JP4274839B2 - X-ray detector scintillator, manufacturing method thereof, X-ray detector and X-ray CT apparatus using the same - Google Patents

Description

【数２】

【００４０】
一方、気泡の移動速度u₀は、式（３）となる。故に、有機樹脂６中に分散する無機化合物粉末粒子７と気泡８の移動速度比は、式（４）で表される。
【００４１】
【数３】

【数４】

【００４２】
例えば、ρ₀=0、ρ_s=4.2g/cm³、ρ=1.4g/cm³、d₀=10μm、d_s=1μmとすると、u₀/u_s=−50となる。即ち、気泡８は無機化合物粉末７と反対方向に、50倍の速度で遠心力とは逆方向に移動する。このことから、遠心注型によって狭くて深い切り込み溝に、気泡がなくなるような状態で効率よく注入できることがわかる。
【００４３】
上述した遠心注型においては、前述の気泡の除去と同時に、無機化合物粉末７の有機樹脂６に対する相対変位が生じる（図４）。その結果、図５に示すように、反射層は注入方向（溝の深さ方向）に無機化合物含有量が段階的に異なる３つの領域Ａ、Ｃ、Ｂに分かれる。上側の領域Ａは無機化合物の含有量が少なく、下側の領域Ｂは無機化合物の含有量が多い。これら領域は、後続するスライス工程で切断されシンチレータとしては利用しない領域であり、できるだけ狭いことが望ましい。これら領域Ａ、Ｂを狭くするためには、式（４）において粒子の密度ρ_sと有機樹脂の密度ρとの差をできるだけ小さくするか、粒子の粒子径ができるだけ小さくする必要がある。具体的には、無機化合物粉末の平均粒径を３μｍ以下とすることにより、領域Ａ、Ｂを全体の厚みの約5％以下に抑え、シンチレータとして利用できる領域Ｃを広くすることができる。
【００４４】
一方、反射層として有効な領域Ｃは、無機化合物粉末の粒子径分布に起因して注入方向に無機化合物含有量の傾斜αを生じる。本発明者らの研究によれば、シンチレータの反射率の変化は、厚さ方向について4%/cm以内であれば許容することができ、反射率の変化4%/cmは無機化合物含有量の傾斜20wt%/cmに対応する。無機化合物粉末の粒子径分布の指標である標準偏差を2.0μm以下にすることにより、無機化合物含有量の傾斜20wt%/cm以下に抑えることができ、感度むらのない検出器を構成することができる。
【００４５】
従って、本発明のシンチレータの製造方法においては、シンチレータとして利用できる領域Ｃをできるだけ広くし且つその厚さ方向の反射率の変化を4%/cm以内に抑えるために、無機化合物粒子として平均粒子径3μｍ以下、標準偏差2.0μｍ以下のものを用いることが望ましい。
【００４６】
こうして反射層形成材料を切り込み溝20に注入した後、有機樹脂を硬化させて（ステップ206）、反射層13を形成する。しかる後に、溝の深さ方向と直交する方向（即ち、ｘ、ｙ平面に平行）に所望の厚さにシンチレータをスライスする（ステップ207）。この場合、図５に示す領域Ａ、Ｂを除去し、領域Ｃからシンチレータとなる部分をスライスする。最後に、必要に応じてスライス面を研磨し（ステップ208）、放射線検出器用シンチレータ100を得る。
【００４７】
尚、反射層は、可視光を遮蔽するためにモリブデン、タングステン、ステンレス等からなる金属遮蔽板やセパレータ板を挿入することができる。反射層に金属遮蔽板等を挿入する場合には、遠心分離注入する前に（ステップ203の前に）、切り込み溝に金属遮蔽板を挿入し、その後反射層形成材料を注入する。これにより例えばＸ線検出器のチャンネル方向に金属遮蔽板が入ったシンチレータを得ることができる。
【００４８】
本発明のシンチレータを放射線検出器として利用するためには、さらにシンチレータ100の周囲及び光検出器が配置される面の反対側に、反射層を形成する。この反射層は、上述した無機化合物粉末を含む有機樹脂を硬化させたものを通常用いるが、不都合がなければ異なる素材であってもよい。
【００４９】
上記製造方法によって製造されたシンチレータは、切り込み溝を形成する加工精度と同程度の寸法精度の反射層を有し、且つ反射層に気泡が含まれることがないので、シンチレータ素子毎の特性のばらつきがなく、検出精度の優れた放射線検出器を提供することができる。
【００５０】
次に本発明の第２の実施形態によるシンチレータ及びそれを用いた放射線検出器を説明する。本実施形態によるシンチレータ200の構成を図６に、それを用いた放射線検出器の構成を図７にそれぞれ示す。図６及び図７において、図１と同じ要素は同じ符号で示している。
【００５１】
本実施形態においても、シンチレータ要素12及び反射層17は、所定の大きさのシンチレータブロックに所定のピッチで所定幅の溝を形成し、この溝に反射層を構成する材料を充填することにより形成されている点は第１の実施形態と同様である。またシンチレータ素材としても第１の実施形態と同様に、例えば発光中心元素がCeで、Gd、Al、Ga、Oを主要元素とするガーネット構造の酸化物蛍光体を好適に用いることができる。
【００５２】
但し、本実施形態のシンチレータ及び検出器は、反射層17の構造に特徴を有し、反射層17を白色の無機化合物粉末を含有する樹脂（以下、白色樹脂という）からなる反射拡散層13とセパレータ板16とから構成している。このようなセパレータ板を挿入することにより、シンチレータ要素間の光の漏洩を防止し、チャンネル間のクロストークをなくすことができる。
【００５３】
セパレータ板16としては、図示するように白色拡散反射層14／金属膜15／白色拡散反射層14の３層構造のセパレータ板16を用いる。このような３層構造のセパレータ板を用いることにより、金属板のみを用いる場合に比べ、反射層の反射率を向上することができ、且つセパレータ板16を反射層17のほぼ中央に位置させることができ、シンチレータ要素に隣接する反射層13及び白色拡散反射層14の厚みをシンチレータ要素毎にほぼ均一にすることができる。
【００５４】
本実施形態のシンチレータ200において、白色拡散反射層13は、その十分厚い試料での拡散反射率Ｒ∞が、セパレータ板16（金属膜15/白色拡散反射層14）の拡散反射率Ｒｂよりも大きいことが好ましい。具体的には白色拡散反射層13の拡散反射率Ｒ∞は97％以上、セパレータ16の拡散反射率Ｒｂは85％以上であることが好ましい。これによりシンチレータ要素界面での拡散反射率を90％とすることができ、シンチレータの光出力を向上することができる。
【００５５】
上述したような拡散反射率を実現するために、白色拡散反射層13は、有機樹脂中に白色の無機化合物を分散させた白色樹脂からなり、無機化合物／（無機化合物＋有機樹脂）の重量比（％）で30〜80wt％であることが好ましい。但し、80wt％を越えると白色樹脂の粘度が極めて高くなり、遠心注入法で注入しても気泡を完全に除去することが困難になるので、重量比は80wt％以下であることが好ましい。無機化合物は、酸化チタン、アルミナ、硫酸バリウム等を使用することができるが、特に酸化チタン（TiO₂）が好適であり、また無機化合物粉末は粒子径が小さく且つ粒子径分布が狭いものが好ましい。有機樹脂としては、エポキシ樹脂、ポリエステル樹脂、アクリル樹脂、フェノール樹脂などの無色透明樹脂のほか、500〜600nm付近の可視光に強い吸収のない白色の樹脂を用いることができる。
【００５６】
また白色反射拡散層14/金属膜15/白色反射拡散層14からなる３層構造のセパレータ板16は、例えば、金属膜の両面に白色顔料を樹脂に分散してなる白色塗料を塗工することにより製造することができる。この場合、金属膜15の材質としては、モリブデン、タングステン、鉛、アルミニウム、ステンレス及びリン青銅などの銅合金等を用いることができる。金属膜の厚さは、実質的に可視光を遮光できる厚さであればよいが、塗工層を形成する作業性等を考慮し、厚さ10〜50μｍの範囲とする。白色拡散反射層14を構成する材料としては、白色拡散反射層13を構成する無機化合物粉末及び有機樹脂を用いることができるが、無機化合物粉末として特に粒子径0.2〜2μｍ程度の酸化チタンが好適である。有機樹脂としては、エポキシ樹脂、ポリエステル樹脂、アクリル樹脂、フェノール樹脂などの無色透明樹脂のほか、500〜600nm付近の可視光に強い吸収のない白色の樹脂を用いることができる。このような無機化合物を塗工することによって白色拡散反射層14を形成する場合、スクリーン印刷法、ドクターブレード法、刷毛塗り、スプレー塗りなど公知の塗装法を採用することができる。白色拡散層14の厚さは、セパレータ板の厚さにより異なるが、例えば10〜60μｍ、好ましくは20〜50μｍとする。
【００５７】
３層構造のセパレータ板は、上述したもののほか、白色ポリマーフィルムに片面にアルミニウム等の金属膜を蒸着等により形成し、その蒸着面に白色ポリマーフィルムを接着することによって製造してもよい。金属蒸着膜の厚さは可視光の遮光が可能な厚さとし、具体的には0.05〜2μｍ程度とする。白色ポリマーフィルムとしては、例えば、白色ポリエステルフィルム、白色ポリエチレンフィルム、白色ポリ塩化ビニルフィルム等を用いることができる。
【００５８】
セパレータ板の厚さは、反射層として形成された溝幅に依存し、溝幅に対し30％以上、90％未満であることが望ましい。セパレータの厚さが30％に満たない場合には、溝幅に対して白色拡散反射層13の占める割合が大きくなるため、白色拡散反射層13の厚さに偏りが生じやすい。一方、セパレータの厚さが90％以上であると、溝にセパレータを挿入し難く、また白色拡散反射層13を形成する白色樹脂を注入する隙間が小さいため白色樹脂の注入が困難になる。これにより気泡の残留などにより拡散反射層13が不均質になり、各シンチレータ要素の特性がばらつきやすい。
【００５９】
次に第２の実施形態によるシンチレータの製造方法を説明する。図８に、製造方法の概要を示す。
【００６０】
まず直方体形状のシンチレータ素材10に、その厚さ方向（ｚ方向）と直交する二方向（図ではｘ方向及びｙ方向として示す）に切り込み溝20を形成する。切り込み溝の深さは、シンチレータ素材の高さよりも浅く、シンチレータ素材は切断されず数mm程度残した状態とする。溝の深さ、幅、ｘ方向及びｙ方向のピッチは、放射線検出器の用途によって異なるが、Ｘ線ＣＴ用のＸ線検出器の場合、例えば溝の深さ10〜30mm、幅0.1〜0.3mm、ピッチ1.0〜2.5mm程度である（ステップ801）。この溝入れも、第１の実施形態と同様に、ワイヤーを往復運動させながら加工するマルチワイヤーソーや、ダイヤモンドで被覆された内周切刃を有するインナーソー等の高精度の加工機械を用いて形成することができ、これにより±0.005mm以下の高精度の加工が可能になる。
【００６１】
このように溝入れした後のシンチレータ素材にアニール処理を行なう（ステップ802）。アニール処理は、シンチレータ素材が酸化物蛍光体である場合に、そのシンチレータ特性を付与するための処理であり、例えば温度1100〜1600℃の高温で数10分〜数時間、酸素中で熱処理する。
【００６２】
一方、シンチレータ素材に形成された溝に挿入するためのセパレータ板を作製する（ステップ803）。セパレータ板は、上述したように金属膜の両面に白色拡散反射層を形成した３層構造のものであり、金属膜の厚さが溝幅の30〜90％のものを用意する。次いでセパレータ板をシンチレータ素材に形成された各溝に配置する（ステップ804）。セパレータ板は、標準的には、ＣＴ画像の分解能に重要な、チャンネル間を分離する溝（例えばｙ方向溝）のみに配置する。この場合にはシンチレータ素材のｙ方向の長さとほぼ同じ長さのセパレータ板をｙ方向溝と同数用意して、ｙ方向溝に挟み込む。またスライス間を分離する溝（例えばｘ方向溝）にもセパレータ板を入れる場合には、例えばシンチレータ素材のｘ方向の長さとほぼ同じ長さのセパレータ板をｘ方向の溝と同数用意し（ｘグループとする）、それぞれにｙ方向の溝のピッチと同じピッチで厚さ方向に1/2の深さの切り込みを形成するとともに、ｙ方向の長さと同じ長さのセパレータ板をｙ方向の溝と同数用意し（ｙグループとする）、これらについてもｘ方向の溝のピッチと同じピッチで厚さ方向に1/2の深さの切り込みを形成し、ｘグループのセパレータ板とｙグループのセパレータ板が直交するように互いの切り込みを上下から噛合わせて、格子状の切り込み溝に対応した格子状のセパレータ板の組み立て体を作製しておくことが好ましい。
【００６３】
このようにセパレータ板を切り込み溝に配置した後、溝内に白色樹脂を注入する（ステップ805）。白色樹脂の注入は第１の実施形態と同様に遠心注入法で行なうことが好ましい。遠心注入法を採用することにより、白色樹脂の粘度が10万cPs程度の高粘度であっても、気泡を生じることなく確実に深い切り込み溝に注入することができる。
【００６４】
尚、白色樹脂の注入に先立って、切り込み溝の表面に上記白色樹脂を塗布しておいてもよい（ステップ803’）。予め溝表面に白色拡散反射層の一部をなす白色樹脂の塗布層を形成しておくことにより、シンチレータと白色拡散反射層との間に空気の層ができるのを確実に防止することができ、高い拡散反射率が達成できる。溝表面に白色樹脂を塗布する方法としては、例えば、遠心注入法により白色樹脂を溝内に充填した後、逆向きに遠心をかけて、溝内の白色樹脂を排出させる方法を採用することができる。
【００６５】
注入した白色樹脂を硬化させた後、切り込み溝に垂直にシンチレータ素材をスライスする（ステップ806、807）。スライスには、例えばマルチワイヤーソー、内周刃スライサー、外周刃スライサー等の機械加工を用いることができる。この場合にも、白色樹脂の注入法として遠心注入法を採用した場合には、白色無機化合物の含有量に傾斜を生じるので、図５に示す傾斜20wt%/cm以下の領域を切り出し、シンチレータとする。最後にスライス面をラップ研磨等することにより目的厚さのシンチレータを得る（ステップ808）。
【００６６】
このように製造したシンチレータを放射線検出器として利用するためには、図７に示したように、放射線の入射面を反射材18で覆うとともに、その反対面を、シンチレータ要素と同一ピッチで光検出器（フォトダイオード）11が形成された基板21に透明接着剤1９等により接着する。
このような放射線検出器の入射面に放射線が入射すると、入射放射線の線量に応じてシンチレータが発光し、その光をフォトダイオードが光電変換する。ここで各シンチレータ要素が、白色拡散反射層13／白色拡散反射層14／金属膜15／白色拡散反射層14／白色拡散反射層13からなる反射層17で分離されているので、要素間のクロストークがなく、シンチレータ要素で発生した光が反射層17で高反射率で反射されるため高い検出出力を得ることができる。
【００６７】
次に本発明のＸ線ＣＴ装置について説明する。図９は、Ｘ線ＣＴ装置の概略を示す図で、この装置はガントリ部60と画像再構成部70とを備え、ガントリ部60には、被検体が搬入される開口部61aを備えた回転円板61と、この回転円板61に搭載されたＸ線管62と、Ｘ線管62に取りつけられＸ線の放射方向を制御するコリメータ63と、Ｘ線管62に対向して回転円板61に搭載されたＸ線検出器64と、Ｘ線検出器64で検出されたＸ線を特定の信号に変換する検出器回路65と、回転円板61の回転及びＸ線束の幅を制御するスキャン制御回路66とを備えている。画像再構成部70は、検査条件などを入力するための入力部71と、画像を表示するモニター72とを備えている。ここでＸ線検出器64として、本発明のシンチレータを用いたＸ線検出器を用いる。
【００６８】
このような構成において、開口部に設置された寝台に被検者を寝かせた状態で、Ｘ線管62からＸ線が照射される。このＸ線はコリメータ63によって指向性を得て、Ｘ線検出器によって検出される。回転円板を被検者の周りを回転させることによって、Ｘ線の照射方向を変えながらＸ線を検出し、画像再構成部70で断層像を作成し、モニター72に表示される。
【００６９】
このＸ線ＣＴ装置は、本発明のシンチレータを用いることによって、Ｘ線感度、線質特性の各素子間、各チャンネル間でのばらつきが小さく、高精度でＸ線を検出できるため、身体頭頂部の断面を画像処理する場合にもアーチファクトを生じず、高画質、高分解能の画像を得ることができる。
【００７０】
【実施例】
以下、本発明の実施例を説明する。
【００７１】
[実施例１]
組成式が(Gd,Ce)_8(1-x)(Al,Ga)_8xO₁₂、X=0.620、Ce/Gd=0.008、Ga/(Ga+Al)=0.44である粉末を用いてホットプレス焼結を行い直径160mm、厚さ約15mmの焼結体を得た。この焼結体の相対密度は99.9％以上であった。この焼結体から、マルチブレードソーを用いてｘ方向、ｙ方向及びｚ方向のサイズが40mm×25mm×約15mmであるシンチレータ素材を8個切り出した。
【００７２】
切り出したブロックに、線径0.16mmのマルチワイヤーソーを用いて、ｘ−ｙ面に対して垂直な格子状の切り込み溝を形成した。まずｘ方向に2.25mmのピッチで溝入れを行い、次にシンチレータ素材を90°回転させ、ｙ方向に1.0mmのピッチで同様に溝入れを行った。溝の深さはいずれも約13mmとした。こうして形成した格子状の切り込み溝は、x方向、y方向ともに何れも溝幅が0.200±0.005mmの精度を有していた。
【００７３】
次に、このシンチレータ素材にシンチレータ特性を付与するための酸素中でアニール処理を行った。熱処理条件は、温度1300℃、4時間とした。上記組成の希土類酸化物蛍光体は、このようなアニール処理によって、Ｘ線感度、残光の減衰率等のＸ線CT用検出器に最適な特性を付与することができることが本発明者らにより確認されている（特願2000-389343号）。
【００７４】
一方、エポキシ樹脂に、粉末平均粒径0.3μmのTiO₂粉末を混合割合（TiO₂／（TiO₂＋エポキシ樹脂））が65wt%となるように添加し、これらを均一になるように混合した。このTiO₂含有エポキシ樹脂の粘度は98,000cPsであった。
【００７５】
アニール処理を行ったシンチレータ素材に有機樹脂との密着性を向上させるための表面処理を施した後、有機樹脂を注型するための注型枠の中に入れ、切り込み溝が形成された表面に、上述のTiO₂含有エポキシ樹脂を配置した。次いで、このシンチレータ素材を注型枠ごと遠心機のバケットにセットして、3500rpmにて5分間回転させ、TiO₂含有エポキシ樹脂を切り込み溝に注型した。注型後のシンチレータ素材を、60℃で3時間加熱し、エポキシ樹脂を硬化させて反射材を形成した。この反射材内部には気泡は見られず、表面から脱離除去されていた。
【００７６】
このように格子状の反射材を形成したシンチレータ素材に対し、ｘ−ｙ面に平行に、即ちz軸に垂直に厚さ2.0mmになるようにマルチワイヤーソーを用いてスライス加工して、シンチレータ要素の周囲4面が反射材で囲まれた5枚のシンチレータ板を作製した。これらシンチレータ板をラッピングマシーンを用いて、シンチレータ板の厚さが1.800±0.005mmとなるように研磨した。以上の工程によって、2.05mm×0.8mm×1.800mmのシンチレータ要素からなる5枚のシンチレータ板が得られた。
【００７７】
シンチレータ板の高さ方向（z軸方向）の反射材のTiO₂含有量を調べるため、EDS（Energy Dispersive Spectorscopy）法を用いてTi元素の含有量を計測した。この結果、1.800mmの高さ方向に対して、0.8wt%の違いが認められた。なお、この測定時の標準偏差は2σで0.31wt%であった。
【００７８】
[実施例２]
実施例１で製造したシンチレータにフォトダイオードを組み合わせて図１に示すような検出器を作り、Ｘ線源（120kV、0.5mA）から15cm離れたところに検出器を置きＸ線感度および残光特性を評価した。その結果、Ｘ線感度は典型的なX線CTシンチレータであるCdWO_４の約２倍とすることができ、300msでの残光の減衰率は約10^-5とすることができた。
【００７９】
[実施例３]
実施例１と同一組成の粉末を用いてホットプレス焼結を行い直径160mm、厚さ約15mmの焼結体を得た。この焼結体から、マルチブレードソーを用いてｘ方向、ｙ方向及びｚ方向のサイズが33mm×25mm×約15mmであるシンチレータ素材を11個切り出した。
切り出したブロックに、線径0.11mmのマルチワイヤーソーを用いて、ｘ−ｙ面に対して垂直な格子状の切り込み溝を形成した。まずｘ方向に1.0mmのピッチで深さ約13mmに溝入れを行い、次にシンチレータ素材を90°回転させ、ｙ方向にも1.0mmのピッチで深さ約13mmに溝入れを行った。こうして形成した格子状の切り込み溝は、x方向、y方向ともに何れも溝幅が0.130±0.005mmの精度を有していた。
【００８０】
次に、このシンチレータ素材にシンチレータ特性を付与するための酸素中でアニール処理を行った。熱処理条件は、温度1300℃、4時間とした。上記組成の希土類酸化物蛍光体は、このようなアニール処理によって、光出力は典型的なＸ線ＣＴ用シンチレータであるCdWO₄の約２倍と大きく、300msでの残光の減衰率は約1×10^-5といった特性が得られた。
【００８１】
一方、厚さ38μｍの白色ポリエステルフィルムの片面に、厚さ0.1μｍのAl膜を蒸着によって形成し、次いでこのAl蒸着面に厚さ38μｍの白色ポリエステルフィルムを接着して、白色ポリエステルフィルム/Al蒸着膜/白色ポリエステルフィルムの３層構造からなるセパレータ板を製造した。このセパレータ板の拡散反射率は、550nmの波長で86％であった。
【００８２】
またシンチレータの溝に注入する白色樹脂として、エポキシ樹脂とTiO₂粉末を重量比で1：1で均一に混合した。この白色樹脂の拡散反射率Ｒ∞は550nmの波長で98％であった。溝入れ後のシンチレータ素材の溝に上記のように製造したセパレータ板を挿入した後、注型枠の中にセットし、この白色樹脂をシンチレータ素材表面に配置した。その後、注型枠を遠心機にセットして、3000rpmで10分間遠心注入を行なった。
【００８３】
注入後、白色樹脂を室温で12時間硬化させた後、さらに60℃で３時間硬化させた。次いでシンチレータ素材の上面に平行に、即ちｚ軸と垂直にマルチワイヤソーを用いてスライス加工し、厚さ方向中央部から厚さ1.95mmのシンチレータ板を５枚切り出した。これらシンチレータ板の両面を、ラッピングマシーンで厚さ1.800±0.005mmとなるように研磨した。以上の加工により、0.87mm×0.87mm×1.800mmのシンチレータ要素からなる、24チャンネル32マルチスライス用シンチレータが５枚製造できた。
【００８４】
[比較例１]
実施例３と同様に切り込み溝を有するシンチレータ素材を作製した。この溝に実施例３と同様のセパレータ板を挿入し、溝とセパレータ板との間の隙間にエポキシ系透明接着剤を注入し硬化させた。その後、実施例３と同様にスライス加工、ラッピングを行い、シンチレータ板を製造した。
【００８５】
[実施例４、比較例２]
実施例３及び比較例１で製造したシンチレータに、それぞれフォトダイオードを組み合わせて図７に示すような検出器を作り、15cm離れたところからＸ線（120kV、0.5mA）を照射し、Ｘ線感度を測定した。その結果、Ｘ線感度は実施例２のシンチレータで製造した検出器（実施例４）は、比較例１のシンチレータで製造した検出器（比較例２）の1.1〜1.2倍のＸ線感度が得られた。また実施例４の検出器は各シンチレータ要素の感度分布のばらつきは5.0％以下であり、均一性にも優れていた。
【００８６】
[実施例５]
実施例３と全く同様に格子状の切り込み溝を有するシンチレータ素材を製造した。一方、セパレータ板として、厚さ10μｍのモリブデン板の両面に白色樹脂をスクリーン印刷によって塗布、硬化し、厚さ35±10μｍの白色拡散反射層を形成し、白色拡散反射層/Mo板/白色拡散反射層の３層構造のセパレータ板を製造した。ここで白色拡散反射層を形成する白色樹脂は、エポキシ樹脂に対し粒径0.25μｍのTiO₂粉末を重量比1：1で均一に混合したものを用いた。このセパレータ板の拡散反射率は、550nmの波長で92〜93％であった。
【００８７】
このセパレータ板をシンチレータ板の溝に挿入した後、実施例３と同じ白色樹脂（エポキシ樹脂：TiO₂粉末＝1：1、拡散反射率Ｒ∞＝98％）を用いて実施例と同様にシンチレータ板の溝に注入、硬化し、スライス加工及びラッピングを行い、0.87mm×0.87mm×1.800mmのシンチレータ板５枚を製造した。
このシンチレータを用いて、検出器を作り、15cm離れたところからＸ線（120kV、0.5mA）を照射し、Ｘ線感度を測定した。その結果、比較例２の検出器の1.15〜1.25倍のＸ線感度が得られた。また各シンチレータ要素の感度分布のばらつきは5.0％以下であり、均一性にも優れていた。
【００８８】
[実施例６]
実施例３と全く同様に格子状の切り込み溝を有するシンチレータ素材を製造した後、このシンチレータ素材の切り込み溝の表面に白色樹脂の塗布層を形成した。白色樹脂としては、実施例３で溝に注入した白色樹脂と同じものを用いた。塗布層の形成のために、まず白色樹脂を遠心注入法により溝に注入し溝内に充填した後、溝の解放部を遠心注入のときと逆向きにセットして、即ち溝の底部が遠心機の中心方向を向くようにして、遠心機を稼動し溝内の樹脂を除去した。遠心機は樹脂の注入時、樹脂の排出時ともに1000rpm、5分間行なった。これにより溝表面に厚さ約30μｍの白色樹脂の塗布層を形成した。この塗布層を室温で12時間硬化させることにより、15μｍ±10μｍの白色拡散反射層を形成した。
【００８９】
こうして表面に白色拡散反射層を形成したシンチレータ素材の溝に、実施例３と同様の白色ポリエステルフィルム/Al蒸着膜/白色ポリエステルフィルムの３層構造からなるセパレータ板を挿入し、さらに切り込み溝とセパレータ板との間に白色樹脂を遠心注入して白色拡散反射層を形成した。白色樹脂としては、エポキシ樹脂とTiO₂粉末を重量比1：1で混合したものを用い、遠心条件は3000rpm、10分間とした。注入後室温で12時間硬化させた後、さらに60℃で3時間硬化した。
次いで実施例３と同様にスライス加工及びラッピングを行い、0.87mm×0.87mm×1.800mmのシンチレータ板５枚を製造した。
【００９０】
このシンチレータを用いて、検出器を作り、15cm離れたところからＸ線（120kV、200mA）を照射し、Ｘ線感度を測定した。その結果、比較例２の検出器の1.1〜1.2倍のＸ線感度が得られた。また各シンチレータ要素の感度分布のばらつきは5.0％以下であり、均一性にも優れていた。
【００９１】
[実施例７]
実施例２で作成したＸ線検出器を、図９のＸ線ＣＴ装置として用い、Ｘ線管電圧120kV、X線管電流175mA、スライス幅10mm、スキャン時間2sの条件で、頭頂部近似ファントムを用いてＸ線CT像の撮影を行った。アーチファクトは見られず高品質の断層像が得られた。
【００９２】
[実施例８]
実施例４で作成したＸ線検出器を、図９のＸ線ＣＴ装置として用い、Ｘ線管電圧120kV、X線管電流175mA、スキャン時間0.8sの条件で、頭頂部近似ファントムを用いてＸ線CT像の撮影を行った。アーチファクトは見られず高品質の断層像が得られた。
【００９３】
【発明の効果】
本発明によれば、４周面を反射層で囲んだ柱状シンチレータを多数配列した検出器において、反射層の厚さばらつき、並びにピッチ精度を、反射層用切り込み溝を形成するために用いた加工機の加工精度と実質的に同程度にまで高めることができると同時に、気泡等の反射層の欠陥が無く、最小限のシンチレータ製造工程で高精度のシンチレータを得ることができる。また本発明によれば、各シンチレータ要素間に設けられる反射層を、第１反射層／第２の反射層／金属膜／第２の反射層／第１の反射層で構成することにより、シンチレータ要素界面において高い拡散反射率を達成することができるとともにシンチレータ要素間のクロストークを確実に防止できるので、検出感度及び検出出力の高い検出器を提供することができる。従って、このシンチレータをＸ線CT装置用Ｘ線検出器に適用することによって、アーチファクトのない高品質の断層像が得られるＸ線CT装置を提供できる。
【図面の簡単な説明】
【図１】本発明が適用される放射線検出器の概略を示す図
【図２】本発明のシンチレータ製造工程の一例を説明するための図
【図３】本発明の遠心注型法のメカニズムを説明するための図
【図４】シンチレータ素材の一部分を説明するための図
【図５】本発明のシンチレータの反射材の無機化合物粉末粒子含有割合を説明するための図
【図６】本発明の第２の実施形態によるシンチレータの構成を示す図
【図７】図６のシンチレータを用いた放射線検出器の構成を示す図
【図８】図６のシンチレータの製造工程の一例を説明するための図
【図９】本発明が適用されるＸ線ＣＴ装置の概略を示す図
【符号の説明】
6・・・有機樹脂
7・・・無機化合物粉末
10・・・シンチレータ素材
13・・・反射層（第１の反射層）
14・・・第２の反射層
15・・・金属膜
16・・・セパレータ板
20・・・切り込み溝
100、200・・・シンチレータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation detector that detects X-rays, γ-rays, and the like, and more particularly to a scintillator for a radiation detector suitable for a radiation detector such as an X-ray CT apparatus or a positron camera, a manufacturing method thereof, and an X-ray using the same. The present invention relates to a line CT apparatus.
[0002]
[Prior art]
Conventionally, as a radiation detector used in an X-ray CT apparatus or the like, a xenon gas chamber, a combination of bismuth germanate (BGO crystal) and a photomultiplier tube, cadmium tungstate (CdWO) _Four ) And photodiodes have been used, but in recent years, rare earth phosphors with high conversion efficiency from radiation to light have been developed, and radiation detectors combining such phosphors and photodiodes have been used. Has been put to practical use.
[0003]
Such a radiation detector has, for example, a structure in which elements provided with reflecting materials are arranged in a straight line or a lattice on four surfaces around a columnar scintillator element, in order to increase the accuracy as a radiation detector. However, the element arrangement pitch and the uniformity of the performance of each element are required.
[0004]
As a method for manufacturing the radiation detector having the above structure, for example, in Patent Document 1, 1) a plurality of plate-like scintillator materials are laminated at a predetermined interval via a reflecting material to form a primary laminated block; The block is cut to a predetermined thickness to produce an intermediate plate composed of a large number of prismatic scintillator materials and reflectors, and 3) the intermediate plate is laminated at predetermined intervals via the reflectors to provide secondary 4) A method of cutting this secondary laminated block into a predetermined thickness is disclosed (referred to as Prior Art 1). In Patent Document 2, 1) a plate-like BGO crystal is formed with notches having a predetermined pitch of 0.5 mm in width and 12 mm in depth, and 2) a resin containing reflector powder in the notches. A method is described in which the solution is filled, and 3) the resin solution is put in a decompression apparatus, and the resin solution is degassed by vacuum, desolvated and dried (referred to as Prior Art 2).
[Patent Document 1]
Japanese Patent Laid-Open No. 11-231061
[Patent Document 2]
Japanese Patent Laid-Open No. 5-19060
[0005]
[Problems to be solved by the invention]
In recent years, with the increase in accuracy of radiation detectors, the scintillator constituting the detector is approximately 1 × 2 × 2 mm. ^Three A material having a size of about a degree has been used, and the thickness of the surrounding reflecting material has been reduced to about several hundred μm. In a detector having such a size, even if the dimensional accuracy of the scintillator element or the reflective material varies by about several tens of μm, the detection accuracy of the detector is affected, and ring-shaped artifacts are generated. Also, if there are bubbles or defects in the reflective material or the interface between the reflective material and the scintillator, the sensitivity distribution of the scintillator elements varies greatly, which also causes artifacts.
[0006]
In such a situation, the prior art 1 has a problem that it is necessary to perform highly accurate lamination twice in order to form a reflector around the scintillator element, which requires a lot of time and labor. . In the prior art 2, the accuracy of the scintillator interval (reflecting material thickness) can be increased to the accuracy of machining by performing vertical and horizontal cut grooves by the same machining, but if the width of the cut grooves is reduced, the resin solution It is difficult to fill the groove into the groove, and even if it can be filled, there is a limit to vacuum defoaming by the decompression device, resulting in variation in residual bubbles for each reflective layer, and a high-precision detector cannot be obtained. There was a problem. Moreover, in the prior art 2, there existed the area | region which was not isolate | separated into the scintillator element in the final form.
[0007]
On the other hand, the material inserted between the scintillator elements includes a reflective material for reflecting the light emitted by the scintillator to increase the output of the scintillator, and a crosstalk between the scintillator elements by suppressing light transmission. There is a shielding material. As the reflective material, a mirror-finished metal plate or a white paint containing a reflective material made of a white pigment such as titanium dioxide or barium sulfate is used. Further, as a material for suppressing light transmission, a heavy metal thin plate such as lead or molybdenum is used.
[0008]
When the material of the reflective layer is filled in the groove formed between the scintillator elements as in the above-described prior art 2, a material in which the reflective material is dispersed in the resin is used. However, the conventional manufacturing method cannot use a high-viscosity material to fill a narrow groove, so there is a limit to the amount of reflective material that can be contained in the reflective layer, and sufficient reflective properties can be obtained. There was no problem of crosstalk.
[0009]
On the other hand, when a scintillator block is manufactured by laminating plate-like scintillator elements, a thin metal plate provided with a coating layer of white paint, a white polymer film, or a separator combining these is used. It is used. Patent Document 3 describes that a separator in which two white films formed with a metal film are laminated so that the metal film is on the inside is described.
[Patent Document 3]
Japanese Patent No. 2930823
[0010]
When a separator with a white paint coating layer on both sides of a metal plate is used, the effect of preventing crosstalk can be improved, but the scintillator element is caused by uneven coating layer thickness. There is a problem that the reflection characteristics vary. On the other hand, when a white film is used, the reflection characteristics are low as compared with a white pigment coating layer, and sufficient performance cannot be obtained in applications requiring extremely high detection sensitivity.
[0011]
It is an object of the present invention to solve various problems related to the above-described conventional manufacturing methods and scintillators and detectors manufactured with materials. That is, an object of the present invention is to provide a manufacturing method capable of manufacturing a highly accurate scintillator for a radiation detector from which the scintillator elements are separated by a relatively simple process, and thereby, variation in sensitivity of the scintillator elements. It is an object of the present invention to provide a highly accurate scintillator for a radiation detector without any problem. Another object of the present invention is to provide a scintillator for a radiation detector having a uniform reflection layer provided between scintillator elements, excellent reflection characteristics, and high detection sensitivity. Furthermore, an object of the present invention is to provide an X-ray CT apparatus that has high detection accuracy and suppresses artifacts by using such a scintillator.
[0012]
[Means for Solving the Problems]
Manufactured by the present invention In the scintillator for radiation detector, a plurality of columnar scintillator elements are arranged in a first direction and a second direction orthogonal to the first direction, respectively, and reflection layers are provided on four surfaces around each scintillator element in the arrangement direction. Scintillator for radiation detector And At least the reflective layer provided between the scintillator elements is made of a resin containing a reflective material, and the content of the reflective material changes monotonously in a direction perpendicular to the arrangement direction. The rate of change in the content of the reflective material is preferably more than 0 wt% / cm and not more than 20 wt% / cm per unit.
[0013]
The method for manufacturing a scintillator for a radiation detector according to the present invention is a method of cutting a rectangular parallelepiped scintillator with a predetermined pitch, a predetermined width, and a predetermined depth along a first direction and a second direction orthogonal to the first direction. Using the centrifuge to form the groove (1), With the centrifugal direction as the injection direction, A step (2) of injecting a resin containing reflector powder into the cut groove, a step (3) of curing the resin, and a third direction orthogonal to the first and second directions after the resin is cured. Surface perpendicular to And a step (4) of cutting along.
[0014]
When the scintillator material is made of a rare earth oxide phosphor, it is preferable to include a step of annealing to enhance the scintillator characteristics. In this case, the step of annealing is performed prior to step (1) and / or It is preferable to carry out between step (1) and step (3). The annealing performed prior to the step (1) can alleviate thermal strain and the like generated during the production of the scintillator material, and the annealing step can be efficiently performed by annealing after forming the cut groove in the step (1). A scintillator having excellent scintillator characteristics can be obtained.
[0015]
The scintillator formed by the manufacturing method of the present invention ensures that the groove is formed without intrusion of air even in a narrow groove or a deep groove by injecting a material constituting the reflective layer into the cut groove by a centrifugal method. Material can be injected into it. The scintillator thus formed has a gradient in the concentration of the reflector powder in the depth direction of the groove. By appropriately selecting the particle size and distribution range of the reflector powder, the reflectivity change in the groove depth direction can be achieved. It can be held within the allowable range.
[0016]
Further, the scintillator of the present invention formed by this manufacturing method can increase the thickness dimension variation of the reflective layer to the same degree as the processing accuracy when forming the cut groove. Specifically, each of the first and second directions can be ± 0.010 mm or less. As a result, a scintillator for a radiation detector with no variation in characteristics among the scintillator elements can be obtained.
[0017]
In the scintillator for radiation detectors of the present invention, preferably, the reflective layer further includes a separator plate at the center thereof. The separator plate has, for example, a three-layer structure in which white diffuse reflection layers are laminated on both surfaces of a metal film.
By inserting a separator plate into a reflective layer made of a resin containing a reflective material, it is possible to further improve the reflection characteristics and light transmission blocking characteristics of the reflective layer. In particular, by adopting a three-layer structure having a white diffuse reflection layer on both sides of the metal film as the separator plate, each scintillator element has two reflection layers on both sides to prevent crosstalk. In addition, reflection characteristics can be greatly improved, and spatial resolution and detection sensitivity can be increased.
[0018]
A scintillator for a radiation detector that achieves the second object of the present invention has a plurality of columnar scintillator elements arranged in a first direction and a second direction orthogonal to the first direction, respectively. In the scintillator for radiation detectors, in which a reflective layer is provided on four surfaces around the direction, the reflective layer is inserted into a first reflective layer made of a resin containing a reflective material, and a central portion of the first reflective layer, And a separator having a second reflective layer in contact with the first reflective layer.
[0019]
In this scintillator for radiation detectors, since the reflective layer is composed of three layers of the first reflective layer / the second reflective layer comprising the white separator / the first reflective layer, high detection sensitivity is realized for each scintillator element. Is done. In particular, when the white separator has a metal film between two white reflective diffusion layers, a high crosstalk preventing effect of the reflective layer can be obtained.
[0020]
Furthermore, in the scintillator for radiation detectors of the present invention, it is desirable that the sufficiently thick diffuse reflectance R∞ of the first reflective layer is larger than the diffuse reflectance Rb of the second reflective layer. Here, the diffuse reflectance of a sufficiently thick sample refers to the diffuse reflectance at a thickness at which the diffuse reflectance does not change even if the thickness of the sample is increased further.
By making the diffuse reflectance R∞ of the first reflective layer larger than the diffuse reflectance Rb of the second reflective layer, the reflectance of the entire reflective layer can be 90% or more, and the scintillator The light output can be improved.
[0021]
The radiation detector of the present invention uses the above-described scintillator of the present invention. Specifically, a scintillator in which a plurality of scintillator elements each having a reflective layer arranged on four columnar circumferential surfaces is arranged, and the scintillator of this scintillator It is provided with a photodetector for detecting luminescence. Since this radiation detector uses the scintillator of the present invention as a scintillator, there is no variation in characteristics between elements, and high detection accuracy can be realized.
[0022]
This X-ray CT apparatus is provided with an X-ray detector having high detection accuracy with no variation in characteristics between the elements, so that ring artifacts are suppressed and a high-quality CT image can be obtained.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a scintillator for a radiation detector of the present invention, a radiation detector using the scintillator, and a manufacturing method thereof will be described.
[0024]
FIG. 1 is a view showing a radiation detector according to a first embodiment of the present invention. This radiation detector includes a plurality of columnar scintillator elements 12 arranged in a lattice pattern and a periphery 4 of the columnar scintillator elements 12. A reflection layer 13 provided on the surface, a photodetector 11 provided on one surface orthogonal to the peripheral surface of the scintillator element 12, and a reflection provided on a surface parallel to the surface provided with the photodetector 11 And a layer 13 '. The figure shows a part of the radiation detector, and shows only three scintillator elements 12 arranged in one direction (paper surface, horizontal direction), but a direction orthogonal to this direction (direction orthogonal to the paper surface). ) Also has a plurality of scintillator elements arranged in a similar structure.
[0025]
As the photodetector 11, a known photodetector such as a photoelectric intensifier tube, a photodiode, or a PIN photodiode can be used.
The scintillator element 12 generates light by receiving X-rays or γ-rays, and is made of a known material such as a rare earth phosphor. As a suitable rare earth-based phosphor, for example, the present inventors have proposed an oxide phosphor having a garnet structure in which the emission center element is Ce and Gd, Al, Ga, and O are main elements (Japanese Patent Application No. 2000-389343). ) Can be used.
[0026]
The reflective layer 13 is made of an organic resin containing an inorganic compound powder as a reflective material. As the organic resin, those with little deterioration and coloring due to radiation and strong adhesive strength are preferable. Specifically, an epoxy resin, an acrylic resin, a phenol resin, or the like can be used.
[0027]
As the inorganic compound powder, a material that can ensure a light reflectance of 90% or more at a wavelength of around 535 nm and is less deteriorated by radiation irradiation is preferable. Specifically, an inorganic compound powder such as titanium oxide, alumina, barium sulfate or the like is used. can do. The inorganic compound powder preferably has a small particle size and a narrow particle size distribution. Specifically, those having an average particle size of 3 μm or less and a particle size distribution (standard deviation) of 2 μm or less, more preferably an average particle size of 1 μm or less and a particle size distribution of 1 μm or less are preferred.
[0028]
The content of the reflective material is 30 to 80 wt% in a weight ratio (%) of the reflective material / (reflective material + resin) in order to reflect as much light generated by the scintillator element as possible and shield the adjacent scintillator element. The range of is preferable. If the content of the reflective material is less than 30 wt%, sufficient reflectivity and shielding properties cannot be obtained, the detection capability is lowered, and crosstalk between scintillator elements occurs. On the other hand, if it exceeds 80 wt%, the viscosity before curing of the resin becomes high, and it becomes difficult to inject the reflective layer forming material between the scintillator elements when forming the reflective layer also by the manufacturing method described later. The viscosity before curing of the reflective layer forming material in which a reflective material is contained in an organic resin is preferably about several thousand to several hundred thousand cPs. The viscosity of such a reflective layer forming material can be adjusted by adjusting the selection of the organic resin, the content of the inorganic compound powder, and the like.
[0029]
Further, the scintillator of the present invention is characterized in that the content of the reflecting material is changed in the height direction of the scintillator. This is due to the manufacturing method of the scintillator of the present invention. By using a manufacturing method that produces a gradient in the concentration of the reflective material, the scintillator of the present invention reflects bubbles harmful to crosstalk. Without being included in the layer, it is possible to obtain a scintillator having excellent reflection characteristics and having no characteristic unevenness in all the reflection layers. The concentration gradient exceeds 0 wt% / cm per unit length and is 20 wt% / cm or less, preferably 10 wt% / cm or less, more preferably 5 wt% / cm or less.
[0030]
When the concentration gradient is 20 wt% / cm or more, the light reflectance of the reflective layer changes by about 4% or more in the thickness direction. If the thickness of the scintillator is about 2.0 mm, the light reflectivity differs by 0.8% depending on the thickness of the scintillator, resulting in non-uniform sensitivity and causing artifacts. Such sensitivity unevenness can be eliminated by setting the concentration gradient to 20 wt% / cm or less.
[0031]
The thickness of the reflective layer varies depending on the radiation detector, but can be, for example, in the range of 0.1 to 0.3 mm. In the radiation detector of the present invention, the accuracy of the width of the reflective layer can be suppressed to ± 0.010 mm or less by manufacturing by the manufacturing method described later. In addition, the radiation detector of the present invention can include a metal shielding plate made of molybdenum, tungsten, stainless steel or the like inside the reflective layer in order to reduce crosstalk between elements.
[0032]
Next, a method for manufacturing the scintillator of the present invention configured as described above will be described.
FIG. 2 is a diagram showing an example of the manufacturing process of the scintillator of the present invention, and shows a case where an oxide phosphor is used as a scintillator material. As shown in the drawing, a rectangular parallelepiped scintillator material 10 is prepared, and 20 cut grooves in two directions perpendicular to one surface of the scintillator material 10 and perpendicular to each other are formed (step 201). In the figure, when the vertical direction of the scintillator material is y, the horizontal direction is x, and the height direction is z, the grooves are formed in the x direction and the y direction so that the depth direction is z. The depth H of the cut groove is shallower than the height Z of the scintillator material, and the scintillator material is not cut and remains in a state of about several mm.
[0033]
The depth, width, pitch in the x direction and y direction of the groove vary depending on the use of the radiation detector, but the depth of the groove is, for example, 10 to 30 mm. In the case of an X-ray detector for X-ray CT, for example, the width is about 0.1 to 0.3 mm and the pitch is about 1.0 to 2.5 mm. In the conventional method of injecting into the groove by the weight of the reflective layer forming material, mechanical pressurizing method such as pressing, and impregnation in vacuum, the reflective layer forming material is injected without generating bubbles in the narrow groove. However, in the method of the present invention, the reflective layer forming material can be surely injected to the bottom without generating bubbles even in the above-described narrow groove or deep groove.
[0034]
Such a cut groove can be formed using a high-precision processing machine such as a multi-wire saw that reciprocates while supplying a wire and a slicer having a cutting blade coated with diamond. Thus, the pitch and width of the groove can be increased to the same level as the accuracy of the processing machine. Specifically, the groove width variation and the pitch variation of the cut groove can be ± 0.010 mm or less. When the variation accuracy is 0.01 mm or more, the accuracy of the detector is lowered, and ring-shaped artifacts are likely to occur.
[0035]
After the cut groove is formed, the scintillator material is annealed (step 202). The annealing treatment is generally performed for imparting scintillator characteristics to the oxide phosphor. For example, the annealing treatment is performed in oxygen at a high temperature of 1100 to 1600 ° C. for several tens of minutes to several hours. Such an annealing process can be performed before the cut groove is formed in the scintillator material. However, in the manufacturing method of this embodiment, the cut groove is formed before the annealing process, so that the annealing efficiency can be improved. it can.
[0036]
Next, a material for forming a reflective layer is injected into the cut groove (steps 203 to 205). Therefore, the scintillator material is first placed in the molding frame so that the cut groove is on the upper surface (step 203), and an uncured organic resin containing a reflective material is placed on the upper surface of the cut groove (step 204), and then centrifuged. Place in machine and centrifuge (step 205). As already described, the material for forming the reflective layer is made of an inorganic resin powder dispersed in an organic resin, and the viscosity is adjusted to be about several thousand to several hundred thousand cps. By using the reflective layer forming material with the adjusted viscosity, the material can be injected to the bottom of the groove by centrifugal casting, and the bubbles in the resin can be substantially eliminated.
[0037]
A mechanism for removing bubbles by centrifugal casting will be described with reference to FIG. The density of the organic resin 6 is ρ, the viscosity is μ, and the density of the inorganic compound powder 7 is ρ. _s , Diameter d _s , The density of bubble 8 is ρ ₀ , Diameter d ₀ And In general, particles in a liquid (diameter d _s , Density ρ _s ) The motion of the particles u _s Then Reynolds number Re (= d _s u _s ρ _s Depending on the range of / μ), Stokes' law, Allen's law and Newton's law apply. In the reflective layer forming material described above, the viscosity μ is large, the resistance of the particle motion is caused solely by friction, the Reynolds number is 5.8 or less, and Stokes' law is applied.
[0038]
According to Stokes' law, the resistance R acting on the particles is R = 3πd _s u _s It is expressed in μ. On the other hand, the effective centrifugal force for relative displacement between the organic resin and the particles is expressed by the following equation (1) when the particles of mass m rotate on the circumference of the radius r at the angular velocity ω. Therefore, the movement speed u of the particles from the balance between the two _s Is represented by equation (2).
[0039]
[Expression 1]

[Expression 2]

[0040]
Meanwhile, bubble moving speed u ₀ Becomes the equation (3). Therefore, the moving speed ratio between the inorganic compound powder particles 7 and the bubbles 8 dispersed in the organic resin 6 is expressed by the formula (4).
[0041]
[Equation 3]

[Expression 4]

[0042]
For example, ρ ₀ = 0, ρ _s = 4.2g / cm ^Three , Ρ = 1.4g / cm ^Three , D ₀ = 10μm, d _s = 1μm, u ₀ / u _s = −50. That is, the bubbles 8 move in the opposite direction to the centrifugal force at a speed 50 times that of the inorganic compound powder 7. From this, it can be seen that the centrifugal casting can efficiently inject the air into the narrow and deep cut groove so that the bubbles are eliminated.
[0043]
In the centrifugal casting described above, relative displacement of the inorganic compound powder 7 with respect to the organic resin 6 occurs simultaneously with the removal of the bubbles (FIG. 4). As a result, as shown in FIG. 5, the reflective layer is divided into three regions A, C, and B in which the inorganic compound content varies stepwise in the injection direction (groove depth direction). The upper region A has a low inorganic compound content, and the lower region B has a high inorganic compound content. These regions are regions that are cut in a subsequent slicing process and are not used as a scintillator, and are desirably as narrow as possible. In order to narrow these regions A and B, the particle density ρ in equation (4) _s And the density ρ of the organic resin should be made as small as possible, or the particle diameter of the particles should be made as small as possible. Specifically, by setting the average particle size of the inorganic compound powder to 3 μm or less, the regions A and B can be suppressed to about 5% or less of the total thickness, and the region C that can be used as a scintillator can be widened.
[0044]
On the other hand, the region C effective as a reflective layer causes an inclination α of the inorganic compound content in the injection direction due to the particle size distribution of the inorganic compound powder. According to the study of the present inventors, the change in the reflectance of the scintillator can be allowed within 4% / cm in the thickness direction, and the change in the reflectance of 4% / cm is the inorganic compound content. Corresponds to an inclination of 20wt% / cm. By setting the standard deviation, which is an index of the particle size distribution of the inorganic compound powder, to 2.0 μm or less, the inclination of the inorganic compound content can be suppressed to 20 wt% / cm or less, and a detector with no sensitivity unevenness can be configured. it can.
[0045]
Therefore, in the scintillator manufacturing method of the present invention, in order to make the region C that can be used as a scintillator as wide as possible and to suppress the change in reflectance in the thickness direction within 4% / cm, the average particle diameter as inorganic compound particles It is desirable to use one having a standard deviation of 3 μm or less and a standard deviation of 2.0 μm or less.
[0046]
After the reflective layer forming material is injected into the cut groove 20 in this way, the organic resin is cured (step 206), and the reflective layer 13 is formed. Thereafter, the scintillator is sliced to a desired thickness in a direction orthogonal to the depth direction of the groove (that is, parallel to the x and y planes) (step 207). In this case, regions A and B shown in FIG. 5 are removed, and a portion to be a scintillator is sliced from region C. Finally, the sliced surface is polished as necessary (step 208) to obtain the radiation detector scintillator 100.
[0047]
The reflective layer can be inserted with a metal shielding plate or separator plate made of molybdenum, tungsten, stainless steel or the like in order to shield visible light. When a metal shielding plate or the like is inserted into the reflective layer, the metal shielding plate is inserted into the cut groove before the centrifugal injection (before step 203), and then the reflective layer forming material is injected. Thereby, for example, a scintillator having a metal shielding plate in the channel direction of the X-ray detector can be obtained.
[0048]
In order to use the scintillator of the present invention as a radiation detector, a reflective layer is further formed around the scintillator 100 and on the opposite side of the surface on which the photodetector is disposed. For this reflective layer, a material obtained by curing the organic resin containing the above-described inorganic compound powder is usually used, but a different material may be used if there is no problem.
[0049]
The scintillator manufactured by the above manufacturing method has a reflective layer having a dimensional accuracy comparable to the processing accuracy for forming the cut groove, and since the reflective layer does not contain bubbles, variation in characteristics of each scintillator element Therefore, it is possible to provide a radiation detector with excellent detection accuracy.
[0050]
Next, a scintillator and a radiation detector using the scintillator according to a second embodiment of the present invention will be described. FIG. 6 shows the configuration of the scintillator 200 according to the present embodiment, and FIG. 7 shows the configuration of a radiation detector using it. 6 and 7, the same elements as those in FIG. 1 are denoted by the same reference numerals.
[0051]
Also in the present embodiment, the scintillator element 12 and the reflective layer 17 are formed by forming a groove having a predetermined width at a predetermined pitch in a scintillator block having a predetermined size and filling the groove with a material constituting the reflective layer. This is the same as in the first embodiment. As the scintillator material, as in the first embodiment, for example, an oxide phosphor having a garnet structure in which the emission center element is Ce and Gd, Al, Ga, and O are main elements can be suitably used.
[0052]
However, the scintillator and detector of the present embodiment are characterized by the structure of the reflective layer 17, and the reflective layer 17 includes a reflective diffusion layer 13 made of a resin containing white inorganic compound powder (hereinafter referred to as a white resin) and It consists of a separator plate 16. By inserting such a separator plate, leakage of light between scintillator elements can be prevented and crosstalk between channels can be eliminated.
[0053]
As the separator plate 16, a separator plate 16 having a three-layer structure of white diffuse reflection layer 14 / metal film 15 / white diffuse reflection layer 14 is used as shown. By using the separator plate having such a three-layer structure, the reflectance of the reflective layer can be improved as compared with the case where only the metal plate is used, and the separator plate 16 is positioned substantially at the center of the reflective layer 17. The thickness of the reflective layer 13 and the white diffuse reflective layer 14 adjacent to the scintillator element can be made substantially uniform for each scintillator element.
[0054]
In the scintillator 200 of the present embodiment, the white diffuse reflection layer 13 has a diffuse reflectance R∞ of a sufficiently thick sample larger than the diffuse reflectance Rb of the separator plate 16 (metal film 15 / white diffuse reflection layer 14). It is preferable. Specifically, the diffuse reflectance R∞ of the white diffuse reflection layer 13 is preferably 97% or more, and the diffuse reflectance Rb of the separator 16 is preferably 85% or more. Accordingly, the diffuse reflectance at the scintillator element interface can be set to 90%, and the light output of the scintillator can be improved.
[0055]
In order to realize the diffuse reflectance as described above, the white diffuse reflection layer 13 is made of a white resin in which a white inorganic compound is dispersed in an organic resin, and the weight ratio of inorganic compound / (inorganic compound + organic resin). (%) Is preferably 30 to 80 wt%. However, if it exceeds 80 wt%, the viscosity of the white resin becomes extremely high, and even if it is injected by the centrifugal injection method, it becomes difficult to completely remove the bubbles. Therefore, the weight ratio is preferably 80 wt% or less. As the inorganic compound, titanium oxide, alumina, barium sulfate, etc. can be used. ₂ The inorganic compound powder preferably has a small particle size and a narrow particle size distribution. As the organic resin, in addition to colorless and transparent resins such as an epoxy resin, a polyester resin, an acrylic resin, and a phenol resin, a white resin that does not absorb strong visible light around 500 to 600 nm can be used.
[0056]
The separator plate 16 having a three-layer structure including the white reflection diffusion layer 14 / metal film 15 / white reflection diffusion layer 14 is, for example, coated with a white paint in which a white pigment is dispersed in a resin on both surfaces of the metal film. Can be manufactured. In this case, as the material of the metal film 15, a copper alloy such as molybdenum, tungsten, lead, aluminum, stainless steel and phosphor bronze can be used. The thickness of the metal film is not particularly limited as long as it can substantially block visible light, but considering the workability for forming the coating layer, the thickness is in the range of 10 to 50 μm. As a material constituting the white diffuse reflection layer 14, inorganic compound powders and organic resins constituting the white diffuse reflection layer 13 can be used, but titanium oxide having a particle diameter of about 0.2 to 2 μm is particularly suitable as the inorganic compound powder. is there. As the organic resin, in addition to colorless and transparent resins such as an epoxy resin, a polyester resin, an acrylic resin, and a phenol resin, a white resin that does not absorb strong visible light around 500 to 600 nm can be used. When the white diffuse reflection layer 14 is formed by coating such an inorganic compound, a known coating method such as a screen printing method, a doctor blade method, a brush coating, or a spray coating can be employed. The thickness of the white diffusion layer 14 varies depending on the thickness of the separator plate, but is, for example, 10 to 60 μm, preferably 20 to 50 μm.
[0057]
The separator plate having a three-layer structure may be manufactured by forming a metal film such as aluminum on one surface of a white polymer film by vapor deposition or the like, and adhering the white polymer film to the vapor deposition surface. The thickness of the metal vapor deposition film is set to a thickness capable of blocking visible light, and specifically, about 0.05 to 2 μm. As a white polymer film, a white polyester film, a white polyethylene film, a white polyvinyl chloride film, etc. can be used, for example.
[0058]
The thickness of the separator plate depends on the groove width formed as the reflective layer, and is desirably 30% or more and less than 90% with respect to the groove width. When the thickness of the separator is less than 30%, since the ratio of the white diffuse reflection layer 13 to the groove width increases, the thickness of the white diffuse reflection layer 13 tends to be biased. On the other hand, when the thickness of the separator is 90% or more, it is difficult to insert the separator into the groove, and it is difficult to inject the white resin because the gap for injecting the white resin for forming the white diffuse reflection layer 13 is small. As a result, the diffuse reflection layer 13 becomes inhomogeneous due to residual bubbles, and the characteristics of the scintillator elements tend to vary.
[0059]
Next, the manufacturing method of the scintillator by 2nd Embodiment is demonstrated. FIG. 8 shows an outline of the manufacturing method.
[0060]
First, cut grooves 20 are formed in a rectangular parallelepiped scintillator material 10 in two directions (shown as an x direction and a y direction in the drawing) perpendicular to the thickness direction (z direction). The depth of the cut groove is shallower than the height of the scintillator material, and the scintillator material is not cut and is left in a state of about several mm. The depth, width, and pitch in the x and y directions of the groove differ depending on the application of the radiation detector, but in the case of an X-ray detector for X-ray CT, for example, the groove depth is 10 to 30 mm and the width is 0.1 to 0.3. mm and a pitch of about 1.0 to 2.5 mm (step 801). As in the first embodiment, this grooving is also performed using a high-precision processing machine such as a multi-wire saw that performs processing while reciprocating the wire, or an inner saw having an inner peripheral cutting blade that is coated with diamond. This makes it possible to process with high accuracy of ± 0.005 mm or less.
[0061]
The scintillator material after grooving is annealed (step 802). The annealing process is a process for imparting scintillator characteristics when the scintillator material is an oxide phosphor. For example, the annealing process is performed in oxygen at a high temperature of 1100 to 1600 ° C. for several tens of minutes to several hours.
[0062]
On the other hand, a separator plate is prepared for insertion into a groove formed in the scintillator material (step 803). As described above, the separator plate has a three-layer structure in which white diffused reflection layers are formed on both surfaces of the metal film, and a metal film having a thickness of 30 to 90% of the groove width is prepared. Next, the separator plate is placed in each groove formed in the scintillator material (step 804). The separator plate is typically disposed only in a groove (for example, a y-direction groove) that separates channels, which is important for the resolution of CT images. In this case, the same number of separator plates as the length in the y direction of the scintillator material are prepared as many as the y direction grooves, and are sandwiched between the y direction grooves. In addition, when a separator plate is also inserted into a groove that separates slices (for example, an x-direction groove), for example, the same number of separator plates as the x-direction groove are prepared with the same length as the scintillator material in the x direction (x Group), and in each case, a notch with a depth of 1/2 in the thickness direction is formed at the same pitch as the groove pitch in the y direction, and a separator plate having the same length as the length in the y direction is formed in the groove in the y direction. The same number as (y group), and also for these, form a notch of 1/2 depth in the thickness direction at the same pitch as the groove of the x direction, and the x group separator plate and the y group separator It is preferable to make an assembly of grid-shaped separator plates corresponding to the grid-shaped cut grooves by meshing the cuts from above and below so that the plates are orthogonal.
[0063]
Thus, after arrange | positioning a separator plate in a notch groove, white resin is inject | poured in a groove | channel (step 805). The white resin is preferably injected by centrifugal injection as in the first embodiment. By adopting the centrifugal injection method, even if the viscosity of the white resin is as high as about 100,000 cPs, it can be reliably injected into the deep cut groove without generating bubbles.
[0064]
Prior to the injection of the white resin, the white resin may be applied to the surface of the cut groove (step 803 ′). By forming a white resin coating layer that forms part of the white diffuse reflection layer on the groove surface in advance, it is possible to reliably prevent an air layer from forming between the scintillator and the white diffuse reflection layer. High diffuse reflectance can be achieved. As a method for applying the white resin to the groove surface, for example, a method in which the white resin is filled in the groove by a centrifugal injection method and then centrifuged in the opposite direction to discharge the white resin in the groove. it can.
[0065]
After the injected white resin is cured, the scintillator material is sliced perpendicular to the cut grooves (steps 806 and 807). For the slicing, for example, machining such as a multi-wire saw, an inner peripheral blade slicer, and an outer peripheral blade slicer can be used. Also in this case, when the centrifugal injection method is adopted as the white resin injection method, the content of the white inorganic compound is inclined, so that a region having an inclination of 20 wt% / cm or less shown in FIG. To do. Finally, a scintillator having a target thickness is obtained by lapping the slice surface (step 808).
[0066]
In order to use the manufactured scintillator as a radiation detector, as shown in FIG. 7, the incident surface of the radiation is covered with a reflector 18 and the opposite surface is detected at the same pitch as the scintillator element. The substrate (photodiode) 11 is bonded to the substrate 21 with a transparent adhesive 19 or the like.
When radiation is incident on the incident surface of such a radiation detector, the scintillator emits light according to the dose of the incident radiation, and the photodiode photoelectrically converts the light. Here, since each scintillator element is separated by the reflection layer 17 comprising the white diffuse reflection layer 13 / white diffuse reflection layer 14 / metal film 15 / white diffuse reflection layer 14 / white diffuse reflection layer 13, the cross between the elements Since there is no talk and the light generated by the scintillator element is reflected by the reflective layer 17 with high reflectivity, a high detection output can be obtained.
[0067]
Next, the X-ray CT apparatus of the present invention will be described. FIG. 9 is a diagram showing an outline of an X-ray CT apparatus, which includes a gantry unit 60 and an image reconstruction unit 70, and the gantry unit 60 includes an opening 61a into which a subject is carried. A disk 61, an X-ray tube 62 mounted on the rotating disk 61, a collimator 63 attached to the X-ray tube 62 to control the X-ray radiation direction, and a rotating disk facing the X-ray tube 62 An X-ray detector 64 mounted on 61, a detector circuit 65 for converting the X-ray detected by the X-ray detector 64 into a specific signal, and the rotation of the rotating disk 61 and the width of the X-ray bundle are controlled. And a scan control circuit 66. The image reconstruction unit 70 includes an input unit 71 for inputting inspection conditions and the like, and a monitor 72 for displaying an image. Here, as the X-ray detector 64, an X-ray detector using the scintillator of the present invention is used.
[0068]
In such a configuration, X-rays are irradiated from the X-ray tube 62 in a state where the subject is laid on a bed installed in the opening. The X-rays are obtained by the collimator 63 and detected by the X-ray detector. By rotating the rotating disk around the subject, X-rays are detected while changing the X-ray irradiation direction, and a tomographic image is created by the image reconstruction unit 70 and displayed on the monitor 72.
[0069]
By using the scintillator of the present invention, this X-ray CT apparatus can detect X-rays with high accuracy with little variation among elements and channels of X-ray sensitivity and quality characteristics. When image processing is performed on the cross section, no image is generated, and an image with high image quality and high resolution can be obtained.
[0070]
【Example】
Examples of the present invention will be described below.
[0071]
[Example 1]
Composition formula is (Gd, Ce) _{8 (1-x)} (Al, Ga) _8x O ₁₂ , X = 0.620, Ce / Gd = 0.008, Ga / (Ga + Al) = 0.44 was used for hot press sintering to obtain a sintered body having a diameter of 160 mm and a thickness of about 15 mm. The relative density of this sintered body was 99.9% or more. Eight scintillator materials having a size in the x, y, and z directions of 40 mm × 25 mm × about 15 mm were cut out from the sintered body using a multi-blade saw.
[0072]
A grid-like cut groove perpendicular to the xy plane was formed on the cut block using a multi-wire saw having a wire diameter of 0.16 mm. First, grooving was performed at a pitch of 2.25 mm in the x direction, then the scintillator material was rotated 90 °, and grooving was similarly performed at a pitch of 1.0 mm in the y direction. The depth of each groove was about 13 mm. The grid-like cut grooves formed in this way had an accuracy of groove width of 0.200 ± 0.005 mm in both the x and y directions.
[0073]
Next, annealing treatment was performed in oxygen for imparting scintillator characteristics to the scintillator material. The heat treatment conditions were a temperature of 1300 ° C. and 4 hours. According to the present inventors, the rare earth oxide phosphor having the above composition can impart optimum characteristics to the detector for X-ray CT, such as X-ray sensitivity and afterglow attenuation rate, by such annealing treatment. It has been confirmed (Japanese Patent Application No. 2000-389343).
[0074]
On the other hand, TiO with a powder average particle size of 0.3 μm was added to the epoxy resin. ₂ Mixing ratio of powder (TiO ₂ / (TiO ₂ + Epoxy resin)) was added to 65 wt%, and these were mixed uniformly. This TiO ₂ The viscosity of the contained epoxy resin was 98,000 cPs.
[0075]
After the surface treatment is applied to the scintillator material that has been annealed to improve the adhesion to the organic resin, it is placed in a casting frame for casting the organic resin, and the surface is provided with a cut groove. TiO mentioned above ₂ A containing epoxy resin was placed. Next, this scintillator material is set together with the casting frame in the bucket of the centrifuge, rotated at 3500 rpm for 5 minutes, TiO ₂ The contained epoxy resin was cast into the cut groove. The cast scintillator material was heated at 60 ° C. for 3 hours to cure the epoxy resin and form a reflective material. No bubbles were found inside the reflector, and it was removed from the surface.
[0076]
The scintillator material thus formed with the lattice-like reflector is sliced using a multi-wire saw so that the thickness is 2.0 mm parallel to the xy plane, that is, perpendicular to the z-axis, and the scintillator Five scintillator plates were fabricated with the four sides of the element surrounded by a reflector. These scintillator plates were polished by using a lapping machine so that the thickness of the scintillator plate was 1.800 ± 0.005 mm. Through the above steps, five scintillator plates made of 2.05 mm × 0.8 mm × 1.800 mm scintillator elements were obtained.
[0077]
Reflector TiO in the height direction (z-axis direction) of the scintillator plate ₂ In order to examine the content, the content of Ti element was measured using an EDS (Energy Dispersive Spectorscopy) method. As a result, a difference of 0.8 wt% was recognized with respect to the height direction of 1.800 mm. The standard deviation at the time of measurement was 0.31 wt% at 2σ.
[0078]
[Example 2]
A detector as shown in FIG. 1 is made by combining the scintillator manufactured in Example 1 with a photodiode, and the detector is placed at a distance of 15 cm from an X-ray source (120 kV, 0.5 mA). X-ray sensitivity and afterglow characteristics Evaluated. As a result, the X-ray sensitivity is CdWO, which is a typical X-ray CT scintillator ₄ The decay rate of afterglow at 300 ms is about 10 ^-Five And was able to.
[0079]
[Example 3]
Hot press sintering was performed using the powder having the same composition as in Example 1 to obtain a sintered body having a diameter of 160 mm and a thickness of about 15 mm. Eleven scintillator materials having a size in the x, y, and z directions of 33 mm × 25 mm × about 15 mm were cut out from the sintered body using a multi-blade saw.
A grid-like cut groove perpendicular to the xy plane was formed on the cut block using a multi-wire saw having a wire diameter of 0.11 mm. First, grooving was performed at a pitch of 1.0 mm in the x direction to a depth of about 13 mm, then the scintillator material was rotated 90 °, and grooving was performed at a pitch of 1.0 mm in the y direction to a depth of about 13 mm. The grid-like cut grooves formed in this way had an accuracy of groove width of 0.130 ± 0.005 mm in both the x and y directions.
[0080]
Next, annealing treatment was performed in oxygen for imparting scintillator characteristics to the scintillator material. The heat treatment conditions were a temperature of 1300 ° C. and 4 hours. The rare earth oxide phosphor having the above composition has a light output of CdWO which is a typical scintillator for X-ray CT by such an annealing process. _Four The afterglow decay rate at 300ms is about 1x10. ^-Five The following characteristics were obtained.
[0081]
On the other hand, an Al film with a thickness of 0.1 μm is formed on one side of a white polyester film with a thickness of 38 μm by vapor deposition, and then a white polyester film with a thickness of 38 μm is adhered to this Al vapor deposition surface, and white polyester film / Al vapor deposition is performed. A separator plate having a three-layer structure of membrane / white polyester film was produced. The separator plate had a diffuse reflectance of 86% at a wavelength of 550 nm.
[0082]
Epoxy resin and TiO are used as white resin to be injected into the scintillator groove. ₂ The powder was uniformly mixed at a weight ratio of 1: 1. The diffuse reflectance R∞ of this white resin was 98% at a wavelength of 550 nm. After inserting the separator plate manufactured as described above into the groove of the scintillator material after grooving, it was set in a casting frame and this white resin was placed on the surface of the scintillator material. Thereafter, the casting frame was set in a centrifuge, and centrifugal injection was performed at 3000 rpm for 10 minutes.
[0083]
After the injection, the white resin was cured at room temperature for 12 hours, and further cured at 60 ° C. for 3 hours. Next, slicing was performed using a multi-wire saw parallel to the upper surface of the scintillator material, that is, perpendicular to the z-axis, and five scintillator plates having a thickness of 1.95 mm were cut out from the central portion in the thickness direction. Both surfaces of these scintillator plates were polished by a lapping machine to a thickness of 1.800 ± 0.005 mm. By the above processing, five 24-channel 32 multi-slice scintillators made of 0.87 mm × 0.87 mm × 1.800 mm scintillator elements were manufactured.
[0084]
[Comparative Example 1]
A scintillator material having cut grooves was produced in the same manner as in Example 3. A separator plate similar to that in Example 3 was inserted into this groove, and an epoxy-based transparent adhesive was injected into the gap between the groove and the separator plate and cured. Thereafter, slicing and lapping were performed in the same manner as in Example 3 to produce a scintillator plate.
[0085]
[Example 4, Comparative Example 2]
The scintillators manufactured in Example 3 and Comparative Example 1 are combined with photodiodes to form a detector as shown in FIG. 7, and X-ray sensitivity (120 kV, 0.5 mA) is irradiated from a distance of 15 cm to detect X-ray sensitivity. Was measured. As a result, the X-ray sensitivity of the detector manufactured with the scintillator of Example 2 (Example 4) is 1.1 to 1.2 times that of the detector manufactured with the scintillator of Comparative Example 1 (Comparative Example 2). It was. In addition, the detector of Example 4 was excellent in uniformity because the variation in sensitivity distribution of each scintillator element was 5.0% or less.
[0086]
[Example 5]
A scintillator material having a grid-like cut groove was manufactured in exactly the same manner as in Example 3. On the other hand, as a separator plate, a white resin is applied to both sides of a 10 μm thick molybdenum plate by screen printing and cured to form a white diffuse reflection layer with a thickness of 35 ± 10 μm. White diffuse reflection layer / Mo plate / white diffusion A separator plate having a three-layer structure of a reflective layer was produced. Here, the white resin forming the white diffuse reflection layer is TiO having a particle diameter of 0.25 μm with respect to the epoxy resin. ₂ The powder was uniformly mixed at a weight ratio of 1: 1. The diffuse reflectance of this separator plate was 92-93% at a wavelength of 550 nm.
[0087]
After inserting the separator plate into the groove of the scintillator plate, the same white resin (epoxy resin: TiO as in Example 3) was used. ₂ (Powder = 1: 1, diffuse reflectance R∞ = 98%) is injected into the groove of the scintillator plate, cured, sliced and lapped in the same manner as in the examples, 0.87mm x 0.87mm x 1.800mm scintillator Five plates were produced.
A detector was made using this scintillator, and X-ray sensitivity was measured by irradiating X-rays (120 kV, 0.5 mA) from a distance of 15 cm. As a result, an X-ray sensitivity of 1.15 to 1.25 times that of the detector of Comparative Example 2 was obtained. Moreover, the variation in sensitivity distribution of each scintillator element was 5.0% or less, and the uniformity was excellent.
[0088]
[Example 6]
A scintillator material having lattice-shaped cut grooves was produced in exactly the same manner as in Example 3, and then a white resin coating layer was formed on the surface of the cut grooves of the scintillator material. As the white resin, the same white resin injected into the grooves in Example 3 was used. In order to form the coating layer, first, white resin is injected into the groove by centrifugal injection method and filled in the groove, and then the groove release part is set in the opposite direction to the centrifugal injection, that is, the groove bottom is centrifuged. The centrifuge was operated so as to face the center of the machine, and the resin in the groove was removed. The centrifuge was used at 1000 rpm for 5 minutes at the time of resin injection and resin discharge. As a result, a white resin coating layer having a thickness of about 30 μm was formed on the groove surface. This coating layer was cured at room temperature for 12 hours to form a white diffuse reflection layer of 15 μm ± 10 μm.
[0089]
A separator plate having a three-layer structure of white polyester film / Al vapor deposition film / white polyester film similar to that in Example 3 is inserted into the groove of the scintillator material having the white diffuse reflection layer formed on the surface in this manner. A white resin was centrifugally injected between the plates to form a white diffuse reflection layer. As white resin, epoxy resin and TiO ₂ A powder mixed at a weight ratio of 1: 1 was used, and the centrifugal conditions were 3000 rpm for 10 minutes. After the injection, it was cured at room temperature for 12 hours, and further cured at 60 ° C. for 3 hours.
Next, slicing and lapping were performed in the same manner as in Example 3 to produce five scintillator plates measuring 0.87 mm × 0.87 mm × 1.800 mm.
[0090]
A detector was made using this scintillator, and X-ray sensitivity was measured by irradiating X-rays (120 kV, 200 mA) from a distance of 15 cm. As a result, an X-ray sensitivity 1.1 to 1.2 times that of the detector of Comparative Example 2 was obtained. Moreover, the variation in sensitivity distribution of each scintillator element was 5.0% or less, and the uniformity was excellent.
[0091]
[Example 7]
The X-ray detector created in Example 2 was used as the X-ray CT apparatus of FIG. 9, and an approximate parietal phantom was obtained under the conditions of an X-ray tube voltage of 120 kV, an X-ray tube current of 175 mA, a slice width of 10 mm, and a scan time of 2 s. An X-ray CT image was taken. High-quality tomographic images were obtained with no artifacts.
[0092]
[Example 8]
The X-ray detector prepared in Example 4 is used as the X-ray CT apparatus of FIG. 9, and the X-ray tube voltage is 120 kV, the X-ray tube current is 175 mA, and the scan time is 0.8 s. A line CT image was taken. High-quality tomographic images were obtained with no artifacts.
[0093]
【The invention's effect】
According to the present invention, in a detector in which a large number of columnar scintillators having four circumferential surfaces surrounded by a reflective layer are arranged, the thickness variation of the reflective layer and the pitch accuracy are processed to form the cut groove for the reflective layer. The processing accuracy of the machine can be increased to substantially the same level, and at the same time, there is no defect in the reflective layer such as bubbles, and a highly accurate scintillator can be obtained with a minimum scintillator manufacturing process. According to the present invention, the reflection layer provided between the scintillator elements is composed of the first reflection layer / second reflection layer / metal film / second reflection layer / first reflection layer, thereby providing a scintillator. A high diffuse reflectance can be achieved at the element interface, and crosstalk between the scintillator elements can be reliably prevented, so that a detector with high detection sensitivity and high detection output can be provided. Therefore, by applying this scintillator to an X-ray detector for an X-ray CT apparatus, an X-ray CT apparatus capable of obtaining a high-quality tomographic image free from artifacts can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a radiation detector to which the present invention is applied.
FIG. 2 is a diagram for explaining an example of a scintillator manufacturing process according to the present invention.
FIG. 3 is a diagram for explaining the mechanism of the centrifugal casting method of the present invention.
FIG. 4 is a diagram for explaining a part of the scintillator material.
FIG. 5 is a view for explaining the content ratio of inorganic compound powder particles in the reflecting material of the scintillator of the present invention.
FIG. 6 is a diagram showing a configuration of a scintillator according to a second embodiment of the present invention.
7 is a diagram showing a configuration of a radiation detector using the scintillator of FIG. 6;
FIG. 8 is a view for explaining an example of a manufacturing process of the scintillator of FIG.
FIG. 9 is a diagram showing an outline of an X-ray CT apparatus to which the present invention is applied.
[Explanation of symbols]
6 ... Organic resin
7 ... Inorganic compound powder
10 ... Scintillator material
13 ... Reflective layer (first reflective layer)
14 ... Second reflective layer
15 ... Metal film
16 ... Separator plate
20 ... notch groove
100, 200 ... Scintillator

Claims (5)

  In the rectangular parallelepiped scintillator material, using a centrifuge, a step of forming slits having a predetermined pitch, a predetermined width, and a predetermined depth along a first direction and a second direction orthogonal to the first direction, Using the centrifugal direction as the injection direction, a step of injecting a resin containing reflector powder into the cut groove, a step of curing the resin, and a third direction orthogonal to the first and second directions after the resin is cured And a method of manufacturing a scintillator for a radiation detector, including a step of cutting along a plane perpendicular to the surface.   Forming a groove having a predetermined pitch, a predetermined width, and a predetermined depth in a rectangular parallelepiped scintillator material along a first direction and a second direction orthogonal to the first direction; A step of inserting a separator having a thickness smaller than the width, a step of injecting a resin containing a reflector powder into the cut groove into which the separator is inserted, using the centrifuge as an injection direction, and the resin A method of manufacturing a scintillator for a radiation detector, comprising: a step of curing; and a step of cutting along a plane orthogonal to a third direction orthogonal to the first and second directions after the resin is cured.   A scintillator for a radiation detector manufactured by the manufacturing method according to claim 1.   The radiation detector provided with the scintillator and the photodetector which detects light emission of this scintillator, The scintillator of Claim 3 was used as the said scintillator, The radiation detector characterized by the above-mentioned.   An X-ray source, an X-ray detector disposed opposite to the X-ray source, a rotating disk that holds the X-ray source and the X-ray detector and is driven to rotate around the subject, 5. An X-ray CT apparatus comprising image reconstruction means for reconstructing a tomographic image of the subject based on the intensity of the X-ray detected by the X-ray detector, wherein the radiation according to claim 4 is used as the X-ray detector. An X-ray CT apparatus using a detector.

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