JPH0373132A - Nuclear magnetic resonance image information leading out device - Google Patents

Abstract

PURPOSE:To allow the selective use of an RF coil always adequate in an inspection section with a high detection sensitivity by allowing the selection of a solenoid coil in a horizontal direction where the axial direction intersects nearly orthogonally with the main static magnetic field and a surface coil for a high-frequency magnetic field to be applied with the coil plane. CONSTITUTION:Opposite magnetic poles 31, 32 are disposed on the right and left of a human body 28 and the direction of the main static magnetic field 33 is set horizontal and is further set perpendicular to the body axis of a body 28 to be inspected. The solenoid coil 26 for RF is disposed in this main static magnetic field 33. The axial direction of the solenoid coil 26 is horizontal. In addition, this direction intersects perpendicularly with the direction of the main static magnetic field 33. The solenoid coil 26 which allows RF detection with a high sensitivity is usable when the entire part of the tomographic image of the head, body or other parts of the body 28 to be inspected is going to be uniformly photographed. The plane of the surface coil 35 is placed under the body 28 to be inspected or placed thereon and the RF detection is similarly executable with the high sensitivity when the narrow range is to be preponderantly inspected.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a device for deriving image information from a subject using nuclear magnetic resonance signals, and in particular the relationship between its static magnetic field, high-frequency magnetic field, and the subject. Related to placement.

"Prior Art" Regarding a device (hereinafter referred to as NMR-CT) that derives image information from a subject using nuclear magnetic resonance (hereinafter referred to as NMR) signals, for example, Japanese Patent Laid-Open No. 57-6347,
Magazine “Image Diagnosis” published by Shujunsha in 1981, Vol. 2, No. 1, 20~
It is shown on page 42, etc.

In the first place, the NMR phenomenon is that when certain atomic nuclei are placed in a static magnetic field, they resonate with a component perpendicular to the static magnetic field of a radio frequency magnetic field (hereinafter referred to as RF) that has a specific frequency proportional to the strength of the static magnetic field. When the atomic nucleus precesses around the applied direction of the static magnetic field at the frequency (resonance frequency), it absorbs that energy and is excited, and when the excitation by RF ends, the absorbed RF energy This is due to the fact that it relaxes while emitting a part of it as an NMR signal. This resonant frequency is known as the Larmor frequency and is ω. -T.+(, where γ is the gyromagnetic ratio of the original t'-nucleus, and H8 is the strength of the static magnetic field.

Therefore, when a magnetic field whose direction is the same as the main static magnetic field and whose strength changes along a certain direction, a so-called gradient magnetic field, is applied superimposed on the spatially uniform raw R field, R
Due to F, the atomic nuclei at each coordinate in the characteristic direction (hereinafter referred to as nuclear spin displacement) precess at different frequencies.

It can be said that NMR-CT uses this property to obtain the spatial distribution of information (nuclear spin density, relaxation time, etc.) contained in the NMR signal. good. FIG. 3 specifically shows the constituent elements of NMR-CT using a Brookcock diagram.

A main static magnetic field is applied to the subject (not shown in the figure) by the main static magnetic field generating magnet 11, and a gradient magnetic field is applied to the subject by the gradient magnetic field generating coil 12. The direction of this gradient magnetic field is 1Til ~ · direction with respect to the main static magnetic field, and the strength is gradient in three mutually intersecting directions, so that the spatial information of the subject can be discriminated from this +i field structure. be made into PF in the resonant frequency band from the transmitter 13
Power is supplied to the RF coil 14, which applies an RF magnetic field perpendicular to the to magnetic field to the subject, so that the generated NMR (, dj) from the subject is received by the RF coil 14. Supplied to machine 15. Reception (after the NMR signal is amplified and detected by three machines 15, A/I) is changed)? Converted to digital chair No. 1 with Rit 16°. The digital intelligence is manually input to the calculation m17 to perform calculations such as image reconstruction, and the image visualized by this autopsy is shown in Table 711.
displayed on the display 18. The main static magnetic field generating means 11 is excited by the static magnetic field generating f stage 19, and the gradient magnetic field generating coil 12
is excited by the gradient VA field generating means 21.

The direction of the magnetic field generated by the main static magnetic field generating magnet 11 and the gradient magnetic field generating coil 12 (hereinafter referred to as two static magnetic field directions) is generated or detected by the RF coil I4.
The most efficient RF application and detection is possible when the magnetic field generation structure is perpendicular to F [field direction (hereinafter referred to as RF direction)]. In order to satisfy this condition, NM
R−C′r is 1. They are roughly divided into two groups based on their magnetic field generation structure. Group l is the main static magnetic field generating means (f11
This is a case in which the direction of the +0 magnetic field caused by the magnetic field (Group 2) is perpendicular to the direction in which the subject is introduced into the main static magnetic field, and Group 2 is a case in which these two directions are almost parallel.

If the main static magnetic field generating means (magnet) currently considered for NMR-CT is divided, it becomes as shown in FIG. Among these, the permanent magnet [I iron core electromagnetic I] is the structure 1-Group 1, and is a superconducting magnet (the shape is coil-like).
It is said that there is no choice but to fall into Group 2. On this point, regular electricity 71! Magnets can be in group I or group 2 by design.

On the other hand, with RF coils, as mentioned earlier, there is a condition that the +0 magnetic field direction and the RF force direction are orthogonal, so if the magnet used is Group 1, a solenoid coil is used, and if the magnet is Group 2, a saddle type coil is used. is often used.

l'? to detect the NMR signal? The sensitivity of the F coil is naturally N
It is one of the important factors that determines the S/N of MR-CT6
Other factors that determine the S/N in NMII-CT include, for example, magnetic field strength, imaging method, and the like. Solenoid coils are about three times better in RF detection sensitivity than saddle-shaped coils, but recently there has been a strong demand for even higher detection sensitivity. Depending on the area to be examined (limited to areas close to the body surface), an RF detection coil called an IC face coil is increasingly being used.

This coil is normally used as shown in Figure 5.
I-reduced and has a spiral shape, the RF direction 1ii1 detected by the surface of the coil is a force 1i+1 normal to the plane of the coil. Therefore, the lJ'-fiber coil is normally used in such a way that the plane of the coil is placed parallel to the surface of the test site.

The subject in NMR-CT is a human body. When inspecting the human body using a surface coil 1
．． The main areas examined are the eyes, breasts, vertebrae, heart, liver,
Kidneys, etc. The human body has an elliptical cross-sectional shape in which the dimension in the left-right direction is larger than in the front-rear force direction, and the dimension in the height direction is overwhelmingly larger than the dimension in the cross-section. Furthermore, in NMR-CT, the test subject is usually examined while lying horizontally on his or her back or stomach. Taking these things into consideration, surface coils detect R by applying the coil plane parallel to the front or back of a lying human body as described above.
It is preferable to use it so that it is perpendicular to the F force direction.

"Problem to be Solved by the Invention" In order to make the direction of RF force detected by the surface coil vertical, the direction of the static magnetic field must be made horizontal according to the above-mentioned condition of perpendicularity to the direction of the static VjL field and the direction of the RF force. .

In NMR-CT using the magnetic field gradient method, which uses a main static magnetic field and gradient magnetic fields with gradient strengths in the same direction as the main static magnetic field and in three directions that cross each other, the main static magnetic field direction in the group 2 magnet system is horizontal. Even if it is parallel to the body axis of the human body, it is originally horizontal. However, in the case of Group 1 magnet systems, conventionally only those with the main static magnetic field direction in the vertical direction have been manufactured.In other words, the main static magnetic field generating means using a permanent magnet has different magnetic poles of the permanent magnet as shown in Figure 6. 22 and 23 are arranged above and below to face each other and are connected to each other by a magnetic yoke 24, and the magnetic poles 22 and 23
A main static magnetic field 25 in the vertical direction is formed between the opposing surfaces. For example, an RFF solenoid coil 26 is placed within this main static magnetic field 25.
The axis of the solenoid coil 26 is horizontal, and the main static magnetic field 25 faces the vehicle surface. Solenoid coil 26
A bed plate 27 is arranged horizontally in parallel with the axis of the solenoid coil 26 so as to be freely removable and removable, and a subject 28 is placed on the bed plate 27. In addition, the main static magnetic field generating means using a normal conducting magnet is the seventh
As shown in the figure, main static magnetic field coils 31 and 32 are arranged vertically and oppositely, and the axes of these main static magnetic field coils 31 and 32 are vertical and on the same line. Although not shown, for example, an RF solenoid coil and a base plate 27 are provided.

In this way, in conventional Group 1 magnet systems, the direction of the static magnetic field is vertical, so the R and F directions of the surface coil cannot be used vertically, and the characteristics cannot be effectively demonstrated. There was a problem.

The purpose of this invention is to increase the RFF output sensitivity by about 3% compared to the saddle type coil.
To provide an NMR-CT that can selectively use the solenoid coil and a surface coil effective for inspection near the human body surface with high detection sensitivity in a Group 1 magnet system that can use a solenoid coil that is twice as superior. .

"Means for Solving the Problem" A nuclear magnetic resonance image information deriving device of the present invention for achieving the above object includes main static magnetic field generating means for forming a main static magnetic field;
In a nuclear magnetic resonance image derivation apparatus comprising a gradient magnetic field forming means for forming gradient magnetic fields tilted in three directions that are the same as the main static magnetic field and intersect with each other, and a high-frequency magnetic field solenoid coil, the main static magnetic field generation The main static magnetic field of the means is formed in the horizontal direction, and the solenoid coil is disposed within the main static magnetic field, and its axial direction is in the horizontal direction that intersects the main static magnetic field perpendicularly to the main static magnetic field. When deriving the magnetic field, the solenoid coil and a surface coil for high-frequency magnetic field, which is used by applying the coil plane to the horizontal surface of the subject introduced into the solenoid coil, are configured so as to be selectable. Nuclear magnetic resonance image derivation device.

As the main static magnetic field generating means in the present invention, either a permanent magnet or an electromagnet can be used.

A coil is generally used as the gradient magnetic field forming means.

As the RF coil for detecting the NMR signal, a solenoid coil with high detection sensitivity is used as described above. This solenoid coil is usually shared even when RF generation occurs. However, as long as RF light is generated, there is no need to worry about detection sensitivity, so a saddle-shaped coil or the like may be used.

As the surface coil, a flat, spiral-shaped one as shown in Fig. 5 is suitably used.Surface coils are generally used for relatively small scales for inspecting superficially local parts of a subject. Since it is a coil of
Used to detect signals. Therefore, when using a surface coil, a solenoid coil or the like is used for RF generation.

To select the solenoid coil and the surface coil when detecting an NMR signal and deriving image information,
This can be easily done by rewiring the solenoid coil output and the separately prepared surface coil output. Further, the wiring may be changed using a changeover switch.

Embodiment 1j Figure 1 shows an example in which a main static magnetic field is formed by a main static magnetic field forming means using a permanent magnet in NMR-CT according to the present invention. (Although a separate coil is used, the circuit is omitted in the figure.) In this embodiment, different magnetic poles 31 and 32 of the permanent magnet are arranged horizontally, facing each other at 7g. A main static magnetic field 33 in the horizontal direction is formed between the opposing surfaces of the R1 pa solenoid coil 26 is arranged within this main static magnetic field 33.The axial direction of the solenoid coil 26 is the horizontal force direction,
And it intersects perpendicularly with the direction of the main static magnetic field 33. A base plate 27 within the solenoid coil 26 is disposed so as to be movable in and out in a direction parallel to the axis of the solenoid coil 26, and a subject 28 is disposed on the base plate 27. That is, the subject 28 is introduced into and led out of the main static magnetic field 33 perpendicularly to the main static magnetic field 33 from the horizontal force direction. magnetic pole 3
1.32 are connected to each other by a magnetic yoke 34. In other words, the opposing magnetic poles 31 and 32 are placed at an angle of °ζh with respect to the human body (subject) 28, and the direction of the main static magnetic field 33 is horizontal and perpendicular to the body axis of the subject 28. There is.

Because of this configuration, 1. 'fJj1. ! ! ! If you want to uniformly image the entire tomographic image of 280 bodies and 1 force and 2 forces,
A solenoid coil 26 capable of highly sensitive RF detection can be used, and when inspecting a narrow area, the plane of the surface coil 35 can be placed below or directly above the subject 2). , similarly, R1-' can be detected with high sensitivity.

"Example 2" When using normally conductive magnetic Zi as the main static magnetic field forming means,
For example, as shown in Fig. 2, the static magnetic field coils 36 and 37 are arranged with tJ 1i11 between the horizontal forces, and their axis is set to water '1L, so that a main static magnetic field is formed in the horizontal direction. An RF solenoid: 1 coil 26 and a base plate 27 are arranged at the opening of the magnetic field coils 36 and 37. 1] Static magnetic field coil 36.
37 is excited by a power source 38.

The gradient magnetic field forming means in the X, I/, and Z directions are horizontally connected by three coils 5 (not shown) and their power supplies.

"Effects of the Invention" As stated above, in the NMR-CT of the present invention, the characteristics of both the solenoid coil and the surface coil, both of which have high detection sensitivity, can be effectively utilized. Therefore, it is possible to always select and use an RF coil suitable for the inspection site.

[Brief explanation of drawings]

Figure 1 shows the NMR- of this invention when a permanent magnet is used.
The main part of the CT is not shown, and Fig. 2 shows the main part of the NMR-Ci'' of this invention when a normal conductive magnet 11 is used; - Figure 4 is a diagram showing an example of CT, Figure 4 is a diagram showing the classification of 11 stages (magnets) from the static fti field, Figure 5 is a diagram showing the shape of a surface coil, Figure 6 is a diagram showing the conventional FIG. 7 is a diagram showing a conventional normal conductive magnet for NMR-CT.

Claims (1)

[Claims] (1) a main static magnetic field forming means for forming a main static magnetic field; a gradient magnetic field forming means for forming gradient magnetic fields tilted in three directions that are the same direction as the main static magnetic field and intersect with each other;
In a nuclear magnetic resonance image information deriving device comprising a solenoid coil for a high frequency magnetic field, the main static magnetic field of the main static magnetic field forming means is formed in a horizontal direction, the solenoid coil is disposed within the main static magnetic field, and Its axial direction is a horizontal direction that intersects the main static magnetic field almost perpendicularly, and when deriving image information, the plane of the coil is applied to the horizontal surface of the solenoid coil and the subject introduced into the solenoid coil. A nuclear magnetic resonance image deriving device characterized in that it is configured such that a surface coil for a high frequency magnetic field can be selected for use in a nuclear magnetic resonance image deriving device.