JPH01280447A - Nuclear spin resonance fault photographing device - Google Patents

Abstract

PURPOSE:To rationally and efficiently correct a magnetic field by making the mass of a magnetic substance to correct a static magnetic field into a specific range and suppressing components except for necessary magnetic field components to be low. CONSTITUTION:A cylinder 7 for fixing a magnetic substance small piece is inserted between a gradient coil 2 and a magnet 1, and it is supported from the magnet 1 along with the gradient coil 2 by a supporter 9. To a non-magnetic cylinder 7, a base seat 5 for fixing a magnetic substance is fitted in a fittable and removable condition, and to the base seat, a magnetic substance small piece 3 correcting a magnetic field is screwed. The magnetic substance small piece 3 is the magnetic substance in the range of an element mass 0.01-30g, the generation of the other term is suppressed to be low, and the rational and economical magnetic field correction is attained. The magnetic substance small piece 3 is screwed to the base seat 5, the base seat 5 is fitted to the cylinder 7 for fixing the magnetic substance small piece in a circumferential direction at an approximately equal interval, and at the time of executing the magnetic field correction, the base seat 5 is removed from the cylinder 7 for fixing the magnetic substance small piece, it is pulled out to a magnet bore, the magnetic substance is fitted, it is sufficient, and at the time of inserting the base seat 5 again, the base seats at both sides are made into guides, and the magnetic field can be efficiently corrected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a nuclear spin resonance tomography apparatus that generates a uniform static magnetic field in a predetermined space, and particularly to rationalization of the static magnetic field generation device and efficiency of magnetic field correction work. The present invention relates to a nuclear spin resonance tomography apparatus suitable for.

[Conventional technology]

Conventionally, regarding magnetic field correction by arranging magnetic materials, Magnetic Resonance in Medicine 1° (1984)
Pages 44 to 65 (Magn, Re5on.

Med, 1 (1984) p. 44-65) (Ref. 1) and Rev. of Scientific Instruments 56(1) (1985) pp. 131-135 (Rev.
(1985) p131-135) (Reference 2). That is, since the magnetic field within the magnet bore is a spherical harmonic function when the area is taken as a sphere, it can be expanded by a Legendre function and an associated Legendre function. The expanded term by the Legendre function is called Z ana1 term, and the expanded term by Legendre associated function is called T essera1 term. Magnetic field correction using a magnetic material means removing the constant term (Zona1 term and Te5sera) by appropriately arranging the magnetic material.
1 term is generated to an arbitrary size, and the expansion coefficient of the magnetic field in the measurement area is set to C1, that is, only a constant term.Reference 1 describes how to generate the Zona1 term and Te5sera1 term using a magnetic material. ing. However, no mention is made of the specific arrangement and support of the magnetic body in consideration of the rationality of the device, the efficiency of magnetic field correction, etc. In addition, Reference 2 describes practical correction effects, focusing on an example of magnetic field correction using an iron rod, but like Reference 1, it does not mention the rationality of the device or the effect of magnetic field correction. It has not been.

The arrangement of the iron pieces in the circumferential direction for generating the T essera1 term is determined by the following method.

1. Magnetic field created by a magnetized piece of iron As shown in Figure 8, the expression for the magnetic field created by a piece of iron placed at position r in a -like magnetic field is as follows.

Xr”Pn, m(cosθ)cosm(φ−ψ)]
-(I=1)2, by arranging iron pieces that do not generate a specific m term in pairs in the azimuth direction, a specific m
can be prevented from occurring.

That is, from equation (I-1), when α is constant, considering the magnetic field due to two iron pieces, cos[m(φ-ψ)] +cos [m(φ-ψ')
]=0 is a necessary and sufficient condition for the m term not to occur.

,',cosmφcos mψ+sin mφsin
mψ+cosmφcosmψ' +sin mφsin
mψ'=OaCO5mφ(cosmψ+cosmψ'
)+sin mφ(sin mψ+sin mψ′)=
0 <”>C011mψ+cosmψ′=0 and sin m
ψ+sin mψ'=Oa1mψ-mψ' I=k π
(k = 1.3.5-)kπ φ1ψ-ψ'I=-(k=1.3.5...) ・・
-(I-2)kπ Therefore, if two iron pieces are arranged at an angle of □ (=1.3.5...), the 1m term will not occur. for example.

If there is a pair of iron pieces on the 180′ opposite side of any iron piece, no term with an odd number of m will occur. (There always exists k that makes the terms with odd number m 0) 3. Summary of magnetic field correction terms Let each term of the spherical harmonic function obtained from formula (I-1) correspond to the so-called magnetic field correction component. , can be summarized as follows. Hereinafter, the correction term will be referred to by its common name.

4. Arrangement of iron that generates the X and Y terms (n=1. m=1
) i) To prevent the occurrence of term m=2.3.4 (m)5
Assume that the term can be ignored due to higher orders. ) Two pieces of iron are placed at a distance of −+ l l.

Therefore, an arrangement as shown in FIG. 9 is adopted. At this time, no matter which iron piece you take, there is one that forms an angle of -11+. In addition, in the case of the arrangement shown in Figure 9, due to the existence of the ±ψ pair, Σ
Cosψ≠0. Since Σsinψ=0, only the X term is generated. (If only the Y term is generated, it is sufficient to shift it by 90 degrees.) Other terms of m=1, such as ZX, ZY, Z"X,
The same applies to the circumferential arrangement for generating terms such as Z''Y (see Table 1-1).

5. X”-Y”, iron arrangement that generates the XY term (n=2
．． m=2) i) Avoid generating terms other than m=2 as much as possible. According to equation (I-2), if all iron pieces form an angle of 180°, all odd terms are eliminated. m
= 45 for all iron pieces to avoid the occurrence of the term 4.
Pairs with an angle of 30' are formed to prevent the occurrence of the m = 6 term. Then, an arrangement as shown in FIG. 10 is obtained. (If you want to generate only the XY term, you can shift it by 45 degrees.) 6. If you ignore terms higher than the 4th term and 5th term of the iron piece arrangement that generates the Te5sera1 term, Te5sera1 term is
The locations of the iron pieces that generate the ra 1 term are limited to the locations shown in FIG.

[Problem to be solved by the invention]

The above-mentioned prior art does not mention the mass of the small magnetic piece for magnetic field correction or the method of supporting and fixing it.

An object of the present invention is to provide a mass of a magnetic body suitable for rational and efficient magnetic field correction and a method of supporting and fixing the mass.

[Means to solve the problem]

The above purpose is to provide a static magnetic field coil that generates a constant static magnetic field,
a magnetic body that corrects the static magnetic field; a cylindrical support that supports the magnetic body and is disposed inside the static magnetic field coil; and a nuclear magnetism generated from the magnetic field to be measured within the corrected static magnetic field. A cylindrical gradient coil disposed inside the support body imparts position information to a resonance signal (hereinafter referred to as an NMR signal), and a pulsed electromagnetic wave is applied to the object to be measured to generate the NMR signal. In a nuclear spin resonance tomography apparatus including an irradiation coil disposed inside the gradient coil and a reception coil disposed inside the gradient coil that receives the NMR signal, the mass of the magnetic body is set to 0. The magnetic body is fixed by a nuclear spin resonance tomography device having a weight in the range of 01 to 30 g, or by screws to a predetermined number of pedestals arranged adjacent to each other in the circumferential direction on the outer surface of the support, or by a nuclear spin resonance tomography device that is a screw itself, or by fixing the support at a position 75 from a predetermined reference point in the circumferential direction of the support.
'~37.5', 52.5'~82°5', 97.
5''~127.5'', 142.5'~172.5'
, 187.5'~217.5", 232°5"~2
62.5', 277.5''~307.5' 322
．． This is achieved by a nuclear spin resonance tomography apparatus in which the angle is within the range of 5' to 352.5 degrees, or by a nuclear spin tomography apparatus in which the support and the gradient coil are both fixed to the static magnetic field coil.

[Example] Hereinafter, the content of the present invention and an example will be explained with reference to FIGS. 1 to 7.

When the magnetic field in the room-temperature bore of the imaging space of a nuclear spin resonance tomography apparatus is subjected to Legendre expansion and the component corresponding to the expansion term is corrected by the arrangement of magnetic pieces, generally components other than the corresponding component occur simultaneously.

At this time, there is a close relationship between the mass of the magnetic material, the sensitivity of the relevant component, and the sensitivity of components other than the relevant component.

Here, a typical example will be explained in which the Legendre function P, (cos θ) term (commonly known as 76 terms) is corrected by the arrangement of small pieces of magnetic material. When trying to generate a ZG term, generally the p2 (cos θ) term (commonly known as the 72 term) and the P4 (c
Even-numbered terms including the osθ) term (commonly known as 74 terms) occur simultaneously. At this time, the 72nd term can be generated independently relatively easily, and it is necessary to suppress the generation of the 24th term as much as possible in order to perform rational and efficient magnetic field correction. Therefore, if we draw a graph with the ratio of the amount generated in term 74 and the amount generated in term 22 on the vertical axis and the weight of the magnetic particles on the horizontal axis, under the condition that the thickness of the magnetic particles is constant, it will look like Figure 7. . In other words, the slope of the 1 generation amount ratio changes around 30g, and 0.
．． It can be seen that by using magnetic pieces in the range of 0.01 to 30 g, the occurrence of item 24 can be suppressed to a lower level than when using magnetic pieces of 30 g or more. Also, the lower limit value is 0.0
1 g is the limit value that can be considered from a commercially profitable point of view. As in the case of correcting this 76th term, 24th term and 22nd term
The relationship between the ratio of the generation amount of the term and the mass of the small magnetic piece also applies to terms other than the zs term. Therefore, by using a small piece of magnetic material for magnetic field correction in the range of 0.01 to 30 g, rational and efficient magnetic field correction can be achieved.

In addition, when the above-mentioned magnetic pieces are screwed onto removable pedestals provided at approximately equal intervals on the cylinder for supporting the magnetic pieces, when changing the plate thickness of the magnetic pieces due to magnetic field correction, There is no need to pull out the cylinder for supporting the magnetic material; all you have to do is pull out the pedestal and replace or add a small piece of magnetic material.The pedestals are aligned circumferentially, so - when you pull out a book, both sides This serves as a guide when the pedestal is reinserted, allowing for rational and efficient magnetic field correction.

Further, the magnetic piece may be a screw itself.Furthermore, the magnetic field correction of Tessera 1 is 7.5''' around the bore center from an arbitrary reference line at the circumferential position of the magnetic piece supporting cylinder. 37.5″' from 52°5° to 82.
5@, 97.5" to 127.5'.

142.5' to 172.5', 187.5' to 217.5', 232.5' to 262.5@,
This can be done by effectively using angles other than 277.5@ to 307.5' and 322.5' to 352.5 degrees, so by fixing the magnetic piece support cylinder and the electromagnet device within the above range. When the magnetic body fixing pedestal is removed from the magnetic piece support cylinder and pulled out of the magnet bore, it is possible to reduce the frequency of one cylinder fixing component getting in the way, and magnetic field correction can be achieved efficiently. Further, the above-mentioned cylinder fixing component is more rational if the gradient coil provided inside the cylinder is fixed to the electromagnet device at the same time.

This will be explained below with reference to the drawings.

FIG. 2 is an overall configuration diagram. A constant static magnetic field is generated by a static magnetic field coil 1, and a small magnetic piece 3 for magnetic field correction is disposed on a cylindrical support disposed inside the static magnetic field coil 1.
The static magnetic field is corrected, and the irradiation coil 23 applies pulsed electromagnetic waves to the object to be measured in the corrected static magnetic field to generate an NMR signal. The gradient coil 2 imparts positional information, and the receiving coil 24 receives the NMR signal to which this positional information is attached, forming an image (not shown).

FIG. 1 is a partial cross-sectional view of one embodiment of the present invention.

1 is a static magnetic field generating magnet that generates a static magnetic field at the center, and 2 is a gradient coil. A cylinder 7 for fixing a small magnetic piece is inserted between the gradient coil 2 and the inner wall of the magnet 1, and is supported from the magnet 1 together with the gradient coil 2 by a support 9.

A magnetic body fixing pedestal 5 is removably attached to the non-magnetic cylinder 7, and a magnetic field correction magnetic piece 3 is screwed to this pedestal.

The magnetic material piece 3 is a magnetic material with an element mass in the range of 0.01 to 30 g, suppresses the generation of other terms, and achieves rational and economical magnetic field correction. The small magnetic pieces 3 are screwed to a pedestal 5, and the pedestal 5 is attached to a cylinder 7 for fixing small magnetic pieces at approximately equal intervals in the circumferential direction.
All you need to do is remove the pedestal 5 from the cylinder 7 for fixing the small magnetic material piece, pull it out of the magnet bore, and attach the magnetic material. When the pedestal 5 is reinserted, the pedestals on both sides serve as guides to efficiently correct the magnetic field. be able to. The support 9 supports the cylinder 7 and the gradient coil 2 at the position shown in the figure.
When the pedestal 5 is pulled out by magnetic field correction, it is less likely to get in the way. Further, the support 9 includes the cylinder 7 and the gradient coil 2.
It is reasonable because it supports the following at the same time. Figure 3 shows
An example of a magnetic material for magnetic field correction is shown. The magnetic material itself may be a screw, or may have a structure in which a screw hole is provided. The screw hole may itself be a screw, or! ! You may also prepare a separate nut for the L hole and tighten it. The shape of the magnetic body is arbitrary, and the size is in the range of 0.01 to 30 g.

FIG. 4 shows an example of a pedestal for fixing magnetic material.

A hole for fixing the magnetic material is placed in the appropriate position of the non-magnetic shape, and the magnetic material is screwed into the hole.

FIG. 5 shows an example of the mounting position range of the cylinder 7 for fixing the small magnetic piece. In the area indicated by the arrow in the figure, there are only a few magnetic bodies to be placed.If you select an appropriate position from among these and attach the cylinder 7 to the magnet 1, you can use the support to pull out the pedestal 5 when correcting the magnetic field. The tool 9 is less likely to get in the way.

FIG. 6 shows an example of the arrangement of the magnetic body fixing pedestal. The above-mentioned pedestal is fixed in a removable manner at approximately equal intervals on the cylinder for fixing the magnetic material, and when correcting the magnetic field, it is only necessary to pull out the pedestal and install the small pieces of magnetic material, and when re-inserting it, The pedestals on both sides serve as guides, allowing efficient magnetic field correction.

As described above, according to this embodiment, by using a small piece of magnetic material in the range of 0.01 to 30 g, it is possible to suppress the magnetic field component to be generated (Legendre expansion term) and other components that occur simultaneously. , reasonable magnetic field correction is possible. Furthermore, by installing removable pedestals at approximately equal intervals on the cylinder 7 for fixing small magnetic pieces, and screwing the small magnetic pieces onto the pedestals, when correcting the magnetic field, only the pedestals can be pulled out and the small magnetic pieces can be fixed. All you have to do is install it, and when reinserting it, the pedestals on both sides serve as guides to efficiently correct the magnetic field. By using the position shown in FIG. 4 to support the magnetic piece fixing cylinder 7 from the magnet bore, the cylinder fixing support is less likely to get in the way when pulling out the magnetic body fixing pedestal. Moreover, this support is rational because it supports the cylinder and also supports the gradient coil at the same time.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

By setting the mass of the magnetic material that corrects the static magnetic field to a range of 0.01 to 3 Og and suppressing components other than the desired magnetic field components, the magnetic field can be corrected rationally and efficiently.

In addition, by arranging a predetermined number of pedestals adjacent to the support in the circumferential direction and screwing the magnetic material to the predetermined pedestals, when magnetic field correction is performed, only the desired pedestals to which the magnetic material to be corrected is attached can be used. can be pulled out, and the adjacent pedestal can be used as an insertion guide during insertion, making it easy to correct the magnetic field.

In addition, the fixed position of the support body is 7.5' to 37.5°.

52.5'~82.5', 97.5'~127.5°
.

142.5@~172.5', 187.5'~217
．． 5', 232.5'' ~ 262.5', 277.5'' ~
307.5', 322.5" to 352.5', the removal and insertion work of the pedestal to which the magnetic body is attached will not interfere with the support of the support during magnetic field correction. Magnetic field correction work can be done efficiently.

Further, by simultaneously fixing the support and the gradient coil to the static magnetic field coil, it is not necessary to fix them separately, and fixing can be carried out rationally.

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view of an embodiment of the present invention, Fig. 2 is an overall configuration diagram, Fig. 3 is a perspective view of the shape of the magnetic body, Fig. 4 is a perspective view of a pedestal for fixing the magnetic substance, and Fig. 5 is a schematic diagram showing the fixing position of the magnetic body fixing cylinder, Figure 6 is a diagram showing the arrangement of the magnetic body fixing pedestal on the magnetic body fixing cylinder, and Figure 7 is the sensitivity of the term that occurs simultaneously with the mass of the magnetic body. 8 to 11 are explanatory diagrams of the prior art. 1... Static magnetic field coil, 2... Gradient coil. 3... Magnetic material small piece for magnetic field correction, 4... Magnetic material fixing screw, 5... Magnetic material fixing pedestal, 7... Magnetic material fixing cylinder, 9... Support tool, 23...・Irradiation coil, 24・
...Receiving coil.

Claims (4)

[Claims] 1. a static magnetic field coil that generates a constant static magnetic field; a magnetic body that corrects the static magnetic field; a cylindrical support that supports the magnetic body and is disposed inside the static magnetic field coil; A cylindrical gradient coil disposed inside the support body imparts position information to a nuclear magnetic resonance signal generated from the object to be measured in a magnetic field; A nuclear spin resonance tomography apparatus comprising: an irradiation coil disposed inside the gradient coil that generates a resonance signal; and a reception coil disposed inside the gradient coil that receives the nuclear magnetic resonance signal. A nuclear spin resonance tomography apparatus characterized in that the mass of the magnetic material is in the range of 0.01 to 30 g. 2. The magnetic body is fixed to a predetermined number of pedestals adjacent to each other in the circumferential direction of the outer surface of the support body by screws, or
2. The device according to claim 1, wherein the device is a screw or a screw itself. 3. The fixed position of the support body is set at 7.5' to 37.5' and 52.5' to 82' from a predetermined reference point in the circumferential direction of the support body.
．． 5', 97.5' to 127.5', 142.5' to 1
72.5', 187.5' to 217.5', 232.5
'~262.5', 277.5'~307.5', 32
3. The device according to claim 1, wherein the range is from 2.5' to 352.5'. 4. Claim 1, wherein the support body and the gradient coil are both fixed to the static magnetic field coil.
3. The device according to 2 or 3.