JP3742690B2 - X-ray CT scanner - Google Patents

Description

【数２】

の式により演算できる。すなわち、前述した図８の（ａ）および（ｃ）の位置態様を採るときは、上記式（１）に基づき、焦点サイズｘおよび本影サイズｙを反映させた開口幅Ｗpre （ｘ，ｙ）が求められる。また同図（ｂ）および（ｄ）の位置態様を採るときは、上記式（２）に基づき、焦点サイズｘおよび「本影＋半影」サイズｚを反映させた開口幅Ｗpre （ｘ，ｚ）が求められる。これらの式から分かるように、本影サイズｙまたは「本影＋半影」サイズｚが変わらず、焦点サイズｘのみが変化する場合は、その変化分をも反映させた開口幅が求められることになる。
【００５８】
なお、この開口幅Ｗpre （ｘ，ｙ）およびＷpre （ｘ，ｚ）は、図７、８の制御が実施される度に上記（１）または（２）式に基づいて演算により求めてもよいが、その演算により求められる開口幅データをテーブルとして予め記憶しておいてもよく、その場合には、テーブルを参照するだけで開口幅Ｗpre を得ることができる。また、かかるテーブルは、実測データを基に作成し記憶しておいてもよい。
【００５９】
次いで図７のステップ４５に移行して、すでに入手しているスキャン方法を判断し、マルチスキャンの場合、ステップ４６で天板の送りピッチを演算する。この送りピッチは図１７（ａ）、（ｂ）に示すように、天板を移動させる距離であり、Ｘ線検出器１１の使用用に指定した検出素子列の撮影領域の中心におけるトータルのスライス幅に一致する距離である。一方、ヘリカルスキャンの場合、ステップ４７で天板の送り速度を演算する。この送り速度は１回転当たりの天板の移動距離として決められる速度で、その移動距離はＸ線検出器１１の指定検出素子列の撮影領域の中心におけるトータルのスライス幅に一致させる。なお、ヘリカルスキャンの場合、別の方法で送り速度を指定してもよい。例えば、スライス方向のサンプリング密度を上げるために、送り速度として、前記指定検出素子列に相当する小数点無しの整数値を選択する代わりに、小数点（端数）を有する半端な値を選択することもできる。
【００６０】
マルチスキャンは、「スキャン・天板移動・スキャン・天板移動…」を繰り返し行うものである。天板移動量を、撮影領域の中心における指定検出素子列に対応した１スキャン当たりのトータルのスライス幅（すなわち、指定された検出素子列全てに入射するＸ線プロファイルの半値幅）と等しくした場合、得られた画像は全て等間隔であり、また個々の画像は互いに隣接した領域から得られたものとなり、画像間のギャップが存在しない。これはシングルスライスＣＴ，マルチスライスＣＴに共に言えることであり、得られた画像から３次元モデルを作成する場合等に有利である。
【００６１】
ヘリカルスキャンは、スキャンと天板移動を同時に行うことで、螺旋状にデータを取得するスキャン方法である。画像を再構成する場合には、再構成する断面に対して、その断面からの距離を係数として収集データを補間する方法が一般的である。ヘリカルスキャンにおいて天板移動速度を、撮影領域の中心における指定検出素子列に対応したトータルのスライス幅と一致させた場合、データ収集領域は１回転進む毎に互いに隣接することになり、欠落のない被写体データの収集が可能となる。
【００６２】
以上のように各種データが得られると、主制御装置３０はステップ４８〜５１にて、データ収集装置１２及び画像再構成装置３５、架台制御装置３３、寝台制御装置３２、並びに高電圧制御装置３１に各々必要情報を出力する。なお、ステップ５１にて高電圧制御装置３１に出力される情報には、大焦点用フィラメントＦＴL を使用するのか、小焦点用フィラメントＦＴS を使用するのかの情報が含まれている。この情報付与により、各制御装置は予め記憶している所定の手順に基づいて動作するので、指令されたスキャンが実行される。
【００６３】
一方、図１０にＸ線検出器１１としてシングルスライス検出器が使われている場合の主制御装置３０の制御例を示す。この制御例はシングルスライスに特有の情報（スライス幅）を取り込むこと、及び前述した２次元検出器を使用した場合には制御の対象外であったポストコリメータ１６が態様によっては新たに加わる点が２次元検出器の場合とは大きく異なる。
【００６４】
具体的には、同図ステップ６０にて、主制御装置３０がスキャンモード（シングルスキャンか、マルチスキャンか、又はヘリカルスキャンか）、スキャン部位及び位置，Ｘ線管電圧及び電流などのスキャン条件の情報（但し後述する「スライス幅」、「収集モード」および「焦点サイズ」の情報は含まない）を入力する。次いでステップ６１で、シングルスライスのスライス幅の情報を入力し、ステップ６２で収集モード（前述と同様に「本影モード」か「本影＋半影モード」か）の情報を入力する。
【００６５】
次いでステップ６３に移行し、前述と同様に、Ｘ線管１１の焦点サイズの情報を入力する。
【００６６】
さらにステップ６４に移行して、プリコリメータ１５のスライス方向の開口幅Ｗpre を演算する。この場合も、プリコリメータ１５のとり得る位置態様が図１１に示す如く判断される。
【００６７】
すなわち、既に入力している収集モード（ステップ６２）が「本影モード」か又は「本影＋半影モード」かが判断される（図１１ステップ６４_１）。これにより、「本影モード」と判断された場合、ステップ６４_２に移行し、既に得ている指定スライス幅（ステップ６１）が回転軸方向における検出器幅に相当する幅に等しいか否かを判断する。この判断でＮＯとなるときは「指定スライス幅＜検出器幅に相当する幅」となる場合であり、その位置態様は図１１（ａ）の如く表わされる。そして、この場合のみ後述するようにポストコリメータ１６が関与する。これに対して、ＹＥＳ、すなわち「指定スライス幅＝検出器幅に相当する幅」となるとき、プリコリメータ１５は同図（ｂ）の位置態様をとる。ステップ６４_１で「本影＋半影モード」が判断された場合（この場合、指定スライス幅＝検出器幅に相当する幅、となることはあり得ない）、説明図（ｃ）の位置態様をとる。なお、同図（ｂ），（ｃ）の位置態様の場合、ポストコリメータ１６は関与しない。ここでいうスライス幅は「Ｘ線プロファイルの半値幅を回転軸中心に投影した値」として定義される。
【００６８】
上記プリコリメータ１５の開口幅Ｗpre は、例えば上述の如く判別した態様毎に、Ｘ線管１０，プリコリメータ１５，被検体のアイソセンタ，及びＸ線検出器１１の各位置データなどを使って前述の式（１）または（２）に基づき、演算またはテーブル参照により求められる。
【００６９】
さらに図１０のステップ６５で、ポストコリメータ１６のスライス方向の開口幅Ｗpostが演算される。この演算は、図１１（ａ）の位置態様のとき（すなわち、指定スライス幅＜検出器幅に相当する幅のとき）のみ行われるもので、ポストコリメータ１６が半影をカットするようにその開口幅Ｗpostが演算される。
【００７０】
次いで主制御装置３０はステップ６６に進んでスキャン法を判断する。もしシングルスキャンであると判断されたときはステップ６９にスキップするが、マルチスキャンであると判断されたとき及びヘリカルスキャンであると判断されたときは、ステップ６７又はステップ６８で天板の送りピッチ又は天板の送り速度がスライス幅を加味して各々演算される。
【００７１】
この後、ステップ６９〜７２の処理が前記図７ステップ４８〜５１の処理と同様に順次実施される。
【００７２】
更に、架台制御装置３３によるコリメータ１５のスライス方向の開口幅制御の例を図１２に基づいて説明する。
【００７３】
すなわち、架台制御装置３３は主制御装置から供給された開口幅Ｗpre を初期値として入力し（同図ステップ８０）、それらのデータに対応した制御信号を架台駆動装置１８に送ることで、プリコリメータ駆動装置１７を作動させ、プリコリメータ１５のスライス方向の実際の開口幅及び／又は位置を指令初期値に合わせる（同図ステップ８１）。
【００７４】
この後、焦点位置検出器２０からの検出信号を入力し（同図ステップ８２）、Ｘ線管１０の発熱などに伴う焦点Ｆの移動量を、例えば図５に示したグラフを表わした記憶テーブル参照によって推定演算する（同図ステップ８３）。
【００７５】
次いでステップ８４に移行して、推定したＸ線焦点Ｆの移動量を加味したプリコリメータ１５の開口幅Ｗpre 又はスライス方向の位置を再演算する。すなわち、焦点Ｆの移動によってＸ線プロファイルＰＬがスライス方向にずれたことを補正する開口データが得られる。この補正用の新たなデータが再び架台駆動装置１２に送られ、その更新された値でプリコリメータ１５の開口幅、位置が修正される（同図ステップ８１）。以下、同様の処理が繰り返される。
【００７６】
なお、上述した図１２の処理に係る焦点移動に対する焦点追従制御にあっては、プリコメータ１５のみを追従させるだけでよく、ポストコリメータ１６はＸ線検出器１１に近いため、このコリメータ１６を追従移動させる必要は無い。Ｘ線検出器１１にシングルスライス検出器が採用されている場合であって、スライス幅＜検出器幅となるプリコリメータ１５の位置態様（すなわち図１１の（ａ）で表わされる位置態様）のとき、ポストコリメータ１６は図１０のステップ６５の処理で演算された開口幅Ｗpostが架台制御装置３３の図示しない処理によって指令される。しかし、この場合もポストコリメータ１６の開口幅ＷpostをＸ線焦点移動に伴って追従制御させることはせず、常に一定値に保持され、半影をカットする。プリコリメータ１５がその他の位置態様、すなわち図８（ａ）〜（ｄ），図１１（ｂ），（ｃ）を採るときは、ポストコリメータ１６はＸ線コリメーションに関与しない。
【００７７】
以上の構成及び処理に係るプリコリメータ１５の動作の典型例を図１３〜１６に示す。この内、図１３は焦点サイズのみを変更した場合のプリコリメータ１５のスライス方向の開口幅の制御例を、図１４は焦点サイズおよび使用検出器列を変更した場合のプリコリメータ１５のスライス方向の開口幅の制御例を、図１５は焦点移動に伴うプリコリメータ１５のスライス方向の開口幅の制御例を、図１６は焦点移動に伴うプリコリメータ１５のスライス方向の開口幅及びその位置の制御例をそれぞれ示す。
【００７８】
いま、Ｘ線検出器１１として２次元検出器を使用し（スライス方向の検出素子列はａ〜ｈとする）、そのスライス方向の一部の検出素子列ｄ，ｅを使用して本影モードのマルチスキャンを実施するものとする。
【００７９】
焦点サイズとして小焦点フィラメントＦＴS による小焦点Ｆが指令されている場合、プリコリメータ１５の開口幅Ｗpre は図１３（ａ）に示すように設定される。すなわち、スキャン条件、１回転当たりのスライス数＝２、収集モード＝本影モード、および焦点サイズ＝小焦点の情報が主制御装置３０に入力されると（図７ステップ４０〜４３）、プリコリメータ１５の位置態様及びスライス方向の開口幅Ｗpre が自動的に決められる（同図ステップ４４）。その位置態様は図８（ｃ）に相当するものであり、また開口幅Ｗpre ＝Ｗpre1は前記式（１）に基づき例えば演算により求められる。さらにスキャン方法はマルチスキャンが指令されているので、その送りピッチがその一部の指定素子列ｄ，ｅに相当する回転中心におけるトータルのスライス幅に等しくなるように自動的に演算される（同図ステップ４５、４６）。そして、入力データ及び演算データは各々、所要のデータ収集装置１３、画像再構成装置３５、架台制御装置３３、寝台制御装置３２、及び高電圧制御装置３１に出力される。高電圧制御装置３１には小焦点を選択するフィラメント選択信号も併せて供給される。このため高電圧制御装置３１は、高電圧発生装置３４から小焦点フィラメントＦＴS にフィラメント電源を供給させる。
【００８０】
この状態から例えば、撮影部位が頭部から腹部に変わるなどの状況に対応してオペレータが焦点サイズＦ＝大焦点への変更のみを欲したとする（管電流以外のスキャン条件、１回転当たりのスライス数、および収集モードは不変とする）。そこでスキャン条件の一つとしての管電流の上昇を指令すると、この管電流の上げに対応したプリセット値として焦点サイズＦ＝大焦点の情報が自動的に読み込まれる（図７、ステップ４３）。これに応答して、プリコリメータ１５の位置態様に応じたプリコリメータ１５の開口幅Ｗpre ＝Ｗpre2が自動的に演算される（図７、ステップ４４）。つまり、位置態様は図１３（ａ）のものと変わらないが、前記式（１）に基づいて求められる開口幅Ｗpre ＝Ｗpre2は焦点Ｆのスライス方向のサイズが大きくなった分だけ大きくなり、Ｗpre2＞Ｗpre1となる開口幅が設定される。そして、図１２の処理を介して（いま焦点位置そのものは変わらないとする）、図１３（ｂ）に示すように、プリコリメータ１５の開口幅Ｗpre がＷpre1からＷpre2に広げられ、使用する検出素子列ｄ，ｅには本影ＲM のみが入射する。
【００８１】
したがって、焦点サイズを大焦点に切り換えた場合でも、使用する検出素子列ｄ，ｅに半影ＲS が入り込んで、本影モードを指定しているにも関わらず、実質的に「本影＋半影」モードになってしまうことはなく、収集モードで指定した通りに本影ＲM のみが入射する。逆に言えば、図１３（ａ）の小焦点の開口幅Ｗpre1のまま大焦点に切り換えたときには、検出素列ｄ，ｅの一部に、焦点のスライス方向のサイズが大きくなった分だけ半影ＲS が入り込む。しかし、本実施形態のように、焦点サイズの切換に合わせてプリコリメータの開口幅も調整しているので、そのような事態の発生が未然に防止される。このため、半影などが入り込むことに因り再構成像の画質が低下してしまうという不具合の発生も確実に回避される。
【００８２】
上述のように焦点サイズを小焦点から大焦点に切り換える場合とは反対に、大焦点から小焦点に切り換えた場合も同様に、図１３（ｂ）から同図（ａ）の状態に開口幅Ｗpre が調整される。つまり、本影ＲM が入射するスライス方向の範囲は検出素子列ｄ，ｅの範囲に止められ、使用しない検出素子列にまで本影が入射することはない。このように本影の入射範囲を必要以上に広げないことによって、Ｘ線検出器１１の外側に漏れる不要なＸ線を極力少なくし、被検体への被爆の影響をより抑えることができる。
【００８３】
また、上述した焦点サイズの切換に加えて、使用する検出素子列を変更する場合の開口幅制御例を図１４（ａ），（ｂ）に示す。
【００８４】
いま、Ｘ線検出器１１として２次元検出器を使用し（スライス方向の検出素子列はａ〜ｈとする）、そのスライス方向の一部の検出素子列ｄ，ｅを使用して本影モードのマルチスキャンを実施するものとする。焦点サイズとして小焦点フィラメントＦＴS による小焦点Ｆが指令されている場合、プリコリメータ１５の開口幅Ｗpre は図１４（ａ）に示すように設定される。すなわち、この場合は前述した図１３（ａ）の場合と同様の処理が行われる。
【００８５】
この状態から例えば、撮影部位が頭部から腹部に変わるなどの状況に対応してオペレータが焦点サイズＦ＝大焦点へ、かつ使用検出素子列の数（すなわち、１回転当たりのスライス数）をｃ〜ｆへの増加を指令したとする（管電流、使用する検出素子列の位置以外のスキャン条件および収集モードは不変とする）。これに応答して、プリコリメータ１５の位置態様に応じたプリコリメータ１５の開口幅Ｗpre ＝Ｗpre2が自動的に演算される（図７、ステップ４４）。つまり、位置態様は図１４（ａ）のものと変わらないが、前記式（１）に基づいて求められる開口幅Ｗpre ＝Ｗpre2は焦点Ｆのスライス方向のサイズが大きくなった分、および、使用検出素子列の増えた分だけ大きくなり、Ｗpre2＞Ｗpre1となる開口幅が設定される。この結果、図１２の処理を介して、図１４（ｂ）に示すように、プリコリメータ１５の開口幅Ｗpre がＷpre1からＷpre2に広げられ、新たに指定した検出素子列ｃ〜ｆには本影ＲM のみが入射する。
【００８６】
したがって、焦点サイズを大焦点に且つ使用する検出素子列を切り換えた場合でも、使用する検出素子列に半影ＲS が入り込んで、本影モードを指定しているにも関わらず、実質的に「本影＋半影」モードになってしまうことはなく、再構成画像の画質低下を防止できる。また、当然に図１４（ｂ）の状態から同図（ａ）の状態へも自動的に開口幅を制御でき、被検体への被爆の影響をより抑えることができる。
【００８７】
一方、焦点Ｆのサイズを切り換えた場合でも、焦点位置はその配置構造上、チャンネル方向にはずれるが、スライス方向には原則としてずれないことにはなっている。しかしながら、焦点サイズの切換に因ってスライス方向にも微妙にずれることがある。この場合でも、図１３および図１４に示す開口幅制御において、そのスライス方向のずれが焦点位置検出器２０により検出されるから、図１２の処理を介してそのずれが自動的に補正される。
【００８８】
なお、図１３および図１４の開口幅制御において、プリコリメータ１５のスライス方向の開口幅とそのスライス方向の位置とを一体に調整するようにしてもよい。
【００８９】
上述した図１３および図１４の開口幅制御は、被検体が変わったときなどに、オペレータにより指令されるスキャン条件および／または焦点サイズの情報に応じて実施されるものであるが、図１５および図１６の開口幅制御はスキャン中であっても自動的に追従制御されるものである。
【００９０】
いま、Ｘ線検出器１１として２次元検出器を使用し（スライス方向の素子列はａ〜ｈとする）、そのスライス方向の一部の検出素子列ｃ〜ｆを指定して本影モードのマルチスキャンを行うものとする。これらの情報を含むスキャン条件、スライス数、収集モード、および焦点サイズが主制御装置３０に入力されると（図７ステップ４０〜４３）、プリコリメータ１５の位置態様及びスライス方向の開口幅が自動的に決められる（同図ステップ４４）。さらにスキャン方法はマルチスキャンが指令されているので、その送りピッチがその一部の指定素子列に相当する回転中心におけるトータルのスライス幅に等しくなるように自動的に演算される（同図ステップ４５、４６）。このようにして入力されたデータ及び演算されたデータは各々、所要のデータ収集装置１３、画像再構成装置３５、架台制御装置３３、寝台制御装置５０、及び高電圧制御装置５１に出力される。
【００９１】
特に、データ収集装置１３は、主制御装置３０から指令された「どの列」（この場合はｃ〜ｆ列）を使うかの列選択信号により、チャンネルごとの列を切り替え、必要なデータを選択して画像再構成装置３５に送る。また、マルチスキャンが指令されているので、ｃ〜ｆ列分に相当するスライス幅が天板の送りピッチとなる。ヘリカルスキャンが指令されているとすると、ｃ〜ｆ列分に相当する撮影領域の回転中心におけるスライス幅が１回転中の天板移動距離となる。これにより、検出器の描く軌跡が全て等間隔となり、再構成におけるデータ補正等の処理が簡単になる。
【００９２】
この結果、主制御装置３０の管理のもとで、各装置が同期をとって動作しデータ収集を行うとともに、その画像を再構成する。このとき、プリコリメータ１５は図１５（図８（ｃ）に相当）に示す位置態様をとる。つまり、プリコリメータ１５のスライス方向の開口幅Ｗpre は２次元検出器１１の検出素子列ａ〜ｈの内の一部の指定素子列ｃ〜ｆに本影ＲM のみが入射するように制御される。
【００９３】
しかも、Ｘ線管１０の管球焦点Ｆ（例えば小焦点、ここでは点として表す）が例えば図１５に示す如く、陽極の曝射時の発熱などに因ってスライス方向に移動することがある。この場合でも、焦点位置移動量の検出に伴う図１２の処理に拠ってプリコリメータ１５の開口幅がリアルタイムに微調整され、検出用の一部の指定素子列ｃ〜ｆには本影ＲM のみが入射する。
【００９４】
このようにプリコリメータ１５の開口幅をフィードバック制御することで、キャリブレーションデータ収集時と実際の撮影時とでＸ線プロファイルが変わるような撮影を行った場合でも、２次元検出器１１の予め指定した検出素子列ｃ〜ｆ（スライス方向のスライス幅に相当）に入射するＸ線強度は常に一定になるから、再構成時のキャリブレーションが良好に掛かり、従来発生していた画像上のアーチファクトやＣＴ値のシフトを防止することができる。またＸ線プロファイルの変化に対する要求が大幅に緩和される。さらに、再構成画像は本影のみを使っているから、何れのスライス面の画質も良好になる。さらに、プリコリメータ１５の開口幅だけを制御すればよいので、駆動対象となるモータ数が開口幅制御用の１つだけで済み、制御が簡単であるという利点もある。
【００９５】
なお、上述した図１５の制御法を２次元検出器の全面、すなわち図１５の例で言えば全部の検出素子列ａ〜ｈを使って本影モードでスキャンする場合（すなわち図８（ａ）の状態）にも同様に好適に適用できる。また、Ｘ線検出器１１としてシングルスライス検出器を使う場合で、本影モードの場合（すなわち図１１ （ａ），（ｂ）の状態）にも好適に実施できる。
【００９６】
一方、図１６に示すスキャンの場合、図１５の場合と同一の条件（２次元検出器，スライス方向の一部の指定検出素子列ｃ〜ｆのみの使用，本影モード，同一焦点サイズ）を採用するが、焦点移動に伴うフィードバック制御量が今度はプリコリメータ１５の各ブレードの「スライス方向の位置」（すなわち、プリコリメータのスライス方向の開口幅及び位置）としている。すなわち、プリコリメータ１５全体のスライス方向の位置がリアルタイムに変更される。この制御は図１２のステップ８２〜８４，８１の一連の処理によってリアルタイムに行われる。
【００９７】
このため、例えばＸ線管１０の焦点Ｆ（例えば小焦点、図では点で表す）が図１６上で矢印で示す如く右側に移動すると、結果的には、プリコリメータ１５のスライス方向の一方のプレードが右側（矢印Ａ₁ ）に移動させられ、且つ、もう一方のブレードも右側（矢印Ａ₂ ）に等距離だけ移動させられる。すなわち、前述した図１５の場合のようにスライス方向のコリメーションを担う両ブレードがスライス方向に対称に動いて開口幅Ｗpre のみを変える制御とは異なり、開口幅Ｗpre 自体及びスライス方向のコリメータ全体の位置が焦点移動量に応じて変わる。
【００９８】
したがって、Ｘ線検出器１１に対するＸ線プロファイルＰＬのスライス方向の位置は変わらず、焦点移動が実際には生じても、見掛け上焦点移動が発生していないことと同じになる。これにより、図１５の場合と同等の作用効果が得られるほか、図１５の方法と比べても、より安定且つ高精度なプロファイルの位置制御を行うことができ、また被曝量を最小限に抑制できるという利点がある。さらに重要なことは、図１６に示すプリコリメータ１５の制御を行った場合、スライス方向の本影の位置が固定される。つまり、本影を受ける検出素子列のＸ線プロファイルの形状は、キャリブレーションデータ収集時と画像データ収集時とで不変である。したがって、そのような本影を受ける検出素子列により検出されたデータを使った画像は常に高品質に保持できるという有利さも在る。
【００９９】
なお、上述した図１６の制御法を２次元検出器の全面、すなわち図１６の例で言えば全部の検出素子列ａ〜ｈを使って本影モードでスキャンする場合（すなわち図８（ａ）の状態）にも同様に好適に適用できる。また、Ｘ線検出器１１としてシングルスライス検出器を使う場合で、本影モードの場合（すなわち図１１ （ａ），（ｂ）の状態）にも好適に実施できる。
【０１００】
一方、「本影＋半影モード」は検査者により必要に応じて選択される（図７、ステップ４２及び図１０、ステップ６２参照）。このように「本影モード」のみならず、「本影＋半影モード」も任意に選択できるようにしたので、半影部分も合せて検出器に入射させることで被曝量を抑えることができ、またマルチスキャンやヘリカルスキャンを高速に行うことができるというメリットがある。この様子を図１７（ａ），（ｂ）に示す。同図（ａ）は「本影モード」のスキャンを、同図（ｂ）は「本影＋半影モード」のスキャンを各々説明するもので、同図（ｂ）の方がＸ線検出器１１上の使用可能な素子列数が多い。これにより、「本影＋半影モード」で高速なスキャンが可能になる。
【０１０１】
ところで、図１７（ａ），（ｂ）では送りピッチまたは送り速度の量を表す矢印は概略的に描かれている。送りピッチや送り速度は実際にはＸ線焦点を点と見做して演算されるので、それらの量を表す矢印は実際には図示のものよりも若干短くなって、トータルのスライス幅に相当する量となる。
【０１０２】
本発明に係る変形例を図１８に基づき説明する。前述した実施形態はＸ線管の管球焦点の移動に応じてプリコリメータ１５のスライス方向の位置及び／又は開口幅をリアルタイムに微調整する構成としたが、かかる変形例はそのような構成を簡略化したものである。具体的には、プリコリメータ１５のスライス方向の開口幅及び／又は位置は一回だけ初期設定することとし、その後は焦点位置の移動があっても、その値を保持する。
【０１０３】
いま、前述した図１５，１６の場合と同様に、２次元検出器の一部の指定検出素子列ｃ〜ｅのみを使って本影モードでスキャンするとする。Ｘ線管１０が最も低い温度状態から最も高い温度状態になって焦点移動が起こったとしても、少なくとも目的とする一部の検出素子列ｃ〜ｅには必ず本影のみが入射するように開口幅Ｗpre （又は位置）が最初に１回だけ設定される。つまり、予め焦点移動を見込んで、使用する検出素子列を決め、開口幅（又はスライス方向の位置）を広めに設定しておく。そして、スキャン前に一度設定したら、その後の開口制御は行わない。
【０１０４】
この焦点移動距離を見込んだ場合の開口幅Ｗpre の設定は定量的には下記の式を用いればよい。前述した図９に示す如く、Ｘ線管１０の焦点Ｆのサイズをｘ、Ｘ線検出器１１上に投影される本影のスライス方向の長さをｙ、Ｘ線検出器１１上に投影される「本影＋半影」のスライス方向の長さをｚ、焦点Ｆとプリコリメータ１５との間の曝射方向の距離をｃ、プリコリメータ１５とＸ線検出器１１との間の曝射方向の距離をｄとし、さらに、図１９に示す如く、スライス方向における予想される最大の焦点移動量をΔｍとすると、プリコリメータ１５の本影モードの開口幅Ｗpre （ｘ，ｙ）および「本影＋半影」モードの開口幅Ｗpre （ｘ，ｚ）は夫々、
【数３】

【数４】

の式により演算できる。なお、この開口幅の設定値は予め式（３）または（４）に基づいて演算しておいて、テーブルとして保有しておくようにしてもよい。
【０１０５】
これにより、Ｘ線ＣＴスキャナの駆動状態に応じてＸ線管の温度が上昇し、管球焦点が例えば図１８中の実線図示の状態から点線図示の状態（Ｘ線管が最高に暖まった状態）に向かって移動した場合でも、Ｘ線検出器１１の指定検出素子列ｃ〜ｅには常に本影のみが入射する。したがって、この変形例によれば、開口制御が一回で済み、制御が簡単化される。この場合にはまた、焦点位置検出器２０が不要になる利点もある。
【０１０６】
さらに、上述した焦点移動を見込んだ開口幅設定の手法には、以下のような種々のファクタを取り込んで、または単独で実施することができる。
【０１０７】
第１に、焦点切換における焦点位置の移動に対する対応策に関する。Ｘ線管１０の焦点を例えば小焦点から大焦点に切り換えると、焦点位置が微妙にずれることがあり得る。Ｘ線管内では、大焦点用フィラメントおよび小焦点用フィラメントは、その構造上、チャンネル方向に並んで設置されているため、焦点を切り換えても通常、チャンネル方向に焦点位置がずれるだけで、スライス方向には原理的にはずれないことになっている。しかしながら、焦点切換によってスライス方向にも微妙にずれを生じることがある。
【０１０８】
そこで、図１９に示す如くの、スライス方向における予想される最大の焦点移動量Δｍに、焦点切換に伴う焦点移動量を加味しておく。または、この最大の焦点移動量Δｍを焦点切換に伴う焦点移動量に等しく設定しておく。これにより、前述した図１８に模式的に表す如く、Ｘ線管１０の温度上昇および焦点切換に拠る焦点移動があっても、または、焦点切換に拠る焦点移動があっても、簡単な開口幅制御でありながら、使用する検出素子列に入射するＸ線プロファイルを常に所望のものに維持できる。
【０１０９】
第２に、フライング焦点の技法における焦点移動の対応に関する。Ｘ線ＣＴスキャナでは、データのサンプリング点を増加させるなどの目的のため、Ｘ線管内で陰極からターゲートに向けて放射する電子ビームを電磁的作用などに因って振り、意図的に焦点位置を変える機能を搭載しているものがある。この焦点位置の移動によって本影のスライス方向の移動が生じる。
【０１１０】
そこで、この場合も図１９に示す如くの、スライス方向における予想される最大の焦点移動量Δｍに、フライング焦点に伴う焦点移動量を加味しておく。または、この最大の焦点移動量Δｍをフライング焦点に伴う焦点移動量に等しく設定しておく。これにより、前述した図１８に模式的に表す如く、Ｘ線管１０の温度上昇および焦点切換に拠る焦点移動があっても、または、フライング焦点に拠る焦点移動があっても、簡単な開口幅制御でありながら、使用する検出素子列に入射するＸ線プロファイルを常に所望のものに維持できる。
【０１１１】
なお、上述した図１８の制御法を２次元検出器の全面、すなわち図１８の例で言えば全部の検出素子列ａ〜ｈを使って本影モードでスキャンする場合（すなわち図８（ａ）の状態）にも同様に好適に適用できる。また、Ｘ線検出器１１としてシングルスライス検出器を使う場合で、本影モードの場合（すなわち図１１ （ａ），（ｂ）の状態）にも好適に実施できる。
【０１１２】
またなお、本発明におけるＸ線管の管球焦点の移動に関するセンサ手段は、上述した構成のものに限定されることなく、例えばＸ線管１０の外周面上に取り付けた赤外線検出器でＸ線管１０の温度変化を検出し、その温度変化に基づいて管球焦点の移動を推定するようにしてもよい。また、例えば実開平２−９１２００号公報記載の如く、Ｘ線管の冷却油の温度を検出する温度検出器であってもよいし、またＸ線管電圧、Ｘ線管電流、Ｘ線照射時間、Ｘ線照射停止時間などのＸ線管の駆動に関する情報を、管球焦点の移動に関する情報として取り込む構造を採ってもよい。
【０１１３】
また、前述した実施形態およびその変形例では、Ｘ線管の焦点サイズの切換を「大」または「小」の２段階としたが、本発明は必ずしもこれに限定されるものではない。例えば、「中」焦点用フィラメントを搭載して、焦点サイズを３段階に切換可能に構成することもできるし、焦点サイズをさらに多くのステップ状に切換可能に構成してもよい。さらには、例えば電磁的作用により電子ビームの形状や位置を制御したり、陰極の位置を機械的に調整したりすることで、任意の大きさの焦点を設定可能なＸ線管に本発明を適用し、任意値に設定された焦点サイズに応じて前述と同様にプリコリメータの開口幅を制御するようにしてもよい。
【０１１４】
さらに、本発明は上述した実施形態、つまり、Ｘ線ビームの本影のみを受ける、２次元検出器の１以上の検出素子列の指定を、実際のＸ線スキャンによる撮影時にその都度行うようにするというスキャナ構成に限定されるものではない。設計上の条件やその他の条件により、その１以上の検出素子列が予め固定的に決まっている場合でも、かかる２次元検出器は本発明のＸ線ＣＴスキャナに好適に適用できる。つまり、そのような場合には、予め決まっている検出素子列によって検出されたデータのみを採用して前述と同様の処理を行うようにデータ収集装置１３への列選択信号を設定しておけばよい。
【０１１５】
さらに、前述した実施形態およびその変形例では、焦点サイズの変更（切換）および焦点位置の移動に伴う、両方のプリコリメータの開口幅制御に対応可能な制御を実施する構成を示したが、焦点サイズの変更（切換）に伴うプリコリメータの開口幅制御のみでも単独に実施できることは勿論である。
【０１１６】
なおまた、本発明は上述した実施形態や変形形態に限定されるものではなく、本発明の基本原理の範囲内で適宜に組み合わせ、変更、変形することが可能である。
【０１１７】
【発明の効果】
以上説明したように、この発明のＸ線ＣＴスキャナによれば、Ｘ線源としてのＸ線管の焦点サイズが変更された場合でも、その変更に応じてプリコリメータの開口幅が、例えば、２次元検出器の使用したい検出素子列に常に本影のみが入射するように制御されることから、焦点サイズが変更された場合でも、本影のみを受けて再構成画像の画質劣化を防止できるとともに、Ｘ線被爆の影響も最小限に抑えることができる。
【０１１８】
また、上述の効果にほか、下記の種々の効果も同時に得られる。すなわち、Ｘ線検出器の検出素子列（２次元検出器の場合、複数の検出素子列の内の指定された検出素子列または予め決まっている検出素子列）のスライス方向の幅全体にＸ線プロファイルの本影のみが入射するので、スライス位置によって画質が変わることも無く、また高い信号値を検出することができ、高画質の再構成象を提供することができる。さらに、プリコリメータのスライス方向の開口幅が、Ｘ線管のＸ線焦点の移動に伴うＸ線ビームのスライス方向の予測される最大移動量に対応した量だけ広く設定されるので、一度そのように開口設定しておくだけで、良好な信号及び画質が得られる。さらにまた、Ｘ線管の管球焦点が温度上昇などに因って移動し、キャリブレーションデータ収集時と撮影時とでＸ線プロファイルが変化した場合でも、プリコリメータのスライス方向の例えば開口幅及び／又は位置などを焦点移動量に応じてリアルタイムに微調整することにより、Ｘ線検出器の指定されたまたは予め決めてある検出素子列のスライス方向の幅全体にわたって本影を入射させることができるので、画像上のアーチファクトやＣＴ値のシフトを排除でき、画質を向上させることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係るＸ線ＣＴスキャナの概要を示すブロック図。
【図２】焦点サイズを切換可能なＸ線管の概略構造図。
【図３】図２中のIII-III 線に沿った側面図。
【図４】Ｘ線検出器とＸ線ビームの入射との位置関係を説明する図。
【図５】Ｘ線検出器の出力とＸ線焦点位置移動量の関係を示すグラフ。
【図６】データ収集装置のブロック図。
【図７】主制御装置で実行される２次元検出器の場合の制御例を示すフローチャート。
【図８】２次元検出器の場合のプリコリメータの位置態様を判断するフローチャート。
【図９】プリコリメータの開口幅制御に関わるパラメータの説明図。
【図１０】主制御装置で実行されるシングルスライス検出器の場合の制御例を示すフローチャート。
【図１１】シングルスライス検出器の場合のプリコリメータの位置態様を判断するフローチャート。
【図１２】架台制御装置で実行される開口制御の一例を示すフローチャート。
【図１３】焦点サイズの切換に伴うプリコリメータの開口幅制御を示す説明図。
【図１４】焦点サイズの切換および使用する検出素子列の変更に伴うプリコリメータの開口幅制御を示す説明図。
【図１５】２次元検出器を使ったときの焦点移動追従制御の一例を示す説明図。
【図１６】２次元検出器を使ったときの焦点移動追従制御の他の例を示す説明図。
【図１７】（ａ），（ｂ）は本影モード，本影＋半影モードのときの送りピッチまたは送り速度の大小を比較説明する図。
【図１８】変形例に係るプリコリメータの開口設定を説明する図。
【図１９】焦点の移動量を説明する図。
【図２０】プリコリメータの役割を説明する図。
【図２１】従来のシングルスライスＣＴにおけるＸ線プロファイルとＸ線検出器の位置関係を説明する図。
【図２２】従来の２次元検出器に係るＣＴにおけるＸ線プロファイルとＸ線検出器の位置関係を説明する図。
【図２３】Ｘ線管の管球焦点の移動を説明する図。
【図２４】シングルスライス検出器に対するプロファイル変化の影響を説明する図。
【図２５】２次元検出器に対するプロファイル変化の影響を説明する図。
【符号の説明】
１ ガントリ
２ 寝台
２ａ 天板
２ｂ 寝台駆動装置
３ 制御キャビネット
１０ Ｘ線管（Ｘ線源）
１１ Ｘ線検出器（２次元検出器またはシングルスライス検出器）
１２ 架台駆動装置
１３ データ収集装置
１５ プリコリメータ
１７ プリコリメータ駆動装置
２０ 焦点位置検出器
３０ 主制御装置
３１ 高電圧制御装置
３２ 寝台制御装置
３３ 架台制御装置
３４ 高電圧発生装置
３５ 画像再構成装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT scanner having a structure in which an X-ray beam exposed from an X-ray tube passes through a subject through a collimator and is incident on an X-ray detector. The present invention relates to an X-ray CT scanner whose size can be changed.
[0002]
[Prior art]
In general, a medical X-ray CT scanner includes a collimator that reduces the thickness of an X-ray beam in the slice direction. This collimator includes a pre-collimator that performs its main function and a post-collimator that is used as an auxiliary.
[0003]
In the X-ray CT scanner, the X-ray beam exposed from the X-ray tube is narrowed down to a fan beam having a slice thickness required for scanning, and this fan beam is transmitted to the subject, and the transmitted beam is detected by X-rays. The precollimator is used for the X-ray diaphragm in this slice direction. That is, as shown in FIG. 20, the precollimator 100 has a slit-like opening, and is interposed between the X-ray tube 101 and the subject 102, and the X-ray beam XB is adjusted by the control mechanism 103 to adjust the opening. A fan beam having a slice thickness of 5 mm is formed. Then, the fan beam that has passed through the subject 102 enters the X-ray detector 104, and image reconstruction is performed based on the detected value. The post-collimator also has a slit-shaped opening, but the mounting position is in the vicinity of the X-ray detector between the subject and the X-ray detector, and the thickness of the fan beam narrowed by the pre-collimator in the slice direction is adjusted. Squeeze more finely as needed.
[0004]
It is known that the X-ray tube can be further increased in size according to the size of the subject. However, no matter how large the focal spot size, it is not infinitely small but has a size in the slice direction. For this reason, when the X-ray beam is pre-collimated by the pre-collimator, the intensity (profile PL) in the slice direction of the X-ray fan beam incident on the X-ray detector has a trapezoidal shape as shown in FIG. 21, for example. When RM (hereinafter referred to as “main shadow”), regions RS and 2RS (hereinafter referred to as “half shadow”) are formed on both sides in the slice direction of the main shadow and having an inclination in intensity.
[0005]
In contrast to the X-ray profile composed of the main shadow RM and the penumbra RS and RS, the conventional scanner receives all of the main shadow RM and the penumbra RS and RS with an X-ray detector. For example, in the single slice CT, a single slice detector in which one row of detector elements is arranged along a channel direction orthogonal to the slice direction is used. Normally, as shown in FIG.
“X-ray beam width in the slice direction” <“detector width in the slice direction” ... “Condition 1”
The positional relationship among the X-ray tube 101 (tube focus F), the pre-collimator 100, and the single slice detector 104 is set so that In multi-slice CT, a two-dimensional detector in which two or more rows of detector elements are arranged along a channel direction orthogonal to the slice direction is used. In this case as well, as shown in FIG. Retained. The two-dimensional detector is a concept including an image intensifier.
[0006]
By the way, in order to obtain an image with an X-ray CT scanner, it is necessary to collect two types of data. That is, calibration data and actual clinical subject data. The calibration data is for correcting variations in sensitivity of each segment of the X-ray detector. For example, X is measured at relatively long intervals (for example, one week, 10 days, etc.) using a known phantom. Line transmission data. The sensitivity correction is performed using calibration data in the data processing process at the time of subject data collection.
[0007]
[Problems to be solved by the invention]
However, the X-ray profile is broken from the solid line state in FIG. 23 to the broken line due to, for example, thermal expansion at the time of exposure of the tube anode, movement of the focal point F due to backlash or deformation of the anode, and the like. Like the transition to the state, the parallel movement in the slice direction causes a state in which the X-ray profile differs between the calibration data collection and the subject data collection, and the sensitivity correction is performed accurately. However, there is a problem that artifacts and shifts in CT values occur in such a reconstructed image.
[0008]
This problem will be described with reference to specific examples of FIGS. FIG. 24 shows the influence of the change in the slice direction of the X-ray profile on the single slice detector. Since the total output of the detector is the integral of the product of the X-ray profile in the slice direction and the detector sensitivity, the X-ray profile is, for example, as shown in FIG. When the state changes from a solid line to a dotted line, when the detector sensitivity in the slice direction is not uniform as shown in FIG.
[0009]
FIG. 25 shows the influence of the change in the slice direction of the X-ray profile on the two-dimensional detector. In the case of a two-dimensional detector, when the calibration data is collected and the object data is collected, for example, when the state changes from a solid line to a dotted line in the same figure, the X-ray intensity is detected in the detection element row corresponding to the penumbra. Changes significantly.
[0010]
As described above, the change in the X-ray profile between calibration data collection and subject data collection may cause artifacts, or the CT value may deviate from the actual value, thereby degrading the image quality and the diagnostic ability. It will cause a situation of letting.
[0011]
Furthermore, when “condition 1” is satisfied as shown in FIG. 22 described above, the penumbra portion is also used for imaging, so the slice plane detected in this penumbra portion is more than that of the main shadow portion. There was also a problem that the image quality deteriorated.
[0012]
On the other hand, the examiner may automatically change the X-ray focal spot size (that is, the intensity of the X-ray beam) by changing the tube current of the X-ray tube according to the size of the subject. . If the focal spot size is changed in this way, the shape of the X-ray profile is also changed. Therefore, in the conventional case, for example, the main shadow and the penumbra are incident on the detector array that is intended to enter only the main shadow. As a result, there was a problem that the image quality deteriorated. In addition, the shadow portion was so large that it protruded from the incident surface of the detector, and there was a situation where it was necessary to worry about exposure to the subject.
[0013]
The present invention has been made by paying attention to the above-described problems of the prior art. In particular, even when the focus size of the X-ray tube is changed, the image quality is reduced due to the shape change in the slice direction of the X-ray profile. The primary purpose is to prevent and minimize the effects of exposure.
[0014]
In addition, the present invention achieves the above first object, and at the same time, can eliminate artifacts and CT value deviations caused by movement in the slice direction of the X-ray profile accompanying movement of the focal point of the X-ray tube, and can achieve high image quality and high accuracy. It is a second object to obtain the image.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the X-ray CT scanner according to the first aspect of the present invention, an X-ray source having a focal point for exposing an X-ray beam, and an object and the X-ray source are interposed. A pre-collimator that narrows the width of the X-ray beam in the slice direction of the subject, and an X-ray detector that receives the X-ray beam that has passed through the subject. A plurality of detection element arrays each including a detection channel are formed by a two-dimensional detector arranged in the slice direction, and designated detection elements in the plurality of detection element arrays are formed in accordance with the focal point size of the X-ray source. Control means for controlling the precollimator so that a row receives a main shadow and a half shadow of the profile of the X-ray beam formed by the precollimator, and is detected by the designated detection element row. And reconstruction means for reconstructing an X-ray CT image based on data, characterized by comprising a.
[0016]
Preferably, detection means for detecting an amount corresponding to the focal point movement of the X-ray source is provided, and the control means is configured to detect the opening width of the pre-collimator in the slice direction based on the detection amount of the detection means, Control at least one of the position in the slice direction of the collimator and the position in the slice direction of the focal point of the X-ray source so that the designated detector element array receives the main shadow of the X-ray beam. Including means.
[0017]
Further, in the X-ray CT scanner according to the invention of claim 2, the X-ray detector is formed by a two-dimensional detector in which a plurality of detection element arrays each including a plurality of detection channels are arranged in the slice direction, and Detection of at least one of the plurality of detection element rows that receives a main shadow and a main shadow of the X-ray beam profile formed by the pre-collimator according to the focal size of the X-ray source. Reconstructing means for reconstructing an X-ray CT image based on data detected by the element array is provided.
[0018]
Preferably, detection means for detecting an amount corresponding to the focal point movement of the X-ray source, an opening width in the slice direction of the pre-collimator based on the detection amount of the detection means, and the slice direction of the pre-collimator in the slice direction Control means for controlling at least one of the position and the position of the focal point of the X-ray source in the slice direction so that the at least one detector element array receives the main shadow of the X-ray beam; Prepare.
[0019]
Furthermore, in the X-ray CT scanner according to the invention of claim 3, the X-ray detector is formed by a two-dimensional detector in which a plurality of detection element arrays each including a plurality of detection channels are arranged in the slice direction, and A first acquisition mode in which image reconstruction is performed based on only the main shadow and the main shadow of the X-ray beam profile formed by the pre-collimator, and both the main shadow and the penumbra Selection means for selecting one of the second acquisition modes for performing image reconstruction based on the data, and the acquisition mode selected by the selection means and the focus size of the X-ray source Control means for controlling the aperture state of the pre-collimator, and scanning means for collecting data based on the collection mode selected by the selection means, And wherein the door.
[0020]
Preferably, detection means for detecting an amount corresponding to the focal point movement of the X-ray source is provided, and the control means is configured to detect the opening width of the pre-collimator in the slice direction based on the detection amount of the detection means, Control of at least one of the position in the slice direction of the collimator and the position in the slice direction of the focal point of the X-ray source so as to prevent the movement of the profile of the X-ray beam incident on the X-ray detector. Means to do.
[0021]
For example, the X-ray source is an X-ray tube that can change the size of the focal point.
[0022]
Preferably, the total slice width at the center of the imaging region by the designated detection element array for each scan by the X-ray beam at the time of multi-scan, and a top plate that is movable in the slice direction and places the subject thereon Determination means for determining a movement distance of the top plate that substantially coincides with the top board, and a top plate control means for controlling the movement of the top board based on the movement distance determined by the determination means.
[0023]
More preferably, the top plate that is movable in the slice direction and on which the subject is placed, and the designated detection for each rotation of the X-ray source and the X-ray detector around the subject during a helical scan. Judgment means for judging the movement distance of the top board according to the total width in the slice direction at the center of the imaging region by the element array, and movement of the top board based on the movement distance judged by the judgment means It can also be set as the structure provided with the top-plate control means to control.
[0024]
Furthermore, setting means for setting the aperture width of the pre-collimator in the slice direction wider by an amount corresponding to the predicted maximum movement amount of the X-ray beam in the slice direction accompanying the focal movement of the X-ray source is provided. be able to. This maximum movement amount can include, for example, a focus movement amount accompanying a change in focus size.
[0025]
Furthermore, an X-ray CT scanner according to the invention of claim 12 is interposed between an X-ray source having a focal point for exposing an X-ray beam and the subject and the X-ray source, and A pre-collimator that narrows the width of the X-ray beam in the slice direction; and an X-ray detector that receives the X-ray beam that has passed through the subject; and the opening width of the pre-collimator in the slice direction and the slice direction Control means for controlling at least one of the positions in accordance with the size of the focal point of the X-ray source.
[0026]
With the above configuration, even when the focus size of the X-ray tube as the X-ray source is changed, the aperture width of the pre-collimator is controlled and the profile of the X-ray beam is adjusted according to the change. This control is performed, for example, so that only the main shadow is always incident on the detection element array desired to be used by the two-dimensional detector. As a result, even when the focal spot size is changed, only the main shadow is received and image quality deterioration of the reconstructed image can be prevented, and the influence of X-ray exposure can be minimized.
[0027]
In accordance with this action, only the main shadow of the X-ray beam is observed over the width in the slice direction of the detection element array of the X-ray detector (in the case of a two-dimensional detector, a detection element array specified at the time of imaging or predetermined). For example, the opening width and / or position of the pre-collimator in the slice direction is controlled so as to be incident. For this reason, even if focal point movement occurs in the X-ray tube, the X-ray intensity of the profile in the slice direction is constant and image quality is not deteriorated.
[0028]
Further, the opening width in the slice direction of the pre-collimator is set wide by an amount corresponding to the predicted maximum movement amount in the slice direction of the X-ray beam accompanying the movement of the X-ray focal point of the X-ray tube. For this reason, a good signal and image quality can be obtained only by setting the aperture once.
[0029]
Further, an amount corresponding to the movement of the X-ray focal point of the X-ray tube is detected, and based on the detected amount, the main shadow of the X-ray beam is a detection element designated or predetermined by the two-dimensional X-ray detector. The precollimator, for example, the opening width in the slice direction and / or the position in the slice direction is controlled so as to be incident over the width in the slice direction of the row. For this reason, even when the amount of movement of the X-ray focal point differs between calibration data collection and imaging, the main shadow part is always incident on the X-ray detector, and stable and good calibration is applied during image reconstruction. Occurrence of artifacts and CT value shifts can be prevented.
[0030]
Furthermore, the operator can arbitrarily select the main shadow mode and the “main shadow + half shadow” mode for scanning.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
An X-ray CT scanner according to an embodiment of the present invention will be described below with reference to FIGS.
[0032]
The X-ray CT scanner shown in FIG. 1 includes a gantry 1, a bed 2, and a control cabinet 3, and is an apparatus that is driven by, for example, the RR method. A top plate 2a is disposed on the top surface of the bed 2 so as to be slidably supported in the longitudinal direction (corresponding to the slice direction (or the rotation axis direction)). A specimen P is placed. The couchtop 2a is inserted into the diagnostic opening of the gantry 1 so as to be able to advance and retract by driving a couch driving device 2b represented by a servomotor. The bed 2 is provided with a position detector (not shown) such as an encoder that detects the position of the table 2a in the longitudinal direction of the bed 2 using an electrical signal. As shown in FIG. 1, the channel direction is defined as a direction orthogonal to the slice direction and the X-ray beam exposure direction.
[0033]
The gantry 1 includes an X-ray tube 10 and an X-ray detector 11 that face each other with a subject P inserted in the opening.
[0034]
Among these, as shown in FIGS. 2 and 3, the X-ray tube 10 functioning as an X-ray source forms a structure of a rotary anode X-ray tube and the size of the focal point can be switched between “large” and “small”. It has become. That is, in the X-ray tube 10, a cathode 10b and a target 10c as an anode are arranged inside the vacuum of the envelope 10a. The cathode 10b is composed of a tungsten filament FT, a converging electrode EL, and the like disposed so as to face the target 10c, and is supported and coupled to the cathode sleeve 10d. As shown in FIG. 3, the filament FT is formed of a large focus filament FTL and a small focus filament FTS juxtaposed in the channel direction at the same position in the slice direction. The filaments are heated by selectively passing currents through the two filaments FTL and FTS via a high voltage control device, which will be described later, and thermoelectrons are emitted toward the target 10c.
[0035]
The target 10c, which is an anode, has a disk shape with a tapered target surface having a target angle θ, and is supported by the rotary anode 10e so as to be rotatable at a high speed. The thermoelectrons emitted from the large-focus or small-focus filaments FTL or FTS collide with the target surface to form an effective focus F, and an X-ray beam is exposed from the site of the effective focus F on the target surface.
[0036]
As a result, the focal point can be selectively set to “large” or “small” by selectively energizing the two filaments FTL and FTS via the high voltage control device. When the large focal length filament FTL is used, the electron beam hits a wider target surface and the effective focal point F becomes larger. Since a larger current can flow through the large focal length filament FTL, the X-ray beam becomes a strong and large fan beam. However, if the focal spot size is large, the individual beams when passing through the subject become thick, and the resolution is lowered. The large focal point is used when it is desired to use stronger X-rays even when the resolution is reduced (for example, when the size of the subject is large). The small focus is the opposite, and is used when the resolution is important. Large focus and small focus are usually used in this way.
[0037]
In many cases, information on the focus size necessary for properly using the focus is given as preset information. Again, the operator can automatically specify the focal spot size by setting the tube current value.
[0038]
The X-ray detector 11 is a two-dimensional detector in which a plurality of detection element arrays having a plurality of detection channels are arranged in the slice direction, or a single element in which one detection element array having a plurality of detection channels is arranged in the slice direction. A slice detector is installed. The X-ray tube 10 and the X-ray detector 11 can be rotated around a rotation shaft in the gantry 1 by a gantry driving device 12. The current signal corresponding to the transmitted X-ray detected by the X-ray detector 11 is converted into a digital quantity by the data acquisition device (DAS) 13 and sent to the control cabinet 3.
[0039]
Further, in the gantry 1, a pre-collimator 15 is provided between the X-ray tube 10 and the subject P, and a post-collimator 16 is provided between the subject P and the X-ray detector 11. The pre-collimator 15 has, for example, two blades that form slit-shaped openings having a constant width in the channel direction and a variable width in the slice direction. The two blades move symmetrically in the slicing direction and can also be moved in the slicing direction by the entire precommeter 15. The opening width and position in the slicing direction of the precommeter 15 are adjusted by a precollimator driving device 17 set in the gantry 1. Thereby, the width of the X-ray beam irradiated from the X-ray tube 10 in the slice direction is narrowed to form a fan beam having a desired width. Since the effective focus F of the X-ray tube 10 has a finite length in the slice direction, a main shadow and a penumbra are formed in the X-ray profile in the slice direction at the detector position in the same manner as described above.
[0040]
Since the opening of the pre-collimator 15 is formed in a slit shape, the above-described problem caused by the penumbra does not occur in the channel direction.
[0041]
Similarly, the post-collimator 16 has a slit-like opening having a constant width in the channel direction and a variable width in the slice direction. The width in the slice direction is adjusted by the post-collimator driving device 18. In this embodiment, the post-collimator 18 has an auxiliary diaphragm function for further narrowing the X-ray beam narrowed by the pre-collimator 15.
[0042]
Both the pre-collimator driving device 17 and the post-collimator driving device 18 include a stepping motor and a slide mechanism, and operate in response to a drive control signal sent from the gantry driving device 12. At least the pre-collimator driving device 17 includes a motor that adjusts the opening width itself and a motor that adjusts the position of the entire opening width in the slice direction.
[0043]
A focal position detector 20 as a focal position sensor is attached in the vicinity of the X-ray detector 11. A part of the X-ray beam exposed by the X-ray tube 10 passes, for example, a pre-collimator 15D for detecting the focal position attached to the side of the pre-collimator 15 in the channel direction, and is then sent to the focal position detector 20 described above. Incident. As shown in FIG. 4, the focal position detector 20 is composed of, for example, two X-ray detectors FD1 and FD2 (each including a scintillator and a photodiode) adjacent to each other in the slice direction. After the conversion, it is sent to a later-described gantry control device of the control cabinet 3.
[0044]
The control cabinet 3 has a high voltage control device 31, a couch control device 32, and a gantry control device 33 that operate in response to a command from the main control device 30 in addition to the main control device 30 that controls the entire system. In particular, the gantry control device 33 calculates the detection signals P1 and P2 of the focal position detector 20, that is, the ratio of the X-ray intensity incident on the two built-in X-ray detectors FD1 and FD2 "(P1-P2) / (P1 + P2)". While calculating, the focal position movement amount is obtained by referring to a storage table in which this ratio and the X-ray focal position movement amount in the slice direction are related in advance. FIG. 5 is a graph showing an example of such association. In a certain focal range, this relationship is almost a straight line.
[0045]
In this gantry control device 33, instead of referring to the above-mentioned storage table, it is also possible to store only the straight line expression representing the characteristics of FIG. 5 in advance and obtain the focal position movement amount by calculation.
[0046]
Further, the control cabinet 3 generates a high voltage that operates in response to a drive signal (including a filament selection signal for selecting either a large focal filament or a small focal filament) from the high voltage control device 31 as shown in FIG. A high voltage generated by the high voltage generator 34 is supplied to the X-ray tube 20. Furthermore, the control cabinet 3 receives an acquisition signal from the data acquisition device 12, an image reconstruction device 35 that reconstructs image data, an image data storage device 36 that stores image data, and a display device that displays a reconstructed image. 37 and an input device 38 for an operator to give a command to the main controller 30.
[0047]
As shown in FIG. 6, when the X-ray detector 11 is a two-dimensional detector, the data acquisition device 13 detects a detection signal of “n channel × f column” (n and f are positive integers greater than “1”). ) To select a detection signal for one column for each channel in accordance with the column selection signal. ₁ , 13A ₂ ... 13A _n And this data selector 13A ₁ ... 13A _n And a data collection unit 13B for amplifying the detection signals selected by the above and A / D conversion. The column selection signal is sent from the main controller 30. The X-ray detection data for each channel generated by the data collection unit 13B is output to the image reconstruction device 35.
[0048]
The main controller 30 manages the entire scanner according to a predetermined procedure. An example thereof is shown in FIGS. The control by the main controller 30 is divided into a case where a two-dimensional detector is used as the X-ray detector 11 and a case where a single slice detector is used.
[0049]
FIG. 7 shows a control example of the main controller 30 when a two-dimensional detector is used as the X-ray detector 11.
[0050]
First, at step 40 in the figure, the main controller 30 determines the scan mode (multi-scan or helical scan), the number of detection element rows designated for data collection and their positions, the scan site and position, the slice thickness, X Information on scanning conditions such as tube voltage and current (however, information on “number of slices per rotation”, “collection mode”, and “focus size” described later is not included) is input.
[0051]
Next, at step 41, information on the number of slices per rotation is input. Further, in step 42, the collection mode (in this embodiment, “main shadow mode” (: mode in which only the main shadow is collected), “main shadow + penumbra mode” (: main shadow and penumbra (part of)) ) And the mode of collecting information). The detection element array used for data collection of the X-ray detector 11 is arbitrarily designated at the time of imaging by an operator, for example.
[0052]
Next, the process proceeds to step 43, and the main controller 30 inputs information on the focus size. Specifically, the tube current value input in step 40 is referred to a table, and information on a focus size predetermined in correspondence with the tube current value is input as preset information. When the tube current value is high, the focus size “large” is commanded, and when the tube current value is low, the focus size “small” is commanded. The tube current value is set by the operator in consideration of the size of the subject.
[0053]
Next, the routine proceeds to step 44, where the width Wpre in the slice direction of the opening of the precommeter 15 is calculated. In this calculation, the main controller 30 determines the position modes that can be taken by the precommeter 15 as shown in FIG.
[0054]
That is, “whether all or some of the plurality of detection element rows of the two-dimensional detector are used” is input information (step 40 in FIG. 7) instructed from the input device 38. Based on the determination (step 44 in FIG. 8). ₁ ). If it is determined that the “all columns” are to be used, the acquisition mode is “main shadow mode” or “main shadow + half shadow” based on the input information commanded from the input device 38 (step 42 in FIG. 7). Mode ”(step 44 in FIG. 8). ₂ ). When the “main shadow mode” is determined, the precollimator 15, the X-ray profile PL, and the X-ray detector 11 have an opening width in the slice direction of the precollimator 15 so that the main shadow covers all element rows. The positional relationship of the explanatory diagram (a) in FIG. 8 is taken. When the “main shadow + half shadow mode” is determined, the positional relationship shown in the explanatory diagram (b) of FIG.
[0055]
Further, step 44 ₁ Step 44 also determines that “partially designated detection element array” is used. ₃ Step 44 ₂ The same judgment is applied. As a result, when the “main shadow mode” is set, as shown in the explanatory diagram (c), the opening width in the slice direction of the pre-collimator 15 is set so that the main shadow covers only a part of the designated detection element rows. Will be controlled. In the “main shadow + penumbra” mode, the positional relationship in the explanatory diagram (d) in which the penumbra enters a further part of the designated part of the element array can be recognized.
[0056]
As described above, when the possible mode of the positional relationship of the pre-collimator 15 is determined in any one of the above explanatory diagrams (a) to (d), the main controller 30 determines the width Wpre of the opening of the pre-collimator 15 in the slice direction. Is calculated. This calculation is obtained on the basis of, for example, the position data of the X-ray tube 10, the precollimator 15, the subject's isocenter, the X-ray detector, and the like according to the above-described positional relationship. This calculation formula is shown below.
[0057]
Now, as shown in FIG. 9, the size of the focal point F of the X-ray tube 10 is x, the length of the main shadow projected on the X-ray detector 11 is y, and the length in the slice direction is projected onto the X-ray detector 11. Ru
The length in the slice direction of “main shadow + half shadow” is z, the distance in the exposure direction between the focal point F and the pre-collimator 15 is c, and the exposure direction between the pre-collimator 15 and the X-ray detector 11 Is the main shadow mode aperture width Wpre (x, y) and main shadow + half-shadow mode aperture width Wpre (x, z) of the pre-collimator 15, respectively.
[Expression 1]

[Expression 2]

It can be calculated by the following formula. That is, when adopting the above-described positions (a) and (c) in FIG. 8, the aperture width Wpre (x, y) reflecting the focal spot size x and the main shadow size y based on the above formula (1). Is required. When the position modes shown in FIGS. 4B and 4D are adopted, the aperture width Wpre (x, z) reflecting the focal spot size x and the “principal shadow + penumbra” size z based on the above formula (2). ) Is required. As can be seen from these equations, when the main shadow size y or the “main shadow + penumbra” size z does not change but only the focal spot size x changes, the aperture width reflecting the change is also required. become.
[0058]
The opening widths Wpre (x, y) and Wpre (x, z) may be obtained by calculation based on the above formula (1) or (2) every time the control of FIGS. However, the opening width data obtained by the calculation may be stored in advance as a table, and in that case, the opening width Wpre can be obtained simply by referring to the table. Further, such a table may be created and stored based on actually measured data.
[0059]
Next, the process proceeds to step 45 in FIG. 7 to determine the already obtained scanning method, and in the case of multi-scan, the top board feed pitch is calculated in step 46. As shown in FIGS. 17A and 17B, this feed pitch is the distance by which the top plate is moved, and is the total slice at the center of the imaging region of the detection element array designated for use of the X-ray detector 11. A distance that matches the width. On the other hand, in the case of helical scan, the top plate feed speed is calculated in step 47. This feeding speed is determined as the moving distance of the top plate per rotation, and the moving distance is made to coincide with the total slice width at the center of the imaging region of the designated detection element array of the X-ray detector 11. In the case of helical scan, the feed rate may be specified by another method. For example, in order to increase the sampling density in the slice direction, instead of selecting an integer value without a decimal point corresponding to the designated detection element array, a half value having a decimal point (fraction) can be selected as the feed rate. .
[0060]
Multi-scan is to repeatedly perform “scan / top plate movement / scan / top plate movement ...”. When the top plate movement amount is equal to the total slice width per scan corresponding to the designated detection element array at the center of the imaging area (that is, the half width of the X-ray profile incident on all the designated detection element arrays) The obtained images are all equally spaced, and the individual images are obtained from areas adjacent to each other, and there is no gap between the images. This is true for both single-slice CT and multi-slice CT, which is advantageous when a three-dimensional model is created from the obtained image.
[0061]
Helical scanning is a scanning method in which data is acquired in a spiral form by simultaneously performing scanning and top plate movement. When reconstructing an image, a general method is to interpolate collected data using a distance from the cross section as a coefficient for the cross section to be reconstructed. In the helical scan, when the top plate moving speed is made to coincide with the total slice width corresponding to the designated detection element array at the center of the imaging region, the data collection regions are adjacent to each other every rotation, and there is no omission. Subject data can be collected.
[0062]
When various data are obtained as described above, the main control device 30 performs the data collection device 12 and the image reconstruction device 35, the gantry control device 33, the bed control device 32, and the high voltage control device 31 in steps 48 to 51. The necessary information is output to each. The information output to the high voltage control device 31 in step 51 includes information on whether to use the large focus filament FTL or the small focus filament FTS. By giving this information, each control device operates based on a predetermined procedure stored in advance, so that the commanded scan is executed.
[0063]
On the other hand, FIG. 10 shows a control example of the main controller 30 when a single slice detector is used as the X-ray detector 11. In this control example, information unique to a single slice (slice width) is taken in, and when the above-described two-dimensional detector is used, a post-collimator 16 that is not subject to control is newly added depending on the mode. This is very different from the two-dimensional detector.
[0064]
Specifically, at step 60 in the figure, the main control device 30 determines the scan conditions (scan mode (single scan, multi-scan or helical scan), scan site and position, X-ray tube voltage and current, etc.) Information (however, information of “slice width”, “collection mode”, and “focus size” described later is not included) is input. Next, in step 61, information on the slice width of a single slice is input, and in step 62, information on the acquisition mode (“main shadow mode” or “main shadow + penumbra mode” as described above) is input.
[0065]
Next, the process proceeds to step 63, and information on the focal size of the X-ray tube 11 is input as described above.
[0066]
Further, the routine proceeds to step 64 where the opening width Wpre of the pre-collimator 15 in the slice direction is calculated. Also in this case, the possible position modes of the pre-collimator 15 are determined as shown in FIG.
[0067]
That is, it is determined whether the acquisition mode (step 62) already input is the “main shadow mode” or the “main shadow + half shadow mode” (step 64 in FIG. 11). ₁ ). As a result, if it is determined that the “main shadow mode” is selected, step 64 ₂ Then, it is determined whether or not the specified slice width already obtained (step 61) is equal to the width corresponding to the detector width in the rotation axis direction. When this determination is NO, it is a case where “designated slice width <width corresponding to detector width”, and the position mode is represented as shown in FIG. Only in this case, the post-collimator 16 is involved as will be described later. On the other hand, when YES, that is, “designated slice width = width corresponding to the detector width”, the pre-collimator 15 takes the position mode shown in FIG. Step 64 ₁ When “main shadow + half shadow mode” is determined in (in this case, the designated slice width cannot be a width corresponding to the detector width), the position mode shown in the explanatory diagram (c) is taken. Note that the post-collimator 16 is not involved in the case of the positions shown in FIGS. The slice width here is defined as “a value obtained by projecting the half-value width of the X-ray profile onto the center of the rotation axis”.
[0068]
The opening width Wpre of the pre-collimator 15 is determined using the position data of the X-ray tube 10, the pre-collimator 15, the subject's isocenter, the X-ray detector 11, etc. Based on the formula (1) or (2), it is obtained by calculation or table reference.
[0069]
Further, in step 65 of FIG. 10, the opening width Wpost of the post collimator 16 in the slice direction is calculated. This calculation is performed only in the position mode shown in FIG. 11A (that is, when the designated slice width <the width corresponding to the detector width), and the aperture is set so that the post-collimator 16 cuts the penumbra. The width Wpost is calculated.
[0070]
Next, main controller 30 proceeds to step 66 to determine the scanning method. If it is determined to be a single scan, the process skips to step 69, but if it is determined to be a multi-scan and if it is determined to be a helical scan, the feed pitch of the top plate is determined in step 67 or step 68. Alternatively, the top plate feed speed is calculated in consideration of the slice width.
[0071]
Thereafter, the processing of steps 69 to 72 is sequentially performed in the same manner as the processing of steps 48 to 51 in FIG.
[0072]
Furthermore, an example of opening width control in the slice direction of the collimator 15 by the gantry controller 33 will be described with reference to FIG.
[0073]
That is, the gantry controller 33 inputs the opening width Wpre supplied from the main controller as an initial value (step 80 in the figure), and sends a control signal corresponding to the data to the gantry driving device 18, thereby precollimator. The drive device 17 is operated to adjust the actual opening width and / or position of the pre-collimator 15 in the slice direction to the command initial value (step 81 in the figure).
[0074]
Thereafter, a detection signal from the focal position detector 20 is inputted (step 82 in the figure), and the movement amount of the focal point F accompanying the heat generation of the X-ray tube 10 is stored in a storage table representing, for example, the graph shown in FIG. An estimation operation is performed by reference (step 83 in the figure).
[0075]
Next, the routine proceeds to step 84 where the opening width Wpre of the pre-collimator 15 taking into account the estimated amount of movement of the X-ray focal point F or the position in the slice direction is recalculated. That is, aperture data for correcting the shift of the X-ray profile PL in the slice direction due to the movement of the focal point F is obtained. The new data for correction is sent again to the gantry driving device 12, and the opening width and position of the pre-collimator 15 are corrected with the updated values (step 81 in the figure). Thereafter, the same processing is repeated.
[0076]
In the focus follow-up control with respect to the focus movement according to the processing of FIG. 12 described above, it is only necessary to cause the pre-collimator 15 to follow, and the post-collimator 16 is close to the X-ray detector 11. There is no need to let them. In the case where a single slice detector is employed for the X-ray detector 11 and the position mode of the pre-collimator 15 where slice width <detector width is satisfied (that is, the position mode represented by (a) in FIG. 11). The post collimator 16 is instructed by the processing (not shown) of the gantry control device 33 for the opening width Wpost calculated in the processing of step 65 in FIG. However, in this case as well, the opening width Wpost of the post-collimator 16 is not subject to follow-up control as the X-ray focal point moves, and is always held at a constant value, and the penumbra is cut. When the pre-collimator 15 takes other positions, that is, FIGS. 8A to 8D, 11B, and 11C, the post-collimator 16 does not participate in X-ray collimation.
[0077]
Typical examples of the operation of the pre-collimator 15 according to the above configuration and processing are shown in FIGS. 13 shows an example of controlling the opening width in the slice direction of the pre-collimator 15 when only the focus size is changed, and FIG. 14 shows the control in the slice direction of the pre-collimator 15 when the focus size and the detector array used are changed. FIG. 15 shows an example of controlling the aperture width in the slice direction of the pre-collimator 15 associated with focal movement, and FIG. 16 shows an example of controlling the aperture width and position of the pre-collimator 15 in accordance with the focal movement. Respectively.
[0078]
Now, a two-dimensional detector is used as the X-ray detector 11 (detection element arrays in the slice direction are a to h), and a part of the detection element arrays d and e in the slice direction is used to perform the main shadow mode. Suppose that multi-scan is performed.
[0079]
When the small focus F by the small focus filament FTS is commanded as the focus size, the opening width Wpre of the pre-collimator 15 is set as shown in FIG. That is, when information on scan conditions, number of slices per rotation = 2, acquisition mode = main shadow mode, and focus size = small focus is input to the main controller 30 (steps 40 to 43 in FIG. 7), the pre-collimator The position mode of 15 and the opening width Wpre in the slice direction are automatically determined (step 44 in the figure). The position mode corresponds to that shown in FIG. 8C, and the opening width Wpre = Wpre1 is obtained by, for example, calculation based on the formula (1). Further, since multi-scan is commanded as the scanning method, the feed pitch is automatically calculated so as to be equal to the total slice width at the rotation center corresponding to some of the designated element arrays d and e (same as above). Steps 45, 46). Then, the input data and the calculation data are respectively output to the required data collection device 13, the image reconstruction device 35, the gantry control device 33, the bed control device 32, and the high voltage control device 31. The high voltage controller 31 is also supplied with a filament selection signal for selecting a small focus. Therefore, the high voltage control device 31 supplies the filament power from the high voltage generator 34 to the small focus filament FTS.
[0080]
From this state, for example, it is assumed that the operator only wants to change the focus size F = large focus in response to the situation where the imaging region changes from the head to the abdomen (scanning conditions other than tube current, per rotation) The number of slices and the collection mode are unchanged.) Therefore, when an increase in tube current as one of the scanning conditions is commanded, information on the focus size F = large focus is automatically read as a preset value corresponding to the increase in tube current (step 43 in FIG. 7). In response to this, the opening width Wpre = Wpre2 of the precollimator 15 corresponding to the position mode of the precollimator 15 is automatically calculated (step 44 in FIG. 7). That is, the position mode is not different from that in FIG. 13A, but the aperture width Wpre = Wpre2 obtained based on the above equation (1) is increased by the size of the focus F in the slice direction, and Wpre2 An opening width satisfying> Wpre1 is set. Then, through the process of FIG. 12 (assuming that the focal position itself does not change), as shown in FIG. 13B, the opening width Wpre of the pre-collimator 15 is expanded from Wpre1 to Wpre2, and the detection element to be used Only the main shadow RM is incident on the columns d and e.
[0081]
Therefore, even when the focus size is switched to the large focus, even though the penumbra RS has entered the detection element arrays d and e to be used and the main shadow mode is designated, the main shadow + half The "shadow" mode is never entered, and only the main shadow RM enters as specified in the acquisition mode. In other words, when switching to the large focus while keeping the aperture width Wpre1 of the small focus in FIG. 13A, a part of the detection element arrays d and e is half the size of the focus in the slice direction. Shadow RS enters. However, since the aperture width of the pre-collimator is adjusted in accordance with the switching of the focus size as in this embodiment, such a situation can be prevented from occurring. For this reason, the occurrence of a problem that the image quality of the reconstructed image is deteriorated due to the penumbra entering or the like is surely avoided.
[0082]
Contrary to the case where the focus size is switched from the small focus to the large focus as described above, the aperture width Wpre is changed from the state shown in FIG. 13B to the state shown in FIG. Is adjusted. That is, the range in the slice direction in which the main shadow RM is incident is limited to the range of the detection element arrays d and e, and the main shadow does not enter the detection element arrays that are not used. Thus, by not extending the incidence range of the main shadow more than necessary, unnecessary X-rays leaking outside the X-ray detector 11 can be reduced as much as possible, and the influence of the exposure on the subject can be further suppressed.
[0083]
Moreover, in addition to the focus size switching described above, examples of aperture width control when changing the detection element array to be used are shown in FIGS.
[0084]
Now, a two-dimensional detector is used as the X-ray detector 11 (detection element arrays in the slice direction are a to h), and a part of the detection element arrays d and e in the slice direction is used to perform the main shadow mode. Suppose that multi-scan is performed. When the small focus F by the small focus filament FTS is commanded as the focus size, the opening width Wpre of the pre-collimator 15 is set as shown in FIG. That is, in this case, the same processing as in the case of FIG.
[0085]
From this state, for example, the operator changes the focus size F = large focus and the number of used detection element rows (that is, the number of slices per rotation) in response to a situation where the imaging region changes from the head to the abdomen. It is assumed that an increase to ~ f is commanded (scanning conditions other than the tube current and the position of the detection element array to be used and the collection mode are unchanged). In response to this, the opening width Wpre = Wpre2 of the precollimator 15 corresponding to the position mode of the precollimator 15 is automatically calculated (step 44 in FIG. 7). That is, the position mode is the same as that in FIG. 14A, but the aperture width Wpre = Wpre2 obtained based on the above formula (1) is the amount of increase in the size of the focus F in the slice direction and the use detection. The opening width is set such that Wpre2> Wpre1. As a result, as shown in FIG. 14B, the opening width Wpre of the pre-collimator 15 is widened from Wpre1 to Wpre2 through the processing of FIG. Only RM is incident.
[0086]
Therefore, even when the focus element size is set to a large focus and the detection element array to be used is switched, the penumbra Rs enters the detection element array to be used and the substantial shadow mode is designated. The “main shadow + half shadow” mode is not set, and the image quality of the reconstructed image can be prevented from being deteriorated. Naturally, the aperture width can be automatically controlled from the state shown in FIG. 14B to the state shown in FIG. 14A, and the influence of the exposure on the subject can be further suppressed.
[0087]
On the other hand, even when the size of the focal point F is switched, the focal point position deviates in the channel direction due to its arrangement structure, but in principle, it does not deviate in the slice direction. However, there may be a slight shift in the slice direction due to the switching of the focus size. Even in this case, in the aperture width control shown in FIGS. 13 and 14, since the shift in the slice direction is detected by the focal position detector 20, the shift is automatically corrected through the processing of FIG. 12.
[0088]
In the opening width control of FIGS. 13 and 14, the opening width in the slice direction of the pre-collimator 15 and the position in the slice direction may be adjusted integrally.
[0089]
The above-described aperture width control in FIGS. 13 and 14 is performed according to the scan condition and / or focus size information instructed by the operator when the subject is changed. The aperture width control in FIG. 16 is automatically controlled to follow even during scanning.
[0090]
Now, a two-dimensional detector is used as the X-ray detector 11 (element rows in the slice direction are a to h), and a part of the detector element rows c to f in the slice direction are designated to perform the main shadow mode. Multi-scan shall be performed. When the scan condition including the information, the number of slices, the acquisition mode, and the focus size are input to the main controller 30 (steps 40 to 43 in FIG. 7), the position mode of the precollimator 15 and the aperture width in the slice direction are automatically set. (Step 44 in the figure). Further, since multi-scan is instructed as the scanning method, the feed pitch is automatically calculated so as to be equal to the total slice width at the rotation center corresponding to a part of the designated element rows (step 45 in the figure). 46). The input data and the calculated data are output to the required data collection device 13, the image reconstruction device 35, the gantry control device 33, the bed control device 50, and the high voltage control device 51, respectively.
[0091]
In particular, the data collection device 13 switches the column for each channel and selects the necessary data according to the column selection signal indicating which column (in this case, the columns c to f) to be used, which is instructed by the main controller 30. Then, it is sent to the image reconstruction device 35. In addition, since multi-scan is instructed, the slice width corresponding to cf rows becomes the top plate feed pitch. If the helical scan is instructed, the slice width at the rotation center of the imaging region corresponding to the columns c to f is the top plate movement distance during one rotation. As a result, the trajectories drawn by the detector are all equally spaced, and processing such as data correction in reconstruction is simplified.
[0092]
As a result, under the management of the main control device 30, each device operates in synchronization to collect data and reconstruct the image. At this time, the pre-collimator 15 takes the position mode shown in FIG. 15 (corresponding to FIG. 8C). That is, the opening width Wpre in the slice direction of the pre-collimator 15 is controlled so that only the main shadow RM is incident on some of the designated element rows c to f of the detection element rows a to h of the two-dimensional detector 11. .
[0093]
In addition, the tube focal point F (for example, a small focal point, represented here as a point) of the X-ray tube 10 may move in the slice direction due to heat generated during exposure of the anode, as shown in FIG. . Even in this case, the aperture width of the pre-collimator 15 is finely adjusted in real time in accordance with the processing of FIG. 12 accompanying the detection of the focal position movement amount, and only the main shadow RM is included in some of the designated element arrays cf for detection. Is incident.
[0094]
By performing feedback control of the aperture width of the pre-collimator 15 in this way, the two-dimensional detector 11 is designated in advance even when imaging is performed such that the X-ray profile changes between calibration data collection and actual imaging. Since the X-ray intensity incident on the detection element arrays c to f (corresponding to the slice width in the slice direction) is always constant, calibration at the time of reconstruction is satisfactorily performed. The CT value can be prevented from shifting. In addition, the demand for changes in the X-ray profile is greatly eased. Furthermore, since the reconstructed image uses only the main shadow, the image quality of any slice plane is improved. Further, since only the opening width of the pre-collimator 15 needs to be controlled, there is an advantage that the number of motors to be driven is only one for controlling the opening width and the control is simple.
[0095]
When the above-described control method of FIG. 15 is used to scan in the full shadow mode using the entire surface of the two-dimensional detector, that is, in the example of FIG. 15, all the detection element arrays a to h (that is, FIG. 8A). In the same manner, the present invention can also be suitably applied. Further, when a single slice detector is used as the X-ray detector 11, it can be suitably implemented also in the case of the main shadow mode (that is, the states of FIGS. 11A and 11B).
[0096]
On the other hand, in the case of the scan shown in FIG. 16, the same conditions as those in FIG. 15 (two-dimensional detector, use of only a part of designated detection element arrays cf in the slice direction, main shadow mode, same focus size) are set. Although employed, the feedback control amount accompanying the focal point movement is now the “position in the slice direction” of each blade of the pre-collimator 15 (that is, the opening width and position in the slice direction of the pre-collimator). That is, the position in the slice direction of the entire precollimator 15 is changed in real time. This control is performed in real time by a series of processes in steps 82 to 84 and 81 in FIG.
[0097]
For this reason, for example, when the focal point F (for example, a small focal point, represented by a dot in the figure) of the X-ray tube 10 moves to the right side as indicated by an arrow in FIG. The blade is on the right (arrow A ₁ ) And the other blade is also on the right (arrow A ₂ ) To the same distance. That is, unlike in the case of FIG. 15 described above, both blades responsible for collimation in the slice direction move symmetrically in the slice direction and change only the aperture width Wpre, so that the position of the aperture width Wpre itself and the entire collimator in the slice direction are changed. Changes according to the amount of focus movement.
[0098]
Therefore, the position of the X-ray profile PL in the slice direction with respect to the X-ray detector 11 does not change, and even if the focus shift actually occurs, it is the same as the apparent focus shift does not occur. As a result, the same operational effects as in the case of FIG. 15 can be obtained, and the position control of the profile can be performed more stably and accurately than the method of FIG. 15, and the exposure dose can be minimized. There is an advantage that you can. More importantly, when the precollimator 15 shown in FIG. 16 is controlled, the position of the main shadow in the slice direction is fixed. That is, the shape of the X-ray profile of the detection element array that receives the main shadow is invariant between the calibration data collection and the image data collection. Therefore, there is also an advantage that an image using data detected by the detection element array that receives such a main shadow can always be maintained in high quality.
[0099]
In the case where the above-described control method of FIG. 16 is used to scan in the full shadow mode using the entire surface of the two-dimensional detector, that is, in the example of FIG. 16, all the detection element arrays a to h (that is, FIG. 8A). In the same manner, the present invention can also be suitably applied. Further, when a single slice detector is used as the X-ray detector 11, it can be suitably implemented also in the case of the main shadow mode (that is, the states of FIGS. 11A and 11B).
[0100]
On the other hand, the “main shadow + half shadow mode” is selected by the inspector as necessary (see FIG. 7, step 42, FIG. 10, step 62). In this way, not only the “main shadow mode” but also the “main shadow + penumbra mode” can be arbitrarily selected, so the exposure can be suppressed by making the penumbra part incident on the detector. In addition, there is an advantage that multi-scan and helical scan can be performed at high speed. This is shown in FIGS. 17 (a) and 17 (b). FIG. 6A illustrates the “main shadow mode” scan, and FIG. 5B illustrates the “main shadow + half shadow mode” scan. The X-ray detector in FIG. 11 has a large number of usable element rows. This enables high-speed scanning in the “main shadow + half shadow mode”.
[0101]
By the way, in FIGS. 17A and 17B, an arrow indicating the amount of feed pitch or feed speed is schematically drawn. Since the feed pitch and feed speed are actually calculated with the X-ray focal point as a point, the arrows representing these amounts are actually slightly shorter than those shown in the figure and correspond to the total slice width The amount to be.
[0102]
A modification according to the present invention will be described with reference to FIG. In the above-described embodiment, the position in the slice direction and / or the aperture width of the pre-collimator 15 is finely adjusted in real time according to the movement of the tube focal point of the X-ray tube. It is a simplified one. Specifically, the opening width and / or position of the pre-collimator 15 in the slice direction is initially set only once, and thereafter the value is held even if the focal position is moved.
[0103]
Now, as in the case of FIGS. 15 and 16 described above, it is assumed that scanning is performed in the main shadow mode using only a part of designated detection element arrays c to e of the two-dimensional detector. Even if the X-ray tube 10 is moved from the lowest temperature state to the highest temperature state and the focal point shifts, the aperture is set so that only the main shadow is always incident on at least some of the target detection element arrays c to e. The width Wpre (or position) is initially set only once. In other words, the detection element array to be used is determined in advance with the focus movement in mind, and the aperture width (or the position in the slice direction) is set wider. Once the setting is made before scanning, the subsequent opening control is not performed.
[0104]
The aperture width Wpre can be set quantitatively using the following equation when the focal distance is expected. 9, the size of the focal point F of the X-ray tube 10 is x, the length of the main shadow projected on the X-ray detector 11 is y, and the length in the slice direction is projected on the X-ray detector 11. The length of the “main shadow + penumbra” in the slice direction is z, the distance in the exposure direction between the focal point F and the precollimator 15 is c, and the exposure between the precollimator 15 and the X-ray detector 11 is performed. Assuming that the distance in the direction is d, and the maximum amount of focal movement expected in the slice direction is Δm, as shown in FIG. 19, the aperture width Wpre (x, y) of the main shadow mode of the pre-collimator 15 and “book” The aperture width Wpre (x, z) in the “shadow + half-shadow” mode is
[Equation 3]

[Expression 4]

It can be calculated by the following formula. The set value of the opening width may be calculated in advance based on the formula (3) or (4) and held as a table.
[0105]
As a result, the temperature of the X-ray tube rises in accordance with the driving state of the X-ray CT scanner, and the tube focus is, for example, from the state shown by the solid line in FIG. 18 to the state shown by the dotted line (the state where the X-ray tube is warmed to the maximum). ), Only the main shadow is always incident on the designated detection element arrays c to e of the X-ray detector 11. Therefore, according to this modification, the opening control is performed only once, and the control is simplified. In this case, there is also an advantage that the focus position detector 20 becomes unnecessary.
[0106]
Further, the above-described method for setting the aperture width in consideration of the movement of the focal point can be implemented by incorporating the following various factors or independently.
[0107]
First, the present invention relates to a countermeasure against the movement of the focus position in the focus switching. When the focal point of the X-ray tube 10 is switched from a small focal point to a large focal point, for example, the focal position may be slightly shifted. In the X-ray tube, because the large focus filament and the small focus filament are arranged side by side in the channel direction due to the structure, even if the focus is switched, the focus position is usually shifted only in the channel direction. The principle is not to deviate. However, there may be a slight shift in the slice direction due to the focus switching.
[0108]
Therefore, as shown in FIG. 19, the focus shift amount accompanying the focus switching is added to the predicted maximum focus shift amount Δm in the slice direction. Alternatively, the maximum focus movement amount Δm is set equal to the focus movement amount accompanying the focus switching. Thereby, as schematically shown in FIG. 18 described above, even if there is a focus shift due to the temperature rise and focus switching of the X-ray tube 10 or a focus shift due to focus switching, a simple aperture width can be obtained. While being controlled, the X-ray profile incident on the detection element array to be used can always be maintained as desired.
[0109]
Secondly, it relates to the correspondence of the focus shift in the flying focus technique. In an X-ray CT scanner, for the purpose of increasing the sampling point of data, the electron beam radiated from the cathode to the gate in the X-ray tube is swung by electromagnetic action, and the focal position is intentionally changed. Some have the ability to change. This movement of the focal position causes the movement of the main shadow in the slice direction.
[0110]
Therefore, in this case as well, as shown in FIG. 19, the focus shift amount accompanying the flying focus is added to the maximum predicted focus shift amount Δm in the slice direction. Alternatively, the maximum focus shift amount Δm is set equal to the focus shift amount associated with the flying focus. Accordingly, as schematically shown in FIG. 18 described above, even if there is a focus shift due to the temperature rise and focus switching of the X-ray tube 10 or a focus shift due to the flying focus, a simple aperture width can be obtained. While being controlled, the X-ray profile incident on the detection element array to be used can always be maintained as desired.
[0111]
When the above-described control method of FIG. 18 is used to scan in the full shadow mode using the entire surface of the two-dimensional detector, that is, in the example of FIG. 18, all the detection element arrays a to h (that is, FIG. 8A). In the same manner, the present invention can also be suitably applied. Further, when a single slice detector is used as the X-ray detector 11, it can be suitably implemented also in the case of the main shadow mode (that is, the states of FIGS. 11A and 11B).
[0112]
In addition, the sensor means relating to the movement of the tube focal point of the X-ray tube in the present invention is not limited to the one having the above-described configuration. The temperature change of the tube 10 may be detected, and the movement of the tube focus may be estimated based on the temperature change. Further, for example, as described in Japanese Utility Model Publication No. 2-91200, it may be a temperature detector that detects the temperature of the cooling oil of the X-ray tube, or the X-ray tube voltage, the X-ray tube current, and the X-ray irradiation time. A structure may be adopted in which information relating to driving of the X-ray tube such as X-ray irradiation stop time is taken in as information relating to movement of the tube focus.
[0113]
In the above-described embodiment and its modifications, the focus size of the X-ray tube is switched in two stages of “large” or “small”, but the present invention is not necessarily limited to this. For example, a “medium” focus filament can be mounted so that the focus size can be switched in three stages, or the focus size can be switched in more steps. Furthermore, for example, the present invention is applied to an X-ray tube capable of setting a focal point of an arbitrary size by controlling the shape and position of an electron beam by electromagnetic action or mechanically adjusting the position of a cathode. The aperture width of the pre-collimator may be controlled in the same manner as described above according to the focus size set to an arbitrary value.
[0114]
Furthermore, in the present invention, one or more detection element arrays of a two-dimensional detector that receives only the main shadow of the X-ray beam are designated each time during imaging by actual X-ray scanning. It is not limited to the scanner configuration. Even when the one or more detection element arrays are fixedly determined in advance according to design conditions and other conditions, such a two-dimensional detector can be suitably applied to the X-ray CT scanner of the present invention. In other words, in such a case, if the column selection signal to the data collection device 13 is set so that only the data detected by the predetermined detection element row is adopted and the same processing as described above is performed. Good.
[0115]
Furthermore, in the above-described embodiment and its modification, the configuration for performing the control corresponding to the aperture width control of both the pre-collimators accompanying the change (switching) of the focus size and the movement of the focus position has been shown. Of course, it can be carried out solely by controlling the opening width of the pre-collimator associated with the change (switching) of the size.
[0116]
The present invention is not limited to the above-described embodiments and modifications, and can be appropriately combined, changed, and modified within the scope of the basic principle of the present invention.
[0117]
【The invention's effect】
As described above, according to the X-ray CT scanner of the present invention, even when the focus size of the X-ray tube as the X-ray source is changed, the opening width of the pre-collimator is, for example, 2 Since the main detector is controlled so that only the main shadow is always incident on the detection element array that the dimension detector wants to use, even if the focal spot size is changed, only the main shadow is received and deterioration of the image quality of the reconstructed image can be prevented. The effects of X-ray exposure can be minimized.
[0118]
In addition to the above-described effects, the following various effects can be obtained simultaneously. That is, X-rays are applied to the entire width in the slice direction of the detection element array of the X-ray detector (in the case of a two-dimensional detector, a designated detection element array or a predetermined detection element array among a plurality of detection element arrays). Since only the main shadow of the profile is incident, the image quality does not change depending on the slice position, a high signal value can be detected, and a high-quality reconstruction image can be provided. Further, the aperture width in the slice direction of the pre-collimator is set wide by an amount corresponding to the predicted maximum movement amount in the slice direction of the X-ray beam accompanying the movement of the X-ray focal point of the X-ray tube. A good signal and image quality can be obtained simply by setting the aperture to. Furthermore, even when the tube focus of the X-ray tube moves due to temperature rise or the like, and the X-ray profile changes between calibration data acquisition and imaging, for example, the aperture width and By fine-tuning the position and the like in real time according to the amount of focal movement, the main shadow can be incident over the entire width in the slice direction of the designated or predetermined detector element array of the X-ray detector. Therefore, artifacts on the image and CT value shift can be eliminated, and the image quality can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of an X-ray CT scanner according to an embodiment of the present invention.
FIG. 2 is a schematic structural diagram of an X-ray tube whose focus size can be switched.
3 is a side view taken along line III-III in FIG.
FIG. 4 is a diagram for explaining the positional relationship between an X-ray detector and the incidence of an X-ray beam.
FIG. 5 is a graph showing a relationship between an output of an X-ray detector and an X-ray focal position movement amount;
FIG. 6 is a block diagram of a data collection device.
FIG. 7 is a flowchart showing a control example in the case of a two-dimensional detector executed by the main controller.
FIG. 8 is a flowchart for determining a position mode of a pre-collimator in the case of a two-dimensional detector.
FIG. 9 is an explanatory diagram of parameters related to aperture width control of the pre-collimator.
FIG. 10 is a flowchart showing a control example in the case of a single slice detector executed by the main control device.
FIG. 11 is a flowchart for determining a position mode of a pre-collimator in the case of a single slice detector.
FIG. 12 is a flowchart showing an example of opening control executed by the gantry control device.
FIG. 13 is an explanatory view showing aperture width control of the pre-collimator accompanying switching of the focal spot size.
FIG. 14 is an explanatory view showing aperture width control of the pre-collimator in accordance with switching of the focus size and change of the detection element array to be used.
FIG. 15 is an explanatory diagram showing an example of focus movement tracking control when a two-dimensional detector is used.
FIG. 16 is an explanatory diagram showing another example of focus movement follow-up control when a two-dimensional detector is used.
FIGS. 17A and 17B are diagrams for comparing and explaining the feed pitch or feed speed in the main shadow mode and the main shadow + half shadow mode.
FIG. 18 is a diagram illustrating aperture setting of a precollimator according to a modification.
FIG. 19 is a diagram for explaining a movement amount of a focal point.
FIG. 20 is a diagram for explaining the role of a pre-collimator.
FIG. 21 is a view for explaining the positional relationship between an X-ray profile and an X-ray detector in a conventional single slice CT.
FIG. 22 is a view for explaining the positional relationship between an X-ray profile and an X-ray detector in CT according to a conventional two-dimensional detector.
FIG. 23 is a diagram for explaining movement of a tube focal point of an X-ray tube.
FIG. 24 is a diagram for explaining the influence of profile change on a single slice detector;
FIG. 25 is a diagram for explaining the influence of a profile change on a two-dimensional detector.
[Explanation of symbols]
1 Gantry
2 sleeper
2a Top plate
2b Sleeper drive
3 Control cabinet
10 X-ray tube (X-ray source)
11 X-ray detector (two-dimensional detector or single slice detector)
12 Base drive unit
13 Data collection device
15 Precollimator
17 Pre-collimator driving device
20 Focus position detector
30 Main controller
31 High voltage controller
32 bed control device
33 Base control device
34 High voltage generator
35 Image reconstruction device

Claims (14)

An X-ray source having a focal point for exposing the X-ray beam; a precollimator that is interposed between the subject and the X-ray source and narrows the width of the X-ray beam in the slice direction of the subject; An X-ray CT scanner comprising: an X-ray detector that receives the X-ray beam that has passed through the subject;
The X-ray detector is formed by a two-dimensional detector in which a plurality of detection element arrays each including a plurality of detection channels are arranged in the slice direction,
According to the size of the focal point of the X-ray source, a specified detection element array of the plurality of detection element arrays is a book in the main shadow and penumbra of the X-ray beam profile formed by the pre-collimator. A control means for controlling the pre-collimator so as to receive a shadow, and a reconstruction means for reconstructing an X-ray CT image based on data detected by the designated detection element array X-ray CT scanner. An X-ray source having a focal point for exposing the X-ray beam; a precollimator that is interposed between the subject and the X-ray source and narrows the width of the X-ray beam in the slice direction of the subject; An X-ray CT scanner comprising: an X-ray detector that receives the X-ray beam that has passed through the subject;
The X-ray detector is formed by a two-dimensional detector in which a plurality of detection element arrays each including a plurality of detection channels are arranged in the slice direction,
Depending on the size of the focal point of the X-ray source, at least one of the plurality of detector element rows that receives a main shadow and a main shadow of the X-ray beam profile formed by the pre-collimator. An X-ray CT scanner comprising reconstructing means for reconstructing an X-ray CT image based on data detected by a detection element array. An X-ray source having a focal point for exposing the X-ray beam; a precollimator that is interposed between the subject and the X-ray source and narrows the width of the X-ray beam in the slice direction of the subject; An X-ray CT scanner comprising: an X-ray detector that receives the X-ray beam that has passed through the subject;
The X-ray detector is formed by a two-dimensional detector in which a plurality of detection element arrays each including a plurality of detection channels are arranged in the slice direction,
A first acquisition mode for performing image reconstruction based on only the main shadow and the main shadow of the X-ray beam profile formed by the pre-collimator, and both the main shadow and the penumbra Selecting means for selecting one of the second acquisition modes in which image reconstruction is performed based on the data according to the above, and the acquisition mode selected by the selection means and the size of the focal point of the X-ray source An X-ray CT scanner comprising: control means for controlling the aperture state of the pre-collimator; and scanning means for collecting data based on the collection mode selected by the selection means. The X-ray CT scanner according to claim 1, wherein the X-ray source is an X-ray tube capable of changing a size of the focal point. The top plate, which is movable in the slice direction and on which the subject is placed, substantially matches the total slice width at the center of the imaging region by the designated detection element array for each scan with the X-ray beam during multi-scan. 5. The apparatus according to claim 1, further comprising: a determination unit that determines a movement distance of the top plate; and a top plate control unit that controls the movement of the top plate based on the movement distance determined by the determination unit. An X-ray CT scanner according to claim 1. A top plate that is movable in the slice direction and on which the subject is placed, and an imaging region by the designated detection element array for each rotation of the X-ray source and the X-ray detector around the subject during a helical scan Determining means for determining the moving distance of the top plate according to the total width in the slice direction at the center of the top, and top plate control for controlling the movement of the top plate based on the moving distance determined by the determining means And an X-ray CT scanner according to any one of claims 1 to 4. And a setting unit configured to widen the opening width of the pre-collimator in the slice direction by an amount corresponding to a predicted maximum movement amount of the X-ray beam in the slice direction accompanying the focal movement of the X-ray source. Item 5. An X-ray CT scanner according to any one of Items 1 to 4. 8. The X-ray CT scanner according to claim 7, wherein the setting means is a means for setting a wide amount corresponding to a maximum movement amount including a movement amount of a focal position in accordance with a change in a focal point size of the X-ray source. Detection means for detecting an amount corresponding to the focal point movement of the X-ray source, and the control means, based on the detection amount of the detection means, the opening width of the pre-collimator in the slice direction, the slice of the pre-collimator Means for controlling at least one of a directional position and a position of the focal point of the X-ray source in the slice direction so that the designated detector array receives the main shadow of the X-ray beam. Item 2. An X-ray CT scanner according to Item 1. Detection means for detecting an amount corresponding to the focal point movement of the X-ray source; an opening width of the pre-collimator in the slice direction based on a detection amount of the detection means; a position of the pre-collimator in the slice direction; and 3. Control means for controlling at least one of the positions in the slice direction of the focal point of the X-ray source so that the at least one detector element array receives the main shadow of the X-ray beam. The described X-ray CT scanner. Detection means for detecting an amount corresponding to the focal point movement of the X-ray source, and the control means, based on the detection amount of the detection means, the opening width of the pre-collimator in the slice direction, the slice of the pre-collimator Means for controlling at least one of a position in the direction and a position in the slice direction of the focus of the X-ray source so as to prevent movement of a profile of the X-ray beam incident on the X-ray detector; The X-ray CT scanner according to claim 3. An X-ray source having a focal point for exposing the X-ray beam; a precollimator that is interposed between the subject and the X-ray source and narrows the width of the X-ray beam in the slice direction of the subject; An X-ray CT scanner comprising: an X-ray detector that receives the X-ray beam that has passed through the subject;
An X-ray CT scanner comprising: control means for controlling at least one of the opening width in the slice direction and the position in the slice direction of the pre-collimator in accordance with the focal spot size of the X-ray source. . The X-ray CT scanner according to claim 12, wherein the X-ray detector is a two-dimensional detector in which a plurality of detection element arrays each including a plurality of detection channels are arranged in the slice direction. The X-ray CT scanner according to claim 12, wherein the X-ray detector is a single slice detector in which detection element rows each including a plurality of detection channels are arranged in a row in a slice direction.

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