JPH0317488B2 - - Google Patents
Info
- Publication number
- JPH0317488B2 JPH0317488B2 JP57171358A JP17135882A JPH0317488B2 JP H0317488 B2 JPH0317488 B2 JP H0317488B2 JP 57171358 A JP57171358 A JP 57171358A JP 17135882 A JP17135882 A JP 17135882A JP H0317488 B2 JPH0317488 B2 JP H0317488B2
- Authority
- JP
- Japan
- Prior art keywords
- magnetic field
- coil
- uniformity
- gradient magnetic
- gradient
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/387—Compensation of inhomogeneities
- G01R33/3873—Compensation of inhomogeneities using ferromagnetic bodies ; Passive shimming
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
Description
【発明の詳細な説明】
〔発明の技術分野〕
本発明は、磁気共鳴現象を利用して、生体内各
組織の特定原子核（通常は水素原子核）密度分布
を被検体外部より無侵襲に測定し、医学用診断の
ための情報を得る磁気共鳴イメージング装置に装
備される傾斜磁場コイルユニツトに関するもので
ある。[Detailed Description of the Invention] [Technical Field of the Invention] The present invention utilizes magnetic resonance phenomena to non-invasively measure the density distribution of specific atomic nuclei (usually hydrogen nuclei) in various tissues within a living body from outside the subject. The present invention relates to a gradient magnetic field coil unit installed in a magnetic resonance imaging apparatus for obtaining information for medical diagnosis.
従来の磁気共鳴イメージング装置に関する技術
の一例として、特開昭54−156596号公報に示され
た磁気共鳴イメージング装置についてのものがあ
る。
An example of a technique related to a conventional magnetic resonance imaging apparatus is a magnetic resonance imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 156596/1983.
この例を引用して、磁気系に関する従来の技術
を説明する。 Citing this example, conventional techniques related to magnetic systems will be explained.
第１図ａ，ｂには４個の主コイルＣ１からなる
空心磁石Ｍが示されており、このコイルＣ１に電
流を流して、磁気共鳴現象を測定するのに必要な
静磁場（通常500〜1500ガウス）を得る。さらに
補正コイルとしてｚ方向傾斜磁場コイルＣ２（第
２図）、ｘ方向傾斜磁場Ｃ３（第３図）、ｙ方向傾
斜磁場コイルＣ４（第３図）が併用される。第３
図でＣ３，Ｃ４は非磁性体からなる支持筒Ｂに固
定され、全体として傾斜磁場コイルユニツトを構
成している。 Figures 1a and b show an air-core magnet M consisting of four main coils C1, and when a current is passed through the coils C1, a static magnetic field (usually 500~ 1500 Gauss). Further, as correction coils, a z-direction gradient magnetic field coil C2 (FIG. 2), an x-direction gradient magnetic field coil C3 (FIG. 3), and a y-direction gradient magnetic field coil C4 (FIG. 3) are used together. Third
In the figure, C3 and C4 are fixed to a support cylinder B made of a non-magnetic material, and constitute a gradient magnetic field coil unit as a whole.
一般に上記形式の空心磁石Ｍは「８オーダーコ
イル」と称され、計算上は、高い磁場の均一性が
得られるはずであるが、実際には次の各要因によ
る均一度の低下がある。 Generally, the air-core magnet M of the above type is called an "8-order coil", and although it should be able to obtain a high degree of uniformity of the magnetic field based on calculations, in reality, the degree of uniformity is reduced due to the following factors.
(イ) ４個のコイルＣ１の位置の誤差。(a) Error in the position of the four coils C1.
(ロ) コイル製作上の誤差。(b) Errors in coil manufacturing.
(ハ) 磁石周囲にある鉄等の強磁性体による磁場歪
み。(c) Magnetic field distortion caused by ferromagnetic materials such as iron around the magnet.
一方、診断用のごとく断層像を得る磁気共鳴イ
メージング装置においては、磁場の均一性は、装
置の性能を決める重要な因子である。 On the other hand, in a magnetic resonance imaging apparatus that obtains tomographic images for diagnostic purposes, the uniformity of the magnetic field is an important factor that determines the performance of the apparatus.
すなわち磁気共鳴イメージング装置における断
層面内の磁気共鳴信号の収集方法は、断層面内の
各位置もしくは各線上毎に磁場強度を微少に変え
それに対応する磁気共鳴信号周波数の相違によつ
て面内の位置の判別を行なう。よつて、理相的に
は、完全に均一な静磁場に、位置に対応して線型
に磁場強度が変化する傾斜磁場を重ねることが望
ましい。しかし実現には前述の理由により、完全
に均一な静磁場は得られないので、実際上は、そ
の不均一度よりも大きな傾斜を有する傾材磁場を
重ねる。このため、不均一度が大きい磁石系では
それに比例して大きな傾斜磁場を用いる必要があ
る。傾斜磁場が印加された状態での断層面内の磁
場の相違をΔHとすると、磁気共鳴信号ｆ（ｔ）
の減衰は
exp（−ｔ／T2−tγΔH）
で表わされる。ここでT2はスピン−スピン緩和
時間、γは磁気回転比とよばれ、ともに物質に固
有な値である。すなわち、ｆ（ｔ）は磁場の相違
ΔHが大きくなるに従つて急激に減衰するため得
られる信号量が減少し断層画像の信号対雑音比
（Ｓ／Ｎ）がそれに対応して悪化する。 In other words, the method of collecting magnetic resonance signals within a tomographic plane in a magnetic resonance imaging device is to slightly change the magnetic field strength at each position or line within the tomographic plane, and to detect the in-plane magnetic resonance signals by varying the corresponding magnetic resonance signal frequency. Determine the position. Therefore, from a theoretical point of view, it is desirable to superimpose a completely uniform static magnetic field with a gradient magnetic field whose magnetic field strength varies linearly depending on the position. However, in practice, for the reasons mentioned above, a completely uniform static magnetic field cannot be obtained, so in practice, gradient magnetic fields having a gradient larger than the non-uniformity are superimposed. Therefore, in a magnet system with a large degree of non-uniformity, it is necessary to use a proportionally large gradient magnetic field. Letting ΔH be the difference in magnetic field within the fault plane when a gradient magnetic field is applied, the magnetic resonance signal f(t)
The attenuation of is expressed as exp(−t/T 2 −tγΔH). Here, T 2 is called the spin-spin relaxation time, and γ is called the gyromagnetic ratio, both of which are values specific to the material. That is, f(t) rapidly attenuates as the magnetic field difference ΔH increases, so the amount of signal obtained decreases and the signal-to-noise ratio (S/N) of the tomographic image deteriorates accordingly.
このように、磁場均一性を向上させることが断
層画像の画質を向上させるために必要欠くべから
ず要素である。これを実現するために従来次のよ
うな方法で磁場均一性の調整を行なつていた。 In this way, improving the magnetic field uniformity is an essential element for improving the image quality of tomographic images. To achieve this, the magnetic field uniformity has conventionally been adjusted using the following method.
(1) ４個の主コイルＣ１の位置を再調整すること
によりコイル製作上の誤差および磁石組立時の
組立精度に起因する均一度の劣化を補正する。
この方法は一個のコイルが200Kg以上あること
から、微妙な調整な実施困難であり、いわば粗
調整にあたるものである。(1) By readjusting the positions of the four main coils C1, deterioration in uniformity due to errors in coil manufacturing and assembly accuracy during magnet assembly is corrected.
Since each coil weighs over 200 kg, this method is difficult to perform delicate adjustments and is equivalent to rough adjustment.
(2) 傾斜磁場コイルユニツトにおける傾斜磁場コ
イルＣ２，Ｃ３，Ｃ４に直流電流を流してｘ、
ｙ、ｚ方向に傾斜した不均一性を補正する。こ
れは例えば第４図ａに示すようなｘ方向に線型
な傾斜の不均一性を有する磁場Hxの場合、ｘ
−ｙ面内の円周上の不均一性を角度に対応させ
て示すと、第４図ｂのようにcosθの関数とな
る。一方ｘ方向傾斜磁場コイルＣ３による傾斜
磁場Hc3も同じくcosθの関数となるので磁場Hx
と符号が逆で、同じ振幅となるようにコイルＣ
３に流す直流電流を調整すると、第４図ｂの磁
場Hc3が得られ、磁場Hxの不均一性を打ち消す
ことができる。この方法では、コイルの位置を
機械的に調整する(1)項の方法に比してより精密
な調整が可能となる。(2) By passing a direct current through the gradient magnetic field coils C2, C3, and C4 in the gradient magnetic field coil unit,
Correct non-uniformity tilted in the y and z directions. For example, in the case of a magnetic field H x with linear gradient inhomogeneity in the x direction as shown in Figure 4a, x
When the non-uniformity on the circumference in the -y plane is shown in correspondence with the angle, it becomes a function of cos θ as shown in FIG. 4b. On the other hand, the gradient magnetic field H c3 due to the x-direction gradient magnetic field coil C3 is also a function of cosθ, so the magnetic field H x
coil C so that it has the opposite sign and the same amplitude as
By adjusting the direct current flowing through the magnetic field H c3 shown in FIG. 4 b, the non-uniformity of the magnetic field H x can be canceled out. This method enables more precise adjustment than the method (1), which mechanically adjusts the position of the coil.
これらの磁場調整により、比較的均一度の良好
な磁場を作り得るが、それでも次のような問題が
あつた。 Although it is possible to create a magnetic field with relatively good uniformity through these magnetic field adjustments, the following problems still occur.
傾斜磁場コイルユニツトにおけるコイル製作上
またはコイル構造上の局所的磁場の歪、例えば、
コイル内外の渡り線部による磁場の局所的不均一
性、および磁石周囲にある鉄等の強磁性体による
局所的不均一性などに対しては、上述した２つの
方法では補正することが困難であり、その部分を
除いた所では比較的高均一な磁場が得られても、
全体として均一性のよい磁場は得られなかつた。 Local magnetic field distortion due to coil fabrication or coil structure in the gradient coil unit, e.g.
It is difficult to correct for local inhomogeneities in the magnetic field due to crossover wires inside and outside the coil, and local inhomogeneities due to ferromagnetic materials such as iron around the magnet, using the two methods described above. Even if a relatively highly uniform magnetic field is obtained except for that part,
A magnetic field with good overall uniformity could not be obtained.
本発明の目的とするところは、磁場の局所的不
均一性を簡単な構成で補正し、より高均一な磁場
を作り、良質な断層像を得ることを可能とする磁
気共鳴イメージング装置用傾斜磁場コイルユニツ
トを提供することにある。
The object of the present invention is to correct local inhomogeneity of a magnetic field with a simple configuration, create a more uniform magnetic field, and provide a gradient magnetic field for a magnetic resonance imaging apparatus that makes it possible to obtain high-quality tomographic images. Our goal is to provide coil units.
本発明は１個以上の強磁体片小を非磁性支持筒
に取着することにより磁場均一性を補正すること
を特徴としている。
The present invention is characterized in that magnetic field uniformity is corrected by attaching one or more ferromagnetic pieces to a non-magnetic support tube.
すなわち既に述べたように、磁石の周囲に強磁
性体が存在すると、磁力線が強磁性体に集中する
ため、磁場が強くなる場所と、弱くなる場所があ
らわれる。小さな強磁性体ではこの傾向は強磁性
体周囲の局所的な部分で顕著にみられるので、こ
れを逆に利用すれば、局所的な不均一性の補正が
可能となるのである。 That is, as already mentioned, when a ferromagnetic material exists around a magnet, the lines of magnetic force are concentrated on the ferromagnetic material, so that there are places where the magnetic field is strong and places where it is weak. In small ferromagnetic materials, this tendency is noticeable in local areas around the ferromagnetic material, so if this is used inversely, it is possible to correct local non-uniformity.
本発明の一実施例の構成を第５図に示す。 The configuration of one embodiment of the present invention is shown in FIG.
第５図において、傾斜磁場コイルユニツトをな
すＣ３，Ｃ４は第３図と同様にｘ方向傾斜磁場コ
イルＣ３、ｙ方向傾斜磁場コイルＣ４であり、こ
れらは非磁性体からなる支持筒１上に固定されて
いる。また支持筒１の軸方向中央部の周上（断層
面に対応する位置）に、強磁性体小片３（第６図
に示す）を取付けるための複数個の取付孔２が設
けられている。第６図にその一部分の断層を示
す。これら第５図および第６図では、強磁性体小
片３を鉄製のねじとし、取付孔２をねじ孔とした
場合を示している。 In FIG. 5, C3 and C4 forming the gradient magnetic field coil unit are the x-direction gradient magnetic field coil C3 and the y-direction gradient magnetic field coil C4, as in FIG. 3, and these are fixed on the support tube 1 made of a non-magnetic material. has been done. Further, a plurality of mounting holes 2 for mounting small ferromagnetic pieces 3 (shown in FIG. 6) are provided on the circumference of the axially central portion of the support tube 1 (at a position corresponding to the tomographic plane). Figure 6 shows a partial fault. 5 and 6 show the case where the small ferromagnetic piece 3 is an iron screw and the mounting hole 2 is a screw hole.
このようにすれば、前述のように主コイルＣ１
および傾斜磁場コイルＣ２，Ｃ３，Ｃ４にて磁場
の均一性調整を行なつた後、調整不可能な局所的
不均一性にについて、強磁性体小片３としてのね
じを取付けるかもしくは取はずすかして補正する
ことができる。 In this way, as mentioned above, the main coil C1
After adjusting the uniformity of the magnetic field with the gradient coils C2, C3, and C4, the screws as the ferromagnetic piece 3 can be installed or removed to correct local non-uniformity that cannot be adjusted. It can be corrected by
ここで局所的磁場強度の調整は、
(1) ねじ３の長さを選択すること、
(2) 孔を設けた別体の強磁性体小片をねじ３によ
つて締付け固定すること、
により容易に行なえる。 Here, the local magnetic field strength can be easily adjusted by (1) selecting the length of the screw 3, and (2) tightening and fixing a separate piece of ferromagnetic material with a hole with the screw 3. can be done.
また、ねじ以外の鉄等の強磁性体小片を取付け
るようにしてもよく、取付孔をねじ孔でなく、い
わゆるばか孔とし、ナツトを用いて強磁性体小片
としてのねじを止めるようにしてもよい。さらに
取付孔は、断面層に対応する個所の円周上一列の
みでなく、その周囲の周上に複数列明けることも
可能である。またコイル等の製造上の理由によ
り、特定の方向に、局所的不均一性があらわれる
ことがあらかじめ予想される方向については、そ
の孔のピツチを他の部分と違えておくことも可能
である。 In addition, a small piece of ferromagnetic material such as iron other than a screw may be attached, and the mounting hole may be a so-called stupid hole instead of a screw hole, and a nut may be used to secure the screw as a small piece of ferromagnetic material. good. Furthermore, the mounting holes can be provided not only in one row on the circumference at a location corresponding to the cross-sectional layer, but also in multiple rows around the circumference. Further, for manufacturing reasons such as a coil, in a specific direction where local non-uniformity is expected to appear in advance, the pitch of the holes can be made different from that in other parts.
さらに強磁性体小片としてセルフタツピングね
じを用い支持筒１に直接ねじ込むようにしてもよ
い。 Furthermore, the small piece of ferromagnetic material may be screwed directly into the support tube 1 using a self-tapping screw.
また、支持筒１を合成樹脂製とすれば、セルフ
タツピングねじ等によるねじ込みも容易に行なえ
る。 Furthermore, if the support tube 1 is made of synthetic resin, it can be easily screwed in using self-tapping screws or the like.
これらの場合は支持筒１に予め取付孔を設ける
必要はなく、強磁性体小片の取付個所も任意に選
定できる。 In these cases, there is no need to provide a mounting hole in the support tube 1 in advance, and the mounting location of the ferromagnetic piece can be arbitrarily selected.
さらに、支持筒１の大きさを、ほとんど変える
ことがないので、磁場空間の利用度は従来とほぼ
変化がない。 Furthermore, since the size of the support cylinder 1 is hardly changed, the degree of utilization of the magnetic field space is almost unchanged from the conventional one.
その他本発明はその要旨を変更しない範囲内で
種々変形して実施することができる。 In addition, the present invention can be implemented with various modifications without changing the gist thereof.
本発明によれば、局所的な磁場の不均一性を安
価に且つ容易に補正することができる磁気共鳴イ
メージング装置用傾斜磁場コイルユニツトを提供
することができる。
According to the present invention, it is possible to provide a gradient magnetic field coil unit for a magnetic resonance imaging apparatus that can inexpensively and easily correct local magnetic field inhomogeneity.
第１図〜第３図は従来装置の磁石系説明図、第
４図ａ，ｂは傾斜磁場コイルによる磁場不均一性
補正の説明図、第５図は本発明の一実施例を示す
斜視図、第６図は同実施例の要部を詳細に示す断
面図である。
Ｃ１……主コイル、Ｃ２……ｚ方向傾斜磁場コ
イル、Ｃ３……ｘ方向傾斜磁場コイル、Ｃ４……
ｙ方向傾斜磁場コイル、１……支持筒、２……強
磁性体小片取付孔、３……強磁性体小片。
1 to 3 are explanatory diagrams of the magnet system of the conventional device, FIGS. 4a and 4b are explanatory diagrams of magnetic field non-uniformity correction using gradient magnetic field coils, and FIG. 5 is a perspective view showing an embodiment of the present invention. , FIG. 6 is a sectional view showing the main part of the same embodiment in detail. C1...main coil, C2...z-direction gradient magnetic field coil, C3...x-direction gradient magnetic field coil, C4...
Y-direction gradient magnetic field coil, 1...Support tube, 2...Small ferromagnetic piece mounting hole, 3...Small ferromagnetic piece.
Claims (1)
にせれぞれＸ、Ｙ、Ｚ軸傾斜磁場コイルを配設し
てなる磁気共鳴イメージング装置用傾斜磁場コイ
ルユニツトにおいて、前記コイルが配設されてい
なく且つ静磁場の略中心位置に相当する前記支持
体の軸方向中央部の周上に、複数個の取付孔を設
け、この取付孔に強磁性体小片を取付けてなるこ
とを特徴とする磁気共鳴イメージング装置用傾斜
磁場コイルユニツト。1. In a gradient magnetic field coil unit for a magnetic resonance imaging apparatus, in which X-, Y-, and Z-axis gradient magnetic field coils are respectively arranged on both sides in the axial direction of a cylindrical support made of a non-magnetic material, the coils are arranged. A plurality of mounting holes are provided on the periphery of the axially central portion of the support body corresponding to the approximate center position of the static magnetic field, and small pieces of ferromagnetic material are attached to the mounting holes. Gradient magnetic field coil unit for magnetic resonance imaging equipment.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP57171358A JPS5960346A (en) | 1982-09-30 | 1982-09-30 | Nuclear magnetic resonance device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP57171358A JPS5960346A (en) | 1982-09-30 | 1982-09-30 | Nuclear magnetic resonance device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5960346A JPS5960346A (en) | 1984-04-06 |
| JPH0317488B2 true JPH0317488B2 (en) | 1991-03-08 |
Family
ID=15921701
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP57171358A Granted JPS5960346A (en) | 1982-09-30 | 1982-09-30 | Nuclear magnetic resonance device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5960346A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0640869B2 (en) * | 1984-01-18 | 1994-06-01 | 株式会社日立メディコ | ΝMR imaging device |
| DE8419763U1 (en) * | 1984-07-02 | 1986-03-20 | Siemens AG, 1000 Berlin und 8000 München | Magnetic resonance tomography device |
| NL8502340A (en) * | 1985-08-26 | 1987-03-16 | Philips Nv | MAGNETIC RESONANCE DEVICE WITH FIELD HOMOGENIZING MAGNETIC ELEMENTS. |
| FR2598809B1 (en) * | 1986-05-13 | 1988-07-22 | Thomson Cgr | MAGNETIC FIELD HOMOGENEITY CORRECTOR BLOCK AND MAGNET PROVIDED WITH SUCH BLOCKS |
| DE3866060D1 (en) * | 1987-08-14 | 1991-12-12 | Siemens Ag | ELECTRIC MAGNET FOR CORE SPIN THOMOGRAPHS. |
| FR2623324A1 (en) * | 1987-11-13 | 1989-05-19 | Thomson Cgr | NMR IMAGING DEVICE, INHOMOGENEITY CORRECTION METHOD AND MAGNET PRODUCTION METHOD IMPLEMENTED IN THE DEVICE |
| JPH01280447A (en) * | 1988-05-02 | 1989-11-10 | Hitachi Ltd | Nuclear spin resonance fault photographing device |
| US4853663A (en) * | 1988-12-22 | 1989-08-01 | General Electric Company | Passive shims for correction of (3,2) and (3,-2) harmonic terms in magnetic resonance magnets |
| GB2276946B (en) * | 1993-04-08 | 1997-04-02 | Oxford Magnet Tech | Improvements in or relating to MRI magnets |
| JP5984405B2 (en) * | 2012-02-01 | 2016-09-06 | 株式会社日立製作所 | Magnetic resonance imaging system |
-
1982
- 1982-09-30 JP JP57171358A patent/JPS5960346A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5960346A (en) | 1984-04-06 |
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