JPH0585174B2 - - Google Patents
Info
- Publication number
- JPH0585174B2 JPH0585174B2 JP59206225A JP20622584A JPH0585174B2 JP H0585174 B2 JPH0585174 B2 JP H0585174B2 JP 59206225 A JP59206225 A JP 59206225A JP 20622584 A JP20622584 A JP 20622584A JP H0585174 B2 JPH0585174 B2 JP H0585174B2
- Authority
- JP
- Japan
- Prior art keywords
- magnetic field
- gradient
- static magnetic
- gradient magnetic
- inspection
- 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 - Fee Related
Links
- 230000003068 static effect Effects 0.000 claims description 17
- 238000007689 inspection Methods 0.000 claims description 16
- 238000005481 NMR spectroscopy Methods 0.000 claims description 13
- 238000009826 distribution Methods 0.000 claims description 13
- 238000001514 detection method Methods 0.000 claims 2
- 238000000034 method Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000003384 imaging method Methods 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 2
- 210000001015 abdomen Anatomy 0.000 description 1
- 238000013170 computed tomography imaging Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000009828 non-uniform distribution Methods 0.000 description 1
- 238000012285 ultrasound imaging Methods 0.000 description 1
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
- G01R33/24—Arrangements or instruments for measuring magnetic variables involving magnetic resonance for measuring direction or magnitude of magnetic fields or magnetic flux
-
- 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
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56563—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Radiology & Medical Imaging (AREA)
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- High Energy & Nuclear Physics (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
Description
〔発明の利用分野〕
本発明は核磁気共鳴（以下、「NMR」という）
を用いた検査装置に関し、特にNMRイメージン
グにおいて、画質劣化の原因となる静磁場の不均
一および傾斜磁場の非直線性の影響を完全に、独
立に補正可能なNMRを用いた検査装置に関す
る。
〔発明の背景〕
従来、人体の頭部、腹部などの内部構造を非破
壊的に検査する装置として、Ｘ線CTや超音波撮
像装置が広く利用されて来ている。近年、核磁気
共鳴現象を用いて同様の検査を行う試みが成功
し、Ｘ線CTや超音波撮像装置では得られない情
報を取得できることが明らかになつて来た。核磁
気共鳴現象を用いた検査装置においては、検査物
体からの信号を物体各部に対応させて分離・識別
する必要がある。その１つに、検査物体に傾斜磁
場を印加し、物体各部の置かれた静磁場を異なら
せ、これにより各部の共鳴周波数あるいはフエー
ズ・エンコード量を異ならせることで位置の情報
を得る方法がある。
その基本原理については、KumarらがJ.Magn.
Reson.（18，69（1975）に、あるいはEdelsteinら
がPhys.Med.Biol.（25，751（1980））に報告して
いるのでここでは省略する。
このようなイメージングにおいては、静磁場の
不均一性および傾斜磁場の非直線性は画質を劣化
させる原因となつている。従来まで、静磁場の不
均一性および傾斜磁場の非直線性の影響について
は、これらの分布が知られているならば補正可能
であることが報告されている（Sekihara et al.
Phys.Med.Biol.29，15（1984）参照のこと）。こ
れらの分布のうち静磁場の不均一分布を測定する
方法については、すでにMaudsleyらがJ.Phys.
E：Sci.Instrum.（17，216（1984））に報告してい
るように、絵素単位の分布までも求めることが可
能である。しかし、傾斜磁場の非直線性を求める
方法については、これまで知られていなかつた。
傾斜磁場を発生するコイルは、通常、静磁場発生
用磁石のボア内に設置されるため、その直線性を
現状以上に高めるのは難かしく、測定対象によつ
ては、その影響を無視できなかつた。そのため、
静磁場の補正だけでは十分な補正が行なえなかつ
た。
〔発明の目的〕
本発明はこのような欠点を鑑がみてなされたも
ので、その目的は静磁場不均一と傾斜磁場の非直
線性とを分離して検出し、それらのうちの少なく
とも一方の影響を補正可能にした検査装置を提供
することを目的とする。
〔発明の概要〕
本発明の要点は、フーリエイメージング法を用
いた検査装置において、視野内における静磁場の
不均一分布および傾斜磁場の分布を求めるのに、
強度の異なる２種類の傾斜磁場（分布は同じとす
る）を用いて両者を分離して検出し、そのデータ
をもとに得られた画像を補正するようにした点に
ある。
これについて、以下、若干補足的説明を行な
う。説明を簡単にするために、２次元で後述する
変形スピンワープ法を例にとつて説明する。
ρ（ｘ，ｙ）を対象のスピン密度分布、Ｅ（ｘ，
ｙ）を静磁場の分布の基準量からのずれ、Gx，y
をそれぞれｘ方向、ｙ方向の傾斜磁場の大きさと
する。ここで、ｘ，ｙ方向の非直線的な傾斜磁場
をGx（ｘ＋εx（ｘ，ｙ）），Gy（ｙ＋εy（ｘ，ｙ））
と
表わす。このように表すとGx，Gyはコイルに流
れる電流に比例し、εx（ｘ，ｙ），εy（ｘ，ｙ）は
コイルの形状により決まる量となる。ここで、εx
（ｘ，ｙ），εy（ｘ，ｙ）はそれらの直線からずれ
た成分を表わす。この時、計測された２次元信号
Ｓ（Gx，ty）は
Ｓ（Gx，ty）＝∬ρ（ｘ，ｙ）exp〔−jγ｛tx（ｘ＋
εx（ｘ，ｙ））Gx
＋（Ｅ（ｘ，ｙ）＋Gyεy（ｘ，ｙ）＋Gyｙ）ty｝〕
dxdy (1)
で表わされる。γは核磁気回転比である。ここ
で、積分変数を
[Field of Application of the Invention] The present invention relates to nuclear magnetic resonance (hereinafter referred to as "NMR")
The present invention relates to an inspection apparatus using NMR, and in particular to an inspection apparatus using NMR that can completely and independently correct the effects of static magnetic field inhomogeneity and gradient magnetic field nonlinearity, which cause image quality deterioration in NMR imaging. [Background of the Invention] Conventionally, X-ray CT and ultrasonic imaging devices have been widely used as devices for nondestructively inspecting the internal structures of the human head, abdomen, and the like. In recent years, attempts to conduct similar tests using nuclear magnetic resonance phenomena have been successful, and it has become clear that information that cannot be obtained with X-ray CT or ultrasound imaging devices can be obtained. In an inspection device that uses nuclear magnetic resonance phenomena, it is necessary to separate and identify signals from an inspection object in correspondence with each part of the object. One method is to obtain position information by applying a gradient magnetic field to the object to be inspected, varying the static magnetic field placed on each part of the object, and thereby varying the resonant frequency or phase encoding amount of each part. . The basic principle is explained by Kumar et al. in J. Magn.
Reson. ( 18 , 69 (1975)), or Edelstein et al. in Phys.Med.Biol. ( 25 , 751 (1980)), so we omit it here. Inhomogeneity and nonlinearity of gradient magnetic fields are causes of deterioration of image quality. Until now, the effects of inhomogeneity of static magnetic field and nonlinearity of gradient magnetic field have been known as distributions. It has been reported that this can be corrected (Sekihara et al.
Phys.Med.Biol. 29 , 15 (1984)). A method for measuring the inhomogeneous distribution of static magnetic fields among these distributions has already been described by Maudsley et al. in J.Phys.
As reported in E:Sci.Instrum. ( 17 , 216 (1984)), it is possible to obtain even the distribution of picture elements. However, until now, there was no known method for determining the nonlinearity of gradient magnetic fields.
The coil that generates the gradient magnetic field is usually installed inside the bore of the magnet for generating the static magnetic field, so it is difficult to improve its linearity beyond the current level, and depending on the object to be measured, the effect of this cannot be ignored. Ta. Therefore,
It was not possible to make sufficient corrections only by correcting the static magnetic field. [Object of the Invention] The present invention was made in view of these drawbacks, and its purpose is to separate and detect static magnetic field inhomogeneity and gradient magnetic field nonlinearity, and to detect at least one of them. An object of the present invention is to provide an inspection device that can correct the influence. [Summary of the Invention] The main point of the present invention is that in an inspection apparatus using the Fourier imaging method, in order to obtain the non-uniform distribution of static magnetic field and the distribution of gradient magnetic field within the field of view,
The key point is that two types of gradient magnetic fields with different strengths (with the same distribution) are used to detect both separately, and the obtained image is corrected based on the data. Regarding this, some supplementary explanation will be given below. To simplify the explanation, a two-dimensional modified spin warp method, which will be described later, will be described as an example. ρ(x, y) is the target spin density distribution, E(x,
y) is the deviation of the static magnetic field distribution from the reference amount, G x , y
Let be the magnitude of the gradient magnetic field in the x direction and the y direction, respectively. Here, the nonlinear gradient magnetic fields in the x and y directions are G x (x+ε x (x, y)), G y (y+ε y (x, y))
It is expressed as Expressed in this way, G x and G y are proportional to the current flowing through the coil, and ε x (x, y) and ε y (x, y) are quantities determined by the shape of the coil. Here, ε x
(x, y) and ε y (x, y) represent components that deviate from those straight lines. At this time, the measured two-dimensional signal S (G x , t y ) is S (G x , t y )=∬ρ(x, y)exp[−jγ{t x (x+
ε x (x, y)) G x + (E (x, y) + G y ε y (x, y) + G y y) t y }]
It is expressed as d x d y (1). γ is the nuclear gyromagnetic ratio. Here, the integral variable is
【表】
〓(2)
1
y′＝y＋εｙ(x,y)＋[Table] 〓(2)
1
y′=y+ε y (x,y)+
Claims (1)
を付ける傾斜磁場発生手段、高周波磁場発生手
段、検査対象からの核磁気共鳴信号を検出する信
号検出手段、該信号検出手段による検出信号の演
算を行なう計算機、及び該計算機による演算結果
の出力手段を有し、前記検査対象のフーリエ空間
における直交座標点を計測する核磁気共鳴を用い
た検査装置において、前記核磁気共鳴信号の検出
時に印加する傾斜磁場の強度を複数通りに変化さ
せて得た複数の再生画像のデータを格納する記憶
装置が設けられ、該記憶装置に記憶された前記複
数の再生画像のデータを読みだして演算により、
前記静磁場および／または傾斜磁場の強度分布を
求めることを特徴とする核磁気共鳴を用いた検査
装置。 ２ 前記静磁場および／または傾斜磁場の強度分
布が前記記憶装置に記憶され、前記記憶装置から
読みだされた前記静磁場および／または傾斜磁場
の強度分布のデータを用いて前記静磁場および傾
斜磁場のもとで計測された再生画像のデータを補
正することを特徴とする特許請求の範囲第１項に
記載の核磁気共鳴を用いた検査装置。 ３ 前記静磁場および／または傾斜磁場の強度分
布を求めるために用いる検査対象は、所定のスピ
ン密度を有する複数の互いに分離した部分をもつ
再生画像を与えることを特徴とする特許請求の範
囲第１項に記載の核磁気共鳴を用いた検査装置。 ４ 前記静磁場および／または傾斜磁場の強度分
布を求めるために用いる検査対象の再生画像は、
閾値処理され背景雑音が除去されていることを特
徴とする特許請求の範囲第１項に記載の核磁気共
鳴を用いた検査装置。[Claims] 1. Means for generating a static magnetic field, gradient magnetic field generating means for creating a magnetic field gradient in the static magnetic field, high frequency magnetic field generating means, signal detecting means for detecting a nuclear magnetic resonance signal from an object to be examined, and detecting the signal. In an inspection apparatus using nuclear magnetic resonance that measures orthogonal coordinate points in Fourier space of the inspection object, the inspection apparatus includes a computer for computing a detection signal by the means, and a means for outputting a calculation result by the computer, and measures a rectangular coordinate point in Fourier space of the inspection object. A storage device is provided for storing data of a plurality of reproduced images obtained by changing the strength of a gradient magnetic field applied at the time of signal detection in a plurality of ways, and the data of the plurality of reproduced images stored in the storage device is read. Then, by calculation,
An inspection device using nuclear magnetic resonance, characterized in that the intensity distribution of the static magnetic field and/or the gradient magnetic field is determined. 2 The strength distribution of the static magnetic field and/or the gradient magnetic field is stored in the storage device, and the data of the strength distribution of the static magnetic field and/or the gradient magnetic field read from the storage device is used to store the static magnetic field and the gradient magnetic field. An inspection apparatus using nuclear magnetic resonance according to claim 1, wherein data of a reproduced image measured under the following conditions is corrected. 3. Claim 1, wherein the inspection object used to determine the intensity distribution of the static magnetic field and/or the gradient magnetic field provides a reproduced image having a plurality of mutually separated parts having a predetermined spin density. An inspection device using nuclear magnetic resonance as described in Section 1. 4 The reproduced image of the inspection object used to determine the intensity distribution of the static magnetic field and/or gradient magnetic field is:
An inspection apparatus using nuclear magnetic resonance according to claim 1, characterized in that background noise is removed by threshold processing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59206225A JPS6184550A (en) | 1984-10-03 | 1984-10-03 | Inspecting device using nuclear magnetic resonance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59206225A JPS6184550A (en) | 1984-10-03 | 1984-10-03 | Inspecting device using nuclear magnetic resonance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6184550A JPS6184550A (en) | 1986-04-30 |
| JPH0585174B2 true JPH0585174B2 (en) | 1993-12-06 |
Family
ID=16519834
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP59206225A Granted JPS6184550A (en) | 1984-10-03 | 1984-10-03 | Inspecting device using nuclear magnetic resonance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6184550A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3581955A1 (en) * | 2018-06-12 | 2019-12-18 | Koninklijke Philips N.V. | Determination of higher order terms of the three-dimensional impulse response function of the magnetic field gradient system of a magnetic resonance imaging system |
-
1984
- 1984-10-03 JP JP59206225A patent/JPS6184550A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6184550A (en) | 1986-04-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| LAPS | Cancellation because of no payment of annual fees |