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JP4653442B2 - Radiation scintillator and radiation image detector - Google Patents

Radiation scintillator and radiation image detector Download PDF

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JP4653442B2
JP4653442B2 JP2004239057A JP2004239057A JP4653442B2 JP 4653442 B2 JP4653442 B2 JP 4653442B2 JP 2004239057 A JP2004239057 A JP 2004239057A JP 2004239057 A JP2004239057 A JP 2004239057A JP 4653442 B2 JP4653442 B2 JP 4653442B2
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scintillator
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scintillator layer
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篤也 吉田
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Canon Electron Tubes and Devices Co Ltd
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Description

本発明は、放射線を可視光に変換する放射線シンチレータ、およびこの放射線シンチレータを用いた放射線画像検出器に関する。   The present invention relates to a radiation scintillator that converts radiation into visible light, and a radiation image detector using the radiation scintillator.

従来、放射線画像検出器は、医療用や工業用非破壊検査などに用いられ、X線像やガンマ線像などの放射線像を電気的な画像信号として取り出す平面放射線画像検出器(以下、FPDという)や放射線像を可視像として取り出すX線イメージ管などがある(例えば、特許文献1、2参照。)。   Conventionally, a radiation image detector is used for medical and industrial nondestructive inspections, and is a planar radiation image detector (hereinafter referred to as FPD) that extracts a radiation image such as an X-ray image or a gamma ray image as an electrical image signal. And an X-ray image tube that extracts a radiation image as a visible image (see, for example, Patent Documents 1 and 2).

FPDには、例えばX線が入射するときに光導電膜で発生した電子−正孔対(e−hペア)を電場で収集して、電荷信号として読み出す直接方式と、X線イメージ管と同様に、放射線シンチレータでX線を可視光に変換し、フォトダイオードで読み出す間接方式との2つの方式がある。   For FPD, for example, a direct method in which electron-hole pairs (e-h pairs) generated in a photoconductive film when X-rays are incident is collected by an electric field and read out as a charge signal, and similar to an X-ray image tube In addition, there are two methods, an indirect method of converting X-rays into visible light with a radiation scintillator and reading out with a photodiode.

図3に示すように、間接方式のFPDは、X線が透過する基板11上に、反射膜12、蛍光体として沃化セシウム(CsI)の柱状結晶によって構成されるCsI層であるシンチレータ層13を少なくとも有する放射線シンチレータ14、および防湿膜15を順次積層させた入力手段としての放射線シンチレータパネル16と、ガラス基板17上にマトリクス状に配置されるスイッチング素子としての図示しない複数のTFT(Thin-Film Transistor)および各TFTに接続されるフォトダイオードを積層した出力手段としての検出器パネル18とを貼り合せて構成されている。防湿膜15と検出器パネル18との界面には必要により光学結合材を注入される。   As shown in FIG. 3, the indirect FPD has a scintillator layer 13 which is a CsI layer composed of a reflective film 12 and a columnar crystal of cesium iodide (CsI) as a phosphor on a substrate 11 through which X-rays are transmitted. A radiation scintillator 14 having at least a radiation scintillator 14 and a radiation scintillator panel 16 as an input means in which a moisture-proof film 15 is sequentially laminated; Transistor) and a detector panel 18 as output means in which a photodiode connected to each TFT is laminated. An optical coupling material is injected into the interface between the moisture-proof film 15 and the detector panel 18 as necessary.

そして、間接方式のFPDが医療用に用いられる場合、人体21を透過したX線像22が、基板11を透過した後、発光点23で可視光24に変換され、検出器パネル18のフォトダイオード上の領域に到達し、電気信号に変換される。フォトダイオードで得られた電荷はTFTのスイッチング動作で順次読み出され、増幅と画像処理を経て、画像信号として図示しないモニタに表示されたり記憶媒体に格納される。   When an indirect FPD is used for medical purposes, the X-ray image 22 transmitted through the human body 21 is transmitted through the substrate 11 and then converted into visible light 24 at the light emitting point 23, and the photodiode of the detector panel 18. It reaches the upper area and is converted into an electrical signal. The electric charge obtained by the photodiode is sequentially read out by the switching operation of the TFT, and after amplification and image processing, it is displayed as an image signal on a monitor (not shown) or stored in a storage medium.

このような間接方式のFPDでは、センサとして固体素子を使用していることからノイズの問題が最も大きな課題としてあり、このノイズを減らすにはシンチレータ層13でのX線吸収率を向上させること、および輝度を高めることが重要であり、また、画質を向上させるには、X線イメージ管と同様に画像分解能特性が重要である。   In such an indirect type FPD, since a solid element is used as a sensor, the problem of noise is the biggest issue. To reduce this noise, the X-ray absorption rate in the scintillator layer 13 is improved. It is important to increase the brightness, and in order to improve the image quality, the image resolution characteristic is important as in the case of the X-ray image tube.

そのため、放射線シンチレータ14において、高画質化を考慮すると、画像分解能、X線吸収率、輝度の3つのそれぞれの均一性が最も重要な指標である。画像分解能の指標には、画像空間方向に周期的に広がった入力信号量(入射線量)の濃淡が、出力信号としてどのように変調するかを数値化した矩形波の場合のCTFの値が最も一般的に使用されている。   For this reason, in the radiation scintillator 14, considering the high image quality, the three respective uniformity of image resolution, X-ray absorption rate, and luminance are the most important indexes. As an index of image resolution, the value of CTF in the case of a rectangular wave in which how the intensity of an input signal amount (incident dose) periodically spread in the image space direction is modulated as an output signal is expressed as the most. Commonly used.

ここで均一性を除いた3つの指標について考え、同一プロセスで膜厚のみを変更すると、互いにトレードオフの関係にある。すなわち、シンチレータ層13の膜厚もしくは単位面積あたりの質量をパラメータにとると、そのパラメータが増大するにつれ、X線吸収率および輝度が増大し、ノイズを低減した画質が得られやすくなるが、その反面、画像分解能特性は低下する。なぜならば、図3に示すように、発光点23からの可視光24が拡がりをもった経路を経てフォトダイオード上に到達することがあるから、膜厚が厚いほどその経路は長くなり、結果的に可視光24の拡がりも大きくなるからである。これは、X線イメージ管の場合でも光電陰極をフォトダイオードに見立てた場合と同様である。また、逆に、パラメータを減少させるにつれ、画像分解能特性は向上するが、その反面、X線吸収率および輝度が低下する。   Here, considering three indices excluding uniformity, if only the film thickness is changed in the same process, there is a trade-off relationship with each other. That is, if the film thickness or mass per unit area of the scintillator layer 13 is taken as a parameter, the X-ray absorption rate and luminance increase as the parameter increases, and it becomes easier to obtain an image quality with reduced noise. On the other hand, the image resolution characteristics deteriorate. This is because, as shown in FIG. 3, the visible light 24 from the light emitting point 23 may reach the photodiode via a spread path, so that the thicker the film thickness, the longer the path. This is because the spread of visible light 24 also increases. This is the same as the case where the photocathode is regarded as a photodiode even in the case of an X-ray image tube. Conversely, as the parameter is decreased, the image resolution characteristics are improved, but on the other hand, the X-ray absorption rate and the luminance are decreased.

また、間接方式のFPDでは、蛍光体材料として、X線イメージ管と同様に、沃化セシウム(CsI)が最も多く用いられている。このCsIが最も有用な材料とされる理由は3つある。まず、第1に、CsIが真空蒸着法で柱状結晶構造になりやすい性質を持っており、結果的に高い画像分解能が得られ、かつ成膜条件にもよるが、シンチレータ層13における柱状結晶の充填率(実際の質量を、理論密度と見かけの体積で割った値)が85%〜92%という比較的高い膜が得られることであり、しかも、真空蒸着法は大面積に対して均一な膜を安価に成膜可能である。第2に、CsIがK吸収端を33.2keV、36.0keVに持っているため、85〜92%の充填率で400〜600μm程度の製造上それほど困難を要しない膜厚で、通常医療用に用いる30〜90keVのX線エネルギー領域で高いX線吸収率特性を持つことである。第3に、CsIは現在知られている放射線シンチレータ14の中で約60000フォトン/MeVという硫酸化ガドリニウム(GOS)と並び、最も高い発光量を得られることである。このような3つの製造上、物性上の理由により、CsIは画像分解能、X線吸収能、輝度、コストを全て両立した放射線シンチレータ14を得るのに最も適した材料といえる。   In the indirect FPD, cesium iodide (CsI) is most frequently used as the phosphor material, as in the case of the X-ray image tube. There are three reasons why CsI is the most useful material. First, CsI has a property of easily forming a columnar crystal structure by a vacuum deposition method, and as a result, a high image resolution can be obtained, and depending on the film formation conditions, the columnar crystals in the scintillator layer 13 can be obtained. A relatively high film with a filling rate (a value obtained by dividing the actual mass by the theoretical density and the apparent volume) of 85% to 92% is obtained, and the vacuum deposition method is uniform over a large area. A film can be formed at low cost. Second, since CsI has a K absorption edge at 33.2 keV and 36.0 keV, it has a film thickness of 85 to 92% with a filling rate of about 400 to 600 μm and does not require much difficulty in manufacturing, and is usually used for medical purposes. It has a high X-ray absorptivity characteristic in the X-ray energy region of 30 to 90 keV used for the above. Third, CsI is the most widely known radiation scintillator 14 along with gadolinium sulfate (GOS) of about 60,000 photons / MeV, and can obtain the highest light emission. For these three reasons of manufacturing and physical properties, CsI can be said to be the most suitable material for obtaining a radiation scintillator 14 having all of image resolution, X-ray absorption capability, luminance and cost.

そして、CsIの柱状結晶を主体とした放射線シンチレータ14において、高画質化を図るうえで必要とする目標仕様値として以下の(1)〜(3)の3点が挙げられる。(1)画像分解能(CTF)値が2Lp/mmにおいて、40%以上であること。(2)加速電圧80kVp、厚み20mmのAlフィルタで、X線吸収率が80%以上であること。(3)加速電圧80kVp、厚み20mmのAlフィルタで、FPDに適用するときの輝度が、従来の膜厚200μm(約0.1g/cm2)のテルビウム付活硫酸化ガドリニウム(GOS)増感紙の1.7倍以上あること。(2)のX線吸収率は、CsIの単位面積あたりの質量のみで決まり、計算から求めることができ、図4に示すように、0.17g/cm2程度が必要であると判る。また、CsIの単位面積あたりの質量が0.17g/cm2以上なら、加速電圧80kVp、厚み20mmのAlフィルタによって作られるX線スペクトル内の30keV、50keV、70keVのいずれのエネルギーのX線も60%以上吸収し、色々な用途に対して高い画質が確保される。
特公平7−73031号公報(第3頁、第1図) 特許3126715号公報(第3−4頁、図2)
In the radiation scintillator 14 mainly composed of CsI columnar crystals, the following three points (1) to (3) are given as target specification values necessary for achieving high image quality. (1) The image resolution (CTF) value is 40% or more at 2 Lp / mm. (2) X-ray absorption is 80% or more with an Al filter having an acceleration voltage of 80 kVp and a thickness of 20 mm. (3) Terbium-activated gadolinium sulfate (GOS) intensifying screen having an acceleration voltage of 80 kVp and a thickness of 20 mm, and having a luminance of 200 μm (about 0.1 g / cm 2 ) when applied to an FPD. There must be at least 1.7 times. The X-ray absorptance of (2) is determined only by the mass per unit area of CsI and can be obtained from calculation. As shown in FIG. 4, it is understood that about 0.17 g / cm 2 is necessary. If the mass per unit area of CsI is 0.17 g / cm 2 or more, X-rays with any energy of 30 keV, 50 keV, and 70 keV in an X-ray spectrum produced by an Al filter having an acceleration voltage of 80 kVp and a thickness of 20 mm are 60. % Or more is absorbed, and high image quality is secured for various uses.
Japanese Examined Patent Publication No. 7-73031 (page 3, FIG. 1) Japanese Patent No. 3126715 (page 3-4, FIG. 2)

上述したように、従来の放射線シンチレータ14では、膜厚をパラメータにとったときのトレードオフの関係を考慮すると、画像分解能、X線吸収率、輝度の3つの指標について、(1)〜(3)の目標仕様値を同時に満たすのが困難で、十分な高画質化が得られない問題がある。   As described above, in the conventional radiation scintillator 14, considering the trade-off relationship when the film thickness is taken as a parameter, the three indices of image resolution, X-ray absorption rate, and luminance are (1) to (3 ) Target specification value is difficult to satisfy at the same time, and sufficient image quality cannot be obtained.

本発明は、このような点に鑑みなされたもので、X線透過率を損なうことなく、画像分解能を向上させ、高画質化できる放射線シンチレータ、およびこの放射線シンチレータを用いた放射線画像検出器を提供することを目的とする。   The present invention has been made in view of the above points, and provides a radiation scintillator capable of improving image resolution and improving image quality without impairing X-ray transmittance, and a radiation image detector using the radiation scintillator. The purpose is to do.

本発明は、少なくとも、真空蒸着法で形成された沃化セシウムからなる柱状結晶のシンチレータ層を有し、このシンチレータ層の膜厚が500μm〜610μmで、かつシンチレータ層における柱状結晶の充填率が70〜81.1%であるものである。 The present invention has at least a columnar crystal scintillator layer made of cesium iodide formed by a vacuum evaporation method. The film thickness of the scintillator layer is 500 μm to 610 μm, and the filling rate of columnar crystals in the scintillator layer is 70. ~ 81.1%.

そして、真空蒸着法で形成された沃化セシウムからなるシンチレータ層における柱状結晶の充填率を70〜81.1%に低下させることで画像分解能を向上させるとともに、シンチレータ層の膜厚を500μm〜610μmにすることで充填率の低下に伴うX線吸収率の低下を補う。したがって、真空蒸着法で形成された沃化セシウムからなるシンチレータ層の膜厚を500μm〜610μmで、かつシンチレータ層における柱状結晶の充填率を70〜81.1%にすることで、X線透過率を損なうことなく、画像分解能が向上し、高画質化が可能となる。 Then, the resolution of the columnar crystals in the scintillator layer made of cesium iodide formed by vacuum deposition is reduced to 70 to 81.1% to improve the image resolution, and the film thickness of the scintillator layer is 500 μm to 610 μm . This compensates for the decrease in the X-ray absorption rate accompanying the decrease in the filling rate. Therefore, the film thickness of the scintillator layer made of cesium iodide formed by the vacuum deposition method is 500 μm to 610 μm, and the filling factor of the columnar crystals in the scintillator layer is 70 to 81.1%, so that the X-ray transmittance is The image resolution can be improved and the image quality can be improved without impairing the image quality.

本発明によれば、真空蒸着法で形成された沃化セシウムからなるシンチレータ層における柱状結晶の充填率を70〜81.1%に低下させることで画像分解能を向上させるとともに、シンチレータ層の膜厚を500μm〜610μmにすることで充填率の低下に伴うX線吸収率の低下を補うことができ、したがって、真空蒸着法で形成された沃化セシウムからなるシンチレータ層の膜厚を500μm〜610μmで、かつシンチレータ層における柱状結晶の充填率を70〜81.1%にすることで、X線透過率を損なうことなく、画像分解能を向上させ、高画質化できる。 According to the present invention, the resolution of the columnar crystals in the scintillator layer made of cesium iodide formed by vacuum deposition is reduced to 70-81.1%, thereby improving the image resolution and the thickness of the scintillator layer. By reducing the filling rate to 500 μm to 610 μm, it is possible to compensate for the decrease in the X-ray absorption rate due to the decrease in the filling rate. Therefore, the thickness of the scintillator layer made of cesium iodide formed by vacuum deposition is 500 μm to 610 μm. In addition, by setting the filling rate of columnar crystals in the scintillator layer to 70 to 81.1%, image resolution can be improved and image quality can be improved without impairing X-ray transmittance.

以下、本発明の一実施の形態を図面を参照して説明する。   Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

なお、背景技術で説明した構成と同じ構成については同一符号を用いて説明する。   The same components as those described in the background art will be described using the same reference numerals.

図3に示すように、放射線画像検出器としての間接方式の平面放射線画像検出器(以下、FPDという)は、X線やガンマ線などの放射線が透過する基板11上に、反射膜12、少なくとも柱状結晶のシンチレータ層13を有する放射線シンチレータ14、および防湿膜15を順次積層させた入力手段としての放射線シンチレータパネル16と、ガラス基板17上にマトリクス状に配置されるスイッチング素子としての図示しない複数のTFTおよび各TFTに接続されるフォトダイオードを積層した出力手段としての検出器パネル18とを貼り合せて構成されている。検出器パネル18と防湿膜15との界面には必要により光学結合材を注入することもできる。   As shown in FIG. 3, an indirect planar radiation image detector (hereinafter referred to as FPD) as a radiation image detector has a reflective film 12, at least a columnar shape, on a substrate 11 that transmits radiation such as X-rays and gamma rays. A radiation scintillator 14 having a crystal scintillator layer 13, a radiation scintillator panel 16 as an input means in which a moisture-proof film 15 is sequentially laminated, and a plurality of TFTs (not shown) as switching elements arranged in a matrix on a glass substrate 17 And a detector panel 18 as an output means in which a photodiode connected to each TFT is laminated. If necessary, an optical coupling material can be injected into the interface between the detector panel 18 and the moisture-proof film 15.

基板11の材料には、ガラス、グラファイト、軽金属(ベリリウム、チタン、アルミニウム)もしくはそれらの合金、セラミックス(アルミナ、ジルコニア、ベリリア)、高分子材料(ポリカーバネート、ポリイミド)などが用いられる。   As the material of the substrate 11, glass, graphite, light metals (beryllium, titanium, aluminum) or alloys thereof, ceramics (alumina, zirconia, beryllia), polymer materials (polycarbonate, polyimide), and the like are used.

反射膜12の材料には、銀合金、銀、アルミニウム、金、銅、バラジウム、白金、クロム、ニッケル、酸化チタン、酸化マグネシウムなどが用いられる。   As the material of the reflective film 12, silver alloy, silver, aluminum, gold, copper, barium, platinum, chromium, nickel, titanium oxide, magnesium oxide, or the like is used.

シンチレータ層13は、基板11に対して交差方向に成長させた沃化セシウム(CsI)の柱状結晶によって構成されるCsI層を有している。図1は放射線シンチレータを表面から撮影した顕微鏡写真(SEM写真)であり、31は柱状結晶、32は隙間で、シンチレータ層13における柱状結晶31の充填率(実際の質量を、理論密度と見かけの体積で割った値)は70〜85%である。また、輝度の向上を目的として、柱状結晶31の先端部相互間の隙間を埋めるように沃化セシウム(CsI)の連続層状の蛍光体層を形成してもよい。   The scintillator layer 13 has a CsI layer composed of columnar crystals of cesium iodide (CsI) grown in a direction crossing the substrate 11. FIG. 1 is a micrograph (SEM photograph) taken from the surface of a radiation scintillator. 31 is a columnar crystal, 32 is a gap, and the filling factor of the columnar crystal 31 in the scintillator layer 13 (actual mass, theoretical density and apparent density) The value divided by the volume is 70-85%. Further, for the purpose of improving the luminance, a continuous layered phosphor layer of cesium iodide (CsI) may be formed so as to fill a gap between the tip portions of the columnar crystals 31.

防湿膜15の材料には、ポリラキシリレン、ポリイミド、ポリ尿素、ポリアミド、ポリウレタン、ポリアゾメチン、ニトロセルロース、酢酸セルロース、ポリカーボネート、ポリエステル、ポリエチレン、ポリ塩化ビニリデン、ナイロン、塩化ビニリデン−塩化ビニル共重合体、塩化ビニリデン−アクリロニトリル共重合体、ポリオレフイン、エポキシ系樹脂、ポリアクリレートといった高分子材料、もしくはそれらと酸化珪素、酸窒化珪素、酸化インジウム、窒化珪素、炭化珪素、アルミナといった薄膜で可視光に対して透明な無機膜との多層膜などが用いられる。 The material of the moisture-proof film 15, poly Pas Rakishiriren, polyimides, polyureas, polyamides, polyurethanes, polyazomethines, nitrocellulose, cellulose acetate, polycarbonate, polyester, polyethylene, polyvinylidene chloride, nylon, vinylidene chloride - vinyl chloride copolymer , High molecular weight materials such as vinylidene chloride-acrylonitrile copolymer, polyolefin, epoxy resin, polyacrylate, and thin films such as silicon oxide, silicon oxynitride, indium oxide, silicon nitride, silicon carbide, alumina against visible light A multilayer film with a transparent inorganic film is used.

そして、間接方式のFPDが医療用に用いられる場合、人体21を透過したX線像22が、基板11を透過した後、シンチレータ層13の発光点23で可視光24に変換され、検出器パネル18のフォトダイオード上の領域に到達し、電気信号に変換される。フォトダイオードで得られた電荷はTFTのスイッチング動作で順次読み出され、増幅と画像処理を経て、画像信号として図示しないモニタに表示されたり記憶媒体に格納される。   When the indirect FPD is used for medical purposes, the X-ray image 22 transmitted through the human body 21 is transmitted through the substrate 11 and then converted into visible light 24 at the light emitting point 23 of the scintillator layer 13, and the detector panel. It reaches the area on 18 photodiodes and is converted into an electrical signal. The electric charge obtained by the photodiode is sequentially read out by the switching operation of the TFT, and after amplification and image processing, it is displayed as an image signal on a monitor (not shown) or stored in a storage medium.

また、放射線シンチレータパネル16は、FPDに適用する場合、次の手順で製造される。反射膜12が形成された基板11を真空蒸着装置の真空槽内にセットし、基板11と対向する方向にCsIを収納した蒸発源を配置する。そして、真空槽内の加熱圧力調整手段で、真空槽内の基板11の温度を所望の柱状結晶および充填率が得られるような条件に調整する。次に、蒸発源を加熱してCsIを沸騰させ、CsIの蒸気を基板11上に送り込み、基板11に対して交差方向に成長させたCsIの柱状結晶31を成膜させる。CsIの柱状結晶31の膜厚もしくは単位面積辺りの質量が所定の値になったところで、蒸発源の加熱をやめ成膜を終了する。次に、基板11の温度が常温になったところで、基板11を真空蒸着装置の真空槽から取り出す。   The radiation scintillator panel 16 is manufactured by the following procedure when applied to an FPD. The substrate 11 on which the reflective film 12 is formed is set in a vacuum chamber of a vacuum vapor deposition apparatus, and an evaporation source containing CsI is disposed in a direction facing the substrate 11. Then, the temperature of the substrate 11 in the vacuum chamber is adjusted to a condition that a desired columnar crystal and a filling rate can be obtained by the heating pressure adjusting means in the vacuum chamber. Next, the evaporation source is heated to boil CsI, vapor of CsI is sent onto the substrate 11, and a columnar crystal 31 of CsI grown in a crossing direction with respect to the substrate 11 is formed. When the film thickness of the CsI columnar crystal 31 or the mass per unit area reaches a predetermined value, heating of the evaporation source is stopped and film formation is completed. Next, when the temperature of the substrate 11 reaches room temperature, the substrate 11 is taken out from the vacuum chamber of the vacuum evaporation apparatus.

シンチレータ層13が形成された基板11は、次に、防湿処理を経た後、上述した(1)〜(3)の目標仕様値が検査され、検出器パネル18との組立工程へと進む。   Next, the substrate 11 on which the scintillator layer 13 is formed is subjected to moisture-proof treatment, and then the target specification values (1) to (3) described above are inspected, and the process proceeds to an assembly process with the detector panel 18.

すなわち、(1)〜(3)の目標仕様値は、(1)画像分解能(CTF)値が2Lp/mmにおいて、40%以上であること、(2)加速電圧80kVp、厚み20mmのAlフィルタで、X線吸収率が80%以上であること、(3)加速電圧80kVp、厚み20mmのAlフィルタで、FPDに適用するときの輝度が、従来の膜厚200μm(約0.1g/cm2)のテルビウム付活硫酸化ガドリニウム(GOS)増感紙の1.7倍以上あること、である。 That is, the target specification values of (1) to (3) are (1) 40% or more when the image resolution (CTF) value is 2 Lp / mm, and (2) an Al filter with an acceleration voltage of 80 kVp and a thickness of 20 mm. The X-ray absorption rate is 80% or more, and (3) the brightness when applied to an FPD with an Al filter having an acceleration voltage of 80 kVp and a thickness of 20 mm has a conventional film thickness of 200 μm (about 0.1 g / cm 2 ). The terbium activated gadolinium sulfate (GOS) intensifying screen is 1.7 times or more.

次に、シンチレータ層13の膜厚とシンチレータ層13における柱状結晶31の充填率との関係について各サンプル1〜11の評価試験を実施し、その結果を図2に示す。この評価試験では、基板11に厚さ0.5mmのガラス板を使用し、この基板11上に銀合金の反射膜12およびこの反射膜12を保護する酸化マグネシウムの保護膜を積層させた後、タリウムドープ沃化セシウム(CsI/TI)をシンチレータ層13として真空蒸着し、防湿膜15としてポリラキシリレンをCVD法で厚さ5μm成膜した後、目標仕様値を満たしたかどうかの評価試験をした。 Next, the evaluation test of each sample 1-11 was implemented about the relationship between the film thickness of the scintillator layer 13, and the filling rate of the columnar crystal 31 in the scintillator layer 13, and the result is shown in FIG. In this evaluation test, a glass plate having a thickness of 0.5 mm was used for the substrate 11, and after a silver alloy reflective film 12 and a magnesium oxide protective film for protecting the reflective film 12 were laminated on the substrate 11, thallium-doped cesium iodide and (CsI / TI) was vacuum deposited as the scintillator layer 13, after the poly-Pas Rakishiriren a thickness of 5μm formed by the CVD method as a moisture-proof film 15, and whether the evaluation tests whether satisfies the target specification value .

サンプル1〜4では、充填率85〜92%を狙って、結果的に充填率87.7%、88.4%、88.1%、88.7%になり、いずれも充填率85%より高くなった。図5には、充填率が88%程度の顕微鏡写真(SEM写真)を示す。   In Samples 1 to 4, aiming at a filling rate of 85 to 92%, the resulting filling rates were 87.7%, 88.4%, 88.1%, and 88.7%, all from a filling rate of 85% It became high. FIG. 5 shows a micrograph (SEM photograph) having a filling rate of about 88%.

サンプル5〜11では、充填率70〜85%を狙って、結果的に充填率82.2%、80.9%、81.1%、73.2%、72.5%、73.4%、73.3%になり、いずれも充填率70〜85%の範囲に入った。   In Samples 5 to 11, aiming at a filling rate of 70 to 85%, the resulting filling rate was 82.2%, 80.9%, 81.1%, 73.2%, 72.5%, 73.4%. 73.3%, both of which were in the range of 70 to 85% filling rate.

図2に示す評価試験の結果から、充填率が85%より高いサンプル1〜4は、膜厚にかかわらず、画像分解能CTFとX線吸収率とのいずれかが(1)(2)の目標仕様値を満たさなかった。   From the results of the evaluation test shown in FIG. 2, the samples 1 to 4 having a filling rate higher than 85% are either (1) or (2), which is either the image resolution CTF or the X-ray absorption rate regardless of the film thickness The specification value was not met.

充填率70〜85%にあるサンプル5〜11のうち、膜厚が500μmより薄いサンプル5、6、8、9は、X線吸収率が(2)の目標仕様値を満たさなかった。   Among Samples 5 to 11 having a filling rate of 70 to 85%, Samples 5, 6, 8, and 9 having a film thickness of less than 500 μm did not satisfy the target specification value of X-ray absorption rate (2).

充填率70〜85%にあるサンプル5〜11のうち、膜厚が500μm以上のサンプル7、10、11は、(1)〜(3)の目標仕様値のすべて満たした。   Of Samples 5 to 11 having a filling rate of 70 to 85%, Samples 7, 10, and 11 having a film thickness of 500 μm or more satisfied all the target specification values (1) to (3).

このように、X線吸収率が低下することを犠牲にして、あえてシンチレータ層13における柱状結晶31の充填率を70〜85%に低下させることで、画像分解能を向上させることができ、また、シンチレータ層13の膜厚を500μm以上に厚くすることで、充填率の低下に伴うX線吸収率の低下を補うことができた。したがって、シンチレータ層13の膜厚を500μm以上で、かつシンチレータ層13における柱状結晶31の充填率を70〜85%にすることで、X線透過率を損なうことなく、画像分解能を向上させ、高画質化できた。   Thus, at the expense of a decrease in the X-ray absorption rate, the image resolution can be improved by reducing the filling rate of the columnar crystals 31 in the scintillator layer 13 to 70 to 85%. By increasing the film thickness of the scintillator layer 13 to 500 μm or more, it was possible to compensate for the decrease in the X-ray absorption rate accompanying the decrease in the filling rate. Therefore, by setting the film thickness of the scintillator layer 13 to 500 μm or more and the filling rate of the columnar crystals 31 in the scintillator layer 13 to 70 to 85%, the image resolution is improved without impairing the X-ray transmittance, and high The image quality was improved.

充填率が70%より小さい場合には、シンチレータ層13の膜厚を500μm以上に厚くしても、X線吸収率の低下を十分に補うことができず、また、充填率が85%より大きい場合には、従来のようにX線吸収率が増加するものの画像分解能が低下し、また、膜厚が500μmより小さい場合にはX線吸収率の低下を十分に補うことができない。   When the filling rate is smaller than 70%, even if the thickness of the scintillator layer 13 is increased to 500 μm or more, the decrease in the X-ray absorption rate cannot be sufficiently compensated, and the filling rate is larger than 85%. In this case, although the X-ray absorption rate increases as in the conventional case, the image resolution decreases, and when the film thickness is smaller than 500 μm, the decrease in the X-ray absorption rate cannot be sufficiently compensated.

そして、このような放射線シンチレータをFPDに適用することにより、画像分解能、X線吸収率、輝度の3つのそれぞれの均一性が向上し、高画質化できる。   By applying such a radiation scintillator to the FPD, the uniformity of each of the image resolution, the X-ray absorption rate, and the luminance is improved, and the image quality can be improved.

また、このような放射線シンチレータをX線イメージ管に適用する場合、シンチレータ層13に用いる蛍光体の添加剤がヨウ化ナトリウムであることから発光波長が異なり、輝度の目標仕様値は特に設定されないが、シンチレータ層13の膜厚を500μm以上で、かつシンチレータ層13における柱状結晶31の充填率を70〜85%にすることで、目標仕様値を満足できる。X線イメージ管の場合、X線像を電子像に変換する入力面、およびこの入力面で変換された電子像を可視像に変換する出力面などを真空外囲器内に配置した構造であり、入力面が入力手段16、出力面が出力手段18である。   Further, when such a radiation scintillator is applied to an X-ray image tube, since the phosphor additive used for the scintillator layer 13 is sodium iodide, the emission wavelength is different, and the target specification value of luminance is not particularly set. The target specification value can be satisfied by setting the thickness of the scintillator layer 13 to 500 μm or more and setting the filling rate of the columnar crystals 31 in the scintillator layer 13 to 70 to 85%. In the case of an X-ray image tube, an input surface that converts an X-ray image into an electronic image and an output surface that converts an electronic image converted on the input surface into a visible image are arranged in a vacuum envelope. Yes, the input surface is the input means 16, and the output surface is the output means 18.

したがって、CsIの柱状結晶31を有する放射線シンチレータは、FPDおよびX線イメージ管のいずれの放射線画像検出器に応用する場合でも、シンチレータ層13の膜厚を500μm以上で、かつシンチレータ層13における柱状結晶31の充填率を70〜85%にすることで、目標仕様値を満足できる。   Therefore, the radiation scintillator having the CsI columnar crystal 31 has a film thickness of the scintillator layer 13 of 500 μm or more and the columnar crystal in the scintillator layer 13 regardless of whether it is applied to any radiation image detector of an FPD or an X-ray image tube. By setting the filling rate of 31 to 70 to 85%, the target specification value can be satisfied.

なお、FPDに適用する放射線シンチレータを製造する場合、ガラス基板17上にTFTアレイとフォトダイオードが形成された検出器パネル18を真空蒸着装置にセットし、この検出器パネル18上にシンチレータ層13を形成してもよい。   When manufacturing a radiation scintillator to be applied to an FPD, a detector panel 18 having a TFT array and a photodiode formed on a glass substrate 17 is set in a vacuum deposition apparatus, and a scintillator layer 13 is formed on the detector panel 18. It may be formed.

また、反射膜12を保護する保護膜としては、酸化マグネシウムのほかに、酸化珪素、酸化チタン、弗化カルシウム、弗化マグネシウムもしくは、防湿膜15の材料を用いてもよい。 Further, as the protective film for protecting the reflective film 12, in addition to magnesium oxide, silicon oxide, titanium oxide, calcium fluoride, magnesium fluoride, or the material of the moisture-proof film 15 may be used.

本発明の一実施の形態を示す放射線シンチレータを表面から撮影した顕微鏡写真(SEM写真)である。It is the microscope picture (SEM photograph) which image | photographed the radiation scintillator which shows one embodiment of this invention from the surface. 放射線シンチレータの膜厚とシンチレータ層における柱状結晶の充填率との関係について各サンプルの評価試験の結果を示す説明図である。It is explanatory drawing which shows the result of the evaluation test of each sample about the relationship between the film thickness of a radiation scintillator, and the filling rate of the columnar crystal in a scintillator layer. 放射線画像検出器の断面図である。It is sectional drawing of a radiographic image detector. CsIの単位面積辺りの質量に対するX線吸収率を示すグラフである。It is a graph which shows the X-ray absorption rate with respect to the mass per unit area of CsI. 従来の放射線シンチレータを表面から撮影した顕微鏡写真(SEM写真)である。It is the microscope picture (SEM photograph) which image | photographed the conventional radiation scintillator from the surface.

符号の説明Explanation of symbols

13 シンチレータ層
14 放射線シンチレータ
16 入力手段としての放射線シンチレータパネル
18 出力手段としての検出器パネル
31 柱状結晶
13 Scintillator layer
14 Radiation scintillator
16 Radiation scintillator panel as input means
18 Detector panel as output means
31 columnar crystals

Claims (2)

少なくとも、真空蒸着法で形成された沃化セシウムからなる柱状結晶のシンチレータ層を有し、
このシンチレータ層の膜厚が500μm〜610μmで、かつシンチレータ層における柱状結晶の充填率が70〜81.1%である
ことを特徴とする放射線シンチレータ。
At least a scintillator layer of columnar crystals made of cesium iodide formed by vacuum deposition;
A radiation scintillator, wherein the scintillator layer has a thickness of 500 μm to 610 μm, and the columnar crystal filling ratio in the scintillator layer is 70 to 81.1%.
放射線を可視光に変換する請求項1記載の放射線シンチレータを有する入力手段と、
前記放射線シンチレータで変換される可視光に基づいて画像情報を出力する出力手段と
を具備していることを特徴とする放射線画像検出器。
Input means having a radiation scintillator according to claim 1 for converting radiation into visible light;
An output means for outputting image information based on visible light converted by the radiation scintillator.
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