JPH0335932B2 - - Google Patents
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- Publication number
- JPH0335932B2 JPH0335932B2 JP61024350A JP2435086A JPH0335932B2 JP H0335932 B2 JPH0335932 B2 JP H0335932B2 JP 61024350 A JP61024350 A JP 61024350A JP 2435086 A JP2435086 A JP 2435086A JP H0335932 B2 JPH0335932 B2 JP H0335932B2
- Authority
- JP
- Japan
- Prior art keywords
- magnetic field
- static magnetic
- signal
- nmr
- 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
- 230000003068 static effect Effects 0.000 claims description 38
- 238000005481 NMR spectroscopy Methods 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 12
- 238000005259 measurement Methods 0.000 claims description 6
- 230000004044 response Effects 0.000 claims description 3
- 238000003325 tomography Methods 0.000 claims description 2
- 238000003384 imaging method Methods 0.000 claims 1
- 238000010586 diagram Methods 0.000 description 3
- 230000010355 oscillation Effects 0.000 description 3
- 239000000498 cooling water Substances 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 230000002542 deteriorative effect Effects 0.000 description 2
- 230000005284 excitation Effects 0.000 description 2
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000002075 inversion recovery Methods 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
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- Magnetic Resonance Imaging Apparatus (AREA)
Description
【発明の詳細な説明】
（産業上の利用分野）
本発明は、被検体中の対象原子核の密度分布等
を核磁気共鳴現象によつて把握する核磁気共鳴断
層撮像装置（以下、NMR−CTという）に関し、
更に詳しくは、スキヤンの各ビユーにおける静磁
場電源の出力の変動量に対応して核磁気共鳴信号
（以下、NMR信号と言う）の位相補正、又は、
周波数のゆらぎ補正をするようにしたNMR−
CTに関する。Detailed Description of the Invention (Industrial Application Field) The present invention relates to a nuclear magnetic resonance tomography apparatus (hereinafter referred to as NMR-CT Regarding)
More specifically, the phase of the nuclear magnetic resonance signal (hereinafter referred to as NMR signal) is corrected in accordance with the amount of variation in the output of the static magnetic field power source in each view of the scan, or
NMR with frequency fluctuation correction
Regarding CT.
（従来の技術）
NMR−CTは、一様な静磁場H0を作る静磁場
コイル及び静磁場H0と同一方向磁場でｘ、ｙ、
ｚの各方向に夫々直線勾配をもつ磁場を作る勾配
磁場コイルから成る磁石部、該磁石部で形成され
る磁場内に設置する被検体に高周波パルス（高周
波電磁波）を印加し、被検体からのNMR信号を
検出する送・受信部、該送・受信部及び前記磁石
部の動作を制御したり、検出データの処理をして
画像表示する制御・画像処理部等を有している。
静磁場コイルは、NMR−CTが常伝導マグネツ
ト方式の場合には、冷却水を用いた温度制御系に
よつて温度制御された状態で、静磁場電源（主磁
場電源）から安定した直流電流の供給を受ける構
成となつている（静磁場電源はコントロール部の
制御により交流を直流に変換して出力する）。(Prior art) NMR-CT uses a static magnetic field coil that creates a uniform static magnetic field H 0 and a magnetic field in the same direction as the static magnetic field H 0 in x, y,
A magnet section consisting of a gradient magnetic field coil that creates a magnetic field with a linear gradient in each direction of z, and a high-frequency pulse (high-frequency electromagnetic wave) is applied to a subject placed within the magnetic field formed by the magnet section. It has a transmitting/receiving section that detects an NMR signal, a control/image processing section that controls the operation of the transmitting/receiving section and the magnet section, processes detected data, and displays an image.
When the NMR-CT is a normal conduction magnet type, the static magnetic field coil receives a stable DC current from the static magnetic field power supply (main magnetic field power supply) while the temperature is controlled by a temperature control system using cooling water. (The static magnetic field power supply converts alternating current to direct current and outputs it under the control of the control unit.)
以上の構成において、静磁場コイルにより所定
の空間（被検体の設置箇所）に所定強度の静磁場
が形成される。一方、制御・画像処理部の制御の
下で、送・受信部は、スピン・エコー法（Spin
Echo法：SE法）等による励起パルスシーケンス
（90゜パルス及び180゜パルスを所定のタイミングで
発生するシーケンス）及びフーリエ変換法による
勾配磁場シーケンスを出力し、そのときのNMR
信号を検出する。又、制御・画像処理部は、上記
シーケンスに従つて収集された多数のNMR信
号、即ち、生データ（raw data）を用いて画像
再構成処理をして断層画像の表示を行う。 In the above configuration, a static magnetic field of a predetermined strength is formed in a predetermined space (place where the subject is installed) by the static magnetic field coil. On the other hand, under the control of the control/image processing section, the transmitting/receiving section uses the spin echo method (Spin
Outputs an excitation pulse sequence (a sequence in which 90° pulses and 180° pulses are generated at a predetermined timing) using the Echo method (SE method), etc. and a gradient magnetic field sequence using the Fourier transform method, and then outputs the NMR
Detect the signal. Further, the control/image processing section performs image reconstruction processing using a large number of NMR signals, that is, raw data, collected according to the above sequence, and displays a tomographic image.
ところで、実際のNMR−CTの静磁場コイル
による静磁場には、冷却水・機器の設置環境の温
度変化等によつて生じる比較的長い周期のドリフ
ト（マグネツト寸法の変化に起因するドリフト）
や静磁場電源のコントロール部の周波数特性、電
源ノイズ、外来ノイズ等によつて生じる比較的短
い周期のドリフトがあることが知られている。こ
れらが存在すると、画像が歪んだり、画像にゴー
ストがはいり画質の低下を招くことになる。 By the way, the static magnetic field generated by the static magnetic field coil of an actual NMR-CT has relatively long period drifts (drifts caused by changes in magnet dimensions) caused by temperature changes in the cooling water and equipment installation environment, etc.
It is known that there are relatively short period drifts caused by the frequency characteristics of the control section of the static magnetic field power supply, power supply noise, external noise, etc. If these exist, the image will be distorted, ghosts will appear in the image, and the image quality will deteriorate.
そこで、従来のNMR−CTは、スキヤン前や
スキヤン中に静磁場強度を測定し、フイードバツ
クをかけて静磁場強度を補正する、いわゆる磁場
ロツク手段を備えている。 Therefore, conventional NMR-CT is equipped with a so-called magnetic field locking means that measures the static magnetic field strength before or during scanning and corrects the static magnetic field strength by applying feedback.
（発明が解決しようとする問題点）
しかし、従来のNMR−CTにあつては、磁場
ロツク手段によつて補正されるのは、比較的長い
周期のドリフトのみであるため、比較的短い周期
のドリフトによる画質の低下を防ぐことができな
いという問題があつた。(Problem to be solved by the invention) However, in conventional NMR-CT, only relatively long period drifts are corrected by the magnetic field locking means, so relatively short period drifts are corrected by the magnetic field locking means. There was a problem in that it was not possible to prevent image quality from deteriorating due to drift.
本発明は、かかる点に鑑みてなされたものであ
り、その目的は、静磁場の比較的短い周期のドリ
フトによる画質の低下を解決したNMR−CTを
提供することにある。 The present invention has been made in view of these points, and its purpose is to provide an NMR-CT that solves the problem of image quality deterioration due to relatively short cycle drift of a static magnetic field.
（問題点を解決するための手段）
上記目的を達成する本発明のNMR−CTは、
スキヤンの各ビユーにおける静磁場電源の出力の
変動量に対応してNMR信号の位相補正、又は、
周波数のゆらぎ補正をするようになつている。(Means for solving the problems) The NMR-CT of the present invention that achieves the above objectives is
Correct the phase of the NMR signal in response to the amount of variation in the output of the static magnetic field power supply in each view of the scan, or
It is designed to correct frequency fluctuations.
（実施例）
以下、図面を参照し本発明について詳細に説明
する。(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.
第１図は、本発明の一実施例を示す構成図であ
る。マグネツトアセンブリ１は、内部に被検体を
挿入するための空間部分（孔）を有し、この空間
部分を取巻くようにして、被検体に一定の静磁場
を印加する静磁場コイルと、勾配磁場を発生する
ための勾配磁場コイル（勾配磁場コイルは、ｘ，
ｙ，ｚの各軸のコイルを備えている）と、被検体
内の原子核のスピンを励起するための高周波パル
スを与えるRF送信コイルと、被検体からの
NMR信号を検出する受信コイル等が配置されて
いる。静磁場コイル、勾配磁場コイル、RF送信
コイル、及び受信コイルは、静磁場電源（主磁場
電源）２、勾配磁場駆動回路３、RF電力増幅器
４及び前置増幅器５夫々に接続されている。静磁
場電源２の出力電圧は、電圧測定回路６によつて
測定され計算機（データ処理部）７に入力され
る。電圧測定回路６は、シーケンス記憶回路８の
制御の下にあり、スキヤンの各ビユーに同期した
測定動作を行う。シーケンス記憶回路８は、計算
機７からの指令に従つて任意のビユーで、ゲート
変調回路９を操作（所定のタイミングによつて
RF発振回路１０の高周波出力信号を変調）し、
SR法に基づく高周波パルス信号をRF電力増幅器
４からRF送信コイルに印加する。又、シーケン
ス記憶回路８は、フーリエ変換法に基づくシーケ
ンス信号によつて勾配磁場駆動回路３、ゲート変
調回路９及びＡ／Ｄ変換器１１を操作する。位相
検波器１２は、RF発振回路１０の出力を参照信
号とし、前置増幅器５の出力信号（受信コイルで
検出されたNMR信号）を位相検波してＡ／Ｄ変
換器１１に与える。Ａ／Ｄ変換器１１は、位相検
波器１２を介して得られるNMR信号をアナロ
グ・デイジタル変換して計算機７に入力する。計
算機７は、操作コンソール１３との間で情報の授
受や種々のスキヤンシーケンスを実現するため
に、シーケンス記憶回路１０の動作の切替えやメ
モリの書替えをしたり、Ａ／Ｄ変換器１１及び電
圧測定回路６からの各データを用いてNMR信号
の位相補正演算及び周波数のゆらぎ補正をすると
共に、画像再構成演算をするようになつている。 FIG. 1 is a configuration diagram showing an embodiment of the present invention. The magnet assembly 1 has a space (hole) into which a subject is inserted, and a static magnetic field coil that applies a constant static magnetic field to the subject and a gradient magnetic field surrounding this space. A gradient magnetic field coil is used to generate x,
), an RF transmitting coil that provides a high-frequency pulse to excite the spin of the atomic nucleus within the subject, and a
Receiving coils and the like for detecting NMR signals are arranged. The static magnetic field coil, gradient magnetic field coil, RF transmitting coil, and receiving coil are connected to a static magnetic field power source (main magnetic field power source) 2, a gradient magnetic field drive circuit 3, an RF power amplifier 4, and a preamplifier 5, respectively. The output voltage of the static magnetic field power supply 2 is measured by a voltage measuring circuit 6 and input to a computer (data processing section) 7. The voltage measurement circuit 6 is under the control of the sequence storage circuit 8, and performs measurement operations in synchronization with each view of the scan. The sequence storage circuit 8 operates the gate modulation circuit 9 (at a predetermined timing) in an arbitrary view according to instructions from the computer 7.
modulate the high frequency output signal of the RF oscillation circuit 10),
A high frequency pulse signal based on the SR method is applied from the RF power amplifier 4 to the RF transmitting coil. Further, the sequence storage circuit 8 operates the gradient magnetic field drive circuit 3, the gate modulation circuit 9, and the A/D converter 11 using a sequence signal based on the Fourier transform method. The phase detector 12 uses the output of the RF oscillation circuit 10 as a reference signal, performs phase detection on the output signal of the preamplifier 5 (NMR signal detected by the receiving coil), and supplies the detected signal to the A/D converter 11 . The A/D converter 11 converts the NMR signal obtained through the phase detector 12 into an analog-to-digital signal and inputs the converted signal to the computer 7 . The computer 7 switches the operation of the sequence storage circuit 10, rewrites the memory, and controls the A/D converter 11 and voltage measurement in order to exchange information with the operation console 13 and perform various scan sequences. Each data from the circuit 6 is used to perform phase correction calculations and frequency fluctuation correction of the NMR signal, as well as image reconstruction calculations.
次に、上記構成の動作について説明する。 Next, the operation of the above configuration will be explained.
先ず、計算機７における補正演算の原理につい
て説明する。今、シーケンス動作中、静磁場H0
に比較的短い周期の変動成分△H0（ｔ）があつた
場合、90゜パルスにより励起されたスピンの位相
歪み△θ及び周波数のゆらぎ△ω（ｔ）は(1)式及
び(2)式となる。 First, the principle of correction calculation in the computer 7 will be explained. Now, during sequence operation, static magnetic field H 0
When there is a fluctuation component △H 0 (t) with a relatively short period in The formula becomes
△θ＝γτ
｛−∫−τ
△
−2τdt＋∫０
△
−τH0（ｔ）dt｝ (1)
△ω（ｔ）＝γ△H0（ｔ） (2)
但し、γ…磁気回転比
τ…エコー時間TEの1/2（第２図参照）
一方、収集データS1（ｔ）と補正データS2（ｔ）
との関係は(3)式となる。△θ＝γτ {−∫−τ △ −2τdt＋∫0 △ −τH 0 (t)dt} (1) △ω(t)=γ△H 0 (t) (2) However, γ...magnetic rotation ratio τ ...1/2 of the echo time TE (see Figure 2) On the other hand, collected data S1 (t) and correction data S2 (t)
The relationship with is expressed as equation (3).
S2（ｔ）＝S1（ｔ）・exp
〔−ｊ｛∫ｔ
△
０ω（ｔ）dt＋△θ｝〕 (3)
従つて、静磁場電源２の出力電圧信号の変動
量、即ち、静磁場の変動成分△H0（ｔ）を求めて
静磁場電源の短期変動の影響を除くことができ
る。S2(t)=S1(t)・exp [−j{∫t△0ω(t)dt+△θ}] (3) Therefore, the amount of variation in the output voltage signal of the static magnetic field power supply 2, that is, the variation of the static magnetic field The influence of short-term fluctuations in the static magnetic field power source can be removed by finding the fluctuation component ΔH 0 (t).
第２図は、SE法に基づくパルス系列でフーリ
エ変換法に従つてデータ収集をするときの動作波
形である。静磁場電源２による均一な静磁場H0
の下で、シーケンス記憶回路８は、勾配磁場駆動
回路３及びゲート変調回路９を操作して、各勾配
磁場及び高周波パルスを発生すると共に、Ａ／Ｄ
変換器１１を操作して位相検波器１２で検波され
たNMR信号をデイジタル信号に変換して計算機
７に入力する。即ち、スライス勾配Gzをかけな
がら（第２図ｂ）90゜パルスを印加する（第２図
ａ）。これにより、被検体の特定のスライス面内
のスピンだけが選択的に励起される。次に、スラ
イス時に生じたスピンの位相ずれを回復するため
のリフエーズ勾配Gz（第２図ｂ）、後でエコー信
号を発生させるためのデイフエーズ勾配Gx（第２
図ｄ）及びワープ勾配Gy（第２図ｃ）を印加後、
全ての勾配を切つて180゜パルスを印加する。これ
により、スピンが反転し、その後の読出し勾配
Gxの印加により（第２図ｄ）スピン・エコー信
号が得られる（第２図ｅ）。このスピン・エコー
信号は、被検体のスピンからの信号強度（スピン
密度と緩和現象とにより決定される）の分布を２
次元フーリエ変換したものの１ラインに相当す
る。ラインの選択はｙ勾配印加量、即ち、ｙ勾配
磁場Gyの大きさと、その印加時間Twとの積によ
つて行われる。以後、勾配Gyを変えて、上記シ
ーケンスを繰返すことにより画像再構成に必要な
データが計算機７に収集される。 FIG. 2 shows operating waveforms when data is collected according to the Fourier transform method using a pulse sequence based on the SE method. Uniform static magnetic field H 0 by static magnetic field power supply 2
Under this, the sequence storage circuit 8 operates the gradient magnetic field drive circuit 3 and the gate modulation circuit 9 to generate each gradient magnetic field and high frequency pulse, and also operates the A/D
The converter 11 is operated to convert the NMR signal detected by the phase detector 12 into a digital signal, which is input to the computer 7. That is, a 90° pulse is applied (FIG. 2a) while applying a slice gradient G z (FIG. 2b). As a result, only spins within a specific slice plane of the subject are selectively excited. Next, a rephase gradient Gz (Fig. 2b) is used to recover the spin phase shift that occurred during slicing, and a dephase gradient Gx (Fig. 2b) is used to generate an echo signal later.
After applying Figure d) and warp gradient G y (Figure 2c),
Cut all slopes and apply a 180° pulse. This causes the spin to flip and the subsequent readout slope to
By applying G x (Fig. 2d), a spin echo signal is obtained (Fig. 2e). This spin echo signal divides the distribution of signal intensity from the spins of the subject (determined by spin density and relaxation phenomena) into 2
This corresponds to one line of the dimensional Fourier transform. The selection of the line is performed based on the amount of y-gradient application, that is, the product of the magnitude of the y-gradient magnetic field Gy and its application time Tw . Thereafter, data necessary for image reconstruction is collected by the computer 7 by changing the gradient G y and repeating the above sequence.
又、上記の動作中、計算機７には電圧測定回路
６の出力信号、即ち、スキヤンの各ビユー毎の静
磁場信号が入力される。計算機７は該入力信号か
ら静磁場の変動成分△H0（ｔ）を求め、(1)式及び
(2)式に基づきスピンの位相歪み△θ及び周波数の
ゆらぎ△ω（ｔ）を算出するると共に、(3)式に基
づき収集データの補正演算を行う。そして、補正
演算されたデータを用いて再構成処理を行う。こ
れにより、静磁場電源２の短期変動の影響が除か
れる。 Further, during the above operation, the output signal of the voltage measuring circuit 6, that is, the static magnetic field signal for each view of the scan is inputted to the computer 7. The computer 7 calculates the fluctuation component ΔH 0 (t) of the static magnetic field from the input signal, and calculates the fluctuation component △H 0 (t) of the static magnetic field and uses equation (1) and
The spin phase distortion Δθ and the frequency fluctuation Δω(t) are calculated based on equation (2), and the collected data is corrected based on equation (3). Then, reconstruction processing is performed using the corrected data. This eliminates the influence of short-term fluctuations in the static magnetic field power source 2.
尚、本発明は、上記実施例に限定するものでは
なく、静磁場電源の出力の測定を電流信号として
取出すようにしてもよい。又、励起パルスはSE
法でなく反転回復法（Inversion Recovery法：
IR法）であつてもよい。更に、周波数のゆらぎ
△ω（ｔ）に関しては、読出し勾配磁場の大きさ
の関係でその影響が無視できる場合には、(2)式に
よる補正、即ち、△ω（ｔ）に関する補正を省略
してもよい。 Note that the present invention is not limited to the above-mentioned embodiment, and the measurement of the output of the static magnetic field power source may be taken out as a current signal. Also, the excitation pulse is SE
Inversion Recovery method:
IR method). Furthermore, regarding the frequency fluctuation △ω(t), if its influence can be ignored due to the magnitude of the readout gradient magnetic field, the correction using equation (2), that is, the correction regarding △ω(t), can be omitted. It's okay.
（発明の効果）
以上、説明の通り、本発明のNMR−CTによ
れば、スキヤンの各ビユーにおける静磁場電源の
出力の変動量に対応してNMR信号の位相補正、
又は、周波数のゆらぎ補正をするようにしたた
め、静磁場の比較的短い周期のドリフトによる画
質の低下を防ぐことができる。(Effects of the Invention) As explained above, according to the NMR-CT of the present invention, the phase correction of the NMR signal is performed in response to the amount of variation in the output of the static magnetic field power supply in each view of the scan.
Alternatively, since the frequency fluctuation is corrected, it is possible to prevent image quality from deteriorating due to relatively short cycle drift of the static magnetic field.
第１図は、本発明の一実施例を示す構成図、第
２図は、本発明の一実施例における動作の説明図
ある。
１……マグネツトアセンブリ、２……静磁場電
源、３……勾配磁場駆動回路、４……RF電力増
幅器、５……前置増幅器、６……電圧測定回路、
７……計算機、８……シーケンス記憶回路、９…
…ゲート変調回路、１０……RF発振回路、１１
……Ａ／Ｄ変換器、１２……位相検波回路、１３
……操作コンソール。
FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation in one embodiment of the present invention. 1... Magnet assembly, 2... Static magnetic field power supply, 3... Gradient magnetic field drive circuit, 4... RF power amplifier, 5... Preamplifier, 6... Voltage measurement circuit,
7...Calculator, 8...Sequence memory circuit, 9...
...Gate modulation circuit, 10...RF oscillation circuit, 11
... A/D converter, 12 ... Phase detection circuit, 13
...Operation console.
Claims (1)
法に基づくシーケンスに従つて勾配磁場及び高周
波電磁波を印加し、核磁気共鳴現象に基づく被検
体のスキヤンデータを収集して画像を再構成する
核磁気共鳴断層撮像装置において、 前記静磁場を作成する静磁場コイルに電力を供
給する電源の出力電圧、又は、出力電流をスキヤ
ンの各ビユーに同期して測定する手段と、該測定
信号の変動量に対応して核磁気共鳴信号の位相補
正、又は、周波数のゆらぎ補正をする手段とを備
えることを特徴とする核磁気共鳴断層撮像装置。[Claims] 1. A gradient magnetic field and high-frequency electromagnetic waves are applied to a subject placed in a static magnetic field according to a sequence based on the Fourier transform method, and scan data of the subject based on the nuclear magnetic resonance phenomenon is collected. In a nuclear magnetic resonance tomography apparatus that reconstructs an image, means for measuring an output voltage or an output current of a power source that supplies power to a static magnetic field coil that creates the static magnetic field in synchronization with each view of the scan; 1. A nuclear magnetic resonance tomographic imaging apparatus comprising means for correcting the phase or frequency fluctuation of a nuclear magnetic resonance signal in response to the amount of variation in the measurement signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61024350A JPS62181034A (en) | 1986-02-06 | 1986-02-06 | Nuclear magnetic resonance tomographic image pickup apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61024350A JPS62181034A (en) | 1986-02-06 | 1986-02-06 | Nuclear magnetic resonance tomographic image pickup apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS62181034A JPS62181034A (en) | 1987-08-08 |
| JPH0335932B2 true JPH0335932B2 (en) | 1991-05-29 |
Family
ID=12135746
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP61024350A Granted JPS62181034A (en) | 1986-02-06 | 1986-02-06 | Nuclear magnetic resonance tomographic image pickup apparatus |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS62181034A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01299543A (en) * | 1988-05-27 | 1989-12-04 | Hitachi Ltd | Inspecting method and device using nuclear magnetic resonance |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57211538A (en) * | 1981-06-24 | 1982-12-25 | Hitachi Ltd | Electromagnet |
| JPS60259940A (en) * | 1984-06-06 | 1985-12-23 | Hitachi Ltd | Magnetic field generator for nmr imaging apparatus |
-
1986
- 1986-02-06 JP JP61024350A patent/JPS62181034A/en active Granted
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57211538A (en) * | 1981-06-24 | 1982-12-25 | Hitachi Ltd | Electromagnet |
| JPS60259940A (en) * | 1984-06-06 | 1985-12-23 | Hitachi Ltd | Magnetic field generator for nmr imaging apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62181034A (en) | 1987-08-08 |
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