JPH0410815B2 - - Google Patents

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.

"Conventional technology" A device (hereinafter referred to as NMR) that derives image information from a subject using nuclear magnetic resonance (hereinafter referred to as NMR) signals.
(written as NMR-CT), for example,
It is shown in Publication No. 57-6347 and in the magazine "Image Diagnosis" published by Shujunsha in 1988, Vol. 2, No. 1, pp. 20-42.

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
This is known as the Larmor frequency, and ω _e =
It is given by γ・H _e . Here, γ is the gyromagnetic ratio of the atomic nucleus, and _He is the strength of the static magnetic field.

Therefore, when a so-called gradient magnetic field, which has the same direction as the main static magnetic field and whose strength changes along a specific direction, is applied superimposed on the spatially uniform main static magnetic field, RF generates the The atomic nuclei at each coordinate in the characteristic direction (hereinafter referred to as nuclear spin) precess at different frequencies.

It can be said that NMR-CT uses this property skillfully to determine the spatial distribution of information contained in NMR signals (nuclear spin density, relaxation time, etc.). FIG. 3 specifically shows the constituent elements of NMR-CT using a block diagram. A main static magnetic field is applied to the subject (not shown) by the main static magnetic field generating magnet 11, and a gradient magnetic field is further applied to the subject by the gradient magnetic field generating coil 12. The direction of this gradient magnetic field is the same as that of the main static magnetic field, and the strength is gradient in three mutually intersecting directions, and this magnetic field configuration makes it possible to discriminate the spatial information of the subject.
PF power in the resonant frequency band is supplied from the transmitter 13 to the RF coil 14, which applies an RF magnetic field perpendicular to the main static magnetic field to the subject, and as a result, the generated NMR signal from the subject is The signal is received by the RF coil 14 and supplied to the receiver 15.
After the NMR signal is amplified and detected by the receiver 15,
The A/D converter 16 converts it into a digital signal.
The digital signal is input to the computer 17 to perform calculations such as image reconstruction, and the image visualized by this calculation is displayed on the display 18. The main static magnetic field generating magnet 11 is excited by the static magnetic field generating means 19, and the gradient magnetic field generating coil 12 is excited by the gradient magnetic field generating means 21.
It is excited by

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 the static magnetic field direction) is the direction of the RF magnetic field generated or detected by the RF coil 14 (hereinafter referred to as the RF direction)
The most efficient RF application and detection is possible when the magnetic field generation structure is orthogonal to the RF field. In order to satisfy this condition, NMR-CT is roughly divided into two groups based on the magnetic field generation structure. group 1
Group 2 is a case where the direction of the main static magnetic field generated by the main static magnetic field generating means (magnet) and the direction in which the subject is introduced into and guided out of the main static magnetic field are perpendicular, and Group 2 is a case where both these directions are parallel to each other.

The main static magnetic field generating means (magnets) currently considered for NMR-CT can be classified as shown in Figure 4. Among these, it is said that permanent magnets and iron-core electromagnets fall into Group 1 due to their structure, and superconducting magnets (having a coil-like shape) must fall into Group 2. In this regard, normal conducting magnets can be in either Group 1 or Group 2 due to their design.

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

The sensitivity of the RF coil that detects NMR signals is naturally one of the important factors that determines the S/N of NMR-CT. Other factors that determine S/N in NMR-CT include, for example, magnetic field strength, imaging method, and the like. Solenoid coils are approximately 3 times better in RF detection sensitivity than saddle-shaped coils, but recently there has been a strong demand for even higher detection sensitivity, and depending on the examination area (limited to areas close to the body surface), RF called Surf S Coil
Detection coils are increasingly being used. As shown in FIG. 5, this SURF S coil usually has a planar spiral shape, and the direction of RF detected by the SURF S coil is perpendicular to the plane of the coil. Therefore, the SURFS coil is usually used in such a manner that the plane of the coil is applied parallel to the surface of the test site.

Most subjects in NMR-CT are human bodies. When examining the human body using a surf coil, the main areas to be examined are the eyes, breasts,
These include the spine, heart, liver, kidneys, etc. The human body has an elliptical cross-sectional shape, with the dimension in the left-right direction larger than the front-back direction, and the dimension in the height direction is overwhelmingly larger than the dimension in the cross-sectional direction. In addition, in NMR-CT, the subject lies horizontally,
Or, it is normal to undergo the examination while lying on your stomach. Taking these things into consideration, it is preferable to use the SURF S coil with its coil plane parallel to the front or back of the lying human body as described above, and the RF direction to be detected to be vertical. .

"Problem to be solved by the invention" In order to make the RF direction detected by the SURF S coil vertical, the direction of the static magnetic field must be made horizontal due to the condition that the direction of the static magnetic field and the RF direction are orthogonal to each other as described above. .

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 transverse. Even though it is parallel to the body axis of a sagging human body, it is originally horizontal. However, in the case of Group 1 magnet systems, only those in which the main static magnetic field direction is vertical are conventionally manufactured. That is, in the main static magnetic field generating means using permanent magnets, as shown in FIG. A main static magnetic field 25 in the vertical direction is formed between the opposing surfaces. For example, an RF solenoid coil 26 is disposed within the main static magnetic field 25, and the axis of the solenoid coil 26 is horizontal and perpendicular to the main static magnetic field 25. 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. The main static magnetic field generating means using normally conducting magnets has main static magnetic field coils 31 and 32 arranged vertically facing each other, as shown in FIG. 7, and the axes of these main static magnetic field coils 31 and 32 are vertical. Although not shown in the figure, an RF solenoid coil, for example, is disposed between these coils 31 and 32.
A base plate 27 is also arranged.

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

The purpose of this invention is to combine the solenoid coil with a surf-s coil, which is effective for inspection near the surface of the human body, in a Group 1 magnet system that can use a solenoid coil, which has an RF detection sensitivity approximately three times better than a saddle-shaped coil. Can be used selectively with high detection sensitivity
Our purpose is to provide NMR-CT.

"Means for Solving the Problems" To achieve the above object, the nuclear magnetic resonance image information deriving apparatus of the present invention includes a main static magnetic field forming means for forming a main static magnetic field, and a main static magnetic field forming means that In a nuclear magnetic resonance image deriving apparatus comprising a gradient magnetic field forming means for forming gradient magnetic fields inclined in three intersecting directions, and a solenoid coil for a high frequency magnetic field, the main static magnetic field of the main static magnetic field forming means is horizontally inclined. The solenoid coil is arranged within the main static magnetic field, and its axial direction is in a horizontal direction substantially perpendicularly intersecting the main static magnetic field, and when deriving image information, the solenoid coil and 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 by applying the coil plane to the horizontal surface of a subject introduced into the solenoid coil. .

As the main static magnetic field forming 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 also used for RF generation. However, as far as RF generation is concerned, there is no need to worry about detection sensitivity, so a saddle-shaped coil or the like may be used.

As the surf coil, one having a planar spiral shape as shown in FIG. 5 is preferably used. In general, a surface coil is a coil of relatively small size for examining a localized area on the surface of a subject, and is therefore usually used to detect NMR signals. Therefore, when using the SURF S coil, the solenoid coil or the like is used for RF generation.

When detecting NMR signals and deriving image information, the solenoid coil and the SurfS coil can be selected by changing the wiring between the output of the solenoid coil and the output of the separately prepared SurfS coil. It's easy to do. Alternatively, the wiring may be changed using a changeover switch.

Embodiment 1 FIG. 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. (The gradient magnetic field forming means uses a separate coil, but it is omitted in the figure.) In this embodiment, different magnetic poles 31 of the permanent magnet,
32 are arranged horizontally to face each other, and a horizontal main static magnetic field 33 is formed between the opposing surfaces of the magnetic poles 31 and 32. Within this main static magnetic field 33
An RF solenoid coil 26 is arranged. The axial direction of the solenoid coil 26 is horizontal and perpendicularly intersects 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 axial direction thereof, 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 from the horizontal direction perpendicularly to the main static magnetic field 33. The magnetic poles 31 and 32 are connected to each other by a magnetic yoke 34. That is, the opposing magnetic poles 31 and 32 are arranged on the left and right sides of the human body (subject) 28, and the direction of the main static magnetic field 33 is horizontal,
Furthermore, it is perpendicular to the body axis of the subject 28.

With this configuration, when uniformly capturing the entire tomographic image of the head or torso of the subject 28, it is possible to use the solenoid coil 26, which is capable of highly sensitive RF detection, and to focus on inspecting a narrow area. In this case, the plane of the SURF S coil 35 should be
Place it under 8 or put it on top of it, and it will have the same high sensitivity.
Can perform RF detection.

"Example 2" When using a normally conducting magnet as the main static magnetic field forming means, for example, as shown in FIG. 2, the static magnetic field coil 3
6 and 37 are arranged to face each other in the horizontal direction, and their axes are set horizontally to form a main static magnetic field in the horizontal direction.The RF solenoid coil 26 and the base plate 27 are arranged between these static magnetic field coils 36 and 37. Allotted. The main static magnetic field coils 36, 37 are excited by a power source 38. Note that the gradient magnetic field forming means in each of the X, Y, and Z directions is constituted by three coils (not shown), their power supplies, and the like.

"Effects of the Invention" As described above, in the NMR-CT of the present invention, the characteristics of both the solenoid coil and the surf S coil, both of which have high detection sensitivity, can be effectively utilized. Therefore, it is possible to always select and use the most suitable RF coil for the examination area.

[Brief explanation of drawings]

Figure 1 shows how this invention works when permanent magnets are used.
Figure 2 is a diagram showing the main parts of NMR-CT of the present invention when a normal conducting magnet is used. Figure 3 is a block diagram showing an example of NMR-CT. Figure 4 shows the classification of static magnetic field generating means (magnets), Figure 5 shows the shape of the SURF S coil, Figure 6 shows the conventional permanent magnet for NMR-CT, and Figure 7 shows the conventional permanent magnet. FIG. 2 is a diagram showing a normal conducting magnet for NMR-CT.

Claims (1)

[Scope of 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 the same direction as the main static magnetic field and in three mutually intersecting directions, and a high frequency magnetic field forming means for forming a main static magnetic field. In a nuclear magnetic resonance image information deriving apparatus equipped with a magnetic field solenoid coil, the main static magnetic field of the main static magnetic field forming means is formed in a horizontal direction perpendicular to a direction in which a subject is introduced into and extracted from the main static magnetic field. , the solenoid coil is disposed within the main static magnetic field, and its axial direction is in a horizontal direction substantially perpendicularly intersecting the main static magnetic field, and when deriving image information, the solenoid coil and the solenoid A nuclear magnetic resonance image information deriving device characterized in that it is configured such that a surface coil for a high frequency magnetic field can be selected for use by applying a coil plane to the horizontal surface of a subject introduced into the coil.