JPS5946545A - Method for generating characteristic magnetic field in nuclear magnetic resonance image method - Google Patents

Abstract

PURPOSE:To generate a rod-shaped characteristic magnetic field with low power consumption, by providing first and second coil groups comprising a plurality of coils, and assembling the coils so that the magnetic field components in the specified directions caused by the coil groups are cancelled each other out in a required range. CONSTITUTION:A pair of differential coils 1 and 1' are provided on an (x) axis, and a pair of differential coils 2 and 2' are provided on a (y) axis. The radiuses of the coils and the interval between the coils 1 and 1' and 2 and 2' are made equal. The number of coil winding or the current value of each of the coils 2 and 2' on the (y) axis is selected to be twice that of the coils 1 and 1' on the (x) axis. Then, the magnetic component in the (x) direction can be made to be zero in a certain range of the value of (x). When a static magnetic field Ho is superimposed in the (x) direction, a rod-shaped characteristic magnetic field extending in the (x) direction can be obtained. Thus, the characteristic magnetic field, which is required for a nuclear magnetic resonance image method, can be generated by a very compact, light, magnetic field forming device.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for generating a characteristic magnetic field in nuclear magnetic resonance imaging, in which all information inside a measured object is visualized and measured by the nuclear magnetic resonance phenomenon. ) is applied to detect nuclear magnetic substances inside the object to be measured, such as H and F.
, Na, K, Mg, O, IiP, etc. are collected externally and imaged. A characteristic magnetic field consisting of a static magnetic field different from the surrounding area is fully applied to the measurement site,
This paper concerns a method of generating a characteristic magnetic field to obtain information only on the part to be measured based on differences in resonance frequencies, and is particularly designed to generate a characteristic magnetic field with low consumption using a small and lightweight device. .

Conventional methods for generating this type of characteristic magnetic field, for example, the method for generating a characteristic magnetic field described in Japanese Patent Laid-Open No. 54-1.83192 proposed by the present inventors, involve In order to obtain magnetic resonance information, a bar-shaped characteristic magnetic field, that is, a bar-shaped focal magnetic field, was generated using a group of parallel wires, but in this conventional method, parallel wires that have no magnetic field component in the length direction Since a bar-shaped characteristic magnetic field was generated by combining the magnetic field generated by the strips and a uniform static magnetic field that is 1.1 larger in the longitudinal direction, it required a group of parallel stripes that were extremely long compared to the mutual spacing. However, the rod-shaped focal magnetic field generation coil must be much larger than the resonant magnetic field detection coil. .

Essential Features of F9T A large power drive system is required to generate a magnetic field, and a large amount of coil material is required, resulting in various drawbacks such as the weight of the device.

In addition, in the conventional characteristic magnetic field generation method described above, the magnetic field has high purity in a plane orthogonal to the static magnetic field! (1) A bar-shaped characteristic magnetic field that is closed in a closed curve without containing any current, and whose magnetic field contour lines are parallel to the direction of the static magnetic field within a required range, is placed approximately parallel to the direction of the static magnetic field. The magnetic field was generated by supplying a current to a group of filaments such that the magnetic fields of the filament canceled each other out at a certain point in space. Further developing this, in other regions where there is only a uniform static magnetic field and a magnetic field component orthogonal to the uniform static magnetic field, and the magnetic field component is zero on a certain spatial line10. This can be reduced to combining a magnetic field that does not become zero.

Generally, when a differential I5 coil group is constructed by supplying current to a plurality of closed loop coils in a direction in which the magnetic fields of the respective coils cancel each other out at a certain spatial point, the coils The magnetic field due to the group becomes zero at the one point mentioned above, and in other regions, even if a uniform static magnetic field is superimposed in any direction, the intensity change of the combined magnetic field of both will depend on the direction of the superimposed static magnetic field. The influence is dominated by the magnetic field component.

Therefore, there is a drawback that only a gradient magnetic field having a gradient of magnetic field strength in the direction of the superimposed applied static magnetic field can be realized.

However, in the above case, if the 'magnetic field component in the direction of the superimposed static magnetic field in the magnetic field produced by the differential coil group can be canceled by some means over the necessary range, the magnetic field component in the direction of the superimposed static magnetic field can be canceled orthogonally to the direction of the superimposed static magnetic field. Since the magnetic field component in the direction of
A bar-shaped focal magnetic field can be realized.

An object of the present invention is to provide a complete method for generating a characteristic magnetic field in nuclear magnetic resonance imaging, which eliminates the above-mentioned conventional drawbacks and generates a rod-shaped characteristic magnetic field with low power consumption using a small and lightweight device. There is a particular thing.

Another object of the present invention is to develop an imaging system for medical diagnosis using nuclear magnetic resonance, which has recently begun to attract attention, that is, a new method of nuclear magnetic resonance that can easily form a linear magnetic field gradient mainly used in imaging methods. The object of the present invention is to provide a method 2 for generating a characteristic magnetic field that enables the imaging method (7).

Still another object of the present invention is to provide a method for generating a characteristic magnetic field that can be applied to a spin density distribution imaging device, a relaxation time distribution imaging device, etc. that apply the nuclear magnetic resonance phenomenon, and can achieve the same effects as described above. It's about doing.

That is, the characteristic magnetic field generation method of the present invention generates a bar-shaped focal magnetic field by compensating the magnetic field component of the magnetic field generated by the differential coil group in the direction of the static magnetic field superimposed on the magnetic field, and also generates a bar-shaped focal magnetic field. Compensation for the magnetic field component of
For example, it is realized by arranging another differential coil group orthogonally to the above-mentioned differential coil group. The zeroth order of the magnetic field due to those coils
The first and second electric currents each supply a current having a magnitude and direction such that the five-term components cancel each other out and become approximately zero.
A rod-shaped The feature is that it generates a magnetic field.

In the following, the invention will be explained in detail with reference to a number of embodiments, with reference to the drawings.

First, as a first example, we will explain the case where two differential coil pairs orthogonal to each other are used as described above.For convenience, the first differential coil pair is aligned with the origin on the X-axis. The coils are arranged symmetrically with respect to each other and each coil surface is perpendicular to the X axis, and each coil is a circular coil with the same radius and number of turns. shall be.

Therefore, the magnetic field component due to the second differential coil pair arranged on the X-axis is given by the following equation for each coordinate axis.

Here, a, , 'bx and Nx are the coil radius, the distance from the origin to the plane of the coil, and the number of turns of the coil, respectively, and ' is the coil current, and for each coil, Assume that the magnetic fields are equal in size and that the magnetic fields from each coil are supplied in directions that cancel each other out.

The magnetic field generated by the first differential coil pair is expressed by the above equation (1
) to (8), since it has magnetic field components in all directions, a bar-shaped focal magnetic field is not formed even if the static magnetic field H8 is superimposed in any direction. 1. In contrast, in the present invention, as described above, all the magnetic field components in a certain direction are actively canceled, and the entire bar-shaped focal magnetic field is generated by applying the static magnetic field in full superimposition in that direction.

Now, if all the second differential coil pairs are placed on the y-axis with respect to the first differential coil pair on the X-ray, then the second differential coil pair placed on the y-axis The magnetic field is given by the following equation for each coordinate axis in exactly the same way as in the first differential coil pair disposed on the X axis.

Here, the definition of the valley symbol is the same as in the first differential coil pair on the X axis.

As mentioned above, the composite magnetic field generated by the two mutually orthogonal differential coil pairs is expressed by the above equations (11 to (3) and equation (7)-(9)
It is given by the following fully synthesized equation.

(15) Therefore, 0 . 0
is selected, and the static magnetic field IX is applied in the direction of its zero component.
By applying 1y HO in a superimposed manner, a bar-shaped focal magnetic field extending in that direction can be obtained.

Therefore, there are the following three types of static magnetic field superposition in the direction of the zero component.

(1) As HxK0, the static magnetic field is superimposed in the H81x direction. Therefore, 0□y=2C1x is selected.

(u) As H and Ki0, a static magnetic field H8 is superimposed in the y direction. Therefore, 0=201y is selected.

X (Ill) Hz is set to 0, and the static magnetic field H8 is superimposed in two directions. Therefore Ozx =01:! / selected.

Among the three types of static magnetic field superimposition described above, the coil arrangement and 15 directions of current in the mode of (i) x-direction static magnetic field superimposition are schematically shown in Figure 1 (a3). Coil pair 1, 1' and differential coil pair 2 on the y-axis.
Assuming that the coil radius of 2' and the coil spacing are equal,
If the number of turns or current value of each of the X-axis differential coil pairs 2, 2' is selected to be twice that of the X-axis differential coil pairs 1, l', . . . , then the value of If the static magnetic field Ho is compressed in the X direction,
A rod-shaped focal magnetic field extending in the X direction is obtained. Regarding the influence of the higher-order terms in the above equations (]3) to (]5), the presence of the higher-order terms causes the shape of the focal magnetic field to collapse and become a distorted shape, so it is desirable that the higher-order terms be as small as possible. However, among such higher-order terms, since the absolute values of diurnal terms of fifth order and higher are extremely small, it is the 8th-order terms that mainly pose a problem. However, -... the coefficient C8X of the cubic term in the above equations (18) to (15)
0 ay is ax, b It is desirable that the above formulas (13) to (
.

(]5) and the HxO equation in the X direction (13
Even if the linear terms in ) do not become completely zero, they are small enough that the influence of their existence does not appear, and for convenience of explanation, the linear terms on the X and y axes are The coil radius of the differential coil pair.

The distance between the coils and the coil spacing was set to be the same, but on the X axis and on the y' axis -
Even if the coil radius or coil spacing differs between people, or even if the differential coil pair is not a circular coil but a coil of another shape, such as an ellipse, Of course, it is sufficient that the coil pairs are arranged in a differential combination, and that the X-direction magnetic field components of the magnetic fields from both coil pairs cancel each other out. be.

Therefore, in the above-mentioned (1) X-direction static magnetic field superposition, 1(
- may be determined by selecting the relationship between the linear term coefficients for the differential coil pair on the y-axis and the differential coil pair on the X-axis as shown in the following equation.

C1y-2GIX (16) Therefore, if the coil radius and coil spacing of the y-axis differential coil pair and the X-axis differential coil pair are equal, the amperage f of the former is twice that of the latter. All you have to do is choose. Therefore, the magnetic field force of the bar-shaped focal magnetic field generated at that time...change is as follows: ClX=C□ (17)
is expressed by the following equation.

Note that the direction of the uniform static magnetic field H8 applied superimposed from the outside is X
direction. Furthermore, in the above explanation, it is implicitly assumed that the points at which the magnetic fields of the X-axis differential coil pair and the Y-axis differential coil pair are zero coincide with each other. Even if the two zero magnetic field points do not match, that is, even if the symmetry axes of the magnetic fields from both differential coil pairs do not intersect, as a result, the center position of the generated bar-shaped focal magnetic field will only shift slightly, Not only does it not pose a major hindrance to forming the desired bar-shaped focal magnetic field of 1°,
Conversely, the fact that there is a margin of zero magnetic field point mismatch can also be utilized for scanning of the focal magnetic field, etc.

Next, among the three types of static magnetic field superposition mentioned above, (II)
In the mode of static magnetic field superposition in the direction, the effects of the X-axis differential, 1° coil pair and the Y-axis differential coil pair are as described above (1) Each effect in the mode of X-direction static magnetic field superposition. It is recognized that there is no need for special explanation as it is merely an exchange for effect.

Next, among the above-mentioned King's static magnetic field superposition, the aspect (+1) is significantly different from the above-mentioned aspects (+) and (1).
112-direction static magnetic field superposition, that is, the direction of the current in the case where the static magnetic field is fully superimposed so that the magnetic field components in two orthogonal directions cancel each other out to the first and second differential coil pairs. The embodiment is schematically shown in Figure 1 (b). In the illustrated embodiment, 01x=-0
1y=G□(19) The change in magnetic field strength when applying a uniform static magnetic field H6 in two directions in a superimposed manner is expressed by the following equation 1. This can be expressed in the same format as Equation (18) in the superimposed mode.

It is assumed that the relationship between the coil radius and the coil spacing is selected so that the coefficient of the 8'-order term in each equation regarding each differential coil pair is sufficiently smaller than the coefficient of the 1st-order term.

Therefore, in the above-mentioned (11132-direction static magnetic field superimposition mode), the amperage of the X-axis differential coil pair 3, 3' and the X-axis differential coil pair 4, 4' is determined by the coil radius and the coil spacing. If they are equal, it is sufficient to select them equally, which is extremely convenient for manufacturing.
In this embodiment (fill Z-direction static magnetic field superimposition 1), the matters regarding changes in the configuration conditions such as the shape and arrangement of the coils are exactly the same as those described above for the embodiment of (1) X-direction static magnetic field superimposition.

In the first embodiment described in detail above, for each differential coil pair, the relationship between the coil radius and the coil spacing is selected such that the 1°8th order term of the equation representing the change in magnetic field strength is approximately zero. Specifically, in the case of a differential coil pair consisting of circular coils, according to the above equation (5),
The following equation is obtained by determining the relationship between the coil radius a and the coil spacing, which sets the coefficient of the third-order term in each equation that expresses the change in magnetic field strength to zero, and the optimum design conditions are set using this equation. can do.

Therefore, under the above-mentioned optimal conditions, the coil spacing in the differential coil pair is larger than the coil diameter, so when the coil diameters of two differential coil pairs to be arranged in combination are made equal, The coils of both differential coil pairs collide with each other (1). In such a case, the coil spacing and coil diameter ak in the differential coil pair, and the ratio b7a-e are constant values. Appropriate changes can be made to prevent the coils of both differential coil pairs from colliding, such as increasing the value while holding it.However, in general, the coefficient of the cubic term should always be set to zero. In addition, when using a coil with a shape other than a circular coil, such as a square or rectangular coil, the above-mentioned method in which the coefficient of the 8th order term is set to zero may not always be possible. It is considered that a situation in which the coil spacing, etc. should be selected based on other conditions different from the optimum condition of -, 2 degrees may well occur.

Next, as a second example, even if the optimal condition for making the coefficient of the cubic term of the equation representing the change in magnetic field strength zero is not satisfied as described above, it is possible to generate all the required bar state and point magnetic fields. In explaining the configuration and arrangement of the magnetic field forming coils, for convenience of explanation, it is assumed that a differential coil pair consisting of circular coils is used as in the case described above.

Generally, in the first embodiment described above, the three types of superimposed static magnetic fields (+) to (changes in magnetic field intensity of the characteristic magnetic field due to the ship) can be expressed by the following equation.

Here, r is the distance from the origin in a plane perpendicular to the direction of the static magnetic field H8, and X is the coordinate axis in the direction of the static magnetic field H8, which is the aspect (1) in the first embodiment described above.
In , X = x, in aspect (1), Xmi2. .

y, in embodiment (ll), x=z, and further,
1f(x2*y"y') is each variable X", 'j2.
Z2(7) is a linear combination formula, and each of the above-mentioned aspects (1
) to (lit) result in different formulas.

Therefore, the second term in the above equation (22) represents the distortion term or error term based on the 8th order term of the equation representing the change in magnetic field intensity due to the differential coil pair, and the characteristic magnetic field expressed by equation (22) is In order to be able to use it as a bar-shaped focal magnetic field, the second term needs to be sufficiently smaller by 10 than the first term over the necessary value range of the variable X. Note that the coefficients 0□ and 08 are proportional to the ampere frequency of the differential coil pair, as given by equations (4), (5) or equation (10), and Ug, respectively, so equation (22) ) is proportional to the square of the ampere frequency, and the coefficient of the second term is proportional to the first power of the ampere frequency. Therefore, when using a pair of differential coils facing each other at an arbitrary interval, if designed to provide a sufficiently large value of amperage,
A bar-shaped focal magnetic field can be formed in the shape 2.1 over the necessary range, and the conditions regarding the coil spacing □ of the differential coil pair can be significantly relaxed. Also, in the following explanation, the case of a differential coil pair using circular coils has been described, but the present invention can be carried out in the same manner as described above for differential coil pairs with coils of other shapes. be able to.

Here, the characteristic magnetic field generation force method according to the present invention described above is different from, for example, the conventional characteristic magnetic field generation method described in Japanese Patent Application Laid-Open No. 188192/1983 proposed by the present inventors as mentioned at the beginning. I would like to say a few words about the superiority and inferiority of the parallel filaments for the conventional bar-shaped focal magnetic field generation, since they do not have a magnetic field component in the length direction from the beginning. While it is not necessary to precisely set the supplied current value, in the combination of the above-described pair of differential coils according to the present invention, magnetic field components in a certain direction cancel each other, and the magnetic field component in that direction Therefore, it is necessary to accurately set the current value supplied to the differential coil pair, but the present invention is better than the conventional method for setting the supply current value.

It will be worse. However, on the other hand, the length of one parallel line group must be set to be sufficiently large compared to its width, and therefore, it cannot help but be large. However, according to the present invention, Since the length and width of the rod-shaped focal magnetic field generating means can be made as large as the diameter of the coil, it has the remarkable advantage that the characteristic magnetic field generating means can be made much smaller than the conventional case using a group of parallel wires. ing.

Furthermore, according to the present invention, when the number of wires and the number of windings of the characteristic magnetic field generating means are all the same as in the conventional method, the length of copper wire required is much shorter, and therefore the driving power is also reduced. It has an excellent advantage of being able to reduce the weight significantly and also being lightweight, and the effects of this advantage are extremely significant in practical use.

Next, as a third embodiment, we will explain the characteristic magnetic field generation according to the present invention in the case where the current coil used as the difference 1 dynamic magnetic field generating means is replaced with a permanent magnet as described above. Generally, the closed loop current is It can be replaced with a plate-shaped magnet having a shape similar to the shape of the outer periphery. Therefore, as mentioned above.

Some current coils of the two differential coil pairs,
Alternatively, even if all current coils are replaced with plate magnets, a bar-shaped focal magnetic field can be generated in the same way as in the first embodiment. An example of a specific configuration and arrangement of the characteristic magnetic field generating means in such a case is schematically shown in FIG. The illustrated arrangement is for each current coil 3, 8' and 4, 4' in the arrangement of the differential coil pair shown in FIG.
e All are replaced with disc-shaped magnets 5.5' and 6,6', respectively, and the two disc-shaped magnets 1...5.5' arranged oppositely on the Two disc-shaped magnets 6 facing each other and facing each other on the y-axis,
If the N poles of 6' are made to face each other, the shape of the lines of magnetic force of the composite magnetic field created by the combination of these magnet pairs will be the same as in the configuration shown in FIG.

In this direction, the magnetic field components in the Z-axis direction due to the magnet pairs on the X-axis and the y-axis cancel each other out, so the magnetic field becomes almost zero. Therefore, by applying the uniform static magnetic field H8 in two axial directions in a superimposed manner, it is possible to generate a bar-shaped focal magnetic field in exactly the same way as in the case described above. ,.

(24) Now, considering the advantages of generating a magnetic field due to the above-mentioned combination of magnet pairs, for the sake of simplicity, ρ':;
When a : b, formula (41) or formula (
10), it becomes "1, (/p)N, so in equation (18) or equation (20), yQ + z2 or '. is x2 + If y2 is replaced with r2 and substituted into the above 0□, Therefore, based on this equation (23), when giving the profile 42 of the same magnetic field strength change, that is, the differential in the first embodiment necessary to generate a bar-shaped focal magnetic field with the same magnetic field strength change. It can be seen that the amperage of the coil pair is related to the following equation (15).

Nl0Cbeρ” (24) Therefore, the characteristic magnetic field generation system where the coil size becomes large and the static magnetic field H
Strong characteristics of 8 In the magnetic field generation system, the number of amperes required for the differential coil pair increases rapidly, and the difficulty of winding, excitation power supply, etc. increases rapidly, making it difficult to implement. A fear arises. On the other hand, in such cases,
If a strong magnet with good characteristics is used in place of the separate current coils, such a magnet can be obtained relatively easily. , a remarkable advantage is obtained that the entire rod-shaped focal magnetic field generator can be configured extremely compactly.

Finally, as a fourth embodiment, the static magnetic field H8 applied in a superimposed manner to form a bar-shaped magnetic field is not a uniform static magnetic field as described above, and the axial direction of the bar-shaped magnetic field is set in any direction from the center. By using a static magnetic field that increases the magnetic field strength, the magnetic field contour surface becomes spherical.

To explain the characteristic magnetic field generation according to the present invention in the case where a completely closed characteristic magnetic field is generated in the form of an ellipsoid, as shown in FIG.
) Two sets of differential coil pairs 7 configured and arranged in the same manner as shown in
, 7' and 8, 8' by 1 degree, on 2 axes, 2
The coil spacing is made wider than the Helmholtz condition where b=a, and a pair of summation coils 9.9' is provided in which a current is passed in the same direction through the pair of coils disposed facing each other in the condition 2b)a.

The magnetic field generated by the summation coil pair 9.9' on the two axes is oriented in almost two directions, and in the axial direction it becomes stronger as it approaches the coil, and in the radial direction of the coil, On the contrary, it has the property of becoming weaker as it approaches the coil. - differential coil pairs 7, 7' and 8, which are arranged oppositely on the X-axis and the y-axis, respectively. As described above for the first embodiment, the composite magnetic field generated by 8' has no magnetic field components in the two axes, and has no magnetic field components on the plane orthogonal to the Z axis, if an appropriate amperage is applied. , it becomes zero on the axis and becomes stronger as the distance from the two axes in the radial direction increases. Therefore, the composite magnetic field generated by both the summation coil pair and the differential coil pair is generated by the two sets of differential magnetic fields on the The tendency of the combined magnetic field of the coil pair to become stronger in the two-axis radial direction cancels out the tendency of the magnetic field of the 11th moving coil pair on the 5.1°X axis to become weaker in the two-axis radial direction. Well, second
In the composite magnetic field with the illustrated configuration, there is a tendency for the magnetic field strength to increase three-dimensionally in any direction from the origin. It is easy to understand that in a magnetic field that has the full magnetic field strength with this tendency, the magnetic field isotome exhibits a closed surface shape around the origin, resulting in a spherical or ellipsoidal magnetic field contour surface as described above. be done.

In addition, in the characteristic magnetic field generation of the above-mentioned seven aspects, 1...
A uniform static magnetic field in the same direction as the zero-order term in the equation that expresses the change in magnetic field strength due to a pair of harmonic coils on the Since the properties do not change, such homogeneous static magnetic fields can be applied in a superimposed manner as desired. In addition, the amperage required for each current coil in such a case changes due to the superimposed application of the uniform static magnetic field, so this must be taken into consideration when removing the application of the uniform static magnetic field. , .

Furthermore, in the above explanation, the case where the distance between the pair of summation coils arranged opposite to each other on the Since the tendency of the magnetic field strength change in is completely opposite to the tendency when the field is made wider than the Helmholtz condition, even if a summation coil pair exhibiting such a tendency is combined with a differential coil pair, the magnetic field strength of the resulting composite magnetic field will be However, since there is no change in the fact that the magnetic field tends to be weaker in the Z-axis direction and stronger in the radial direction, the I11 magnetic field contour surface does not have a three-dimensionally closed shape as described above. However, even in the case of bending, if the uniform static magnetic field H8 is superimposed and applied in the opposite direction to the zero-order term of the pair of biaxial wave coils, the uniform static magnetic field H8 and the magnetic field due to the pair of biaxial wave coils can be In the composite magnetic field with 141,
A magnetic field strength is obtained that is weakest at the biaxial origin, becomes stronger as the distance to both sides in the biaxial direction increases, and conversely becomes weaker in the radial direction. Therefore, if the coil spacing of the pair of wave coils on the X-axis is narrower than the Helmholtz condition, 2
・.

In this case, it is possible to generate a characteristic magnetic field having a closed magnetic field contour surface in a spherical or ellipsoidal shape.

As is clear from the above song 1, according to the present invention, 2
By arranging differential coil pairs or differential magnet pairs orthogonally to these differential pairs, or by arranging summation coil pairs orthogonally to these differential pairs, a bar-shaped focal magnetic field in a desired direction can be generated by applying uniform static magnetic fields in a superimposed manner. By compensating the magnetic field strength in a desired direction so that it can be formed, the characteristic magnetic field necessary for nuclear magnetic resonance imaging is generated by an extremely small and large magnetic field forming device. This has the remarkable effect of making it possible to obtain internal information easily and reliably.

[Brief explanation of the drawing]

Figures 1 (a) and middle) are perspective views schematically showing examples of the configuration and arrangement of current coils for generating a characteristic magnetic field according to the present invention, and Figure 2 is a configuration of a magnet plate for generating a characteristic magnetic field. FIG. 3 is a perspective view schematically showing an example of the arrangement. FIG. 3 is a perspective view schematically showing another example of the arrangement of current coils for generating a magnetic field. Ru. ] , ]';2,2';8,3';4,4';7,7
';818'...Differential coil pair, 5r 5': 6
, 6'... Differential magnet pair, 9.9'... Harmonic coil pair. Patent Applicant: Utsunomiya University President Akira Kei Figure 1 <a) (b) (32) Figure 2 χ Figure 3 7'H. l l γ7 / Procedural Amendment September 27, 1981 1, Case Description 1982 Patent Application No. 1544191 2, Title of Invention Characteristic Magnetic Field Generation Method in Nuclear Magnetic Resonance Imaging 3, Person Making Amendment Case Relationship with Patent Applicant Utsunomiya University President Koshi Sera Sera Telephone (581) 2241 (Representative) and 1 other person Correct as shown below. [2.Claim L] Each of the coils is composed of a plurality of coils, and at a predetermined position between the coils, the zero-order term components of the magnetic field due to the coils cancel each other out and become 3 or almost zero. A first and a second coil group each supplying a current having a magnitude and direction are provided, and the first and second coil groups are arranged such that the magnetic field component in a predetermined direction by the coil group is within a required range. A nuclear magnetic resonance imaging device is characterized in that a bar-shaped characteristic magnetic field is generated by combining the magnetic fields so as to cancel each other out. Characteristic magnetic field generation method in imaging method. By superimposing a substantially uniform static magnetic field in a direction in which the magnetic field component of the composite magnetic field produced by the first and second coil groups becomes 1 [zero or almost zero, the magnetic field strength is increased to 11.
1(2) Claim No. 1 is characterized in that the magnetic field is substantially parallel to a direction in which no magnetic field component of the magnetic field exists, and is a closed curve in a plane perpendicular to that direction.
Characteristic magnetic field generation method in nuclear magnetic resonance imaging method described in Section 2. & For each, two coils are differentially combined on the same axis so that the magnetic fields cancel each other out, and the coil spacing is set to minimize the 8th order term of the magnetic field strength change. said first and second differential coil pairs such that the change in magnetic field strength is represented by a linear equation substantially within a required range.
5 The second coil group is configured, and the axes of the first and second differential coil pairs are orthogonal to each other, and the magnetic field generated by the first and second differential coil pairs is A current of such magnitude and direction that the magnetic field components in a predetermined direction cancel each other by 1° is applied. 2. A method for generating a characteristic magnetic field in nuclear magnetic resonance imaging according to claim 1, wherein said magnetic field is supplied to said first and said second differential coil pairs, respectively. Nuclear magnetic resonance imaging according to claim 8, characterized in that a substantially uniform static magnetic field is superimposed in a direction in which no magnetic field component of the composite magnetic field generated by the first and second differential coil pairs exists. Characteristic magnetic field in the method, 1 generation method. 5. The nucleus according to claim 8 or 1.4, characterized in that the amperage of the first and second differential coil pairs is set so that an arbitrary coil spacing can be obtained. Characteristic magnetic field generation method in magnetic resonance imaging. a) At least a portion of the first and second coil groups are replaced with magnets similar to the closed loop currents in those coil groups.2.1. Characteristic magnetic field generation method in the described nuclear magnetic resonance imaging method. I Consists of a combination of coils or magnets, with an axial magnetic field component at a predetermined position. The static magnetic field is generated by a magnetic field generating means that generates a minimum magnetic field and generates a composite magnetic field that combines the magnetic field and the magnetic fields generated by the first and second coil groups. A 3° method for generating a characteristic magnetic field in nuclear magnetic resonance imaging according to claim 2 or 4. 2. Corrected "There is a drawback that it cannot be realized." in lines 2 to 8 of page 7 of the specification to "It cannot be realized.""Focus magnetic field" has been corrected to "bar-shaped characteristic magnetic field," and "Conventional disadvantages" in line 11 of the same page has been corrected to "disadvantages of the conventional bar-shaped characteristic magnetic field generation method using a group of parallel wires," also in line 16 of the same page. Delete the first line of page 8. 8. Delete "further" in the second line of page 8, and replace "applicable to equipment, etc....conspicuously" in lines 4 and 5 with "applicable to equipment, etc." ”, “focal magnetic field” in line 10 of the same page is corrected to “one characteristic magnetic field”, and “habo zero” in line 16 of the same page is corrected to “zero to habo zero”. 4 On page 9, line 8 of the same document, after “For convenience,” “Figure 1 (a)
and (b) denoted as 1, 1' and 8, 8', respectively. 5. Correct "bar-shaped focal magnetic field" in line 10 of page 11 to "bar-shaped focal magnetic field" and correct "on X-ray" to "on X-axis" in line 15 of the same page, and ,'' followed by [Figure 1 (a) and (b)
) as 2, 2' and 4, 4' respectively. 6. Correct "focal magnetic field" in line 5 of page 14 of the same document to "characteristic magnetic field." 7, page 15, lines 8 to 4 and 6, page 1
Page 6, line 20, page 17, line 14, lines 1510 to 16 and lines 17 to 18, page 21, line 5
lines to lines 6, page 22, lines 8 and 20, page 28, line 11, page 24, line 5, page 2'5, line 4
20, line 1, page 26, lines 18 to 14, and line 9, page 15, page 27, "focal magnetic field" is corrected to "characteristic magnetic field." 8. On page 28, line 8, "approaching the coil" is corrected to "separating in the radial direction." 9. "Wading coil pair" on page 81, lines 5 and 6 (
6) Corrected to ``pair of circular or rectangular harmonic coils,'' and corrected ``bar-shaped focal magnetic field'' in line 7 of the same page to ``one bar-shaped characteristic magnetic field.'' Representative Patent Attorney Akatsuki Sugimura Funagai] Famous procedural amendment October 6, 1981 1. Case description 1982 Patent Application No. 154491 2. Title of invention Characteristic magnetic field generation method in nuclear magnetic resonance imaging 3. Relationship with the case of the person making the amendment Patent applicant: President of Utsunomiya University Koshibe Sera Tel: (581) 2241 (Representative) 1 other person 5゜6, Subject of amendment: Detailed explanation of one invention in the specification.
Column ``Brief Description of Drawings'', ``1 Drawing'' 7. Contents of amendment (as attached) 1 The following is added in the second line of page 5 of the specification. "Here, an example of a schematic configuration of a nuclear magnetic resonance imaging apparatus to which the present invention is applied is shown in FIG. 1 constitutes a basic pulse NMR device together with transmitter coil b, receiver coil b, and static magnetic field generating magnet b5 in unit 2.Transmitter coil b0 and receiver coil b2. The shaft is arranged in a direction perpendicular to the uniform static magnetic field H8 generated by the static magnetic field generating magnet b5, and the object to be measured is placed inside it.Nuclear magnetic substances such as protons in the object's body are It has a uniquely determined Larmor frequency 1., and R of a frequency equal to that Larmor frequency.
When the F magnetic field is applied to the object to be measured by the transmitter coil b0, a nuclear magnetic resonance phenomenon occurs within the object to be measured, and a signal of that frequency is induced in the receiver coil b2. 1.1 (2) Since the frequency is uniquely determined by the magnetic field strength, it is possible to
Suring Target: MT) only NM
In order to obtain the R information, a nonlinear characteristic magnetic field in which the change in magnetic field strength within the region MT is extremely small and the magnetic field strength changes rapidly outside the region MT is applied by the characteristic magnetic field generating coil b. Application of such a characteristic magnetic field causes a difference in nuclear magnetic resonance frequency between the region MT and the outside thereof, so that information of only the region MT is generated due to the difference. can be selectively measured separately from information outside of it. This characteristic magnetic field is electrically scanned by the scanning coil b8 in the unit 12 without changing its shape, and as a result, NMR parameters such as spin density distribution and nuclear magnetic relaxation time in the object to be measured are mapped. It can be visualized and displayed. Here, the configuration and operation of each unit will be explained in detail.Unit 1 constitutes the circuit system of a basic pulse NMR apparatus; Kit 2 is a magnet b for generating a static magnetic field, and its. Characteristic magnetic field generation/scanning coil b8 arranged in a static magnetic field. b
, and transmitter/receiver coil b1. It consists of b2. In addition, the characteristic magnetic field generation/scanning coil b8
．． b. is due to its configuration. Depending on the case, it may be arranged outside the static magnetic field generating magnet b5. Unit 8 is a drive source for unit 2, and unit 4 is a computer d0 that controls the entire device and controls the irradiation pulse magnetic field, sampling of measurement data, 11° frequency analysis, image display, etc. It consists of a peripheral device d. In the configuration as described above, the RF signal from the RF oscillator a0 with a frequency equal to the Larmor frequency corresponding to the central magnetic field strength of the characteristic magnetic field provided by the unit 2 enters the waveform shaping and gating circuit a8; calculator d1
is gated by the output pulse of the program pulse generator a2 controlled by the RF power amplifier 2. to produce an RF pulse having a predetermined frequency spectrum. . a, after being amplified by the transmitter coil b
0. In this way, the RF magnetic field is applied to the object to be measured by the transmitter coil b0, and the RF magnetic field having a predetermined frequency spectrum is applied to the object to be measured. Nuclear magnetization in a predetermined region surrounding the center of the characteristic magnetic field within is selectively excited. The excited nuclear magnetization produces a magnetization component in the direction perpendicular to the static magnetic field, and the magnetization component is
The maximum value is reached when the F pulse satisfies the so-called 90° pulse condition. 14. Next, when the excitation RF pulse ends, the nuclear magnetization component in the direction orthogonal to the static magnetic field performs free two-difference motion at the Larmor frequency corresponding to the magnetic field strength at each position of the characteristic magnetic field, and moves to the receiver coil b2. Induces a minute RF voltage. The RF voltage of part 1-1 is amplified by the front and main amplifiers a5 and a6, and then subjected to phase sensitive detection. This FID signal is A/D
After being converted into digital clothing by the converter a8, the frequency is analyzed by the computer d□1 using a so-called FFT method, and a frequency component corresponding to the central magnetic field strength of the characteristic magnetic field is extracted. Simultaneously with this frequency component extraction, a characteristic magnetic field scanning signal is sent from the computer d□, and a scanning current is supplied to the characteristic magnetic field scanning coil b8 via the D/A converter C, so that the characteristic magnetic field almost changes its shape. scanned spatially. Along with such scanning, in certain characteristic magnetic fields, the central magnetic field strength 1. . An offset occurs, but this offset is compensated for by a compensation coil co-located within the scanning coil b8, so that the Larmor frequency at the center of the characteristic magnetic field is always kept constant. The drive current supplied to this compensation coil was also calculated. given by machine d0. By performing the characteristic magnetic field scanning described above and mapping the intensity of the Larmor frequency magnetization component corresponding to the central magnetic field strength of the characteristic magnetic field, a spin density image can be directly obtained. For example, it is possible to directly measure T□ and T2, and visualization is also possible. In addition,
In order to extract the Larmor frequency magnetization component corresponding to the central magnetic field strength of the characteristic magnetic field, in addition to the digital arithmetic processing by a computer as described above, a narrowband) selective amplifier,
It is clear that direct analog circuit processing could also be used, such as with lock-in amplifiers. The present invention provides a specific method for generating a characteristic magnetic field using the characteristic magnetic field generating coil 11 in a nuclear magnetic resonance imaging apparatus having the configuration and arrangement as described above. " 2, page 9, line 8, 1 for convenience, 1 Figure 2 (
a) and (b), respectively designated as 1,1' and 3,8'. 3. After “against,” in line 15 of the 11th summer of the same year, [2nd
(as shown as 2.2' and 4,4' in Q and (b), respectively). 4 Add "Fig. 1 (a)" to "Fig. 2 (
a)”. 5. "Figure 1 (b)" on page 18, lines 10 to 11
" is corrected to "Figure 2 (b)". 6. Corrected “Figure 2” in line 6 of page 25 to “Figure 3” and changed “Figure 1 (b)” in lines 6 to 7 and line 15 of the same page.
” should be corrected to “Figure 2 (b)”. 7. "Figure 8" on page 27, line 18 of the same page is changed to "Figure 4." and "Figure 1 (b)" in line 19 of the same page is corrected to "Figure 2 (b)." 8. On page 29, line 8, "2nd illustration" is corrected to "4th illustration". 9. Add the following on page 81, line 2: 1
[In addition, in the above description, the X-axis direction summation coil pair is
By using a rectangular rectangular coil having sufficient length in the X-axis direction and the Y-axis direction instead of using a circular coil, it is possible to apply other types of features and generation of a characteristic magnetic field. Now, as shown in FIG. 5, when using a pair of rectangular power coils 12.12' that is sufficiently long in the y@force direction compared to the width in the X-axis direction, the width of the square coil pair 12.12' is Between the coils in the X-axis direction 1. . If the relationship between the distance and the coil width in the X-axis direction is set appropriately, 1
The magnetic field generated by the rectangular coil pair 12, 12' becomes stronger as it moves away from the center point in the X-axis direction, and becomes weaker as it moves away from the center point in the X-axis direction1. Therefore, the manner in which the magnetic field strength changes becomes a quadratic function in both the X and Z axis directions. Also,
If the rectangular coil pair 12.12' is sufficiently long in the y-axis direction, its magnetic field strength will hardly change in the y-axis direction. Therefore, regarding the aspect of change in magnetic field strength of the entire coil system shown in FIG. 5, the differential coil pair. 10. The magnetic field due to 10 and 11, 11 increases the magnetic field strength quadratically in both the x and y axes with respect to the composite magnetic field of the entire coil system, and changes the magnetic field strength in the x-axis direction. On the contrary, the magnetic field produced by the rectangular wave coil pair 12°12'
The effect is that the magnetic field strength is increased in a quadratic manner and the magnetic field strength is decreased in a quadratic manner in the X-axis direction. Therefore, the differential coil pair 1.0. TO'O1. . and 11, 11' effects and square wave coil pair 1
The effects of 2 and 12' are opposite to each other in the X-axis direction, so if the drive current value supplied to the square wave coil pair 12 and 12 is appropriately set, the effects of both will be canceled out. The magnetic field strength can be made to hardly change in the 1° direction of the X axis. On the other hand, in the y-axis direction and the X-axis direction, differential coil pairs 10, 10 and 11.1
1' and square wave coil pair 12.12 on the composite magnetic field strength of the entire magnetic field.Since there is no change in the effect of The field increases quadratically in the direction, and the magnetic field is closed in a circular or elliptical shape around the X axis.
It has a rod-like shape extending in the axial direction. Therefore, the 55th
The illustrated coil system can generate a bar-shaped characteristic magnetic field in a direction perpendicular to the static magnetic field H8. It is of course possible to generate a rod-shaped characteristic magnetic field extending in the y-axis direction in the same manner as described above by using a pair of rectangular coils extending in the x-axis direction. ” 10, page 81, line 18, the following is added, 1
``Figure 1 is a block diagram showing an example of the schematic configuration of a nuclear magnetic resonance imaging apparatus to which the present invention is applied.'' Line 14 of the same page, ``
"Figure 1" was corrected to "Figure 2.""Figure2" in line 17 of the same page was corrected to "Figure 8.1." Corrected to ``Figure''. 11, page 32, line 1, add the following, 1
．． . "ao・0Ry generator, aQ...program pulse generator, as...waveform shaping and gate circuit, a...
・RF power amplifier, a, ... preamplifier, C6...
・Main amplifier, C7...phase sensitive detector, as...A
/D converter, b□...Transmitter coil, b2・
...Register I. -Ba coil, b...Characteristic magnetic field scanning coil, b'4.
・・Characteristic magnetic field generation coil, b, ・・Magnet for generating uniform static magnetic field, c, c ・・D/A converter, c, 0
48...DC power amplifier, C5...Highly stable DC power amplifier, do...Control computer, d2...Peripheral device, "+10" after "18,8'" on the 8th line .10
'1111. Add IIJ and add J, 12°12' after "Wado coil pair" on the 4th line of the same page.
. . . add a pair of rectangular harmonic coils. 12. In the drawings, Figure 1 (a), (b), Figure 2 and Figure 8 - Figure 2 (a), ■) as per the attached corrected drawings,
We have corrected Figures 3 and 4, and newly submitted Figures 1 and 5. (18) Male figure (ay (': () h 5

Claims (1)

[Claims] 14 Each of the coils is composed of a plurality of coils, and has a size such that the zero-order term components of the magnetic field due to the coils cancel each other out and become almost zero at a predetermined position between the coils. A first and a second coil group each supplied with a current having a direction are provided, and the first and the first
゛. The second coil group is combined so that the magnetic field components in a predetermined direction by the coil groups cancel each other out in a required range, thereby generating a bar-shaped characteristic magnetic field. Characteristics of magnetic resonance imaging +5 magnetic field generation method. By superimposing a substantially uniform static magnetism ta in the direction in which the magnetic field component of the composite magnetic field generated by the first and second coil groups becomes substantially zero, the high purity of the magnetic field strength, etc. The coil 2.1 is made to be substantially parallel to a direction in which no magnetic field component exists, and to be a closed curve in a plane perpendicular to that direction. 5 methods for generating a % magnetic field in nuclear magnetic resonance imaging according to item 1. 8. Two coils are differentially combined on the same axis so that the magnetic fields from those coils cancel each other out, and the coil spacing is set so that the third-order term of the change in magnetic field strength is minimized. The first and the twentieth differential coil pairs constitute the first and second coil groups, and the magnetic field strength changes are represented by a linear equation within a qualitatively required range; and the axes of the second differential coil pair are arranged to be orthogonal to each other, and the magnetic field components in the predetermined direction of the magnetic fields by the first and second differential coil pairs cancel each other out; supplying currents in the same direction to the first and second differential coil pairs, respectively. A characteristic magnetic field generation method in nuclear magnetic resonance imaging according to claim 1'1, characterized in that the magnetic field generation method is 0. Table 1. Directions in which there is no magnetic field component of the composite magnetic field produced by the first and second differential coil pairs Characteristic magnetic field generation method in magnetic resonance imaging. and at least a part of the second coil group is replaced with a magnet similar to the current flowing through the closed loop 1 in those coil groups. Characteristic magnetic field generation method in nuclear magnetic resonance imaging. 7. Consists of a combination of coils or magnets, 2.
(8) Magnetic field strength contours in a composite magnetic field in which a total magnetic field is generated whose axial magnetic field component is minimal at a predetermined position, and that magnetic field is combined with the magnetic fields from the first and second coil groups. The nucleus according to claim 2 or 4, characterized in that the static magnetic field is generated by a magnetic field generating means configured such that the surface is a closed curved surface in the form of a spherical or ellipsoidal surface. Characteristic magnetic field generation method in magnetic resonance imaging.