JP3569049B2

JP3569049B2 - High frequency coil for magnetic resonance imaging

Info

Publication number: JP3569049B2
Application number: JP23575995A
Authority: JP
Inventors: 和也岡本
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1995-09-13
Filing date: 1995-09-13
Publication date: 2004-09-22
Anticipated expiration: 2015-09-13
Also published as: JPH0975322A

Description

【０００１】
【発明の属する技術分野】
本発明は、静磁場中に置かれた被検体に対する高周波磁場の印加及び被検体からの磁場共鳴信号の検出のうち少なくとも一方を行う磁気共鳴映像装置用高周波コイルに関する。
【０００２】
【従来の技術】
磁気共鳴映像装置においては、一般に、被検体に静磁場を印加すると共に、高周波磁場の送信と勾配磁場の印加を所定のシーケンスにより行うことによって磁気共鳴信号を生じさせ、この磁気共鳴信号を受信し処理して画像を再構成する。高周波磁場の送信と磁気共鳴信号の受信は、高周波コイルを介して行われる。
【０００３】
近年、動きの速い部位（心臓など）の撮像を可能とする高速イメージング法（撮像時間が数１０ｍｓ）では、観測時間を短縮したことによるＳ／Ｎ低下が大きな問題となっている。また同じく脳の局所血流の微妙な変化を捉える脳機能イメージングにおいても同様の高速イメージング法を用いるため高Ｓ／Ｎ化が不可欠である。
【０００４】
高Ｓ／Ｎに信号を観測するためには、高周波コイルの構成が重要ポイントとなる。高周波コイルで観測する信号Ｓ／Ｎは、Ｂ_１／Ｒ^１／２に比例する。
ここでＢ_１は高周波コイルに１アンペアの電流を流したときに観測領域で発生する磁場の強さであり、高周波コイルを小さくする事により大きくすることができる。Ｒは高周波コイルの高周波抵抗を示すが、コイル由来の高周波損失と被検体由来の高周波損失に分けられる。通常被検体由来の損失は避けようなないため、できるだけコイル由来の高周波損失が少なくなるようにする。相対的に被検体由来の損失が支配的になるようにすればよいため、高周波コイル内の被検体の充填率を上げるようにすればよい。
【０００５】
ところが、通常胸腹部を撮像する全身用コイルは、磁石のカバーの内側に納められるため、被検体に比べ非常に大きく、Ｂ_１が小さくなるだけでなく充填率を下げている。また頭部用コイルについても頭部を載せるヘッドレストが十分余裕を持って納まるように大きめの円筒状に作られており、被検体に密着させないことによりＢ_１を下げている。
【０００６】
【発明が解決しようとする課題】
このように従来は、胸腹部あるいは頭部をイメージングする場合、Ｓ／Ｎ最大となる最適な高周波コイルの構成をとっていなかった。
本発明の目的は、被検体に密着し易い楕円筒型でＱＤ型の磁気共鳴映像装置用高周波コイルを提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、静磁場中に置かれた被検体に対する高周波磁場の印加及び被検体からの磁場共鳴信号の検出のうち少なくとも一方を行う磁気共鳴映像装置用高周波コイルにおいて、全体がほぼ楕円筒状に構成されるものであって、前記楕円の一軸に対してほぼ４５°の４方向に円筒軸に平行に設けられる４本のウイング導体と、これらウイング導体の両端に各々設けられる楕円状リング導体と、少なくとも一方のコイル端に設けられるエンド導体と、前記４本のウイング導体と少なくとも一方の前記リング導体及び前記エンド導体とに接続されるキャパシタンスと、前記ウイング導体と前記リング導体又は前記エンド導体の接続部間のほぼ中間に各々挿入されるキャパシタンスとを具備し、前記隣り合って並んだウイング導体に直列に接続されたキャパシタンス又は同じく平行に並んだウイング導体、前記リング導体の接続部とエンド導体接続部に挿入されたキャパシタンスより、各々９０°位相の異なる高周波電力を供給又は高周波信号を検出するとともに、前記高周波電力を供給又は高周波信号を検出する側でないウイング導体の部分が、軸に平行に分割されて開閉可能に構成されている。
本発明は、静磁場中に置かれた被検体に対する高周波磁場の印加及び被検体からの磁場共鳴信号の検出のうち少なくとも一方を行う磁気共鳴映像装置用高周波コイルにおいて、全体がほぼ楕円筒状に構成されるものであって、前記楕円の一軸に対してほぼ４５°の４方向に円筒軸に平行に設けられる４本のウイング導体と、このウイング導体の両端に直接接続される楕円状リング導体と、少なくとも一方のコイル端に設けられるエンド導体と、前記４本のウイング導体と前記リング導体とのほぼ同じ接続点と前記エンド導体との間に接続されるキャパシタンスと、前記リング導体における前記ウイング導体との４つの接続部間のほぼ中間に各々挿入されるキャパシタンスとを具備し、前記隣り合って並んだウイング導体に直列に接続されたキャパシタンス又は同じく平行に並んだウイング導体、前記リング導体の接続部とエンド導体接続部に挿入されたキャパシタンスより、各々９０°位相の異なる高周波電力を供給又は高周波信号を検出するとともに、前記高周波電力を供給又は高周波信号を検出する側でないウイング導体の部分が、軸に平行に分割されて開閉可能に構成されている。
本発明は、静磁場中に置かれた被検体に対する高周波磁場の印加及び被検体からの磁場共鳴信号の検出のうち少なくとも一方を行う磁気共鳴映像装置用高周波コイルにおいて、全体がほぼ楕円筒状に構成されるものであって、前記楕円の一軸に対してほぼ４５°の４方向に円筒軸に平行に設けられる４本のウイング導体と、このウイング導体の両端に直接接続される楕円状リング導体及びエンド導体と、前記ウイング導体と前記リング導体及び前記エンド導体との接続部間のほぼ中間に各々挿入されるキャパシタンスとを具備し、前記４本のウイング導体は楕円筒軸方向に分割され且つこれら分割されたウイング導体は前記キャパシタンスにより接続されてなり、前記隣り合って並んだウイング導体に直列に接続されたキャパシタンス又は同じく平行に並んだウイング導体、前記リング導体の接続部とエンド導体接続部に挿入されたキャパシタンスより、各々９０°位相の異なる高周波電力を供給又は高周波信号を検出するとともに、前記高周波電力を供給又は高周波信号を検出する側でないウイング導体の部分が、軸に平行に分割されて開閉可能に構成されている。
【０００８】
このような構成の本発明に係る磁気共鳴映像装置用高周波コイルによれば、平行に並んだウイング導体部に直列に挿入されたキャパシタンス、又は同じく平行に並んだウイング導体・リング導体の接続部とエンド導体接続部に挿入されたキャパシタンスより、各々９０°位相の異なる高周波電力を供給又は高周波信号を検出することができる。さらに、エンド導体は楕円状のリング導体でもよいし、楕円筒の軸にほぼ垂直な板状か曲面状の導体で構成しても良い。板状か曲面状の導体で構成することにより均一領域を拡大できる。またこのような高周波コイルにおいて高周波電力を供給又は高周波信号を検出する側でない反対側のウイング導体は軸に平行に分割されていても良い。こうすることにより、非可塑性の材料で覆い、フレキシブルに開いたり閉じたりできる。
【０００９】
【発明の実施の形態】
図１は、本発明の一実施形態に係る磁気共鳴映像装置用高周波コイルを示す図である。図１において、本実施形態の高周波コイルは、ほぼ楕円筒状に構成され、長軸あるいは短軸に対してほぼ４５°の４方向に円筒軸に平行な４本のウイング導体１ａ−１ｄを持つ。これは、楕円筒上に導体板状に形成されている。
【００１０】
ウイング導体１ａ−１ｄの両端に各々楕円状のリング導体２ａ−２ｂを持ち、各々４本のウイング導体１ａ−１ｄとリング導体２ａ−２ｂは直接接続され、ほぼ同じ接続点でエンド導体３ａ−３ｂとキャパシタンス４ａ−４ｈにより接続されている。また、接続されたリング導体２ａ，２ｂはそれぞれウイング導体１ａ−１ｂとの４つの接続部間のほぼ中間にキャパシタンス５ａ−５ｄ，５ｅ−５ｈを挿入する形で分割されている。
【００１１】
給電は、リング導体２ａとエンド導体３ａ間に挿入されたキャパシタンス４ｃ，４ｄより行われている。通常、エンド導体３ａと給電用同軸ケーブル６ａ，６ｂのアース導体（被覆導体）７ａ，７ｂを接続し、リング導体２ａ側からキャパシタンス８ａ，８ｂを介して同軸ケーブル６ａ，６ｂの芯線に接続する。
【００１２】
図１では円偏波を発生する目的のために、直交する２方向に高周波磁場を発生させるべく２つの給電用ケーブル６ａ，６ｂを接続している。この場合、２つの給電点間のアイソレーションを十分取る必要があるが、アイソレーション確保のためには、リング導体２ａ又は２ｂに挿入されたキャパシタンス５ａ−５ｈの値を調整する。上下方向のキャパシタンス５ａ，５ｃ，５ｅ，５ｇ、また左右方向のキャパシタンス５ｂ，５ｄ，５ｆ，５ｈは、ペアで変えた方が望ましい。これらキャパシタンス５ａ，５ｃ，５ｅ，５ｇ、また左右方向のキャパシタンス５ｂ，５ｄ，５ｆ，５ｈは、可変容量コンデンサを用いてもよい。
【００１３】
エンド導体３ａ，３ｂは、傾斜磁場コイル駆動時にエンド導体３ａ，３ｂに渦電流が発生しないように、十分に容量の大きいキャパシタンスを１ケ所以上挿入するとよい。さらにウイング導体１ａ−１ｄは、幅広であるとやはり渦電流が多く流れ画像化時に悪影響を及ぼす。この渦電流の影響を避けるため、例えば図２のように高周波電流の流れにできるだけ沿った形でスリット９ａ，９ｂを挿入し、渦電流ループの発生を妨げるためキャパシタンス１０ａ−１０ｃを挿入することが望ましい。
【００１４】
図１の構成を分かりやすくするために、図３では、図１の実施形態の磁気共鳴映像装置用高周波コイルの電気的等価回路を示す。エンド導体３ａ，３ｂの位置は、図３から類推されるように、図１の如くリング導体２ａ，２ｂの内側に置く必要はない。外側でも、軸方向に隣接する位置でもよく、電気的回路が図３と等価であればよい。
【００１５】
図３において、ウイング導体１ａ−１ｄの中心を通るように点線で示されているのは、電気的中点であり、この位置で楕円上のリング導体１１をウイング導体１ａ−１ｄに接続しても問題はなく、さらに接続後軸方向の半分を取り除いても使用上問題はない。
【００１６】
図４は接続後軸方向の半分を取り除いた場合の実施形態を示す図である。もちろん、リング導体１１には渦電流の発生を抑えるため１ケ所以上十分容量の大きいキャパシタンスを挿入するのが望ましい。
【００１７】
本発明のコイルは、楕円柱形状であるため、人胴体に適用する場合は、長軸を水平方向に、短軸を上下方向にする。その際、被検者に装着するには開閉機構がある方が望ましい。
【００１８】
図５は、本発明の高周波コイルを開閉式にするための一例を示している。本コイルでは、ウイング導体に流れる高周波電流は、リング導体、あるいはエンド導体では２方向に分割される。よって、幅広なウイング導体のほぼ真ん中で軸方向に入れたスリットで分割しても高周波電流のパスに影響を与えない。つまり電気的に接続する必要はない。もちろんこの際、図１ではウイング導体とリング導体の接点とエンド導体を接続するキャパシタンス（容量Ｃ）を各々１つしか示していないが、例えばウイング１ｂを分割する場合には、容量Ｃ／２のキャパシタンス１２ａ，１２ｂ又は１２ｃ，１２ｄをそれぞれ２つ並列に並べ、その間で分割するようにする。エンド導体３ａ，３ｂも同じ位置で切断することにより、この位置で完全にコイルを切断することが可能である。
【００１９】
図６は本例の断面を示す図である。コイルを可塑性を有する支持部材１３で覆い、被検者に入ってもらうときは切断部を開き、切断部を閉じる際には接続部に例えばマジックテープ１４を用いることにより容易に被検者に装着できるようになる。
【００２０】
本発明の高周波コイルの適用としては、頭部も非常によい対象である。頭部に適用する際には、長軸を上下方向に、短軸を左右方向にした方が望ましい。
図７は本発明の高周波コイルを頭部に適用する際の例を示す。これは基本的には図３の等価回路で示されるコイルの例であるが、まず、図４と同様にウイング導体の中点でリング導体を接続する形状をしている。この場合、リング導体２１付近はキャパシタンスが集まっている側と軸上反対の位置にあり構成上電界が弱いため、こちらから頭部を挿入しても、電界由来のコイルロスを抑えることができる。またキャパシタンスが集まった給電点側のエンド導体２２を導体板、又は頭頂部の曲面形状に合わせた形にすることにより、頭頂部の高周波磁場均一性を向上させることができる。
【００２１】
これは従来鳥かご型コイルでも類似の手法が提案されているが、これらの例で導体板などで覆うのは、キャパシタンスの集まった給電点側よりもむしろ、本実施形態でウイング導体の中点で接続したリング導体２１の部分である。エンド導体２２の構成については、やはり傾斜磁場コイル駆動時の渦電流を抑えるため図８のように網状にするか、図９のように複数の導体２３に分割して十分容量の大きなキャパシタンス２４で接続する。その他誘電体を挟んだ両面基板を用いて各々の導体面の分割を互い違いに行う、等の操作により、隣接する導体間を直流的には切断するものの高周波的には接続状態にする種々の手法を用いることができる。
【００２２】
また図１０のように頭部用コイルは被検体との密着度を高めるため、ヘッドレスト２５と一体型で形成しても良い。図１０ではヘッドレスト２５はまた寝台２６に固定されている。
【００２３】
図１１は本発明の別の実施形態に係る磁気共鳴映像装置用高周波コイルを示す図である。４本のウイング導体３１ａ−３１ｄと両側のリング導体３２ａ，３２ｂはキャパシタンス３３ａ−３３ｄ，３３ｅ−３３ｈにより接続され、ほぼ同じ接続部でさらにエンド導体３４ａ，３４ｂにも付加的な接続導体３５ａ−３５ｄ，３５ｅ−３５ｈにより接続され、エンド導体においてエンド導体３４ａ，３４ｂとリング導体３２ａ，３２ｂ各々の４つの接続部のほぼ中間にキャパシタンス３６ａ−３６ｄ，３６ｅ−３６ｈが挿入されている。
【００２４】
給電は、リング導体３２ａとウイング導体３１ａ，３１ｂ間に挿入されたキャパシタンス３３ａ，３３ｂより行われている。ここではリング導体３２ａと給電用同軸ケーブル３７ａ，３７ｂのアース側導体３８ａ，３８ｂ（被覆導体）を接続し、ウイング導体３１ａ，３１ｂからキャパシタンス３９ａ，３９ｂを介して同軸ケーブルの芯線に接続する。
【００２５】
図１１では円偏波を発生する目的のために、直交する２方向に高周波磁場を発生させるべく、隣接するリング導体／ウイング導体間キャパシタンスに給電用ケーブル３７ａ，３７ｂを接続している。この場合２つの給電点間のアイソレーションを十分取る必要があるが、そのためには、エンド導体３４ａ，３４ｂに挿入されたキャパシタンスの値を調整する。上下方向のキャパシタンス３６ａ，３６ｃ，３６ｅ，３６ｇ、また左右方向のキャパシタンス３６ｂ，３６ｄ，３６ｆ，３６ｈはペアで変えた方が望ましい。上下方向のキャパシタンス３６ａ，３６ｃ，３６ｅ，３６ｇ、また左右方向のキャパシタンス３６ｂ，３６ｄ，３６ｆ，３６ｈは可変容量コンデンサを用いてもよい。
【００２６】
リング導体３２ａ，３２ｂは、傾斜磁場コイル駆動時にリング導体に渦電流が発生しないように、十分に容量の大きいキャパシタンスを１ケ所以上挿入するとよい。ウイング導体３１ａ−３１ｄに渦電流が多く流れるのを避けるための方法は、図４と同様である。
【００２７】
図１１の構成を分かりやすくするために、図１２では、図１１の実施形態の磁気共鳴映像装置用高周波コイルの電気的等価回路を示す。エンド導体３４ａ，３４ｂの位置は、図１２から類推されるように、図１１のごとくリング導体３２ａ，３２ｂの内側に置く必要はない。外側でも、軸方向に隣接する位置でもよく、電気的回路が図１２と等価であればよい。
【００２８】
図１２でウイング導体３１ａ−３１ｄの中心を通るように点線で示されているのは、電気的中点であり、この位置で楕円上のリング導体をウイング導体に接続しても問題はなく、さらに接続後軸方向の半分を取り除いても使用上問題はない。これは図１の実施形態に対して図４の変形例があり得るのと同様である。もちろん、リング導体には渦電流の発生を抑えるため１ケ所以上十分容量の大きいキャパシタンスを挿入するのが望ましい。図１１の実施形態のコイルを人胴体に適用する場合は、長軸を水平方向に、短軸を上下方向にする。その際、被検者に装着するには開閉機構がある方が望ましい。
【００２９】
図１３は、図１１の実施形態のコイルを開閉式にするための一例を示している。本コイルでは、ウイング導体３１ｃに流れる高周波電流は、リング導体３１ａ，３２ｂ、あるいはエンド導体３４ａ，３４ｂでは２方向に分割される。よって、幅広なウイング導体の真ん中で軸方向に入れたスリットで分割しても高周波電流のパスに影響を与えない。つまり電気的に接続する必要はない。もちろんこの際、図１１ではウイング導体３１ｃとリング導体３２ａ，３２ｂを接続する容量Ｃのキャパシタンスをそれぞれ１つしか示していないが、ウイング導体３１ｃを分割する場合には、容量Ｃ／２のキャパシタンス４０ａと４０ｂ，４０ｃと４０ｄを２つ並列に並べ、その間にスリットが入るようにする。リング導体３２ａ，３２ｂ、エンド導体３４ａ，３４ｂも同じ位置で切断することにより、この位置で完全にコイルを切断することが可能である。その際リング導体３２ａ，３２ｂ、エンド導体３４ａ，３４ｂは切断端で各々接続導体４１ａ−４１ｄで接続する。コイルを可塑性を有する支持部材で覆い、被検者に入ってもらうときは切断部を開き、切断部を閉じる際には接続部に例えばマジックテープを用いることにより容易に被検者に装着できるようになる。これは図６の例と同様である。
【００３０】
図１１の実施形態の高周波コイルも、頭部に適用できる。長軸を上下方向に、短軸を左右方向にし図７の様に構成できる。図７の例ではエンド導体を導体板で形成しているが、図１１の例ではリング導体を導体板で形成すればよい。また図１０のように頭部用コイルは被検体との密着度を高めるため、ヘッドレスと一体型で形成しても良い。
【００３１】
また図１２から容易に推察されるように、ウイング導体３１ａ−３１ｄとキャパシタンス３３ａ−３３ｈは直列に接続されていればよいので、図１１のようにウイング導体の両側にキャパシタンスを設けるのではなく、真ん中に配置しても構わない。その場合は構造的には図２のようになる。
【００３２】
以上の例では、送受信兼用の例を示したが、受信専用に構成しても良い。その際には、図１４に示すようにコイルを構成するキャパシタンスのうちの一部のキャパシタンスＣ′５１に並列に、インダクタンスＬ′５２とクロスダイオード５３を直列に結合したものを接続すればよい。その際、本発明の高周波コイルの共鳴高周波をω_ｏとしたとき、ω_ｏ ^２＝１／（Ｌ′Ｃ′）になるようにする。またクロスダイオード５３の代わりにピンダイオードを用いることもできる。
【００３３】
【発明の効果】
以上のように本発明によれば、胸腹部や頭部の高Ｓ／Ｎな画像が得られるようになり、また、分割してフレキシブルに構成することにより、被検体に容易に装着可能な楕円筒型でＱＤ型の磁気共鳴映像装置用高周波コイルを提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る磁気共鳴映像装置用高周波コイルの概略を示す図。
【図２】図１の高周波コイルのウイング導体の別の構成例を示す図。
【図３】図１の高周波コイルの電気的等価回路を示す図。
【図４】図１の高周波コイルを軸方向に非対称に構成した例を示す図。
【図５】図１の高周波コイルを被検体に取り付けやすくするため切断して開閉できるようにした例を示す図。
【図６】図５のコイルを可塑性を有するカバーで覆った場合の断面図を示す図。
【図７】図４のコイルを頭部用に構成した例を示す図。
【図８】図７の高周波コイルのエンド導体の別の構成例を示す図。
【図９】図７の高周波コイルのエンド導体のさらに別の構成例を示す図。
【図１０】図７の高周波コイルをヘッドレストと一体に構成した例を示す図。
【図１１】本発明の別の実施形態に係る磁気共鳴映像装置用高周波コイルの概略を示す図。
【図１２】図１１の高周波コイルの電気的等価回路を示す図。
【図１３】図１１の高周波コイルを被検体に取り付けやすくするため切断して開閉できるようにした例を示す図。
【図１４】本発明の高周波コイルを受信専用として用いるとき送信状態にて高周波コイルをＯＦＦ（周波数の離調）状態にするトラップ回路の例を示す図。
【符号の説明】
１ａ−１ｄウイング導体２ａ，２ｂリング導体
３ａ，３ｂエンド導体
４ａ−４ｈリング導体とエンド導体間キャパシタンス
５ａ−５ｈリング導体キャパシタンス６ａ，６ｂ同軸ケーブル
７ａ，７ｂアース側導体８ａ，８ｂキャパシタンス
９ａ，９ｂスリット１０ａ，１０ｃキャパシタンス
１１リング導体
１２リング導体とエンド導体間キャパシタンス
１３被可塑性支持部材１４マジックテープ
２１リング導体２２銅板状エンド導体
２３分割されたエンド導体２４キャパシタンス
２５ヘッドレスト２６寝台
３１ａ−３１ｄウイング導体３２ａ，３２ｂリング導体
３３ａ−３３ｈウイング導体とリング導体間キャパシタンス
３４ａ，３４ｂエンド導体
３５ａ−３５ｈリング導体とエンド導体間接続導体
３６ａ−３６ｈエンド導体キャパシタンス
３７ａ，３７ｂ同軸ケーブル３８ａ，３８ｂアーク側導体
３９ａ，３９ｂキャパシタンス
４０ａ−４０ｄウイング導体とリング導体間キャパシタンス
４１ａ−４１ｄリング導体とエンド導体間接続導体
５１キャパシタンス５２インダクタンス
５３クロスダイオード[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject.
[0002]
[Prior art]
In a magnetic resonance imaging apparatus, generally, a static magnetic field is applied to a subject, a magnetic resonance signal is generated by performing transmission of a high-frequency magnetic field and application of a gradient magnetic field in a predetermined sequence, and the magnetic resonance signal is received. Process and reconstruct the image. Transmission of a high-frequency magnetic field and reception of a magnetic resonance signal are performed via a high-frequency coil.
[0003]
In recent years, in a high-speed imaging method (imaging time of several tens of milliseconds) that enables imaging of a fast-moving part (such as a heart), a decrease in S / N due to a reduction in observation time has become a serious problem. Similarly, in brain function imaging for capturing subtle changes in local blood flow in the brain, a high S / N ratio is indispensable because a similar high-speed imaging method is used.
[0004]
In order to observe a signal at a high S / N, the configuration of the high-frequency coil is an important point. Signal S / N for observing high-frequency coil _is proportional to B ^{1 / R 1/2.}
Here, B ₁ is the strength of the magnetic field generated in the observation region when a current of 1 amp is passed through the high frequency coil, and can be increased by reducing the size of the high frequency coil. R represents the high-frequency resistance of the high-frequency coil, and is divided into high-frequency loss derived from the coil and high-frequency loss derived from the subject. Normally, loss from the subject cannot be avoided, so that high-frequency loss from the coil is reduced as much as possible. Since the loss due to the subject may be relatively dominant, the filling rate of the subject in the high-frequency coil may be increased.
[0005]
However, the whole body coil for capturing a normal chest abdomen, since it is housed inside the cover of the magnet, much larger than the subject, B ₁ is lowered filling rate as well as decreases. Also it is made in a large cylindrical so headrest mounting the head fits well in advance also head coil, and lower the B ₁ by not in close contact with the subject.
[0006]
[Problems to be solved by the invention]
As described above, conventionally, when imaging the thorax abdomen or the head, an optimal high-frequency coil configuration that maximizes the S / N has not been adopted.
An object of the present invention is to provide an elliptic cylindrical QD type high frequency coil for a magnetic resonance imaging apparatus which is easily adhered to a subject.
[0007]
[Means for Solving the Problems]
The present invention provides a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject. And four wing conductors provided in parallel to the cylindrical axis in four directions substantially at 45 ° to one axis of the ellipse, and elliptical ring conductors provided at both ends of the wing conductors, respectively. An end conductor provided at at least one coil end, a capacitance connected to the four wing conductors and at least one of the ring conductor and the end conductor, and an end conductor of the wing conductor and the ring conductor or the end conductor. ; and a capacitance are respectively inserted approximately halfway between the connecting portions, which are connected in series aligned wings conductor adjacent said Capacitance or the wing conductors also arranged in parallel, from the capacitance inserted in the connection portion of the ring conductor and the end conductor connection portion, while supplying or detecting a high-frequency power having a phase different from each other by 90 ° and detecting the high-frequency power. The portion of the wing conductor that is not on the side that detects the supply or the high-frequency signal is divided parallel to the axis and is configured to be openable and closable .
The present invention provides a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject. Four wing conductors provided parallel to a cylindrical axis in four directions substantially at 45 ° to one axis of the ellipse, and an elliptical ring conductor directly connected to both ends of the wing conductor An end conductor provided at at least one end of the coil, a capacitance connected between substantially the same connection point between the four wing conductors and the ring conductor, and the end conductor, and the wing in the ring conductor. A capacitance inserted approximately at an intermediate point between the four connection portions with the conductor, and a key connected in series to the adjacent wing conductors. From the capacitance inserted into the connection part of the ring conductor and the end conductor connection part, the wing conductor arranged in parallel with the pasitance or the same is supplied with a high-frequency power having a phase difference of 90 ° or a high-frequency signal is detected, and the high-frequency power is detected. The portion of the wing conductor that is not on the side that detects the supply or the high-frequency signal is divided parallel to the axis and is configured to be openable and closable.
The present invention provides a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject. Four wing conductors provided parallel to a cylindrical axis in four directions substantially at 45 ° to one axis of the ellipse, and an elliptical ring conductor directly connected to both ends of the wing conductor And an end conductor, and a capacitance inserted substantially in the middle between the connection portions of the wing conductor, the ring conductor, and the end conductor. The four wing conductors are divided in an elliptic cylinder axis direction, and These divided wing conductors are connected by the capacitance, and the capacitance or the capacitance connected in series to the adjacent wing conductors is set. From the capacitances inserted in the wing conductors arranged in parallel to each other, the connection portion of the ring conductor and the end conductor connection portion, supplying high-frequency power having a 90 ° phase difference or detecting a high-frequency signal, and supplying the high-frequency power or The portion of the wing conductor which is not on the side for detecting the high-frequency signal is divided in parallel with the axis and configured to be openable and closable.
[0008]
According to the high frequency coil for a magnetic resonance imaging apparatus according to the present invention having such a configuration, the capacitance inserted in series in the wing conductor portion arranged in parallel, or the connection portion of the wing conductor / ring conductor also arranged in parallel. From the capacitance inserted in the end conductor connection portion, it is possible to supply high frequency power having a phase difference of 90 ° or to detect a high frequency signal. Further, the end conductor may be an elliptical ring conductor, or may be a plate-like or curved-surface conductor substantially perpendicular to the axis of the elliptical cylinder. A uniform area can be expanded by using a plate-shaped or curved conductor. Further, in such a high-frequency coil, the wing conductor on the opposite side from the side for supplying the high-frequency power or detecting the high-frequency signal may be divided in parallel to the axis. In this way, it can be covered with a non-plastic material and opened and closed flexibly.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram illustrating a high-frequency coil for a magnetic resonance imaging apparatus according to an embodiment of the present invention. In FIG. 1, the high-frequency coil of the present embodiment is formed in a substantially elliptical cylindrical shape, and has four wing conductors 1a to 1d parallel to the cylindrical axis in four directions of approximately 45 ° with respect to the long axis or the short axis. . This is formed in a conductor plate shape on an elliptic cylinder.
[0010]
Elliptical ring conductors 2a-2b are provided at both ends of the wing conductors 1a-1d, respectively. Four wing conductors 1a-1d and the ring conductors 2a-2b are directly connected to each other, and the end conductors 3a-3b are connected at substantially the same connection points. And capacitances 4a-4h. Further, the connected ring conductors 2a and 2b are divided in such a manner that capacitances 5a-5d and 5e-5h are inserted almost in the middle between four connecting portions with the wing conductors 1a-1b.
[0011]
Power is supplied from capacitances 4c and 4d inserted between the ring conductor 2a and the end conductor 3a. Normally, the end conductor 3a is connected to the ground conductors (covered conductors) 7a, 7b of the power supply coaxial cables 6a, 6b, and the ring conductor 2a is connected to the core wires of the coaxial cables 6a, 6b via the capacitances 8a, 8b.
[0012]
In FIG. 1, two power supply cables 6a and 6b are connected to generate a high-frequency magnetic field in two orthogonal directions for the purpose of generating circularly polarized waves. In this case, it is necessary to ensure sufficient isolation between the two feeding points, but in order to ensure the isolation, the values of the capacitances 5a to 5h inserted in the ring conductor 2a or 2b are adjusted. The capacitances 5a, 5c, 5e, 5g in the vertical direction and the capacitances 5b, 5d, 5f, 5h in the horizontal direction are preferably changed in pairs. Variable capacitance capacitors may be used for these capacitances 5a, 5c, 5e, 5g and the capacitances 5b, 5d, 5f, 5h in the horizontal direction.
[0013]
In the end conductors 3a and 3b, it is preferable to insert one or more sufficiently large capacitances so that an eddy current is not generated in the end conductors 3a and 3b when the gradient magnetic field coil is driven. Furthermore, if the wing conductors 1a to 1d are wide, eddy currents also flow a lot and adversely affect imaging. In order to avoid the influence of the eddy current, for example, as shown in FIG. 2, it is necessary to insert the slits 9a and 9b along the flow of the high-frequency current as much as possible, and to insert the capacitances 10a to 10c to prevent the generation of the eddy current loop. desirable.
[0014]
FIG. 3 shows an electrical equivalent circuit of the high-frequency coil for the magnetic resonance imaging apparatus of the embodiment of FIG. 1 for easy understanding of the configuration of FIG. The position of the end conductors 3a, 3b does not need to be located inside the ring conductors 2a, 2b as shown in FIG. 1, as inferred from FIG. It may be on the outside or at a position adjacent in the axial direction, as long as the electric circuit is equivalent to FIG.
[0015]
In FIG. 3, what is indicated by a dotted line so as to pass through the center of the wing conductors 1a-1d is an electrical midpoint. At this position, the elliptical ring conductor 11 is connected to the wing conductors 1a-1d. There is no problem, and there is no problem in use even if half of the axial direction is removed after connection.
[0016]
FIG. 4 is a diagram showing an embodiment in which half of the axial direction is removed after connection. Of course, it is desirable to insert a capacitance having a sufficiently large capacitance at one or more locations in the ring conductor 11 in order to suppress the generation of eddy current.
[0017]
Since the coil of the present invention has an elliptical column shape, when applied to the human torso, the long axis is in the horizontal direction and the short axis is in the up and down direction. At this time, it is desirable that an opening / closing mechanism be provided for mounting on the subject.
[0018]
FIG. 5 shows an example in which the high-frequency coil of the present invention is opened and closed. In this coil, the high-frequency current flowing through the wing conductor is split in two directions at the ring conductor or the end conductor. Therefore, even if it is divided by an axially inserted slit substantially in the middle of the wide wing conductor, the path of the high-frequency current is not affected. That is, there is no need to electrically connect. Of course, at this time, FIG. 1 shows only one capacitance (capacitance C) for connecting the contact between the wing conductor and the ring conductor and the end conductor, but when dividing the wing 1b, for example, Two capacitances 12a and 12b or two capacitances 12c and 12d are arranged in parallel and divided between them. By cutting the end conductors 3a and 3b at the same position, it is possible to completely cut the coil at this position.
[0019]
FIG. 6 is a diagram showing a cross section of this example. The coil is covered with a support member 13 having plasticity, and when the subject is to be inserted into the subject, the cut portion is opened, and when the cut portion is closed, the connection portion is easily attached to the subject by using, for example, a magic tape 14. become able to.
[0020]
For the application of the high-frequency coil of the present invention, the head is also a very good target. When applied to the head, it is desirable to have the long axis in the up-down direction and the short axis in the left-right direction.
FIG. 7 shows an example in which the high-frequency coil of the present invention is applied to a head. This is basically an example of the coil shown in the equivalent circuit of FIG. 3, but first has a shape in which the ring conductor is connected at the midpoint of the wing conductor as in FIG. In this case, since the vicinity of the ring conductor 21 is located on the axially opposite position to the side where the capacitance is gathered and the electric field is weak due to the configuration, even if the head is inserted from here, the coil loss due to the electric field can be suppressed. In addition, by forming the end conductor 22 on the feed point side where the capacitance is gathered into a shape conforming to the conductor plate or the curved surface shape of the crown, the uniformity of the high-frequency magnetic field at the crown can be improved.
[0021]
In this case, a similar technique has been proposed for a birdcage coil, but in these examples, covering with a conductor plate or the like is not performed at the feeding point side where the capacitance is gathered, but at the middle point of the wing conductor in the present embodiment. This is the part of the ring conductor 21 connected. Regarding the configuration of the end conductor 22, a net is formed as shown in FIG. 8 in order to suppress eddy currents when the gradient magnetic field coil is driven, or the end conductor 22 is divided into a plurality of conductors 23 as shown in FIG. Connecting. Various methods of cutting adjacent conductors in direct current but connecting them in high frequency by performing operations such as alternately dividing each conductor surface using a double-sided substrate sandwiching a dielectric. Can be used.
[0022]
Further, as shown in FIG. 10, the head coil may be formed integrally with the headrest 25 in order to increase the degree of adhesion to the subject. In FIG. 10, the headrest 25 is also fixed to the bed 26.
[0023]
FIG. 11 is a view showing a high-frequency coil for a magnetic resonance imaging apparatus according to another embodiment of the present invention. The four wing conductors 31a-31d and the ring conductors 32a, 32b on both sides are connected by capacitances 33a-33d, 33e-33h, and additional connection conductors 35a-35d are connected to the end conductors 34a, 34b at substantially the same connection portions. , 35e-35h, and capacitances 36a-36d, 36e-36h are inserted in the end conductors approximately at the middle of the four connection portions of the end conductors 34a, 34b and the ring conductors 32a, 32b.
[0024]
Power is supplied from capacitances 33a and 33b inserted between the ring conductor 32a and the wing conductors 31a and 31b. Here, the ring conductor 32a and the earth-side conductors 38a and 38b (covered conductors) of the power supply coaxial cables 37a and 37b are connected, and the wing conductors 31a and 31b are connected to the core wires of the coaxial cables via the capacitances 39a and 39b.
[0025]
In FIG. 11, the power supply cables 37a and 37b are connected to the capacitance between adjacent ring conductors / wing conductors in order to generate high-frequency magnetic fields in two orthogonal directions for the purpose of generating circularly polarized waves. In this case, it is necessary to obtain sufficient isolation between the two feeding points. To this end, the value of the capacitance inserted in the end conductors 34a and 34b is adjusted. It is desirable that the capacitances 36a, 36c, 36e, 36g in the vertical direction and the capacitances 36b, 36d, 36f, 36h in the horizontal direction be changed in pairs. Variable capacitance capacitors may be used for the vertical capacitances 36a, 36c, 36e, 36g and the horizontal capacitances 36b, 36d, 36f, 36h.
[0026]
In the ring conductors 32a and 32b, it is preferable to insert one or more capacitances having sufficiently large capacitance so that an eddy current is not generated in the ring conductor when the gradient magnetic field coil is driven. A method for avoiding a large amount of eddy current flowing through the wing conductors 31a to 31d is the same as that in FIG.
[0027]
In order to make the configuration of FIG. 11 easy to understand, FIG. 12 shows an electrical equivalent circuit of the high frequency coil for the magnetic resonance imaging apparatus of the embodiment of FIG. As shown in FIG. 12, the positions of the end conductors 34a and 34b need not be located inside the ring conductors 32a and 32b as shown in FIG. It may be on the outside or at a position adjacent in the axial direction, as long as the electric circuit is equivalent to FIG.
[0028]
In FIG. 12, what is indicated by a dotted line passing through the center of the wing conductors 31a to 31d is an electrical midpoint, and there is no problem even if the elliptical ring conductor is connected to the wing conductor at this position. Further, even if half of the axial direction is removed after connection, there is no problem in use. This is similar to the possible modification of FIG. 4 with respect to the embodiment of FIG. Of course, it is desirable to insert a capacitance having a sufficiently large capacity at one or more locations in the ring conductor in order to suppress the generation of eddy current. When the coil of the embodiment of FIG. 11 is applied to the human torso, the long axis is in the horizontal direction and the short axis is in the up and down direction. At this time, it is desirable that an opening / closing mechanism be provided for mounting on the subject.
[0029]
FIG. 13 shows an example in which the coil of the embodiment shown in FIG. 11 is opened and closed. In the present coil, the high-frequency current flowing through the wing conductor 31c is split in two directions by the ring conductors 31a and 32b or the end conductors 34a and 34b. Therefore, even if the division is made by the slit inserted in the axial direction in the middle of the wide wing conductor, the path of the high-frequency current is not affected. That is, there is no need to electrically connect. Of course, at this time, only one capacitance C is shown in FIG. 11 for connecting the wing conductor 31c and the ring conductors 32a and 32b. However, when the wing conductor 31c is divided, the capacitance 40a having the capacitance C / 2 is used. And 40b, 40c and 40d are arranged in parallel, and a slit is inserted between them. By cutting the ring conductors 32a and 32b and the end conductors 34a and 34b at the same position, it is possible to completely cut the coil at this position. At this time, the ring conductors 32a and 32b and the end conductors 34a and 34b are connected at the cut ends by connection conductors 41a to 41d, respectively. The coil is covered with a supporting member having plasticity, so that the cut portion is opened when the subject is to be inserted into the subject, and when the cut portion is closed, the connection portion is easily attached to the subject by using, for example, a Velcro tape. become. This is similar to the example of FIG.
[0030]
The high-frequency coil of the embodiment of FIG. 11 can also be applied to the head. With the long axis in the up-down direction and the short axis in the left-right direction, it can be configured as shown in FIG. In the example of FIG. 7, the end conductor is formed of a conductor plate, but in the example of FIG. 11, the ring conductor may be formed of a conductor plate. Further, as shown in FIG. 10, the head coil may be formed integrally with the headless in order to increase the degree of adhesion to the subject.
[0031]
Further, as can be easily inferred from FIG. 12, since it is sufficient that the wing conductors 31a to 31d and the capacitances 33a to 33h are connected in series, instead of providing the capacitance on both sides of the wing conductor as shown in FIG. It may be placed in the middle. In that case, the structure is as shown in FIG.
[0032]
In the above example, an example in which transmission and reception are both performed has been described. In this case, as shown in FIG. 14, a capacitor in which an inductance L'52 and a cross diode 53 are connected in series may be connected in parallel with a part of the capacitance C'51 constituting the coil. At this time, when the resonance high frequency of the high frequency coil of the present invention is ω _o , ω _o ² = 1 / (L′ C ′). Further, a pin diode can be used instead of the cross diode 53.
[0033]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain high S / N images of the thorax and abdomen and the head, and by dividing and flexibly configuring, an ellipse that can be easily attached to a subject. It is possible to provide a cylindrical QD-type high frequency coil for a magnetic resonance imaging apparatus.
[Brief description of the drawings]
FIG. 1 is a view schematically showing a high-frequency coil for a magnetic resonance imaging apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing another configuration example of the wing conductor of the high-frequency coil of FIG. 1;
FIG. 3 is a diagram showing an electrical equivalent circuit of the high-frequency coil shown in FIG. 1;
FIG. 4 is a diagram showing an example in which the high-frequency coil of FIG. 1 is configured to be asymmetric in the axial direction.
FIG. 5 is a diagram showing an example in which the high-frequency coil of FIG. 1 can be cut and opened to facilitate attachment to a subject.
FIG. 6 is a sectional view showing a case where the coil of FIG. 5 is covered with a cover having plasticity.
FIG. 7 is a diagram showing an example in which the coil of FIG. 4 is configured for a head.
8 is a diagram showing another example of the configuration of the end conductor of the high-frequency coil of FIG. 7;
9 is a diagram showing still another configuration example of the end conductor of the high-frequency coil of FIG. 7;
FIG. 10 is a diagram showing an example in which the high-frequency coil of FIG. 7 is integrated with a headrest.
FIG. 11 is a view schematically showing a high-frequency coil for a magnetic resonance imaging apparatus according to another embodiment of the present invention.
FIG. 12 is a diagram showing an electrical equivalent circuit of the high-frequency coil shown in FIG. 11;
FIG. 13 is a diagram showing an example in which the high-frequency coil of FIG. 11 is cut and opened to facilitate attachment to a subject.
FIG. 14 is a diagram showing an example of a trap circuit for turning off the high-frequency coil (frequency detuning) in the transmission state when the high-frequency coil of the present invention is used only for reception.
[Explanation of symbols]
1a-1d Wing conductor 2a, 2b Ring conductor 3a, 3b End conductor 4a-4h Capacitance between ring conductor and end conductor 5a-5h Ring conductor capacitance 6a, 6b Coaxial cable 7a, 7b Earth-side conductor 8a, 8b Capacitance 9a, 9b Slit 10a, 10c Capacitance 11 Ring conductor 12 Capacitance between ring conductor and end conductor 13 Plastic support member 14 Magic tape 21 Ring conductor 22 Copper plate end conductor 23 Divided end conductor 24 Capacitance 25 Headrest 26 Bed 31a-31d Wing conductor 32a, 32b Ring conductors 33a-33h Capacities 34a, 34b between wing conductors and ring conductors End conductors 35a-35h Ring conductors and connection conductors 36a-36h between end conductors De conductor capacitance 37a, 37b coaxial cable 38a, 38b arc side conductor 39a, 39b capacitance 40a-40d wing conductor and the ring conductor capacitances 41a-41d ring conductor and the end conductor between the connection conductor 51 capacitance 52 inductance 53 Cross diode

Claims

In a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject,
Four wing conductors provided in parallel with the cylindrical axis in four directions substantially at 45 ° to one axis of the ellipse, and are provided at both ends of these wing conductors. An elliptical ring conductor to be provided; an end conductor provided at at least one coil end; a capacitance connected to the four wing conductors and at least one of the ring conductor and the end conductor; A capacitance inserted between the ring conductors or between the connection portions of the end conductors, respectively.
The high-frequency power having a phase difference of 90 ° from the capacitance connected in series to the adjacent wing conductors or the wing conductors similarly arranged in parallel, and the capacitance inserted in the connection portion of the ring conductor and the end conductor connection portion. A magnetic resonance characterized in that a portion of the wing conductor that is not supplying the high-frequency signal or detecting the high-frequency signal and that is not on the side that supplies the high-frequency signal or detects the high-frequency signal is divided parallel to the axis so as to be openable and closable. High frequency coil for video equipment.

In a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject,
The whole is configured in a substantially elliptical cylindrical shape, and four wing conductors are provided parallel to the cylindrical axis in four directions of approximately 45 ° with respect to one axis of the ellipse, and directly connected to both ends of the wing conductor. An elliptical ring conductor to be connected, an end conductor provided on at least one coil end, and a capacitance connected between substantially the same connection point between the four wing conductors and the ring conductor and the end conductor. A capacitance inserted between the four connection portions of the ring conductor with the wing conductor, respectively.
The high-frequency power having a phase difference of 90 ° from the capacitance connected in series to the adjacent wing conductors or the wing conductors similarly arranged in parallel, and the capacitance inserted in the connection portion of the ring conductor and the end conductor connection portion. A magnetic resonance characterized in that a portion of the wing conductor that is not supplying the high-frequency signal or detecting the high-frequency signal and that is not on the side that supplies the high-frequency signal or detects the high-frequency signal is divided parallel to the axis so as to be openable and closable. High frequency coil for video equipment.

In a high-frequency coil for a magnetic resonance imaging apparatus that performs at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject,
The whole is configured in a substantially elliptical cylindrical shape, and four wing conductors are provided parallel to the cylindrical axis in four directions of approximately 45 ° with respect to one axis of the ellipse, and directly connected to both ends of the wing conductor. An elliptical ring conductor and an end conductor to be connected, and a capacitance inserted substantially at an intermediate portion between connection portions of the wing conductor, the ring conductor, and the end conductor,
The four wing conductors are divided in the axis direction of the elliptical cylinder, and the divided wing conductors are connected by the capacitance,
The high-frequency power having a phase difference of 90 ° from the capacitance connected in series to the adjacent wing conductors or the wing conductors similarly arranged in parallel, and the capacitance inserted in the connection portion of the ring conductor and the end conductor connection portion. A magnetic resonance characterized in that a portion of the wing conductor that is not supplying the high-frequency signal or detecting the high-frequency signal and that is not on the side that supplies the high-frequency signal or detects the high-frequency signal is divided parallel to the axis so as to be openable and closable. High frequency coil for video equipment.

4. The high frequency coil for a magnetic resonance imaging apparatus according to claim 1 , wherein one axis of the ellipse is a major axis or a minor axis of the ellipse .