JPH06133945A - Method for adjusting static magnetic field uniformity in mri and mrs - Google Patents
Method for adjusting static magnetic field uniformity in mri and mrsInfo
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- JPH06133945A JPH06133945A JP4292614A JP29261492A JPH06133945A JP H06133945 A JPH06133945 A JP H06133945A JP 4292614 A JP4292614 A JP 4292614A JP 29261492 A JP29261492 A JP 29261492A JP H06133945 A JPH06133945 A JP H06133945A
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- magnetic field
- static magnetic
- primary
- homogeneity
- mri
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、磁気共鳴（ＭＲ：ｍａ
ｇｎｅｔｉｃ ｒｅｓｏｎａｎｃｅ）現象を利用して被
検体（生体）のスライス画像等の形態情報を得るＭＲＩ
装置及びその現象を利用してスペクトロスコピー等の生
体情報を得るＭＲＳ（ＭＲスペクトロスコピー）装置に
おける静磁場均一性の調整方法に関する。BACKGROUND OF THE INVENTION The present invention relates to magnetic resonance (MR: ma).
MRI that obtains morphological information such as a slice image of a subject (living body) by utilizing the phenomenon of "gone".
The present invention relates to a device and a method of adjusting static magnetic field homogeneity in an MRS (MR spectroscopy) device that obtains biological information such as spectroscopy by utilizing the phenomenon.
【０００２】[0002]
【従来の技術】一般に、ＭＲＩ装置及びＭＲＳ装置は、
静磁場の均一性を確保して形態情報及び生体情報を精度
良く求めることが要求される。その要求は、静磁場空間
の中に被検体が存在することにより直交３軸方向（Ｘ，
Ｙ，Ｚ方向）において線形に変化している一次の静磁場
不均一成分を補正することによりほぼ達成される。そこ
で、従来においては、傾斜磁場電源の直流分またはＸ，
Ｙ，Ｚの一次のシムコイルに流す電流を順次変化させな
がら被検体よりのＭＲ信号を収集し、時間領域の信号の
減衰的定数またはフーリエ変換した後のスペクトルの線
幅より、関心領域の均一性が最適になる設定値を探す方
法（一次のオートシミング）で求めた設定値に従って上
記した一次の静磁場不均一成分を補正することにより、
静磁場均一性を得るようにしていた。2. Description of the Related Art Generally, an MRI apparatus and an MRS apparatus are
It is required to accurately obtain the morphological information and the biological information while ensuring the uniformity of the static magnetic field. The requirement is that the presence of the subject in the static magnetic field space causes the three orthogonal directions (X,
This is almost achieved by correcting the linear static magnetic field inhomogeneity component that linearly changes in the Y and Z directions). Therefore, conventionally, the DC component of the gradient magnetic field power supply or X,
The MR signal from the object is collected while sequentially changing the currents flowing in the primary shim coils of Y and Z, and the homogeneity of the region of interest is obtained from the decay constant of the signal in the time domain or the line width of the spectrum after Fourier transform. By correcting the above-mentioned primary static magnetic field inhomogeneity component according to the setting value obtained by the method for finding the optimum setting value (first-order auto shimming),
The static magnetic field uniformity was obtained.
【０００３】[0003]
【発明が解決しようとする課題】しかしながら、従来の
ように一次のオートシミングでＸ，Ｙ，Ｚの各補正値
（傾斜磁場電源のＤＣオフセットまたはシム電源の電流
値）が最適になる点を探し出す場合、通常１０〜２０回
の試行が必要であり、通常３〜５分の所要時間となる。
これにともない、従来においては、患者毎に一次のオー
トシミングを行うと、検査時間がその分延長し、患者の
負担が大きくなるという不具合があった。However, as in the prior art, a point where each correction value of X, Y, and Z (DC offset of the gradient magnetic field power source or current value of the shim power source) is optimized in the first-order auto shimming is searched for. In this case, 10 to 20 trials are usually required, which usually takes 3 to 5 minutes.
Along with this, conventionally, there has been a problem that if primary auto-shimming is performed for each patient, the examination time will be extended by that amount and the burden on the patient will increase.
【０００４】本発明は、上記した事情に着目してなされ
たもので、その目的とするところは、一次の静磁場不均
一性を補正するうえでの最適値を短時間且つ確実に得る
ことができるＭＲＩ及びＭＲＳにおける静磁場均一性の
調整方法を提供することにある。The present invention has been made by paying attention to the above-mentioned circumstances, and an object thereof is to reliably obtain an optimum value for correcting primary static magnetic field inhomogeneity in a short time. An object of the present invention is to provide a method of adjusting static magnetic field homogeneity in MRI and MRS that can be performed.
【０００５】[0005]
【課題を解決するための手段】本発明は、上記の目的を
達成するため、ＭＲＩ及びＭＲＳで静磁場均一性を調整
する際、静磁場空間の中に被検体が存在することにより
生じると予測される一次の静磁場不均一成分に対応させ
て仮に与えた一次のシム設定値をあらかじめ定めた２点
に設定した条件下で被検体よりの磁気共鳴信号を収集
し、収集した磁気共鳴信号をフーリエ変換して得られる
周波数スペクトルの帯域より一次の静磁場不均一成分を
計算により求め、求めた一次の静磁場不均一成分を打ち
消す量を一次のシム設定値として静磁場均一性の調整を
行うことを特徴とする。In order to achieve the above object, the present invention is predicted to occur due to the presence of an object in a static magnetic field space when adjusting the static magnetic field homogeneity by MRI and MRS. The magnetic resonance signals from the subject are collected under the condition that the provisional primary shim set values corresponding to the primary static magnetic field inhomogeneity components are set at two predetermined points, and the collected magnetic resonance signals are The static magnetic field inhomogeneity component of the frequency spectrum obtained by the Fourier transform is calculated, and the static magnetic field homogeneity is adjusted with the amount of canceling the calculated primary static magnetic field inhomogeneity component as the primary shim setting value. It is characterized by
【０００６】[0006]
【作用】本発明によるＭＲＩ及びＭＲＳにおける静磁場
均一性の調整方法にあっては、一次の静磁場不均一性は
２点測定すれば計算できることに着目し、経験則より想
定される大きさの一次のシム設定値をあらかじめ定めた
２点に設定して被検体よりのＭＲ信号を収集し、この収
集したＭＲ信号をフーリエ変換して得られる周波数スペ
クトルの帯域より一次の静磁場不均一成分を計算により
求める。こうして求めた一次の静磁場不均一成分を打ち
消すことができるよう一次のシム設定値を調整して被検
体をＭＲ撮影すれば、静磁場均一性がほぼ確保された状
態下でデータ収集を行える。In the method for adjusting the static magnetic field homogeneity in MRI and MRS according to the present invention, attention is paid to the fact that the primary static magnetic field inhomogeneity can be calculated by measuring at two points, and the magnitude assumed by the empirical rule is used. The primary shim set value is set to two predetermined points, MR signals from the subject are collected, and the primary static magnetic field inhomogeneity component is obtained from the band of the frequency spectrum obtained by Fourier transforming the collected MR signals. Calculated. If MR imaging of the subject is performed by adjusting the primary shim setting value so as to cancel the primary static magnetic field inhomogeneity component thus obtained, data acquisition can be performed in a state where the static magnetic field homogeneity is almost secured.
【０００７】[0007]
【実施例】図１は、本発明の静磁場均一性の調整方法が
適用されるＭＲＩ装置の全体構成を示す図である。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the overall construction of an MRI apparatus to which the method for adjusting the static magnetic field uniformity of the present invention is applied.
【０００８】このＭＲＩ装置は、主磁石１による静磁場
空間に配置した被検体Ｐに対し、ＲＦコイル２によりＲ
Ｆパルスを印加すると同時に傾斜磁場コイル３によりエ
ンコード用、リード用、スライス用の各傾斜磁場ＧE ，
ＧR ，ＧS を印加することによって、被検体Ｐに生じた
ＭＲ信号をプローブ４により受信し、受信したＭＲ信号
を受信器５で検波後にコンピュータシステム６へ送出す
る。そして、コンピュータシステム６において収集した
ＭＲ信号を基に断層像を再構成し、モニタ７上にその断
層像を表示する。この際、コンピュータシステム６の制
御下でシーケンサ８によりパルスシーケンスを実施して
送信器９及び傾斜磁場電源１０を駆動し、ＲＦコイル２
からＲＦパルスが発生させ、傾斜磁場コイル３から各傾
斜磁場ＧE ，ＧR ，ＧS が発生させる。In this MRI apparatus, an RF coil 2 is used to make a R
At the same time as the application of the F pulse, the gradient magnetic field coils 3 encode, read, and slice gradient magnetic fields G E ,
By applying G R and G S , the MR signal generated in the subject P is received by the probe 4, and the received MR signal is detected by the receiver 5 and sent to the computer system 6. Then, the tomographic image is reconstructed based on the MR signals collected in the computer system 6, and the tomographic image is displayed on the monitor 7. At this time, under the control of the computer system 6, the sequencer 8 executes a pulse sequence to drive the transmitter 9 and the gradient magnetic field power supply 10, and the RF coil 2
To generate RF pulses, and the gradient magnetic field coils 3 generate respective gradient magnetic fields G E , G R , and G S.
【０００９】このようにＭＲＩ装置によって被検体Ｐを
撮影する前に、予め被検体Ｐに対応させて静磁場均一性
を調整する必要がある。As described above, it is necessary to adjust the static magnetic field homogeneity corresponding to the subject P in advance before the subject P is imaged by the MRI apparatus.
【００１０】そこで、本実施例では、静磁場均一性を調
整するために、傾斜磁場電源１０ののＤＣオフセット電
源を正及び負の一定値に設定して被検体ＰよりのＭＲ信
号をコピュータシステム１で収集し、コンピュータシス
テム１において収集したＭＲ信号をフーリエ変換して得
られる周波数スペクトルの帯域より一次の静磁場不均一
成分を計算により求め、求めた一次の静磁場不均一成分
を打ち消すことができるよう傾斜磁電源１０のＤＣオフ
セット電流の正及び負の一定値を補正し、静磁場均一性
の調整を行うものとしている。Therefore, in this embodiment, in order to adjust the homogeneity of the static magnetic field, the DC offset power supply of the gradient magnetic field power supply 10 is set to a constant positive and negative value, and the MR signal from the subject P is measured by the computer system. It is possible to cancel the first-order static magnetic field inhomogeneity component obtained by calculating the first-order static magnetic field inhomogeneity component from the band of the frequency spectrum obtained by Fourier transforming the MR signal collected by the computer system 1 and collected in the computer system 1. As much as possible, the positive and negative constant values of the DC offset current of the gradient magnetic power source 10 are corrected to adjust the static magnetic field uniformity.
【００１１】例えば、図２のように静磁場空間の中に被
検体Ｐが存在し、Ｘ方向にはｘ1 からＸ2 までの△ｘの
幅を占めているとする。ここで、Ｘ方向の静磁場不均一
性のＸ1 成分がｈｘ［Ｈz ／ｍ］あるとする。これを補
正するためには、−ｈｘ［Ｈz ／ｍ］の磁場をＸの傾斜
磁場コイルで発生させて打ち消せばよい。なお、Ｘの傾
斜磁場コイルに代えてＸのシムコイルとすることもでき
る。要するに、ｈｘ［Ｈz ／ｍ］が測定できれば、これ
を打ち消すようにＸの傾斜磁コイル又はＸのシムコイル
から磁場を発生させればよい。For example, it is assumed that the subject P exists in the static magnetic field space as shown in FIG. 2 and occupies the width of Δx from x 1 to X 2 in the X direction. Here, it is assumed that the X 1 component of the static magnetic field inhomogeneity in the X direction is hx [H z / m]. In order to correct this, a magnetic field of −hx [H z / m] may be generated by the X gradient magnetic field coil and canceled. An X shim coil may be used instead of the X gradient magnetic field coil. In short, if the measurement is hx [H z / m], the magnetic field from the shim of the gradient magnetic coil or X of X may be generated so as to cancel it.
【００１２】まず、図３に示すパルスシーケンスにより
被検体ＰよりのＭＲ信号を収集する。信号収集期間中、
Ｘ方向には＋ｇｘの傾斜磁場がかけられている。ｇｘの
量は予想される関心領域内の不均一性よりも大きく設定
する必要がある。得られたＭＲ信号（ここではスピンエ
コー）をフーリエ変換すると、この周波数スペクトルの
帯域ｆａは、信号収集時の一次の傾斜ｈｘ＋ｇｘと物体
のＸ方向の幅△ｘとの積となり次の(1) 式で表わせる。First, the MR signal from the subject P is acquired by the pulse sequence shown in FIG. During the signal acquisition period,
A gradient magnetic field of + gx is applied in the X direction. The amount of gx should be set larger than the expected non-uniformity within the region of interest. When the obtained MR signal (spin echo in this case) is Fourier-transformed, the band fa of this frequency spectrum becomes a product of the primary slope hx + gx at the time of signal acquisition and the width Δx of the object in the X direction. It can be expressed by a formula.
【００１３】 ｆａ＝（ｇｘ＋ｈｘ）△ｘ (1) 次に、図４に示すパルスシーケンスにより同様に信号収
集してフーリエ変換すると、この周波数スペクトルの帯
域ｆｂは、１ｇｘ１＞１ｈｘ１であるから、次の(2) 式
となる。Fa = (gx + hx) Δx (1) Next, when signals are similarly collected and Fourier transformed by the pulse sequence shown in FIG. 4, the band fb of this frequency spectrum is 1gx1> 1hx1. It becomes formula (2).
【００１４】 ｆｂ＝（ｇｘ−ｈｘ）△ｘ (2) 上記(1),(2) より ｆａ／ｆｂ＝（ｇｘ＋ｈｘ）／（ｇｘ−ｈｘ） (3) であり、故に、 ｈｘ＝［（ｆａ−ｆｂ）／（ｆａ＋ｆｂ）］・ｇｘ の如く、Ｘ方向の一次の静磁場不均一成分ｈｘが計算で
きる。Fb = (gx−hx) Δx (2) From the above (1) and (2), fa / fb = (gx + hx) / (gx−hx) (3), and therefore hx = [(fa The primary static magnetic field inhomogeneity component hx in the X direction can be calculated as −fb) / (fa + fb)] · gx.
【００１５】従って、−ｈｘに相当する傾斜磁場をＸの
傾斜磁場コイルまたはシムコイルにより発生させればＸ
1 の成分のシム調整ができる。Therefore, if the gradient magnetic field corresponding to -hx is generated by the X gradient magnetic field coil or shim coil, X
Shim adjustment for component 1 is possible.
【００１６】同様にＹ方向，Ｚ方向の均一性は、図３，
図４のＧｘをＧｙ，Ｇｚに置き換えて実施することによ
り調整できる。Similarly, the uniformity in the Y and Z directions is shown in FIG.
It can be adjusted by replacing Gx in FIG. 4 with Gy and Gz.
【００１７】以上の操作は、６回のＭＲ信号の収集を行
うだけでよいことから、繰り返し時間ＴＲを例えば２０
０ｍｓとしても、１、２秒の収集時間と僅かな演算時間
内で全ての処理が終了する。Since the above operation only needs to acquire the MR signals 6 times, the repetition time TR is set to, for example, 20.
Even if it is 0 ms, all the processing is completed within a collection time of 1 or 2 seconds and a short calculation time.
【００１８】このようなことから、本実施例によれば、
被検体（患者）毎にシミングのためのプリスキャンを実
施して静磁場の均一性を最適に設定し、この状態下で撮
影することにより、画像Ｓ／Ｎ等の画質向上を図れる。From the above, according to this embodiment,
By performing a pre-scan for shimming for each subject (patient) to optimally set the homogeneity of the static magnetic field, and imaging under this state, the image quality such as the image S / N can be improved.
【００１９】以上、ＭＲＩ装置において静磁場均一性の
調整を行う場合についての実施例を説明したが、本発明
は例えばＭＲＳ装置にてスペクトロスコピーの情報を得
る際に有効である。即ち、スペクトロスコピーの情報を
得る場合、高い静磁場均一性を要求されるが、この要求
を満たすためのシミングを被検体毎に行う場合、上記実
施例のようにＸ，Ｙ，Ｚの各方向での一次の静磁場不均
一成分を測定し、それを打ち消すようにシム設定値を求
めて静磁場均一性を確保すればよいことから、全検査時
間を従来に比較して大幅に短縮できることになる。Although the embodiment for adjusting the static magnetic field homogeneity in the MRI apparatus has been described above, the present invention is effective in obtaining spectroscopy information in the MRS apparatus, for example. That is, when obtaining the information of the spectroscopy, high static magnetic field homogeneity is required, but when shimming for satisfying this requirement is performed for each subject, it is necessary to perform X, Y, Z directions as in the above embodiment. Since the static magnetic field uniformity can be secured by measuring the primary static magnetic field inhomogeneity component in step 1 and finding the shim setting value to cancel it, it is possible to significantly reduce the total inspection time compared to the conventional method. Become.
【００２０】[0020]
【発明の効果】以上説明したように本発明によれば、一
次の静磁場不均一性を２点測定し、この測定値に対応さ
せてシム測定値を求めて一次の静磁場均一性の調整を行
うため、従来に比べて静磁場均一性の調整に要する所要
時間が大幅に短縮され、全検査時間を短縮することが可
能となる。As described above, according to the present invention, the primary static magnetic field inhomogeneity is measured at two points and the shim measurement value is obtained corresponding to the measured values to adjust the primary static magnetic field homogeneity. Therefore, the time required to adjust the static magnetic field homogeneity is significantly shortened as compared with the conventional method, and the total inspection time can be shortened.
【図１】本発明の静磁場均一性の調整方法が適用される
ＭＲＩ装置の全体構成を示す図である。FIG. 1 is a diagram showing an overall configuration of an MRI apparatus to which a method for adjusting static magnetic field uniformity according to the present invention is applied.
【図２】静磁場空間の中に被検体を配置した場合の不均
一性のＸ1 成分について説明するために用いた図であ
る。FIG. 2 is a diagram used for explaining an inhomogeneity X 1 component when a subject is placed in a static magnetic field space.
【図３】傾斜磁場電源のＤＣオフセット電流を正の一定
値に設定するためのパルスシーケンスを示す図である。FIG. 3 is a diagram showing a pulse sequence for setting a DC offset current of the gradient magnetic field power supply to a positive constant value.
【図４】傾斜磁場電源のＤＣオフセット電流を負の一定
値に設定するためのパルスシーケンスを示す図である。FIG. 4 is a diagram showing a pulse sequence for setting the DC offset current of the gradient magnetic field power supply to a negative constant value.
１ 主磁石 ２ ＲＦコイル ３ 傾斜磁場コイル ４ プローブ ５ 受信器 ６ コンピュータシステム ７ モニタ ８ シーケンサ ９ 送信器 １０ 傾斜磁場電源 1 Main Magnet 2 RF Coil 3 Gradient Magnetic Field Coil 4 Probe 5 Receiver 6 Computer System 7 Monitor 8 Sequencer 9 Transmitter 10 Gradient Magnetic Field Power Supply
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.5 識別記号 庁内整理番号 ＦＩ 技術表示箇所 9219−2Ｊ Ｇ０１Ｎ 24/06 Ｇ ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. 5 Identification code Internal reference number FI technical display location 9219-2J G01N 24/06 G
Claims (1)
する際、静磁場空間の中に被検体が存在することにより
生じると予測される一次の静磁場不均一成分に対応させ
て仮に与えた一次のシム設定値をあらかじめ定めた２点
に設定した条件下で被検体よりの磁気共鳴信号を収集
し、収集した磁気共鳴信号をフーリエ変換して得られる
周波数スペクトルの帯域より一次の静磁場不均一成分を
計算により求め、求めた一次の静磁場不均一成分を打ち
消す量を一次のシム設定値として静磁場均一性の調整を
行うことを特徴とするＭＲＩ及びＭＲＳにおける静磁場
均一性の調整方法。1. When adjusting the homogeneity of a static magnetic field by MRI and MRS, it is provisionally given in correspondence with a first-order static magnetic field inhomogeneity component expected to occur due to the presence of an object in a static magnetic field space. Magnetic resonance signals from the subject are collected under the condition where the primary shim set values are set to two predetermined points, and the static magnetic field of the primary magnetic field is not detected from the band of the frequency spectrum obtained by Fourier transforming the collected magnetic resonance signals. A method for adjusting the static magnetic field homogeneity in MRI and MRS, characterized in that the homogeneity component is obtained by calculation, and the static magnetic field homogeneity is adjusted with the amount of canceling the obtained primary static magnetic field inhomogeneity component as the primary shim setting value. .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29261492A JP3367693B2 (en) | 1992-10-30 | 1992-10-30 | Magnetic resonance apparatus and method for adjusting uniformity of static magnetic field in magnetic resonance apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29261492A JP3367693B2 (en) | 1992-10-30 | 1992-10-30 | Magnetic resonance apparatus and method for adjusting uniformity of static magnetic field in magnetic resonance apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH06133945A true JPH06133945A (en) | 1994-05-17 |
| JP3367693B2 JP3367693B2 (en) | 2003-01-14 |
Family
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Family Applications (1)
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| JP29261492A Expired - Fee Related JP3367693B2 (en) | 1992-10-30 | 1992-10-30 | Magnetic resonance apparatus and method for adjusting uniformity of static magnetic field in magnetic resonance apparatus |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100311074B1 (en) * | 1997-06-30 | 2001-12-28 | 윤종용 | Mri apparatus |
| JP2009000538A (en) * | 2000-02-24 | 2009-01-08 | Toshiba America Mri Inc | Method and system for measuring and compensating for eddy currents induced during nmr imaging operations |
| CN109799471A (en) * | 2019-01-11 | 2019-05-24 | 中国科学院苏州生物医学工程技术研究所 | A kind of magnetic resonance spectrum imaging analogy method and system, storage medium, electronic equipment |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101921968B1 (en) | 2016-12-15 | 2018-11-27 | 가천대학교 산학협력단 | Magnetic resonance imaging acquistion method having a wide range of image contrast |
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1992
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100311074B1 (en) * | 1997-06-30 | 2001-12-28 | 윤종용 | Mri apparatus |
| JP2009000538A (en) * | 2000-02-24 | 2009-01-08 | Toshiba America Mri Inc | Method and system for measuring and compensating for eddy currents induced during nmr imaging operations |
| CN109799471A (en) * | 2019-01-11 | 2019-05-24 | 中国科学院苏州生物医学工程技术研究所 | A kind of magnetic resonance spectrum imaging analogy method and system, storage medium, electronic equipment |
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| Publication number | Publication date |
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| JP3367693B2 (en) | 2003-01-14 |
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