JP2671364B2 - Inspection equipment using nuclear magnetic resonance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention measures nuclear magnetic resonance (hereinafter, referred to as “NMR”) signals from hydrogen, phosphorus, etc. in a living body to determine the nuclear density distribution and relaxation time. The present invention relates to an inspection device using NMR that visualizes distribution and the like.

[Conventional technology]

2. Description of the Related Art Conventionally, an X-ray CT or an ultrasonic imaging apparatus has been widely used as a device for nondestructively inspecting the internal structure of a human body such as a head and abdomen. In recent years, attempts to perform similar tests using NMR phenomena have been successful, and it has become possible to acquire various types of information that could not be obtained with X-ray CT or ultrasonic imaging devices.

In the inspection device using the NMR phenomenon, it is necessary to separate and identify the signal from the inspection object corresponding to each part of the object, and one of them is to apply a gradient magnetic field to the inspection object and place each part of the object. Another method is to obtain position information by changing the magnetic field and then the resonance frequency or phase encoding amount of each part. The basic principle of this method is described in Journal of Magnetic Resonance (J.Magn.Reson.) Vol. 18, pp. 69-83 (1975),
Physics of Medinsin & Biology (Phys.Med. & Biol.) Vol. 25, pp. 751-756 (1
980) etc.

By the way, since the SN ratio in NMR increases in proportion to the 1 to 1.5th power of the static magnetic field H, the magnetic field strength should be increased as much as possible.
Attempts are being made to improve the SN ratio. The transmission / reception coil that has been used up to now (hereinafter simply referred to as “coil”) is a solenoid or a saddle type coil. However, as the magnetic field strength increases, the resonance frequency also increases. There has been a problem that the NMR frequency approaches or reverses, resulting in a decrease in sensitivity during reception or a decrease in generation efficiency of a high-frequency magnetic field during transmission.

In response to this, a new shape coil (referred to as “Alderman type coil”) has been proposed by Alderman et al. For the basic principles of this method, see the journal
The Journal of Magnetic Resonance (J.Magn.Reso
n.) Volume 36, pp. 447-451 (1975) has a related article.

FIGS. 5 and 6 show the above-mentioned Alderman type coil. FIG. 5 is a perspective view of the coil, FIG. 6 is an equivalent circuit diagram, and FIG. 7 is a feeding point of FIGS. 5 and 6. It is a figure which shows a tuning and matching circuit connected to A and A '. 4 in each figure
A, 4B are arms, 21-28 are wings, 31-34, 41 and 42
Is a capacitor, and 61 and 62 are guide rings.

[Problems to be solved by the invention]

The Alderman type coil has a decrease in sensitivity at the time of reception due to the approach or reversal of the self-resonance frequency and the NMR frequency of the coil due to the increase of the resonance frequency accompanying the increase of the magnetic field strength, or the transmission. Although it has been very effective in solving the problem of the reduction in the generation efficiency of the high-frequency magnetic field, it has been found that it has the following problems.

That is, the above-mentioned Alderman type coil has one feeding point.
This is the point where the tuning / matching circuit is connected at points (A and A'in FIGS. 5 and 6). As a tuning / matching circuit,
Although a modified example as shown in FIG. 8 is also conceivable, in the following description, the case of using the configuration example shown in FIG. 7 will be described.

In the tuning / matching circuit shown in FIG. 7, the capacitor 41
Let C _{1 be} the capacitance of C ₁ and C 42 be the capacitance of C ₂ , then feed point A,
A'will be connected to the transmitter or receiver via the combined capacity C ₁ C ₂ / C ₁ + C ₂ .

For this reason, the symmetry of the coil shown in FIGS. 5 and 6 is broken, which disturbs the potential distribution in the conductors that form the coil itself, expands the effect of the load on the human body, and breaks the uniformity. There was a problem. This causes the image quality to be deteriorated by appearing as "shading" on the image.

The present invention has been made in view of the above circumstances, and an object thereof is to solve the above-mentioned problems in the inspection apparatus using the conventional NMR, and to make the potential distribution in the conductor forming the coil uniform. NMR that can prevent deterioration of image quality
It is to provide an inspection device using the.

[Means for solving the problem]

The above-described object of the present invention is to provide a magnetic field generating means for each of a static magnetic field, a gradient magnetic field and a high frequency magnetic field, a signal detecting means for detecting an NMR signal from an inspection object, and a computer for calculating a detection signal of the signal detecting means. In an inspection apparatus using NMR having a means for outputting a calculation result by the computer, near a position symmetrical to a feeding point with respect to a symmetry axis and a plane of symmetry in one or both of the high-frequency magnetic field generation means and the signal detection means. In addition, it is constituted by an inspection device using NMR characterized by having a capacitance.

[Action]

In the inspection apparatus using NMR according to the present invention, capacitors are inserted at points symmetrical with respect to the feeding point of the coil. Also, the inserted capacitors 51, 52, 53 are
Since the capacitance is substantially equal to the combined capacitance of the capacitors 41 and 42 of the matching circuit, the symmetry of the coil can be improved. Therefore, it is possible to make the electric potential distribution in the conductors that make up the coil uniform, less susceptible to the effects of the human body,
It is possible to realize an inspection device using NMR equipped with a coil having good uniformity.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 4 is a block diagram of an inspection apparatus using NMR which is an embodiment of the present invention. In the figure, 1 is a control device, 2 is a high frequency pulse generator, 3 is a power amplifier, 4 is a high frequency magnetic field and a coil for both transmission and reception (or 4 is a high frequency magnetic field for detecting a signal generated from a target object 17). There are two types of coils: a generated coil and a reception coil for detecting a signal), 6 is an amplifier, 7 is a detector, and 8 is a signal processing device. In addition, 9, 10, 11 are respectively
Coils 12, 13 and 14 for generating a gradient magnetic field in the z direction and a direction perpendicular to the z direction are power supply units for driving the coils 9, 10 and 11, respectively. The gradient magnetic field generated by these coils makes the magnetic field distribution in the space where the inspection object is placed a distribution having a desired gradient.

The control device 1 has a function of outputting various commands to each device at a fixed timing. The output of the high-frequency pulse generator 2 is amplified by the power amplifier 3 to excite the coil 4. The signal component received by the coil 4 passes through the amplifier 6, is detected by the detector 7, and is converted into an image by the signal processing device 8.

The static magnetic field is generated by the coil 15 driven by the power supply 16. A human body 17 as an inspection object is installed on a bed 18, and the bed 18 is configured to be movable on a support base 19.

The present invention relates to an improvement of the coil 4.
The coil 4 has, for example, a diameter of 500 mm and a length of about 500 mm.

FIG. 1 is a perspective view showing details of the coil 4 of FIG. 4, and FIG. 2 is an equivalent circuit diagram of FIG. The Alderman type coil comprises two sets of signal electrodes consisting of arms 4A, AB and wings 21-28, a guard ring 61 facing wings 21-24 and a guard ring facing wings 25-28.
The capacitors 31 to 34 for adjusting the resonance frequency are respectively composed of wings 62, 24; 22, 23; 25, 28;
Connected between 6,27.

A tuning / matching circuit composed of capacitors 41 and 42 is connected to the feeding point as shown in FIG. 1 to perform impedance matching with a preamplifier or the like and fine adjustment of the resonance frequency. The capacitors 51, 52, 53 have a capacity equivalent to the combined capacity of the capacitors 41, 42, and the capacitor 51 includes the capacitors 31 to
With respect to the plane passing through 34, it is connected between the wings 21 and 22 and the guard ring 61 at a point symmetrical to the feeding point (position of the capacitors 41 and 42). In addition, the capacitor 52 is located at a position symmetrical with respect to the feeding point with respect to the center of the coil.
It is connected between 5,26 and the guard ring 62. Similarly, the capacitor 53 is connected at a position symmetrical to the feeding point with respect to the plane perpendicular to the central axis of the coil.

By thus connecting the capacitors 51 to 53 between the wings and the guard ring, the coil shown in FIG. 1 becomes a coil having good symmetry. The symmetry means that the cross section (plane A) passing through the center P of the coil and the coil center axis (XX ′) shown in FIG. 3 and the plane passing through the coil center line XX ′ (for example, plane B, It is symmetrical about plane C).

As a result, it is possible to make the potential distribution in the conductors that form the coils uniform, and it is possible to realize an inspection apparatus using NMR that is equipped with coils with good uniformity that is not easily affected by the human body or the like.

In the above embodiment, capacitors are inserted at three points which are symmetrical to the feeding point, but the present invention should not be limited to this, and as long as the symmetry is not impaired, it is at a point symmetrical to the feeding point. Other than the capacitor, it may be inserted in another place.

Regarding the Alderman coil itself,
The self-resonance frequency is limited to 100 MHz, so that it may not be possible to follow the increase in the resonance frequency accompanying the increase in magnetic field strength. The measures for this will be described below. That is, while making the transmission / reception area equal to or more than the conventional one, equipped with a coil capable of easily increasing the self-resonant frequency, an embodiment of the inspection apparatus using NMR,
This will be described below.

The features of the inspection apparatus using NMR shown in the present embodiment are that magnetic field generating means for static magnetic field, gradient magnetic field and high frequency magnetic field, signal detecting means for detecting an NMR signal from an inspection object, and the signal detecting means. NMR having a computer for performing the operation of the detecting means of the means and means for outputting the operation result by the computer
In the inspection device using, for one or both of the high-frequency magnetic field generation means and the signal detection means,
The point is that the length in the same direction as the static magnetic field is shorter than the length in the direction perpendicular to the static magnetic field.

In the inspection apparatus using NMR shown in the present embodiment, the coil 4 has the same length in the same direction as the static magnetic field than the length in the direction perpendicular to the static magnetic field, so that the reactance and the capacitance of the coil are reduced. Becomes smaller. Therefore, the self-resonant frequency of the coil is significantly improved, and it is possible to follow the increase of the resonance frequency accompanying the increase of the magnetic field strength.

In addition, if a plurality of the coils are arranged in the direction of the static magnetic field, there is an effect that the reception signal area is expanded and the sensitivity unevenness is reduced. This effect holds true not only for the above-mentioned coil but also for a conventional coil.

 Hereinafter, a specific description will be given.

FIG. 9A shows a slot resonator type embodiment, and FIG. 9B shows a saddle type embodiment. In the coil shown in the present embodiment, the self-resonance frequency can be arbitrarily set by adjusting the length of the coil in the same direction as the static magnetic field to be shorter than the length in the direction perpendicular to the static magnetic field. For example,
Self-resonant frequency is 40MH when diameter is 500mm and length is 500mm.
z, but if the length is 100 mm, the self-resonant frequency is 90 MH
z. Thus, reducing the length reduces the reactance and capacitance, resulting in
It becomes possible to raise the self-resonant frequency. The ninth
In the figures (a) and (b), 4 is a coil, 4A and 4B are arms, 21 to 24 are wings, and 63 is an insulator.

FIG. 10 shows another embodiment. As is clear from the figure, the coil shown in this embodiment is a plurality of the coils shown in FIG. 9 (a). In this embodiment, the coil shown in FIG. 9A is used, but it goes without saying that a conventional coil (for example, the coil shown in FIG. 5) may be used. The same applies to the examples described below. In this embodiment, there is an advantage that the transmission / reception area can be arbitrarily expanded by adjusting the number of coils. The symbols are attached according to FIG. 9 (a). Further, FIG. 11 shows an embodiment in the case of a saddle type coil.

As shown in FIGS. 10 and 11, shortening the length of the coil also reduces sensitivity unevenness. FIG. 12 shows a drive system for the coil. In this case, the S / N ratio at the coil output end does not change as compared with the conventional coil, but S
And N increase. For example, when 20 coils are arranged, both S and N in the coil are 4.5 times.

Conventionally, the system noise was largely dependent on the performance of the preamplifier.
By doubling, the noise of the coil becomes dominant,
Since the noise contribution of the preamplifier is reduced, the SN ratio is improved.

FIG. 13 shows a coil drive system. In this case, unlike the case of FIG. 12, an example in which an amplifier is connected to each coil is shown. In the case of such a configuration, since a small-sized amplifier can be used, it is not necessary to use a special element, and the effect of improving economy and reliability can be obtained.

FIGS. 14 (a) and 14 (b) show a composite example of the examples shown in FIGS. 12 and 13. Depending on the application and the performance of the amplifier, one coil or a plurality of coils may be provided. The blocks are connected in parallel, and an amplifier is added to each of the blocks.

In each of the above embodiments, the application of the present invention is described as the transmission / reception coil 4 for generating the high frequency magnetic field and detecting the signal generated from the target object 17, but as is well known, the high frequency magnetic field is used. The coil for generating and the signal detecting coil for detecting the signal generated from the target object 17 may be separate coils, and the present invention is also effective in this case.

〔The invention's effect〕

As described above, according to the present invention, the magnetic field generating means for the static magnetic field, the gradient magnetic field and the high frequency magnetic field, and
A high-frequency magnetic field generating means and a signal detecting means in an inspection apparatus using NMR, which has a signal detecting means for detecting an NMR signal, a calculator for calculating a detection signal of the signal detecting means, and an output means for outputting a calculation result by the calculator. Since the capacitance is added near the position of symmetry with respect to the feed point with respect to the axis of symmetry and the plane of symmetry in either or both of
This has the remarkable effect of realizing an inspection apparatus using NMR, which can make the potential distribution in the conductors forming the coil uniform and prevent deterioration of image quality.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a high frequency magnetic field generating and signal detecting coil which is a main part of an inspection apparatus using NMR showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG. FIG. 4 is a diagram for explaining the symmetry of the coil, FIG. 4 is an overall configuration diagram of the inspection apparatus using the NMR of the embodiment, FIG. 5 is a perspective view showing an Alderman type coil, and FIG. 6 is an equivalent circuit diagram of FIG. 7 and 8 are views showing an example of a tuning / matching circuit, FIGS. 9 to 11 are perspective views of gradient magnetic field generating and signal detecting coils showing other embodiments, and FIGS. The figure shows the drive system of the coil. 1: Control device, 2: High frequency pulse generator, 3: Power amplifier, 4:
High frequency magnetic field generation and signal detection coil, 6: signal detection system, 7: A /
D converter, 8: Signal processing device, 9, 10, 11: Gradient magnetic field generating coil, 15: Static magnetic field generating coil, 17: Target object, 4A, 4B: Arm, 31 to 34, 41 to 42, 51 to 53 : Capacitor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiki Murakami 1-280 Higashi-Kengokubo, Kokubunji-shi, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Hideki Kono 1-280 Higashi-Kengokubo, Kokubunji-shi, Tokyo Hitachi Ltd. Central Research Institute (56) Reference JP 62-207943 (JP, A) JP 61-56947 (JP, A) JP 61-73061 (JP, A) JP 59-99239 (JP, A) JP-A-63-115551 (JP, A)

Claims (5)

(57) [Claims] 1. An inspection apparatus using nuclear magnetic resonance comprising magnetic field generating means for static magnetic field, gradient magnetic field and high frequency magnetic field, and signal detecting means for detecting a nuclear magnetic resonance signal from an inspection object. One or both of the generating means and the signal detecting means are respectively provided at opposing positions on the outer peripheral surface of the cylinder, and the arm portion parallel to the central axis of the cylinder and the arm portion are provided. First and second outer conductors having wing portions extending in two directions along the outer periphery from both ends in the direction of the central axis, and the first and second outer conductors, respectively.
Cylindrical first and second inner conductors provided to face the wing portions of the second outer conductor, respectively, and the wing portion of the first outer conductor and the second outer conductor The wing portion of the first outer conductor is connected by capacitance, and has a feeding point at the one wing portion of the first outer conductor and the first inner conductor facing the one wing portion, It is composed of an Alderman type coil having a tuning / matching circuit at the feeding point, and electrostatic capacitance is added in the vicinity of a plurality of positions symmetrical to the feeding point with respect to the symmetry axis and plane of symmetry of the Alderman type coil. , The plurality of positions are positions between the wing portion of one of the second outer conductors and the first inner conductor, and the wing portion of the other of the first outer conductor and the second inner portion A position between the conductor and the second outer conductor Wherein the the other of said wing portion second
An inspection apparatus using nuclear magnetic resonance, which includes a position between the inner conductor and the inner conductor. 2. The inspection apparatus using nuclear magnetic resonance according to claim 1, wherein the added capacitance is the tuning /
An inspection apparatus using nuclear magnetic resonance, which has an electrostatic capacity equivalent to a combined electrostatic capacity of a plurality of electrostatic capacities constituting a matching circuit. 3. The inspection apparatus using nuclear magnetic resonance according to claim 1, wherein the axial length of the Alderman-shaped coil parallel to the direction of the static magnetic field is the static magnetic field. An inspection apparatus using nuclear magnetic resonance, characterized in that the diameter is shorter than the diameter of the Alderman type coil perpendicular to the direction. 4. The nuclear magnetic resonance inspection apparatus according to claim 3, wherein a plurality of the Alderman type coils are arranged in a direction parallel to the direction of the static magnetic field. Inspection device using resonance. 5. The nuclear magnetic resonance inspection apparatus according to claim 4, wherein at least a part of the plurality of Alderman-shaped coils arranged in parallel is connected in parallel. Inspection device using magnetic resonance.