JP3548664B2 - Phase contrast X-ray imaging device - Google Patents

Description

【００２１】
図８は縞走査法を実施するためにＸ線干渉計のビームパス中に配置される位相板の例を示し、これを動かして位相差が調整できる。（ａ）は楔形の位相板２５を利用する場合で、Ｘ線干渉形の一方のビームパスに挿入して楔２５の傾斜方向に移動できるようにする。Ｘ線位相板による位相シフト量はＸ線位相板の厚さに比例するので、図７の矢印のように楔２５を動かせばＸ線が通過する位置での厚さを変えられ、楔２５の移動量に比例した位相差を与えることができる。ただし、このタイプの位相板は、Ｘ線ビームの中に位相勾配を発生させる効果があり、結果的に等間隔の干渉縞を生成する。前記縞走査法を用いて得られる位相シフト分布像からこの位相勾配を差し引けば求める像（被写体の位相シフト分布像）が得られるので原理上問題ないが、縞走査の精度が悪い場合は、楔２５による干渉縞が位相シフト分布像に痕跡として残り、縞状のアーチファクトとなってしまうという欠点がある。（ｂ）は板状の位相板２６を矢印のように回転させることで位相板の厚さを変え、位相差を調整する方式である。位相板２６自体が干渉縞を生成することはないので、楔型位相板２５を使う場合のようなアーチファクトの心配はない。その代り、位相板の回転角は与える位相差に対して比例関係にないので、予め回転角と位相差を校正する必要がある。（ｃ）は同じ形状の楔２７、２７’を反平行に重ねたもので、少なくとも一方の楔を傾斜方向に移動させて位相差を調整する方式である。楔の移動量が与える位相差に比例するという（ａ）の利点、および縞状のアーチファクトが発生する心配がないという（ｂ）の利点を兼ね備える方式である。なお、上記（ａ）、（ｂ）および（ｃ）のいずれの場合においても、位相板の挿入位置は図１に示したビーム６ａ、６ｂ、７ａおよび７ｂのいずれでもよい。（ｄ）も同じ目的のものであるが、二つのビームパス、たとえば、図１のビーム６ａ、７ａに同じ形状の楔型位相板２８、２８’を同じ向きで一つずつ挿入する方法である。位相差を調整するためには少なくとも一方の楔を矢印に示す傾斜方向に動かせば良い。
【００２２】
本発明は太いＸ線ビームが利用でき、かつ各ミラー間の距離を十分に大きく取れるＸ線干渉計を実現することで、位相コントラストＸ線撮像法の医療診断装置への応用を可能とした。また、Ｘ線干渉図形のままでは診断に利用できないばあいがあるので、干渉図形から位相分布像が得られる工夫を施し、装置の調整具合によらず、常に同じコントラストの像を提供できるようになった。本発明の装置を用いて位相コントラストマモグラフィ、位相コントラストアンジオグラフィ等の新しい診断手法が実現でき、更に、被写体を回転して複数の投影方向から位相シフト分布像を取得し、処理すれば位相コントラストＸ線ＣＴが実現できる。これらの手段により、従来法では診断が難しい生体中の軟部組織（癌等）を約千倍の像感度で診断できる。また、人体へのＸ線照射量も従来法に比べて大幅に軽減できる。更に、Ｘ線干渉計を通るＸ線ビームは平面波に近いので像のぼけが少なく、５０μｍ以下の空間分解能の画像を得ることができる。
【００２３】
図９に、図４で説明したＸ線ハーフミラーのユニットを使用して構成したマモグラフィ装置の全体構成を示す。各ユニットはステージ３６および３７に固定されている。本実施例ではステージ３６には図６に示したθ軸調整用の回転ステージが採用され、ステージ３７にはθ軸とω軸の調整のため、前述したように、図６に示したθ軸調整用の回転ステージと図７に示したω軸調整用の回転ステージ２００とを２段重ねしたステージが採用されている。なお、θ軸またはω軸の調整は相対的なものであるから、これを逆関係にしてもユニット９、９’の相対的回転角は同じように調整できる。ステージ３６、３７は共通の除振台３９の上に配置されており、更に装置全体がチャンバ５１の中に納められているが、図では、チャンバーの外側の線のみが５１で示されている。ユニット９、９’の側面は鏡面に研磨されており、この鏡面を利用した光の反射により、オートコリメータ３０７でユニット９（Ｘ線ハーフミラー１、２ａ）に対するユニット９’（Ｘ線ハーフミラー２ｂ 、３）の相対的な回転角θおよびωの診断に先立つ粗調整を行う。オートコリメータ３０７から発せられた光３０８はユニット９の側面を反射して戻り、光３０９は直角プリズム３１０および３１１を介してユニット９’の側面を反射して戻る。光３０８、３０９の戻り位置を調べることで角度θ、ωの粗調整のための信号が得られる。尚、研磨面と結晶格子面の角度はできるだけ二つのユニットで同じになるよう工作するが、予めＸ線を用いて両ユニット間のずれを調べておき、それを考慮の上粗調整するのが良い。また、二つのユニットが離れているため、プリズムやミラーを用いて光路を変更させるが、このときの光学素子による影響も予め測定しておき、補正するのが良い。粗調整の操作は追って説明する。
【００２４】
ユニット９のＸ線ハーフミラー１に入射するＸ線は、Ｘ線ハーフミラー１によりビーム６ａと７ａに分かれ、ビーム６ａはＸ線ハーフミラー２ａによりビーム６ｂと６ｃに分かれる。ビーム７ａはＸ線ハーフミラー２ｂによりビーム７ｂと７ｃに分かれる。ビーム６ｂとビーム７ｂはＸ線ハーフミラー３により干渉してビーム６ｄと７ｄとして出力される。被検者４９の被検査部位５０はビーム６ｂのパスに挿入する。このとき、ビーム６ｃはチャンバ５１のビーム６ｃが当たる部分に貼り付けられたシールド板５３により被検者４９にあたらないようにされる。なお、被験者４９はビーム７ｂの位置に配置しても同様な診断ができ、その場合凹部の設置位置はビーム７ｂ側となる。また、撮像に先立って、被検査部位（乳房）５０をホルダ５４によって所定の位置で一定厚さに圧迫し、例えば床に仮固定する。ただし、ホルダ５４には多少平行移動および回転できるだけの自由度を設け、撮像の柔軟性を確保するのが良い。５５および５６は位相板およびその駆動台であり、干渉図形のままで診断が難しいときは、縞走査法により位相シフト分布像で診断できるようにビーム７ａのパスに設置される。駆動台５６は駆動時の振動が除振台３９に伝わるのを避け、チャンバ５１の天井に固定されている。位相板の駆動は、コンピュータ６０からの指令を受けた制御装置３２８の信号により行われる。５７および５８はＸ線強度モニタで、ビーム７ｃおよびビーム６ｄを受けるように配置される。さらに８１もＸ線強度モニタであるが、これは、ビーム７ａの所定のビーム位置の端部に配置され、ビーム７ａの端部のＸ線を受ける。これらのＸ線強度モニタ５７、５８および８１には例えばＰＩＮダイオード検出器を用い、Ｘ線があたったときに流れる電流を計測する方法が簡便である。また、これらのＸ線強度モニタ５７、５８および８１の出力を使用して診断に先立つ粗調整を行う。なお、検査部位５０の干渉図形はビーム６ｄおよび７ｄでほぼ同じものが観察され、ここではビーム７ｄを受けるように配置したＸ線二次元センサ５９で干渉図形を検出したが、 Ｘ線強度モニタ５８をＸ線二次元センサとして、Ｘ線干渉図形を取得するものとしても良い。図の例では、Ｘ線強度モニタ５８をＸ線二次元センサとして、Ｘ線二次元センサ５９のＸ線干渉図形とは別に干渉計の安定化のためのフィードバック信号として利用した。Ｘ線二次元センサ５８、５９はカメラコントローラ６３’、６３で駆動され、カメラコントローラ６３’、６３はコンピュータ６０によって制御されている。コンピュータ６０内で稼働している制御プログラムによって撮像が指示され、取得画像はカメラコントローラ６３’、６３を介してコンピュータ６０のメモリに蓄えられる。このメモリーに貯えられた画像データから診断が行われ、且つ、フィードバックによる安定化の制御信号が制御装置３２５に出される。コンピュータ６０からの指令を受けた制御装置３２５の信号により、２段重ねとされたステージ３７の圧電素子に電圧制御信号が与えられθ、ωのフィードバックが行われるが、この具体例については後述する。
【００２５】
ユニット９のＸ線ハーフミラー１に入射するＸ線は、隔壁５２を介して隔離された部屋に配置されたＸ線源３３から供給するのが望ましい。 被検者４９への不必要な被爆を避けるとともにＸ線源３３から発生する振動がＸ線干渉計に伝わるのを防止することができるからである。
【００２６】
Ｘ線源３３から放出されるＸ線を単色器３４を用いて特定のエネルギーのＸ線ビーム４を取りだし、撮像装置へ導いた。単色器３４は非対称反射（図３（ａ）において、０＜α＜θの場合）でビーム４の横幅を広げる作用も兼ねている。回折指数はＸ線ハーフミラーのものと同じにした方がよく、（２２０）、（４４０）、（４００）、（４２２）等が望ましい。Ｘ線源３３は図９の紙面の方向で横長であるほうが単色器３４でビーム幅を広げるのに有利であり、強いＸ線ビームが干渉計内に形成される。単色器３４直後にシャッタ３５を設け、撮像時以外の不必要なＸ線照射は行わないようにする。このシャッタ３５はＸ線源３３直後にあっても良い。
【００２７】
次に、診断に先立つ粗調整と干渉計の安定化のためのフィードバック制御について説明する。
【００２８】
まず、Ｘ線強度モニタ８１の出力に着目してする。Ｘ線ハーフミラーは回折条件を満たしているときのみ正常に機能するものであるから、 Ｘ線ハーフミラー１のθが適切でないとＸ線が適切にＸ線ハーフミラーを透過しない。 Ｘ線強度モニタ８１は、ビーム７ａの端部に配置されているから、θが適切でないときはほとんどＸ線が感知されない。したがって、 Ｘ線強度モニタ８１にほとんどＸ線が感知されないときは、Ｘ線強度モニタ８１の出力がほぼ最大になるようθを修正する信号をステージ３６に与える。つぎに、オートコリメータ３０７から出された光３０８、３０９のユニット９（Ｘ線ハーフミラー１、２ａ）およびユニット９’（Ｘ線ハーフミラー２ｂ、３）の両側面からの反射光を調べて、この反射光が平行になるようにステージ３７に角度θ、ωの調整のための信号与える。前記の粗調整後、Ｘ線画像センサ５９に干渉図形が現れるまでステージ３７の二つの圧電素子を制御して回転二軸（θおよびω）をスキャンして干渉図形を見つける。一旦干渉縞が得られれば、この干渉縞が最適状態になるように回転二軸（θおよびω）を制御して診断に入ることができる。
【００２９】
一旦干渉縞が得られて診断に入ることができた後も、高精度の調整の必要なθ軸、ω軸がドリフトすると干渉図形が変化する。そのため、被験者の診断中はＸ線画像センサ５８に得られる干渉図形をモニタすることによりＸ線干渉計の安定化を図ることができる。θ軸、ω軸がドリフトすると干渉図形が変化するが、その様子は各軸で異なる。θ軸の場合、二つのビーム６ｂ、７ｂの見かけ上の位相差が変化し、一方、ω軸がドリフトする場合は回転モアレに似た縞が発生して、ω軸のドリフトの量に依存してこれが伸縮する。したがって、 Ｘ線画像センサ５８に得られる干渉図形をカメラコントロール６３’を介してコンピュータ６０による処理で変化をキャンセルするようにフィードバック制御をすることで安定した診断ができる。
【００３０】
縞走査法による画像取得が必要なときは、位相差を変化させながら複数の画像（干渉図形）を取得するよう、コンピュータ６０内で稼働している制御プログラムが位相板の駆動台５６およびカメラコントローラ６３に命令を発する。得られた画像から（１）式に基づく演算をコンピュータ６０が施し、生成された位相シフト分布像をコンピュータ６０の表示装置に表示する。
【００３１】
図１０に、前述した実施例１の構成をチャンバ５１を装着した状態で見た斜視図を示した。ビーム６ｂは窓７１を通って一旦チャンバ５１の外へ導き出され、被験者４９の検査部位５０（図では省略）を透過した後、再びチャンバ５１内へ窓７２を通って入り、干渉ビーム６ｄ、７ｄが窓７３を通ってチャンバ５１外へ導かれ、計測される。尚、窓７１、７２、７３はＸ線をあまり吸収しないプラスチック板等でチャンバ５１内外を隔てており、被検者４９が発する熱（体温、息等）が光学系に影響することはない。なお、図では、入射するＸ線の表示は省略した。
【００３２】
図１１は、 Ｘ線干渉計としては前述した実施例１と同じ構成であるが、より速い変動としての振動に対する対策を施した実施例の概要を示す。
【００３３】
Ｘ線ハーフミラーのユニット９、９’が相対的に振動しているとＸ線干渉縞が速い周波数で空間的に揺れるため、見かけ上干渉縞の鮮明度が低下したり見えなくなる場合がある。従って、ユニット９、９’に振動が伝わらないよう工夫する必要がある。本実施例では図に示すように、Ｘ線ハーフミラー１、２ａおよび、２ｂ、３をプール４５０に固定し、プール内に粘性の高い液体（例えば油）を満たして、Ｘ線ハーフミラー１、２ａおよび、２ｂ、３のみが液面より上に表れるようにする。プール４５０は除振台３９の上に載せられ、全体はチャンバ５１で覆われている。こうすることで高い周波数成分の振動が抑えられ、干渉縞の鮮明度が向上する。チャンバ５１の壁に設けられたＸ線の通過窓４５２、４５３、４５４、４５５には金属ベリリウムが張り付けてあり、外部の空気が流れ込まないようになっている。他の窓材としては、ポリマーフィルムや薄いアルミ板、ガラス板等が使える。
【００３４】
この実施例は、通常用いられる防音室、防音壁および除振台を採用するに加え、干渉計のＸ線ハーフミラーより下部を粘性の高い液体中に沈めた例である。
【００３５】
実施例２
この実施例は、図２（ａ）に示すように独立した３枚のＸ線ハーフミラー１、２および３を使用してＸ線干渉計を構成するものである。図１２にこの実施例でＸ線ハーフミラー を調整する場合に必要な自由度を示した。 Ｘ線反射ミラーの場合も同様である。実施例１について図４で説明したと同様に、この図においても矢印を付して示す太い実線はハーフミラーの中心部に入射し、中心部から出射するＸ線を示す。５は結晶の回折格子面の一部を代表して示し、回折格子面５の法線方向をｘ軸、散乱面（図中ｘ線ビームの進行方向を示す矢印を含む面）の法線方向をｙ軸、 ｘ軸およびｙ軸に垂直な軸をｚ軸とする。また、 ｘ軸、ｙ軸およびｚ軸回りの回転軸をそれぞれφ軸、θ軸およびω軸とする。Ｘ線ハーフミラーの平行移動に関してはｘ軸の精度が厳しく要求され、数分の１Å以下の精度が必要になる。ｚ軸に関しては１μｍの精度で十分であり、ｙ軸は特に厳密な微調整の必要はない。回転に関してはθ軸はブラッグ回折条件に関係する軸であり、十分の１秒以下の精度が必要である。θ軸と直交しかつ結晶表面と垂直な方向のω軸は百分の一秒以下の精度が必要である。φ軸に関しては特に厳密な微調整の必要はない。したがって、重要な微調軸はｘ、ｚ、ω、θ軸である。
【００３６】
図１３に示すように、各Ｘ線ハーフミラー１、２、３は、円柱形のシリコンのインゴット３２を縦割りにして作製した。Ｘ線ハーフミラーとして機能する結晶板３０はベース３１と一体となるように破線で示すインゴット３２から削り出される。Ｘ線ハーフミラー１、２、３の回折面は（２２０）、（４４０）、（４００）、（４２２）等を使うのがよい。
【００３７】
図１４は数分の１Å以下の位置制御を実現するためのｘ軸方向の移動ステージ３００の構成例を、中央に平面図、左側および右側にそれぞれ側面図をとって示す。ステージ３００は一軸平行移動ステージであり、厚板の鋼材からワイアーカット加工で切り出して作製された。ステージ取り付け部３０１と可動部３０２とが平行に配置され、支持部３０３、３０４により連結されている。支持部３０３、３０４はそれぞれ括れた部分Ａ〜Ｄを介して連結される。ステージ取り付け部３０１の一端には逆Ｌ字型の圧電素子取り付け部３０５が設けられる。可動部３０２の一端には括れた部分Ｆを介して、てこ３０６の一端が連結される。てこ３０６の他端と圧電素子取り付け部３０５との間には圧電素子３１０が設けられる。括れた部分Ｆに近い位置に括れた部分Ｅが形成され、この一端はてこ３０６に他端はステージ取り付け部３０１に支持される。てこ３０６の圧電素子３１０が設けられた面の反対側の面とステージ取り付け部３０１との間に電極３１２ａ、３１２ｂが設けられる。括れた部分Ａ〜Ｆが弾性的に変形するとする。圧電素子３１０に加える電圧の極性と大きさを制御するとこれに応じて圧電素子３１０が伸縮し、可働部３０２が矢印の方向に変位する。その際、点Ｅ、Ｆが支点および作用点に相当するので、圧電素子３１０の伸縮長さがてこの原理で縮小され、可動部３０２の微少な位置制御ができる。距離の比ａ／ｂを選ぶことで縮小率が決まる。また、電極３１２ａ、３１２ｂ間の静電容量を測定することで圧電素子３１０の伸縮量をモニタすることができる。図１４に示す両側面図から分かるように、ステージ取り付け部３０１に対して可動部３０２、支持部３０３、３０４およびてこ３０６は底面がごくわずか高く形成され、さらに可動部３０２の上面は他の部分よりごくわずか高く形成されている。これによって、可動部３０２の動きがスムースになるとともに二段重ねとしたときにも支障無く制御できる。
【００３８】
本実施例においてもω軸やθ軸の制御が必要でありこれに利用できる回転ステージが必要であるが、それぞれの回転軸に対して、図６、図７で説明した回転ステージが使用できるから、この実施例における回転ステージの構成例の図示は省略する
図１２で説明したように、Ｘ線ハーフミラーにとって重要な微調軸はｘ、ｚ、ω、θ軸であるから、図１４、図６、図７に示したステージを多段に重ねて、これらを調整可能として独立のＸ線ハーフミラーを支持することができる。たとえば、図１４に示したステージを９０°ずらせて上下に重ねて配置し、下段のステージのステージ取り付け部３０１を独立した各Ｘ線ハーフミラーの共通の除振台に固定し、下段のステージの可動部３０２に上段のステージのステージ取り付け部３０１を固定するものとする。そうすると、たとえば下段のステージの可動部がｘ軸方向に対応して制御されるものとすれば、上段のステージの可動部はｚ軸方向に対応して制御されることになる。同様に、図６、図７に示した回転ステージを実施例１で２段重ねとして使用したと同様にすれば、この実施例においても、ω、θ軸の制御ができる。図１４に示したステージの２段重ねの上段のステージの可動部に、図６、図７に示した回転ステージの２段重ねの下段のステージの固定側の厚板１０１を固定すれば、図７に示したステージの回転側の厚板２０２は、 ｘ、ｚ、ω、θ軸の４軸に対応して制御されることになる。
【００３９】
第１の実施例と異なり、この実施例では、独立のＸ線ハーフミラー１、２、３を個々に制御する必要がある。Ｘ線ハーフミラー１に対してはθ軸の調整ステージ３６を、Ｘ線ハーフミラー２に対してはθ軸およびω軸の２段重ねの調整ステージ３７を、 Ｘ線ハーフミラー３に対しては上述のθ軸およびω軸の回転ステージおよびｘ軸およびｙ軸の平行移動ステージの４段重ねの圧電ステージ３８をそれぞれ設け、これを介して除振台３９上に配置した。図１２のｘ軸に相当する方向の変位を検出するためにレーザ干渉形４２も除振台３９上に配置した。レーザ干渉計４２から出るレーザビーム４５は圧電素子ステージ３８上に固定された反射鏡４８（コーナーキューブ等）で反射されてレーザ干渉計４２に戻される。除振台３９には被験者４９の検査部位５０をＸ線ビームパス６ｂに挿入できるように凹部を設けた。なお、被験者４９はビーム７ｂの位置に配置しても同様な観察ができ、その場合凹部の設置位置はビーム７ｂ側となる。また、Ｘ線干渉計、レーザ干渉計の動作の安定化および被験者４９の安全のために、除振台３９の形状に合わせたチャンバ５１を設け、Ｘ線干渉計、レーザ干渉計と外部との接触を絶つとともにＸ線シールド５３を設け必要なＸ線以外のＸ線が被験者４９に照射されないようにすること、また、撮像に先立って、検査部位（乳房）５０をホルダ５４によって所定の位置で一定厚さに圧迫し、例えば床に仮固定する。ただし、ホルダ５４には多少平行移動および回転できるだけの自由度を設け、撮像の柔軟性を確保するのが良いことは実施例１と同じである。５５および５６は位相板およびその駆動台であり、実施例１と同様に、干渉図形のままで診断が難しいときは、縞走査法により位相シフト分布像で診断できるようにビーム７ａのパスに設置される。位相板の駆動は、コンピュータ６０からの指令を受けた制御装置３２８の信号により行われる。また、５７、５８および８１は強度モニタで、実施例１と同様に配置され、Ｘ線ハーフミラー１、２、３の粗調整に用いられる。検査部位５０の干渉図形はビーム６ｄおよび７ｄでほぼ同じものが観察されるが、ここでも、実施例１と同様に、ビーム７ｄを受けるように配置したＸ線二次元センサ５９で干渉図形を検出した。
【００４０】
強度モニタ５７、５８および８１によるＸ線ハーフミラー１、２、３の粗調整について説明する。この実施例でも実施例１と同様に、強度モニタ８１の出力がほぼ最大になるようにＸ線ハーフミラー１のθの粗調整を行う。次いで、強度モニタ５７の出力がほぼ最大になるようにＸ線ハーフミラー２のθの粗調整を行う。その後、強度モニタ５８の出力がほぼ最大になるようにＸ線ハーフミラー３のθの粗調整を行う。
【００４１】
前記の粗調整後、Ｘ線画像センサ５９に干渉図形が現れるまでステージ３７の二つの圧電素子を制御して回転二軸（θおよびω）をスキャンし、ステージ３８の三つの圧電素子を制御して回転二軸（θおよびω）およびｚ軸をスキャンして干渉図形を見つける。一旦干渉縞が得られれば、この干渉縞が最適状態になるように回転二軸（θおよびω）を制御して診断に入ることができる。
【００４２】
Ｘ線二次元センサ５８、５９はカメラコントローラ６３’、６３で駆動され、カメラコントローラ６３’、６３はコンピュータ６０によって制御されている。コンピュータ６０内で稼働している制御プログラムによって撮像が指示され、取得画像はカメラコントローラ６３’、６３を介してコンピュータ６０のメモリに蓄えられる。このメモリーに貯えられた画像データから診断が行われ、且つ、フィードバックによる安定化の制御信号が制御装置３２５に出される。コンピュータ６０からの指令を受けた制御装置３２５の信号により、ステージ３６、２段重ねとされたステージ３７および４段重ねのステージ３８の圧電素子に電圧制御信号が与えられθ、ωおよびｘ軸のフィードバックが行われるが、この具体例については後述する。
【００４３】
一旦干渉縞が得られて診断に入ることができた後も、高精度の調整の必要なθ軸、ω軸およびｘ軸がドリフトすると干渉図形が変化する。実施例１と同様に、被験者の診断中はＸ線画像センサ５８に得られる干渉図形をモニタすることによりＸ線干渉計の安定化を図ることができる。θ軸、ω軸のドリフトについては実施例１で説明した通りであり、 ｘ軸のドリフトもθ軸と同様に、二つのビーム６ｂ、７ｂの見かけ上の位相差が変化する。したがって、 Ｘ線画像センサ５８に得られる干渉図形をカメラコントロール６３’を介してコンピュータ６０による処理で変化をキャンセルするようにフィードバック制御をすることで安定した診断ができる。
【００４４】
縞走査法による画像取得が必要なときは、実施例１と同様にして生成された位相シフト分布像をコンピュータ６０の表示装置に表示すればよい。
【００４５】
図１６は、図１５に示した装置の４段重ねのステージ３８をコンピュータで駆動、制御するためのブロック図を示す。ステージ３６および３７の制御は実施例１で説明したと同様であり、説明を省略する。 Ｘ線ハーフミラー３を支持している圧電素子ステージ３８は、図１２で説明したｘ、ｚ、ωおよびθ軸を調整するために、図１４に示す構造の平行移動ステージ６５ａ、６５ｂおよび図６、図７に示す構造の回転ステージ６４ａ、６４ｂを前述したような組み合わせで構成したものである。圧電素子ステージ３８は、複数のチャンネルを持つ圧電素子コントローラ６１により駆動される。圧電素子コントローラ６１の出力により圧電素子ステージ３８が駆動されるとき、平行移動ステージ６５ａ、６５ｂの可動部の動きに対応した静電容量センサ３１２ａ、３１２ｂの出力の変化を圧電素子コントローラ６１が読取り、圧電素子コントローラ６１は圧電素子のヒステリシスを補正した電圧を圧電素子に出力する。また、センサ出力はコンピュータ６０へも伝えられる。レーザ干渉計４２はレーザビーム４５を発しており、圧電素子ステージ３８上にＸ線ハーフミラー３とともに設置された反射鏡４８がレーザビーム４５を反射し、レーザ干渉計４２に戻す。レーザ干渉計４２は圧電素子ステージ３８の位置（ｘ軸方向）が変化したとき、その変化量を検出、出力し、Ａ／Ｄコンバータ６２を介してコンピュータ６０へ伝える。コンピュータ６０内で稼働している制御プログラムは伝えられた信号を処理し、フィードバック信号として圧電素子にかける電圧の変更を圧電素子コントローラ６１に指示する。強度モニタ５７、５８からの信号はコンピュータ６０内で稼働している制御プログラムの補助データとして、フィードバック信号の調整に使われる。Ｘ線二次元センサ５９はカメラコントローラ６３で駆動され、カメラコントローラ６３はコンピュータ６０によって制御されている。コンピュータ６０内で稼働している制御プログラムによって撮像が指示され、取得画像はカメラコントローラ６３を介してコンピュータ６０のメモリに蓄えられる。
【００４６】
縞走査法による画像取得が必要なときは、実施例１と同様、位相差を変化させながら複数の画像（干渉図形）を取得して、得られた画像から（１）式に基づく演算をコンピュータ６０が施し、生成された位相シフト分布像をコンピュータ６０の表示装置に表示する。
【００４７】
図１５と図１６とを対照して分かるように、図１６では、図面を簡単化するために、制御用のコンピュータへの信号の伝送および制御用のコンピュータから各ステージへの制御信号の伝送の線は一部の表示を省略した。
【００４８】
なお、本実施例では、すべてのＸ線ハーフミラー１．２および３に調整のためのステージを設けたが、これらのミラーの調整は相対的なものであるので、三つのミラーのうち一つを固定とすることができるのは言うまでもなかろう。
【００４９】
実施例１、２の変形として、被験者４９をビーム７ａのパスに入れることもできる。この場合は、実施例２で必要であったシールド板５３を省略できるメリットがある。もちろん本発明では、弱いＸ線で良いからシールド板５３を省いても被験者４９に照射されるＸ線は２倍になるのみであるので、従来法よりＸ線被爆線量は遥かに低い。しかしＸ線被爆線量は少ないほど良いことおよびＸ線干渉計のＸ線入射側と出射側を反転させてもほぼ同じ性能が期待できるので、被験者４９の入るビームパスを７ａにしても良い。同様に、実施例１では、被験者４９の位置をビーム６ａのパスとしても同じである。ただし、これらの場合には、検査部位５０を通ったＸ線が二次元検出器５９に到達するまでに２枚のＸ線ハーフミラー２、３を通過することになるので得られる画像の空間分解能はやや低下する。この実施例では被検者４９の利用できるスペースが広くなり、被検者４９が撮像の際に姿勢を保持するのが楽になる。また装置全体の大きさも小さくできる。また、縞走査法を適用するための位相板の挿入されるパスもどちらでも良い。
【００５０】
図１７は、Ｘ線干渉計のための、より強力なＸ線源の例を示す。
【００５１】
Ｘ線干渉計は準単色Ｘ線に対して機能するので、迅速に撮像するためにはある程度強力なＸ線源を使用するのが有利である。前述の実施例の光学系の場合、Ｘ線源の形状として鉛直方向には細い必要があるが、水平方向には長くても構わない。従って、特に電子線励起或はレーザー励起の線源を使用する場合、図のように構成するのが有効である。
【００５２】
図１７において、５４０はターゲット、５４１は回転軸、５４２はＸ線発生部位、５４３は電子線源或はレーザー光源、５４４は電子線或はレーザー、５４５はＸ線、５４６はフィルタである。図ではターゲット５４０の部分の平面図をも併記した。この構成によれば、電子線或はレーザー光５４４をターゲット５４０上で線状に走査して横長のＸ線源５４２を形成することができる。これによりターゲットに与える熱を比較的分散させることができるので、より多くのＸ線５４５をＸ線干渉計に導くことができる。
【００５３】
また、図は省略したが、Ｘ線干渉計へより良質のＸ線ビームを供給するために、各実施例における結晶３４の反射方向を変えたり、２枚以上の結晶を連続して反射させる単色器とするのも有効である。
【００５４】
なお、上記のいずれの実施例においても、Ｘ線ハーフミラーまたはＸ線ハーフミラーユニットは、それぞれ取り付け位置に関わらず、実質的に同じ構造に作るのが有利である。したがって、除振台に取り付ける際、制御ステージの有無、あるいは制御ステージの構成の差異によってＸ線ハーフミラーまたはＸ線ハーフミラーユニットの底面の高さが除振台表面から異なることにことなる。これに対しては、図面によっては説明をしなかったが、スペーサー等を挿入して高さ合わせをすることは当然である。
【００５５】
本発明は、高感度の撮像ができるので、本来、造影剤の注入は不要となるが、特定の興味ある部位のコントラストを強調したいときには併用しても良い。この場合、従来法のように重元素からなる造影剤を使用しなくてはならないという制限はなく、造影剤の材料を幅広く求めることができる。
【００５６】
【発明の効果】
本発明によれば、広い観察視野を有する高感度の位相コントラストＸ線撮像装置を得ることができる。
【図面の簡単な説明】
【図１】公知の一体型Ｘ線干渉計を示す図。
【図２】（ａ）（ｂ）（ｃ）および（ｄ）は、独立のＸ線ハーフミラーによって構成されたＸ線干渉計のビームパスの基本的な構成を示す図。
【図３】（ａ）（ｂ）および（ｃ）は結晶表面と回折格子面が成す角度αの違いによる回折様式の違いを示す模式図。
【図４】本発明の実施例１で使用するＸ線ハーフミラーユニットの形状とその調整軸を示す図。
【図５】図４に示すＸ線ハーフミラーユニットを円柱形のシリコンのインゴットから切り出す様子を示す図。
【図６】本発明の実施例１における回転軸θのための圧電素子駆動ステージの構成例を示す平面図および側面図。
【図７】本発明の実施例１における回転軸ωのための圧電素子駆動ステージの構成例を示す平面図および側面図。
【図８】（ａ）（ｂ）（ｃ）および（ｄ）は縞走査法のための位相板の構成を示す図。
【図９】本発明の実施例１の位相コントラストマモグラフィ装置の全体の構成を示す平面図。
【図１０】本発明の実施例１の位相コントラストマモグラフィ装置にチャンバを付けた状態で見た斜視図。
【図１１】本発明の実施例１の位相コントラストマモグラフィ装置に振動抑制対策を施したチャンバの内部構造の概略を示す斜視図。
【図１２】本発明の実施例２で使用するＸ線ハーフミラーの形状とその調整軸を示す図。
【図１３】図１２に示すＸ線ハーフミラーを円柱形のシリコンのインゴットから切り出す様子を示す図。
【図１４】本発明の実施例２における平行移動軸ｘのための圧電素子駆動ステージの構成例を示す平面図。
【図１５】本発明の実施例２の位相コントラストマモグラフィ装置の全体の構成を示す図。
【図１６】位相コントラストマモグラフィ装置を駆動制御するためのブロック図。
【図１７】線状光源としてのＸ線源の構成例と干渉計との配置関係を示す図。
【符号の説明】
６ａ、６ｂ、７ａおよび７ｂ：ビームパス、９，９’： Ｘ線ハーフミラーユニット、３６：ユニット９の調整ステージ、３７： ユニット９’の調整ステージ、３９：除振台、４９：被検者、５０：被検査部位、１００，２００：回転ステージ、３２：インゴット、２５，２６，２７，２８：楔型位相板、５１：チャンバ、５３：シールド板、５４：ホルダ、５５：位相板、５６：位相板の駆動台、６０：コンピュータ、５７，５８，８１：Ｘ線強度モニタ、５９：Ｘ線二次元センサ、６３’，６３：カメラコントローラ、５２：隔壁、３３：Ｘ線源、３４：単色器、３５：シャッタ、７１，７２，７３：窓、１０１，２０１：固定部、１０２，２０２：回転部、１０３，１０４，２０３：結合部１０５：保持部、１０３：支持ボルト、１０８，２０５：圧電素子、２０７：ボルト、２０４：括れた部分、３０７：オートコリメータ、３０８，３０９：光、３１０，３１１：直角プリズム、３２５，３２８：制御装置、４５０：プール、４５２、４５３、４５４、４５５： Ｘ線の通過窓。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a phase contrast X-ray imaging apparatus, and more particularly, to an X-ray imaging apparatus using a phase contrast that has extremely high image sensitivity as compared with a conventional X-ray imaging method that relies on absorption contrast. INDUSTRIAL APPLICABILITY The present invention is suitable for observation of a soft tissue or the like of a living body having a small X-ray absorptivity, and can be used as a medical diagnostic apparatus because a relatively wide observation field of view can be secured.
[0002]
[Prior art]
All of the X-ray imaging devices currently in practical use obtain image contrast depending on the magnitude of X-ray absorption. The absorption of X-rays is larger for heavier elements, and it is easy to form X-ray shadows if the subject contains more heavy elements. On the other hand, a substance made of a light element that does not absorb much X-rays is too transparent to X-rays, and a sufficient contrast cannot be obtained. In a medical X-ray diagnostic apparatus, a method of emphasizing image contrast by injecting a contrast agent containing a heavy element into a subject, if possible, for such a hard-to-observe target (soft tissue), if possible. Has been taken. In the case where there is no suitable contrast agent such as an X-ray diagnostic apparatus (mammography apparatus) for diagnosing breast cancer, an effort is made to increase the image sensitivity as much as possible using X-rays having relatively low energy. This is because the absorption of X-rays is inversely proportional to the cube of the X-ray energy, and the contrast is easily obtained. However, since the X-ray exposure is also inversely proportional to the cube of the X-ray energy, the increase in the X-ray exposure due to the use of low energy X-rays must be accepted. Also, it cannot be said that a diagnostically sufficient image can be obtained.
[0003]
On the other hand, there is an imaging method in which contrast is obtained not by absorption of X-rays but by a phase shift. Since the cross section of the phase shift is about 1000 times larger than that of the light element than the interaction cross section of the X-ray absorption, observation with sensitivity several hundred times higher than the conventional one can be performed. This indicates that it is possible to observe a subject that is unlikely to generate an X-ray shadow by a conventional method without using a special contrast agent, and has been experimentally proved. Although an X-ray phase contrast image is observed using an X-ray interferometer, the observation field of view is narrow due to the limitation of the size of a configurable interferometer, and application to a medical diagnostic apparatus is difficult as it is. Phase contrast radiography (A. Momose, et al., Med. Phys., 22, 5-380 (1995)) and phase contrast X-ray CT (A. Momose, et al.) Rev. Sci. Instrument 66, 1434-1436 (1995), U.S. Patent 5,173,928).
[0004]
Currently known X-ray interferometers are manufactured by integrally cutting the whole from a single crystal mass such as silicon as shown in FIG. When the three crystal plates 1, 2, and 3 are parallel to each other and are arranged at equal intervals, and the incident X-ray 4 satisfies the diffraction condition with respect to the crystal lattice plane 5 where the incident X-ray 4 exists, the incident X-ray 4 becomes two beams 6a. , 7a, which are likewise separated again in the second crystal plate 2 into two beams 6b and 6c and 7b and 7c, the beams 6b and 7b being combined in the third crystal plate 3 and interfering. That is, the three crystal plates 1, 2, and 3 serve as an X-ray half mirror. When the subject 8 is inserted into one of the beam paths, for example, the beam 6b, the phase of the X-ray is shifted, and interference patterns appear on the X-ray beams 6d and 7d passing through the third crystal plate 3. The size of the observation field of view corresponds to the thickness of the X-ray beam passing through the interferometer, but it is required that the two beams formed in the interferometer be completely separated (not overlap), To make it thicker, the entire interferometer must be made larger. Considering that the entire interferometer is cut out of a single crystal lump and the size of currently available silicon ingots is limited, the observation field that can be secured is at most about 2 cm square.
[0005]
Also, an X-ray interferometer in which two X-ray half mirrors are formed on two independent crystal units is reported (P. Becker and U. Bonse, J. Appl. Cryst., 7, 593-598 (1974)). There is research on the necessary coordination axis, but no practical progress has been made.
[0006]
[Problems to be solved by the invention]
In order to widen the observation field of view in the phase contrast X-ray imaging method and use it for medical diagnosis technology, an X-ray interferometer capable of securing a wide field of view must be developed. An object of the present invention is to broaden an observation field of view by independently producing a plurality of conventionally formed X-ray half mirrors within a necessary range and disposing them separately. Separating each X-ray half mirror configured as an integral type, the P.C. As pointed out by Becker et al, it is important to adjust the relative position of each X-ray half mirror. Therefore, when the X-ray wavelength is particularly short for medical applications, it is extremely short, several tenths of a millimeter, and it is important to devise a means for arranging and adjusting independently manufactured X-ray half mirrors with an accuracy corresponding to this. Become.
[0007]
According to the present invention, an observation field of view exceeding 2 cm square can be secured, and medical diagnostic applications to various imaging methods using X-ray phase contrast (phase contrast mammography, phase contrast angiography, phase contrast X-ray CT, etc.) are possible. It becomes possible.
[0008]
Although an interferogram can be acquired using an X-ray interferometer, it must be noted that the interferogram does not always provide information necessary for diagnosis when applied to medical diagnosis technology. That is, the interference graphic shows some pattern related to the structure inside the subject, and how to read the diagnostic information from it is practically important. The interferogram represents the contour line of the phase shift of the X-ray generated by transmitting through the subject. The magnitude of the X-ray phase shift greatly depends on the shape of the entire subject, and two interferometers are formed in the interferometer. It is also affected by the phase difference of the beam (it is zero if an interferometer is ideally constructed, but is not zero because an adjustment error generally occurs). Thus, for example, the cancerous tissue does not always look bright or dark, but looks bright or dark depending on the size of the tumor and the adjustment of the optical system. Since the brightness of the image of the normal tissue changes similarly, it is difficult to find a specific lesion such as cancer from only the interferogram. Therefore, image processing independent of the state of the optical system is required. For this purpose, it is preferable to convert the interferogram into a phase shift distribution image for measurement. The phase shift distribution image shows the spatial distribution of the phase shift of the X-ray by the subject, and the image contrast basically does not change even if the state of the optical system changes.
[0009]
[Means for Solving the Problems]
FIG. 2 illustrates some basic configurations of a beam path of an X-ray interferometer configured by independent X-ray half mirrors. FIG. 2A is an example in which the half mirrors 1, 2, and 3 shown in FIG. 1 are simply separated into independent shapes. FIG. 2B is a diagram in which the central half mirror is further divided into two independent half mirrors 2a and 2b. FIG. 2C shows an example in which a space for inserting a subject (the space between the half mirror 2a and the half mirror 3) is widened by separating the mirror into mirrors and displacing the mirrors in opposite directions. Each of the two half mirrors 1 and 2a and the two half mirrors 2b and half mirror 3 of the example are integrated as one set, and a set of two independent half mirrors is configured as units 9 and 9 'as a whole. This is an example. In this case, the half mirrors 1 and 2a and the half mirrors 2b and 3 of the units 9 and 9 'can be manufactured by being cut out from a silicon columnar ingot, and it is easy to form the half mirrors in parallel. Note that this example is similar to that of P. Corresponds to that studied by Becker et al. FIG. 2D shows an example in which X-ray reflection mirrors 10, 10 'are used in place of the half mirror 2 at the center. This is because the central half mirrors 2, 2a, 2b in FIGS. 2 (a), 2 (b), and 2 (c) substantially function as mirrors for changing the direction of propagation of X-rays. It is devised so as to avoid loss of beam intensity due to the half mirror.
[0010]
FIGS. 3A, 3B and 3C are schematic diagrams showing the difference in the diffraction pattern due to the difference in the angle α between the crystal surface and the diffraction grating surface, and the difference between the X-ray reflecting mirror and the X-ray half mirror by the crystal. It is shown. In each of the figures, a cross-sectional view of the crystal is shown, and a horizontal line shown in the figure indicates a lattice plane of the crystal. Assuming that the crystal surface 11 and the lattice plane 5 involved in diffraction have an angle α as shown in FIG. _B As α <θ _B Then, it functions as an X-ray reflection mirror, and becomes as shown in FIG. 3B (α = 0 ° in this example). α> θ _B Then, it functions as an X-ray half mirror and becomes as shown in FIG. 3C (α = 90 ° in this example). In these figures, solid lines with arrows indicate X-rays that enter or exit. In the case of (b), the reflectivity is 80% to 90% with respect to the X-ray satisfying the Bragg condition, and the efficiency as a mirror is superior to the case of (c). There is an inconvenience that a long reflecting surface is required when the object is handled.
[0011]
Other configurations of the interferometer are conceivable, but basically, the two beam paths should be considered to be approximately equal in length. This is because the coherence of the X-ray beam is generally not perfect, and as the difference in path length increases, the coherence decreases and the sharpness of the observed interference fringes decreases.
[0012]
In any of the configurations shown in FIG. 2, it is necessary to adjust the relative position of each X-ray half mirror or X-ray reflection mirror with an accuracy smaller than the X-ray wavelength. Further, an angle adjusting mechanism is required to satisfy the Bragg diffraction condition.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Example 1
FIG. 4 shows a phase contrast mammography apparatus using the units 9 and 9 'having a common substrate for each set of the two X-ray half mirrors 1, 2a and 2b and 3 shown in FIG. The shape of the X-ray half mirror for Embodiment 1 of the present invention and the adjustment axis thereof are shown. In this figure, a thick solid line with an arrow indicates an X-ray that enters the center of the half mirror and exits from the center. Reference numeral 5 denotes a part of the diffraction grating surface of the crystal as a representative, the normal direction of the diffraction grating surface 5 is the x-axis, and the normal direction of the scattering surface (the surface including an arrow indicating the traveling direction of the x-ray beam in the drawing). Is defined as a y-axis, an axis perpendicular to the x-axis and the y-axis is defined as a z-axis. The rotation axes around the x-axis, y-axis, and z-axis are referred to as φ-axis, θ-axis, and ω-axis, respectively. When a unit having this configuration is used, there is an advantage that the parallel movement of the x-axis, the y-axis, and the z-axis does not affect the interference phenomenon and adjustment is unnecessary. This is because the two X-ray half mirrors move in parallel in the same manner, and the influence on the phase of the X-rays is cancelled. Regarding the rotation of the θ axis, when (440) reflection is used and the interval between the X-ray half mirrors of the unit is set to 80 cm, 1 × 10 ^-10 Accuracy less than rad is required. Regarding the rotation of the ω axis, the (440) reflection is used, the interval between the X-ray half mirrors of the unit is set to 80 cm, the wavelength of the X-ray is set to 0.2 °, and the distance between the X-ray source and the imaging device (the embodiment shown in FIG. 9) Assuming that the distance between the X-ray source 33 and the X-ray two-dimensional sensor 59 in the example) is 10 m, 1 × 10 ^-7 Accuracy less than rad is required. There is no need to strictly fine-tune the φ axis. Therefore, only the rotation of the ω and θ axes needs to be adjusted.
[0014]
FIG. 5 is a diagram showing a state in which each of the two X-ray half mirrors 1, 2a, 2b, and 3 is cut out from one ingot 32 as units 9 and 9 'having a common substrate. In this figure, when FZ silicon having a nominal diameter of 6 inches is used, it is easy to make the effective area of the X-ray half mirror 10 cm square and to set the interval between the X-ray half mirrors to about 80 cm. When the units 9 and 9 'are cut out from a cylindrical silicon single crystal ingot, unless the beam is formed substantially along the longitudinal direction of the units 9 and 9' of the X-ray half mirror as shown in FIG. This imposes certain restrictions on the growth axis of the ingot and the crystal lattice plane used for diffraction. For example, when X-rays of 60 keV are used for (440) reflection, a wide field of view can be efficiently secured by using an ingot grown in a direction inclined by 6 degrees from the <111> axis to the <110> axis.
[0015]
FIG. 6 is a plan view and a side view illustrating a configuration example of the rotation stage 100 for controlling the θ axis according to the first embodiment. A coupling part 103 that functions as a fulcrum of rotation and a coupling part 104 that functions as a spring part so that one of the two thick plates functions as the fixed part 101 and the other thick plate functions as the rotating part 102. Have been. This structure is manufactured by wire cutting from a single thick plate, for example. The holding part 105 is fixed to the side surface of the fixing part 101 near the coupling part 104 by the support bolt 106. A piezoelectric element 108 is provided between a side surface of the rotating unit 102 near the coupling unit 104 and the holding unit 105. The piezoelectric element 108 is set so that the rotating unit 102 is slightly spread rightward in the figure when no control voltage is applied. Therefore, for example, when the X-ray half-mirror units 9 and 9 ′ are fixed on the upper surface of the rotating unit 102 as shown by broken lines in the figure and the polarity and magnitude of the voltage applied to the piezoelectric element 108 are controlled, the piezoelectric The element 108 expands and contracts, the rotating part 102 is displaced in the direction of the arrow with respect to the fixed part 101, and the rotating part 102 can rotate about the coupling part 103.
[0016]
The fixed portion 101 and the rotating portion 102 are formed such that the rotating portion 102 slightly rises from the bottom surface of the fixed portion 101, as is apparent from the side view. As a result, the rotating unit 102 can rotate smoothly. Further, each thick plate of the fixed portion 101 and the rotating portion 102 may be formed from an independent thick plate. In this case, instead of the connecting portions 103 and 104, a connecting point having a fulcrum and a spring function may be used as described in the configuration of FIG.
[0017]
FIG. 7 is a plan view and a side view illustrating a configuration example of a rotation stage 200 for controlling the ω axis according to the first embodiment. The side surfaces of each thick plate are joined by the joining portion 203 such that one of the two thick plates functions as the fixing portion 201 and the other thick plate functions as the rotating portion 202. Since the connecting portion 203 is connected to each other by a bolt 207 and functions as a fulcrum of rotation and has a spring function, a portion 204 confined at the center is formed. A piezoelectric element 205 is provided between opposing surfaces of the thick plates opposite to the joint 203. The piezoelectric element 205 is set so that the rotating unit 202 is slightly pushed upward in a side view as viewed from the lower surface side in the drawing when no control voltage is applied. Accordingly, for example, when the X-ray half-mirror units 9 and 9 ′ are fixed on the upper surface of the rotating unit 202 as shown by broken lines in the figure and the polarity and magnitude of the voltage applied to the piezoelectric element 205 are controlled, the piezoelectric The element 205 expands and contracts, the rotating part 202 is displaced in the direction of the arrow with respect to the fixed part 201, and the rotating part 202 can rotate with the constricted part 204 of the coupling part 203 as a fulcrum.
[0018]
As described above, in this embodiment, the fine adjustment axes that are important for the X-ray half mirror are the θ and ω axes, and when they are independently adjusted, the stages shown in FIGS. However, when it is desired to adjust both the θ and ω axes of one X-ray half mirror, the stages shown in FIGS. 6 and 7 may be multi-tiered and adjusted independently. For example, the fixed part 201 of the stage 200 shown in FIG. 7 is fixed on the movable part 102 of the stage 100 shown in FIG. As shown, the X-ray half mirror unit 9 (9 ') may be fixed at an angle of 6 degrees. Here, the unit 9 (9) of the X-ray half mirror is fixed from the ingot grown in the direction inclined from the <111> axis to the <110> axis by 6 degrees for use in (440) reflection. ') Is cut out. Then, for example, the movable part 102 of the lower stage 100 is controlled corresponding to the θ axis, and the movable part 202 of the upper stage 200 is controlled corresponding to the ω axis.
[0019]
Next, a method for obtaining diagnostic information from the interferogram will be described. Considering the conventional method using the absorption contrast, the contrast is basically not changed by the optical system, and the contrast is never inverted. This is because the projection of the X-ray absorption coefficient, which is an intrinsic amount of the substance, determines the image contrast. In the phase contrast method of the present invention as well, if the optical system is ideally made, an image having an image contrast showing the distribution of the amount (refractive index) inherent to the substance should be obtained as an interferogram. In the method, an image having an image contrast indicating the distribution of the refractive index is not always obtained. In this case, it can be said that this image cannot be used for diagnosis. On the other hand, considering that the projection of the refractive index corresponds to the X-ray phase shift, if an image showing the phase shift distribution is obtained, it can be used for diagnosis at any time. Therefore, a method for obtaining a phase shift distribution image from an X-ray interference pattern is required. Several methods for determining the phase shift from the interferogram have been established in the study of visible light interference optics. Among them, one of the methods that can be used for an X-ray interferometer is the fringe scanning method (JH. Bruning, et al., Appl. Opt., 33, 2693-2673 (1974)). In this method, a phase shift distribution image is provided by calculation from a plurality of interferograms obtained while gradually changing the relative phase difference between two interfering X-ray beams. Now, assuming that M interferograms are obtained while changing the phase difference by 2π / M at a time, the phase shift distribution image can be obtained by calculating the argument of (Equation 1) according to the principle of the fringe scanning method. is there.
[0020]
(Equation 1)

[0021]
FIG. 8 shows an example of a phase plate arranged in the beam path of the X-ray interferometer for performing the fringe scanning method, and the phase difference can be adjusted by moving the phase plate. (A) shows a case in which a wedge-shaped phase plate 25 is used. The wedge-shaped phase plate 25 is inserted into one of the beam paths of the X-ray interference type so that the wedge 25 can be moved in the inclined direction. Since the amount of phase shift by the X-ray phase plate is proportional to the thickness of the X-ray phase plate, the thickness at the position where the X-rays pass can be changed by moving the wedge 25 as shown by the arrow in FIG. A phase difference proportional to the amount of movement can be provided. However, this type of phase plate has the effect of generating a phase gradient in the X-ray beam, resulting in the generation of equally spaced interference fringes. By subtracting this phase gradient from the phase shift distribution image obtained using the fringe scanning method, an image to be obtained (a phase shift distribution image of the subject) can be obtained, so there is no problem in principle. There is a disadvantage that interference fringes due to the wedges 25 remain as traces in the phase shift distribution image, resulting in stripe-like artifacts. (B) shows a method in which the thickness of the phase plate is changed by rotating the plate-like phase plate 26 as shown by the arrow, and the phase difference is adjusted. Since the phase plate 26 itself does not generate interference fringes, there is no need to worry about an artifact as in the case where the wedge-shaped phase plate 25 is used. Instead, the rotation angle of the phase plate is not proportional to the given phase difference, so it is necessary to calibrate the rotation angle and the phase difference in advance. (C) is a method in which wedges 27 and 27 'of the same shape are stacked in anti-parallel, and a method in which at least one of the wedges is moved in an inclined direction to adjust a phase difference. This method has both the advantage of (a) that is proportional to the phase difference given by the movement amount of the wedge and the advantage of (b) that there is no concern that stripe-like artifacts occur. In any of the cases (a), (b) and (c), the phase plate may be inserted at any of the beams 6a, 6b, 7a and 7b shown in FIG. (D) has the same purpose, but is a method in which wedge-shaped phase plates 28, 28 'having the same shape are inserted one by one into two beam paths, for example, the beams 6a, 7a in FIG. In order to adjust the phase difference, at least one of the wedges may be moved in the direction indicated by the arrow.
[0022]
The present invention makes it possible to apply a phase contrast X-ray imaging method to a medical diagnostic apparatus by realizing an X-ray interferometer that can use a thick X-ray beam and can take a sufficiently large distance between mirrors. In addition, since there is a case where the X-ray interferogram cannot be used for diagnosis as it is, a device for obtaining a phase distribution image from the interferogram is devised so that an image with the same contrast can always be provided regardless of the adjustment condition of the apparatus. became. New diagnostic methods such as phase contrast mammography and phase contrast angiography can be realized using the apparatus of the present invention. Furthermore, by rotating the subject and acquiring and processing phase shift distribution images from a plurality of projection directions, the phase contrast is obtained. X-ray CT can be realized. By these means, a soft tissue (cancer or the like) in a living body, which is difficult to diagnose by the conventional method, can be diagnosed with about 1000 times the image sensitivity. Further, the amount of X-ray irradiation on the human body can be significantly reduced as compared with the conventional method. Furthermore, since the X-ray beam passing through the X-ray interferometer is close to a plane wave, the image is less blurred, and an image with a spatial resolution of 50 μm or less can be obtained.
[0023]
FIG. 9 shows the overall configuration of a mammography apparatus configured using the unit of the X-ray half mirror described in FIG. Each unit is fixed to stages 36 and 37. In the present embodiment, the rotation stage for the θ-axis adjustment shown in FIG. 6 is adopted as the stage 36, and the stage 37 is used for adjusting the θ-axis and the ω-axis as described above. A stage in which a rotating stage for adjustment and a rotating stage 200 for adjusting the ω-axis shown in FIG. It should be noted that since the adjustment of the θ axis or the ω axis is relative, the relative rotation angles of the units 9 and 9 ′ can be adjusted in the same way even if the relation is reversed. The stages 36 and 37 are arranged on a common anti-vibration table 39, and the whole apparatus is housed in a chamber 51. In the figure, only the line outside the chamber is indicated by 51. . The side surfaces of the units 9 and 9 'are polished to mirror surfaces, and by means of light reflection using the mirror surfaces, the unit 9' (X-ray half mirror 2b) with respect to the unit 9 (X-ray half mirrors 1 and 2a) by the autocollimator 307. 3) Rough adjustment is performed prior to the diagnosis of the relative rotation angles θ and ω. Light 308 emitted from the autocollimator 307 reflects off the side surface of the unit 9 and the light 309 reflects off the side surface of the unit 9 ′ via the right-angle prisms 310 and 311 and returns. By examining the return positions of the lights 308 and 309, a signal for coarse adjustment of the angles θ and ω can be obtained. It should be noted that machining is performed so that the angle between the polished surface and the crystal lattice surface is the same in the two units as much as possible. good. Further, since the two units are separated from each other, the optical path is changed using a prism or a mirror, but it is preferable that the influence of the optical element at this time is measured in advance and corrected. The operation of the coarse adjustment will be described later.
[0024]
The X-rays incident on the X-ray half mirror 1 of the unit 9 are split by the X-ray half mirror 1 into beams 6a and 7a, and the beam 6a is split into beams 6b and 6c by the X-ray half mirror 2a. The beam 7a is split into beams 7b and 7c by the X-ray half mirror 2b. The beam 6b and the beam 7b interfere with each other by the X-ray half mirror 3 and are output as beams 6d and 7d. The inspection site 50 of the subject 49 is inserted into the path of the beam 6b. At this time, the beam 6c is prevented from hitting the subject 49 by the shield plate 53 attached to a portion of the chamber 51 where the beam 6c hits. Note that the same diagnosis can be made even when the subject 49 is arranged at the position of the beam 7b, and in this case, the installation position of the recess is on the beam 7b side. In addition, prior to imaging, the region to be inspected (breast) 50 is pressed to a predetermined thickness at a predetermined position by the holder 54 and temporarily fixed to, for example, a floor. However, it is preferable to provide the holder 54 with a certain degree of freedom for parallel movement and rotation to secure imaging flexibility. Reference numerals 55 and 56 denote phase plates and their driving bases, which are installed in the path of the beam 7a so that a diagnosis can be made with a phase shift distribution image by a fringe scanning method when diagnosis is difficult with an interference figure. The drive table 56 is fixed to the ceiling of the chamber 51 so as to prevent the vibration during driving from being transmitted to the vibration isolation table 39. Driving of the phase plate is performed by a signal of the control device 328 which has received a command from the computer 60. 57 and 58 are X-ray intensity monitors arranged to receive the beam 7c and the beam 6d. Further, an X-ray intensity monitor 81 is arranged at an end of a predetermined beam position of the beam 7a and receives an X-ray at the end of the beam 7a. For these X-ray intensity monitors 57, 58 and 81, for example, a method of measuring a current flowing when X-rays are applied using a PIN diode detector is simple. Also, coarse adjustments prior to diagnosis are performed using the outputs of these X-ray intensity monitors 57, 58 and 81. It should be noted that almost the same interferogram of the inspection part 50 is observed in the beams 6d and 7d. Here, the interferogram was detected by the X-ray two-dimensional sensor 59 arranged to receive the beam 7d. May be used as an X-ray two-dimensional sensor to acquire an X-ray interferogram. In the illustrated example, the X-ray intensity monitor 58 is used as an X-ray two-dimensional sensor, and is used as a feedback signal for stabilizing the interferometer separately from the X-ray interferogram of the X-ray two-dimensional sensor 59. The X-ray two-dimensional sensors 58 and 59 are driven by camera controllers 63 'and 63, and the camera controllers 63' and 63 are controlled by a computer 60. The imaging is instructed by the control program running in the computer 60, and the acquired images are stored in the memory of the computer 60 via the camera controllers 63 'and 63. Diagnosis is performed from the image data stored in the memory, and a control signal for stabilization by feedback is output to the control device 325. A voltage control signal is given to the piezoelectric elements of the two-staged stage 37 by a signal of the control device 325 receiving a command from the computer 60, and feedback of θ and ω is performed. This specific example will be described later. .
[0025]
The X-rays incident on the X-ray half mirror 1 of the unit 9 are desirably supplied from an X-ray source 33 disposed in a room isolated via a partition 52. This is because unnecessary exposure to the subject 49 can be avoided and vibration generated from the X-ray source 33 can be prevented from being transmitted to the X-ray interferometer.
[0026]
The X-ray emitted from the X-ray source 33 was used to extract an X-ray beam 4 having a specific energy using a monochromatic device 34, and was guided to an imaging device. The monochromatic device 34 also has the function of expanding the width of the beam 4 by asymmetrical reflection (in the case of 0 <α <θ in FIG. 3A). It is preferable that the diffraction index is the same as that of the X-ray half mirror, and (220), (440), (400), (422) and the like are desirable. If the X-ray source 33 is horizontally long in the direction of the paper of FIG. 9, it is advantageous to widen the beam width by the monochromatic device 34, and a strong X-ray beam is formed in the interferometer. A shutter 35 is provided immediately after the monochromatic device 34 so that unnecessary X-ray irradiation other than during imaging is not performed. This shutter 35 may be located immediately after the X-ray source 33.
[0027]
Next, feedback control for rough adjustment prior to diagnosis and stabilization of the interferometer will be described.
[0028]
First, attention is paid to the output of the X-ray intensity monitor 81. Since the X-ray half mirror functions normally only when the diffraction condition is satisfied, the X-ray does not properly pass through the X-ray half mirror unless θ of the X-ray half mirror 1 is appropriate. Since the X-ray intensity monitor 81 is disposed at the end of the beam 7a, X-rays are hardly detected when θ is not appropriate. Therefore, when almost no X-rays are detected by the X-ray intensity monitor 81, a signal for correcting θ is given to the stage 36 so that the output of the X-ray intensity monitor 81 becomes almost maximum. Next, reflected light from both sides of the unit 9 (X-ray half mirrors 1 and 2a) and the unit 9 '(X-ray half mirrors 2b and 3) of the light 308 and 309 emitted from the autocollimator 307 is examined. A signal for adjusting the angles θ and ω is given to the stage 37 so that the reflected light becomes parallel. After the coarse adjustment, the two piezoelectric elements of the stage 37 are controlled to scan the two axes of rotation (θ and ω) until an interference pattern appears on the X-ray image sensor 59, thereby finding the interference pattern. Once the interference fringes are obtained, the diagnosis can be started by controlling the two rotating axes (θ and ω) so that the interference fringes are in an optimal state.
[0029]
Even after the interference fringes are once obtained and the diagnosis can be started, if the θ-axis and the ω-axis which need to be adjusted with high precision drift, the interferogram changes. Therefore, during the diagnosis of the subject, the X-ray interferometer can be stabilized by monitoring the interferogram obtained by the X-ray image sensor 58. When the θ-axis and the ω-axis drift, the interferogram changes, but the state differs for each axis. In the case of the θ-axis, the apparent phase difference between the two beams 6b and 7b changes. On the other hand, when the ω-axis drifts, fringes similar to a rotating moiré are generated, depending on the amount of drift of the ω-axis. This expands and contracts. Therefore, stable diagnosis can be performed by performing feedback control on the interferogram obtained by the X-ray image sensor 58 through the camera control 63 'to cancel the change by processing by the computer 60.
[0030]
When the image acquisition by the fringe scanning method is necessary, a control program running in the computer 60 is used to acquire a plurality of images (interferograms) while changing the phase difference. Issue an instruction to 63. The computer 60 performs an operation based on the expression (1) from the obtained image, and displays the generated phase shift distribution image on a display device of the computer 60.
[0031]
FIG. 10 shows a perspective view of the configuration of the first embodiment as viewed with the chamber 51 mounted. The beam 6b is led out of the chamber 51 once through the window 71, passes through the examination site 50 (not shown) of the subject 49, and then enters the chamber 51 again through the window 72, and the interference beams 6d and 7d Is led out of the chamber 51 through the window 73 and measured. The windows 71, 72, 73 are separated from the inside and outside of the chamber 51 by a plastic plate or the like that does not absorb much X-rays, and the heat (body temperature, breath, etc.) generated by the subject 49 does not affect the optical system. In the drawing, the display of the incident X-rays is omitted.
[0032]
FIG. 11 shows an outline of an embodiment in which an X-ray interferometer has the same configuration as that of the above-described first embodiment, but takes measures against vibration as faster fluctuation.
[0033]
If the units 9 and 9 'of the X-ray half mirror are relatively vibrating, the X-ray interference fringes spatially fluctuate at a high frequency, so that the apparent sharpness of the interference fringes may be reduced or become invisible. Therefore, it is necessary to take measures to prevent vibrations from being transmitted to the units 9 and 9 '. In this embodiment, as shown in the figure, the X-ray half mirrors 1, 2a, 2b, and 3 are fixed to a pool 450, and the pool is filled with a highly viscous liquid (eg, oil). Only 2a, 2b, and 3 appear above the liquid level. The pool 450 is placed on the vibration isolation table 39, and the whole is covered with the chamber 51. By doing so, vibration of high frequency components is suppressed, and the definition of interference fringes is improved. Metal beryllium is adhered to X-ray passing windows 452, 453, 454, and 455 provided on the wall of the chamber 51 so that external air does not flow. As other window materials, a polymer film, a thin aluminum plate, a glass plate, or the like can be used.
[0034]
This embodiment is an example in which a normally used soundproof room, a soundproof wall and a vibration isolation table are employed, and the lower part of the interferometer below the X-ray half mirror is immersed in a highly viscous liquid.
[0035]
Example 2
In this embodiment, as shown in FIG. 2A, an X-ray interferometer is constituted by using three independent X-ray half mirrors 1, 2, and 3. FIG. 12 shows the degree of freedom necessary for adjusting the X-ray half mirror in this embodiment. The same applies to the case of an X-ray reflection mirror. As in the first embodiment described with reference to FIG. 4, also in this figure, a thick solid line indicated by an arrow indicates an X-ray that enters the center of the half mirror and exits from the center. Reference numeral 5 denotes a part of the diffraction grating surface of the crystal as a representative, the normal direction of the diffraction grating surface 5 is the x-axis, and the normal direction of the scattering surface (the surface including an arrow indicating the traveling direction of the x-ray beam in the drawing). Is defined as a y-axis, an axis perpendicular to the x-axis and the y-axis is defined as a z-axis. The rotation axes around the x-axis, y-axis, and z-axis are referred to as φ-axis, θ-axis, and ω-axis, respectively. With respect to the parallel movement of the X-ray half mirror, the precision of the x-axis is strictly required, and the precision is required to be a fraction of a degree or less. An accuracy of 1 μm is sufficient for the z-axis, and the y-axis does not need to be strictly fine-tuned. Regarding rotation, the θ-axis is an axis related to the Bragg diffraction condition, and requires a sufficient accuracy of 1 second or less. The ω axis perpendicular to the θ axis and perpendicular to the crystal surface needs an accuracy of 1/100 second or less. There is no need to strictly fine-tune the φ axis. Therefore, the important fine adjustment axes are the x, z, ω, and θ axes.
[0036]
As shown in FIG. 13, each of the X-ray half mirrors 1, 2, and 3 was manufactured by vertically dividing a cylindrical silicon ingot 32. The crystal plate 30 functioning as an X-ray half mirror is cut out from an ingot 32 shown by a broken line so as to be integrated with the base 31. It is preferable to use (220), (440), (400), (422), and the like for the diffraction surfaces of the X-ray half mirrors 1, 2, and 3.
[0037]
FIG. 14 shows a configuration example of a moving stage 300 in the x-axis direction for realizing position control of a fraction of a degree or less, with a plan view at the center and side views at the left and right sides. The stage 300 is a uniaxial translation stage, and is manufactured by cutting out a thick steel material by wire cutting. The stage mounting section 301 and the movable section 302 are arranged in parallel and connected by support sections 303 and 304. The support parts 303 and 304 are connected via constricted parts A to D, respectively. An inverted L-shaped piezoelectric element mounting portion 305 is provided at one end of the stage mounting portion 301. One end of the lever 306 is connected to one end of the movable portion 302 via a constricted portion F. A piezoelectric element 310 is provided between the other end of the lever 306 and the piezoelectric element mounting section 305. A narrowed portion E is formed at a position close to the narrowed portion F, and one end of the narrowed portion E is supported by the lever 306 and the other end is supported by the stage mounting portion 301. Electrodes 312a and 312b are provided between the stage mounting portion 301 and the surface of the lever 306 opposite to the surface on which the piezoelectric element 310 is provided. It is assumed that the confined portions A to F are elastically deformed. When the polarity and magnitude of the voltage applied to the piezoelectric element 310 are controlled, the piezoelectric element 310 expands and contracts accordingly, and the movable part 302 is displaced in the direction of the arrow. At this time, since the points E and F correspond to the fulcrum and the action point, the length of expansion and contraction of the piezoelectric element 310 is reduced by the leverage principle, and fine position control of the movable portion 302 can be performed. The reduction ratio is determined by selecting the distance ratio a / b. Further, the amount of expansion and contraction of the piezoelectric element 310 can be monitored by measuring the capacitance between the electrodes 312a and 312b. As can be seen from the side views shown in FIG. 14, the movable portion 302, the support portions 303 and 304, and the lever 306 have a slightly lower bottom surface with respect to the stage mounting portion 301, and the upper surface of the movable portion 302 has another portion. It is formed very slightly higher. Thereby, the movement of the movable portion 302 can be controlled smoothly and can be controlled without any trouble even when the movable portion 302 is stacked in two stages.
[0038]
Also in the present embodiment, control of the ω axis and the θ axis is required, and a rotary stage that can be used for this is required. However, since the rotary stages described with reference to FIGS. 6 and 7 can be used for each rotary axis. The illustration of the configuration example of the rotary stage in this embodiment is omitted.
As described with reference to FIG. 12, the fine adjustment axes important for the X-ray half mirror are the x, z, ω, and θ axes. Therefore, the stages shown in FIGS. An independent X-ray half mirror can be supported as adjustable. For example, the stage shown in FIG. 14 is shifted vertically by 90 ° and placed one above the other, and the stage mounting portion 301 of the lower stage is fixed to a common vibration isolation table of each independent X-ray half mirror, It is assumed that the stage mounting portion 301 of the upper stage is fixed to the movable portion 302. Then, for example, if the movable section of the lower stage is controlled corresponding to the x-axis direction, the movable section of the upper stage is controlled corresponding to the z-axis direction. Similarly, if the rotary stages shown in FIGS. 6 and 7 are used in a two-stage stack in the first embodiment, the ω and θ axes can be controlled also in this embodiment. If the thick plate 101 on the fixed side of the lower stage of the two-stage rotating stage shown in FIGS. 6 and 7 is fixed to the movable part of the upper stage of the two-stage overlapping stage shown in FIG. The thick plate 202 on the rotating side of the stage shown in FIG. 7 is controlled corresponding to four axes of x, z, ω, and θ axes.
[0039]
Unlike the first embodiment, in this embodiment, it is necessary to control the independent X-ray half mirrors 1, 2, and 3 individually. For the X-ray half mirror 1, a θ-axis adjustment stage 36, for the X-ray half mirror 2, a two-stage adjustment stage 37 for the θ-axis and ω-axis, and for the X-ray half mirror 3, A four-stage piezoelectric stage 38 of the above-described θ-axis and ω-axis rotation stages and the x-axis and y-axis parallel movement stages was provided, respectively, and disposed on the vibration isolation table 39 via this. In order to detect a displacement in a direction corresponding to the x-axis in FIG. The laser beam 45 emitted from the laser interferometer 42 is reflected by a reflecting mirror 48 (corner cube or the like) fixed on the piezoelectric element stage 38 and returned to the laser interferometer 42. The anti-vibration table 39 was provided with a concave portion so that the inspection site 50 of the subject 49 could be inserted into the X-ray beam path 6b. The same observation can be performed even when the subject 49 is arranged at the position of the beam 7b. In this case, the installation position of the concave portion is on the beam 7b side. In order to stabilize the operation of the X-ray interferometer and the laser interferometer and to secure the subject 49, a chamber 51 is provided according to the shape of the vibration isolation table 39, and the X-ray interferometer and the laser interferometer are connected to the outside. The X-ray shield 53 is provided while the contact is cut off, so that X-rays other than the required X-rays are not irradiated to the subject 49. Further, prior to imaging, the examination site (breast) 50 is held at a predetermined position by the holder 54. It is pressed to a certain thickness and temporarily fixed to the floor, for example. However, as in the first embodiment, it is preferable to provide the holder 54 with a certain degree of freedom for parallel movement and rotation to ensure imaging flexibility. Reference numerals 55 and 56 denote phase plates and their driving bases, which are installed in the path of the beam 7a so as to be able to diagnose with a phase shift distribution image by a fringe scanning method when diagnosis is difficult with an interference figure as in the first embodiment. Is done. Driving of the phase plate is performed by a signal of the control device 328 which has received a command from the computer 60. Reference numerals 57, 58 and 81 denote intensity monitors which are arranged in the same manner as in the first embodiment and are used for coarse adjustment of the X-ray half mirrors 1, 2, and 3. Almost the same interference pattern at the inspection site 50 is observed with the beams 6d and 7d, but here, similarly to the first embodiment, the X-ray two-dimensional sensor 59 arranged to receive the beam 7d detects the interference pattern. did.
[0040]
The coarse adjustment of the X-ray half mirrors 1, 2, and 3 by the intensity monitors 57, 58, and 81 will be described. In this embodiment, as in the first embodiment, the coarse adjustment of θ of the X-ray half mirror 1 is performed so that the output of the intensity monitor 81 becomes almost maximum. Next, coarse adjustment of θ of the X-ray half mirror 2 is performed so that the output of the intensity monitor 57 becomes almost maximum. Thereafter, the coarse adjustment of θ of the X-ray half mirror 3 is performed so that the output of the intensity monitor 58 becomes almost maximum.
[0041]
After the coarse adjustment, the two piezoelectric elements of the stage 37 are controlled to scan the two axes of rotation (θ and ω) until an interference pattern appears on the X-ray image sensor 59, and the three piezoelectric elements of the stage 38 are controlled. Scan the rotating two axes (θ and ω) and the z axis to find the interferogram. Once the interference fringes are obtained, the diagnosis can be started by controlling the two rotating axes (θ and ω) so that the interference fringes are in an optimal state.
[0042]
The X-ray two-dimensional sensors 58 and 59 are driven by camera controllers 63 'and 63, and the camera controllers 63' and 63 are controlled by a computer 60. The imaging is instructed by the control program running in the computer 60, and the acquired images are stored in the memory of the computer 60 via the camera controllers 63 'and 63. Diagnosis is performed from the image data stored in the memory, and a control signal for stabilization by feedback is output to the control device 325. A voltage control signal is applied to the piezoelectric elements of the stage 36, the two-stage stage 37, and the four-stage stage 38 according to a signal from the control device 325 which has received a command from the computer 60. Feedback is performed, and this specific example will be described later.
[0043]
Even after the interference fringes are once obtained and the diagnosis can be started, the interferogram changes when the θ-axis, ω-axis and x-axis, which require high-precision adjustment, drift. As in the first embodiment, during diagnosis of the subject, the X-ray interferometer can be stabilized by monitoring the interferogram obtained by the X-ray image sensor 58. The drifts of the θ axis and the ω axis are as described in the first embodiment, and the drift of the x axis also changes the apparent phase difference between the two beams 6b and 7b similarly to the θ axis. Therefore, stable diagnosis can be performed by performing feedback control on the interferogram obtained by the X-ray image sensor 58 through the camera control 63 'to cancel the change by processing by the computer 60.
[0044]
When it is necessary to obtain an image by the fringe scanning method, the phase shift distribution image generated in the same manner as in the first embodiment may be displayed on the display device of the computer 60.
[0045]
FIG. 16 shows a block diagram for driving and controlling a four-stage stage 38 of the apparatus shown in FIG. 15 by a computer. The control of the stages 36 and 37 is the same as that described in the first embodiment, and the description is omitted. The piezoelectric element stage 38 supporting the X-ray half mirror 3 has parallel moving stages 65a and 65b having the structure shown in FIG. 14 and FIG. 6 for adjusting the x, z, ω and θ axes described in FIG. And the rotary stages 64a and 64b having the structure shown in FIG. The piezoelectric element stage 38 is driven by a piezoelectric element controller 61 having a plurality of channels. When the piezoelectric element stage 38 is driven by the output of the piezoelectric element controller 61, the piezoelectric element controller 61 reads a change in the output of the capacitance sensors 312a, 312b corresponding to the movement of the movable parts of the parallel movement stages 65a, 65b. The piezoelectric element controller 61 outputs a voltage corrected for the hysteresis of the piezoelectric element to the piezoelectric element. The sensor output is also transmitted to the computer 60. The laser interferometer 42 emits a laser beam 45, and a reflecting mirror 48 provided on the piezoelectric element stage 38 together with the X-ray half mirror 3 reflects the laser beam 45 and returns the laser beam 45 to the laser interferometer 42. When the position (x-axis direction) of the piezoelectric element stage 38 changes, the laser interferometer 42 detects and outputs the amount of change, and transmits it to the computer 60 via the A / D converter 62. The control program running in the computer 60 processes the transmitted signal and instructs the piezoelectric element controller 61 to change the voltage applied to the piezoelectric element as a feedback signal. The signals from the intensity monitors 57 and 58 are used as auxiliary data for a control program running in the computer 60 to adjust the feedback signal. The X-ray two-dimensional sensor 59 is driven by a camera controller 63, which is controlled by a computer 60. The imaging is instructed by a control program running in the computer 60, and the acquired image is stored in the memory of the computer 60 via the camera controller 63.
[0046]
When it is necessary to obtain an image by the fringe scanning method, a plurality of images (interferograms) are obtained while changing the phase difference as in the first embodiment, and a calculation based on the equation (1) is performed from the obtained image. The generated phase shift distribution image is displayed on a display device of the computer 60.
[0047]
As can be seen by contrasting FIGS. 15 and 16, FIG. 16 shows, for simplicity of the drawing, the transmission of signals to the control computer and the transmission of control signals from the control computer to each stage. Lines are partially omitted.
[0048]
In this embodiment, the stages for adjustment are provided for all the X-ray half mirrors 1.2 and 3. However, since the adjustment of these mirrors is relative, one of the three mirrors is used. It goes without saying that can be fixed.
[0049]
As a modification of the first and second embodiments, the subject 49 can be put in the path of the beam 7a. In this case, there is an advantage that the shield plate 53 required in the second embodiment can be omitted. Of course, in the present invention, even if the shield plate 53 is omitted, the X-ray irradiated to the subject 49 is only doubled, so that the X-ray exposure dose is much lower than the conventional method. However, since the smaller the X-ray exposure dose, the better, and the same performance can be expected even if the X-ray incidence side and the emission side of the X-ray interferometer are reversed, the beam path into which the subject 49 enters may be set to 7a. Similarly, in the first embodiment, the position of the subject 49 is the same as the path of the beam 6a. However, in these cases, the X-rays that have passed through the inspection site 50 pass through the two X-ray half mirrors 2 and 3 before reaching the two-dimensional detector 59. Slightly decreases. In this embodiment, the space available for the subject 49 is widened, and it becomes easy for the subject 49 to maintain a posture during imaging. Further, the size of the entire apparatus can be reduced. Further, the path into which the phase plate for applying the fringe scanning method is inserted may be either.
[0050]
FIG. 17 shows an example of a more powerful X-ray source for an X-ray interferometer.
[0051]
Since X-ray interferometers work on quasi-monochromatic X-rays, it is advantageous to use a somewhat powerful X-ray source for rapid imaging. In the case of the optical system of the above-described embodiment, the shape of the X-ray source needs to be thin in the vertical direction, but may be long in the horizontal direction. Therefore, especially when an electron beam excitation or laser excitation source is used, it is effective to configure as shown in the figure.
[0052]
In FIG. 17, 540 is a target, 541 is a rotation axis, 542 is an X-ray generation site, 543 is an electron beam source or laser light source, 544 is an electron beam or laser, 545 is an X-ray, and 546 is a filter. In the figure, a plan view of the target 540 is also shown. According to this configuration, a horizontally long X-ray source 542 can be formed by linearly scanning the electron beam or the laser beam 544 on the target 540. This makes it possible to relatively disperse the heat applied to the target, so that more X-rays 545 can be guided to the X-ray interferometer.
[0053]
Although illustration is omitted, in order to supply a higher quality X-ray beam to the X-ray interferometer, the reflection direction of the crystal 34 in each embodiment is changed, or a single color in which two or more crystals are continuously reflected is used. It is also effective to use a container.
[0054]
In any of the above-described embodiments, it is advantageous that the X-ray half mirror or the X-ray half mirror unit has substantially the same structure regardless of the mounting position. Therefore, the height of the bottom surface of the X-ray half mirror or the X-ray half mirror unit differs from the surface of the anti-vibration table due to the presence or absence of the control stage or the difference in the configuration of the control stage when attached to the anti-vibration table. To this end, although not described in some drawings, it is natural that the height is adjusted by inserting a spacer or the like.
[0055]
According to the present invention, injection of a contrast agent is basically unnecessary because high-sensitivity imaging can be performed. However, it may be used together when it is desired to enhance the contrast of a specific site of interest. In this case, there is no limitation that a contrast agent composed of a heavy element must be used unlike the conventional method, and a wide range of materials for the contrast agent can be obtained.
[0056]
【The invention's effect】
According to the present invention, it is possible to obtain a high-sensitivity phase contrast X-ray imaging device having a wide observation field of view.
[Brief description of the drawings]
FIG. 1 is a diagram showing a known integrated X-ray interferometer.
FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating a basic configuration of a beam path of an X-ray interferometer configured by independent X-ray half mirrors.
FIGS. 3A, 3B, and 3C are schematic diagrams showing a difference in diffraction mode due to a difference in an angle α between a crystal surface and a diffraction grating surface.
FIG. 4 is a diagram showing a shape of an X-ray half mirror unit used in Embodiment 1 of the present invention and an adjustment axis thereof.
FIG. 5 is a diagram showing a state in which the X-ray half mirror unit shown in FIG. 4 is cut out from a cylindrical silicon ingot.
FIGS. 6A and 6B are a plan view and a side view illustrating a configuration example of a piezoelectric element driving stage for the rotation axis θ according to the first embodiment of the present invention.
7A and 7B are a plan view and a side view illustrating a configuration example of a piezoelectric element driving stage for the rotation axis ω according to the first embodiment of the present invention.
8 (a), (b), (c) and (d) are diagrams showing a configuration of a phase plate for a fringe scanning method.
FIG. 9 is a plan view showing the overall configuration of the phase contrast mammography apparatus according to the first embodiment of the present invention.
FIG. 10 is a perspective view of the phase contrast mammography apparatus according to the first embodiment of the present invention with a chamber attached.
FIG. 11 is a perspective view schematically showing the internal structure of a chamber in which the phase contrast mammography apparatus according to the first embodiment of the present invention has a vibration suppression measure.
FIG. 12 is a diagram showing a shape of an X-ray half mirror used in Embodiment 2 of the present invention and an adjustment axis thereof.
FIG. 13 is a view showing a state in which the X-ray half mirror shown in FIG. 12 is cut out from a cylindrical silicon ingot.
FIG. 14 is a plan view showing a configuration example of a piezoelectric element driving stage for a translation axis x in Embodiment 2 of the present invention.
FIG. 15 is a diagram illustrating an overall configuration of a phase contrast mammography apparatus according to a second embodiment of the present invention.
FIG. 16 is a block diagram for driving and controlling a phase contrast mammography apparatus.
FIG. 17 is a diagram showing a configuration example of an X-ray source as a linear light source and an arrangement relationship between the X-ray source and an interferometer.
[Explanation of symbols]
6a, 6b, 7a and 7b: beam path, 9, 9 ': X-ray half mirror unit, 36: adjustment stage of unit 9, 37: adjustment stage of unit 9', 39: anti-vibration table, 49: subject, 50: Inspection site, 100, 200: Rotating stage, 32: Ingot, 25, 26, 27, 28: Wedge phase plate, 51: Chamber, 53: Shield plate, 54: Holder, 55: Phase plate, 56: Phase plate drive platform, 60: computer, 57, 58, 81: X-ray intensity monitor, 59: X-ray two-dimensional sensor, 63 ', 63: camera controller, 52: partition, 33: X-ray source, 34: monochromatic Container, 35: shutter, 71, 72, 73: window, 101, 201: fixed part, 102, 202: rotating part, 103, 104, 203: coupling part 105: holding part, 103: support bolt, 108, 05: piezoelectric element, 207: bolt, 204: constricted portion, 307: autocollimator, 308, 309: light, 310, 311: right angle prism, 325, 328: control device, 450: pool, 452, 453, 454, 455: X-ray passage window.

Claims (9)

A first half mirror for converting incident X-rays into two beams that interfere with each other, two reflecting mirrors for reflecting each of the two beams by the first half mirror, and one of the reflecting mirrors detection of detecting the second half mirror for combining the resulting beam by the beam and another one reflecting mirror which is obtained by inserting an object into the resulting beam, a beam coupled by a half mirror of the second by And a processing unit for obtaining an image of the subject based on the output of the detector. The first half mirror and the second half mirror are installed on a common anti-vibration table. At least one is characterized by the Turkey be installed on a common anti-vibration table via a mirror adjusting mechanism for adjusting the relative positional relationship of the respective half mirrors phase contrast X of Imaging device. A first half mirror for converting incident X-rays into two beams that interfere with each other, and third and fourth half mirrors for converting each of the two beams by the first half mirror into two beams. A second half mirror that combines a beam obtained by inserting a subject into a beam obtained by one of the third and fourth half mirrors and a beam obtained by another half mirror; A detector for detecting the beam combined by the second half mirror; and a processing unit for obtaining an image of the subject based on the output of the detector. The first half mirror and the third half mirror The fourth half mirror and the second half mirror are cut out from one single crystal material ingot and have a common base, and the fourth half mirror and the second half mirror are cut from one single crystal material ingot. And a half mirror set cut out from each ingot is set on a common anti-vibration table, and at least one of the two half mirror sets is set for each half mirror. A phase contrast X-ray imaging apparatus, which is installed on a common anti-vibration table via a mirror adjustment mechanism that adjusts a relative positional relationship between sets. 3. The phase contrast X-ray imaging apparatus according to claim 2, wherein the half mirror is cut out from a single crystal material ingot. A first half mirror for converting incident X-rays into two beams that interfere with each other, and third and fourth half mirrors for converting each of the two beams by the first half mirror into two beams. A second half mirror that combines a beam obtained by inserting a subject into a beam obtained by one of the third and fourth half mirrors and a beam obtained by another half mirror; A detector for detecting the beam combined by the second half mirror; and a processing unit for obtaining an image of the subject based on the output of the detector. The first half mirror and the third half mirror A single half crystal is cut out from one single crystal material ingot and configured as a first half mirror set having a common base, and the fourth half mirror and the second half mirror are formed into one single crystal. Cut out from the ingot of the material and configured as a second half mirror set having a common base, each half mirror set is installed on a common anti-vibration table, and at least one of the two half mirror sets is Installed on a common anti-vibration table via a mirror adjustment mechanism that adjusts the relative positional relationship between each half mirror set, and shines light on the mirror-finished surface of the base of each half mirror set. A phase contrast X-ray imaging apparatus comprising means for detecting the angle of the reflected light. The phase contrast X-ray imaging apparatus according to claim 2, wherein a phase shifter is inserted in a beam path in which a subject is not inserted among the two beams that interfere with each other. Bragg diffraction that changes the apparent phase difference between two beams combined by a second half mirror to adjust the relative position of the first half mirror set and the second half mirror set. A mirror adjustment mechanism for adjusting a θ axis related to a condition, a mirror adjustment mechanism for adjusting a ω axis in a direction orthogonal to the θ axis and perpendicular to the crystal surface of the half mirror in one of the two half mirror sets. A processing unit that obtains an image of the subject based on an output of a detector that detects the beam combined by the second half mirror, after the interferogram is once observed by the detector, When a change in the apparent phase difference is detected, a control signal for canceling the change in the phase difference is given to one of the mirror adjustment mechanisms that adjusts the θ-axis. axis 5. The phase contrast X-ray imaging apparatus according to claim 4, wherein a control signal for canceling fringes similar to the rotating moiré is provided to a mirror adjusting mechanism for adjusting the rotational moire. A first half mirror, a second half mirror, and a mirror adjustment mechanism for adjusting a relative positional relationship between the half mirrors are installed on a common anti-vibration table, and are mounted on the anti-vibration table together with the anti-vibration table. 5. The phase-contrast X-ray imaging apparatus according to claim 4, wherein a certain apparatus is housed in one chamber, and a window of a member that allows transmission of X-rays is provided only in a portion that becomes a passage of X-rays for irradiating an object. An anti-vibration table was provided in the chamber, the half mirror was mounted in a pool containing a highly viscous liquid supported by the anti-vibration table, and only the half mirror was exposed from the liquid surface. The phase contrast X-ray imaging apparatus according to claim 7. The phase contrast X-ray imaging apparatus according to claim 7, wherein the inside of the chamber is evacuated.

Images