphor layer reached the values shown in Tables 1 and 2, the deposition was terminated and a phosphor layer was formed on the substrate.

(Formation of protective layer)
The substrate on which the phosphor layer is formed is placed in the vapor deposition chamber of the CVD apparatus and exposed to the vapor in which the polyparaxylylene raw material is sublimated, so that the entire surface of the substrate on which the phosphor layer is formed is 20 μm. A scintillator panel was obtained by coating with a thick polyparaxylylene film.

(Evaluation)
The obtained scintillator panel is set in PaxScan (Varian FPD: 1313, 2520, 4030), the sharpness when the radiation incident surface of the FPD is upward, and the center of the scintillator panel when the radiation incidence surface is downward. The sharpness of the part was evaluated by the method shown below. The results are shown in Tables 1 and 2.

  The pressure of the flat light-receiving element surface and the scintillator panel is pressed by placing a urethane foam sheet on the radiation incident side (the side without the phosphor) of the scintillator panel and the carbon plate of the radiation incident window. It was adjusted by changing.

<Evaluation method of sharpness>
X-rays with a tube voltage of 80 kVp were irradiated to the radiation incident surface side of the FPD through a lead MTF chart, and image data was detected and recorded on a hard disk. Thereafter, the recording on the hard disk was analyzed by a computer, and the modulation transfer function MTF (MTF value at a spatial frequency of 1 cycle / mm) of the X-ray image recorded on the hard disk was used as an index of sharpness. In the table, the higher the MTF value, the better the sharpness. MTF is an abbreviation for Modulation Transfer Function.

  The evaluation results are shown in Table 1.

  As is clear from the results shown in Tables 1 and 2, it can be seen that the examples according to the present invention are superior in sharpness as compared with the comparative examples.

DESCRIPTION OF SYMBOLS 1 Radiation image detector 11 Case 12 Scintillator panel 13 Planar light receiving element 14 Protective cover 15 Cushion layer 121 Phosphor layer 122 Substrate 124 Protective film 1241 First protective film 1242 Second protective film 61 Vapor deposition device 62 Vacuum container 63 Boat (covered Filling member)
64 Holder 65 Rotating mechanism 66 Vacuum pump

Claims (4)

A scintillator panel having a radiation transparent substrate and a CsI phosphor layer formed in a columnar shape by a vapor phase method;
A protective cover disposed on the radiation incident side of the scintillator panel on the side opposite to the phosphor layer through the radiation transmissive substrate;
A planar light-receiving element that is provided on the opposite side of the protective cover via the scintillator panel and in which a plurality of light-receiving pixels are arranged in a two-dimensional manner to photoelectrically convert light from the scintillator panel;
A radiation image detector comprising:
The radiation transmissive substrate has a thickness of 50 to 500 μm and has a flexibility selected from a polyimide film, a cellulose acetate film, a polyester film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyamide film, a triacetate film, and a polycarbonate film. The mass W (g) of the scintillator panel satisfies the relationship of the following formula (1) with respect to the area S (cm ² ) of the radiation transmissive substrate,
Furthermore, the scintillator panel is pressed against the planar light receiving element at a pressure of 1 kPa or more and 20 kPa or less by a cushion member or a cushioning mechanism using air pressure arranged between the scintillator panel side surface of the protective cover and the scintillator panel. A radiation image detector.
Equation (1) W (g) < 0.31 (g / cm 2) × S (cm 2)   The radiation image detector according to claim 1, wherein the phosphor layer has a thickness of 400 to 1000 μm.   The radiation image detector according to claim 1, wherein the cushion member is made of a silicon-based or urethane-based foam material.   The radiation image detector according to any one of claims 1 to 3, wherein the protective cover is made of a material containing aluminum or carbon.

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