JPH05261081A - Inspecting system using nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To enable the constitution of a QD coil which can receive a rotating magnetic field and carp improve sensitivity by constituting a signal detecting means with plural conductive loops and combining first and second coils having the magnetic flux directions in an image pickup section intersecting orthogonally with each other. CONSTITUTION:This detector is constituted of a controller 5, a high-frequency pulse generator 6, a coil 8 in common use for signal transmitting and receiving which generates a high-frequency magnetic field and detects the signal generated from an object 20 to be inspected, a detecter 10 and a signal processor 11, etc. The coil 8 is constituted of the two coils in which currents flow reversely from each other. These coils are disposed in superposition and are so constituted that the images of the same image pickup sections can be picked up. The sensitivity directions of the two coils intersect orthogonally with each other in the image pickup sections when the currents are passed reverseklyin these coils. These; coils are so disposed as to intersect orthogonally with the direction of the static magnetic field, by which the constitution of the QD coil with the two coils is enabled and the signals are received with the good sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures nuclear magnetic resonance (hereinafter referred to as "NMR") signals from hydrogen, phosphorus, etc. in a living body and visualizes nuclear density distribution and relaxation time distribution. NM
The present invention relates to an inspection device using the R phenomenon.

[0002]

2. Description of the Related Art Conventionally, X-ray CT and ultrasonic imaging devices have been widely used as devices for nondestructively inspecting internal structures such as the head and abdomen of a human body. In recent years, an attempt to perform the same examination using the NMR phenomenon has succeeded, and it has become possible to acquire various kinds of information that could not be obtained by the X-ray CT or the ultrasonic imaging apparatus.

First, the basic principle of the NMR phenomenon will be briefly described below. The nucleus is composed of protons and neutrons, and is regarded as a nuclear spin that rotates with angular momentum I as a whole.

Now, let us consider hydrogen nuclei. The hydrogen nucleus consists of one proton and rotates in the spin quantum number 1/2. Since the proton has a positive charge, the magnetic moment μ
And each nucleus can be thought of as a very small magnet (for example, in a ferromagnetic substance such as iron, magnetization occurs as a whole because the directions of the magnets described above are aligned. The above-mentioned magnets have different directions and no magnetization is generated as a whole. However, even in this case, when the static magnetic field H is applied, the respective atomic nuclei are aligned in the direction of the static magnetic field). In case of hydrogen nucleus, spin quantum number is 1
Since it is / 2, it is divided into two energy levels of -1/2 and +1/2. The difference ΔE between the energy levels is generally expressed by the following equation.

ΔE = γhH / 2π (Equation 1) where γ: gyromagnetic ratio, h: Planck's constant, and H: static magnetic field strength.

By the way, in general, a force of μ × H is applied to the atomic nucleus by the static magnetic field H, so that the atomic nucleus precesses around the axis of the static magnetic field at an angular velocity ω (Larmor angular velocity) shown by the following equation.

Ω = γH (Equation 2) When an electromagnetic wave (radio wave) having a frequency ω is applied to a system in such a state, a nuclear magnetic resonance phenomenon occurs, and generally an atomic nucleus corresponds to an energy difference ΔE represented by Equation 1. It absorbs the energy that is generated and shifts to a higher energy level. At this time, even if many various nuclei exist, not all the nuclei cause the nuclear magnetic resonance phenomenon. This is because the gyromagnetic ratio γ is different for each atomic nucleus, so that the resonance frequency expressed by Equation 2 is different for each atomic nucleus and only a specific atomic nucleus corresponding to the applied frequency resonates.

Next, the nucleus that has been transferred to a higher level by radio waves returns to the original level after a time determined by a certain time constant (called relaxation time). At this time, the angular frequency ω is changed from the nuclei transferred to the high level by radio waves.
The nuclear magnetic resonance signal of is emitted.

Here, the above relaxation time is further determined by spin-
It is divided into lattice relaxation time (longitudinal relaxation time) T ₁ and spin-spin relaxation time (transverse relaxation time) T ₂ . Generally, in the case of a solid, the spin-spin relaxation time T ₂ becomes short because interactions between spins are likely to occur. Since the absorbed energy first moves to the spin system and then to the lattice system, the spin-lattice relaxation time T ₁ is the spin-spin relaxation time T
_This is a very large value compared to ₂ . However, in the case of liquid, since the molecules are freely moving, the spin-spin and spin-lattice energy exchanges are about the same in ease.

The phenomenon described above is the same for phosphorus nuclei, carbon nuclei, sodium nuclei, fluorine nuclei, oxygen nuclei, etc., in addition to hydrogen nuclei.

In the inspection apparatus using the NMR phenomenon based on the above-mentioned basic principle, the signal from the inspection object is separated and separated.
It is necessary to identify, but one of them is to apply a gradient magnetic field to the inspection object, make the magnetic field placed on each part of the object different, and then make the resonance frequency or phase encode amount of each part different There is a way to get. The basic principle of this method is described in JP-A-55-20495, Journal of Magnetic Resonance (J. Magn. Res).
on. ) Vol. 18, pp. 69-83 (1975), Physics of Medicine & Biology (Phys. Med. & Biol.) Vol. 25, 751-75.
Although detailed description is omitted because it is reported on page 6 (1980), the principle of the most frequently used spin echo method will be briefly described below (see FIG. 3).

As shown in the overall configuration diagram of FIG.
Is a gradient magnetic field coil 1 of X, Y, Z for generating gradient magnetic fields in three directions orthogonal to the coil 18 for generating a static magnetic field H.
6, 17 and 15 (see FIG. 2) are installed in a high frequency magnetic field coil 8 for generating a high frequency magnetic field. Here, since the direction of the static magnetic field is generally the Z axis, the X and Y axes are as shown in FIGS. 1 and 2. Here, the subject 20
To image the cross section (X-Y plane) of, the gradient magnetic field and the high frequency magnetic field are driven according to the spin echo sequence shown in FIG. This will be described below with reference to FIG. 3. In the period A, the high frequency power amplitude-modulated with the gradient magnetic field Gz applied to the subject 20 is applied to the high frequency coil 8. The magnetic field strength of the cross section is the sum H + z of the static magnetic field H and the gradient magnetic field strength zGz at the position z.
It is indicated by Gz. On the other hand, since the amplitude-modulated high frequency power of the frequency ω has a specific frequency band ω ± Δω, the frequency ω or the gradient magnetic field strength is satisfied so as to satisfy ω ± Δω = γ (H + zG _z ) ... By selecting G _z , the hydrogen nuclear spins in the cross section will be excited. Here, γ represents the gyromagnetic ratio of hydrogen nuclei.
In the period B, the nuclear magnetic field excited previously by applying the gradient magnetic field G _y for Δt causes the resonance signal to have a frequency shift represented by Δω ′ = γyG _y Δt (Equation 4) depending on the position of _y . Period D
At, the resonance signal is collected while the gradient magnetic field G _x is applied.
At this time, the nuclear spin excited in the period A has a frequency difference represented by Δω ″ = γxG _x (Equation 5) depending on the position x. In the period C, a spin echo of the excited nuclear spin is obtained. A high-frequency magnetic field of 180 degrees and a gradient magnetic field G _z are applied to the period E. The period E is a waiting time until the nuclear spins return to equilibrium. The amplitude value of the gradient magnetic field G _y of the period B is changed by 256 steps and repeated. When the resonance signal is collected, 256 × 256 data can be obtained, and an image can be obtained by subjecting these data to two-dimensional Fourier transform.

In the imaging by the inspection apparatus using the NMR phenomenon as described above, improving the efficiency of the coil for generating or receiving the high frequency magnetic field has become an important issue for improving the image quality and shortening the imaging time. .. Conventionally, the surface coil has been used as a coil for imaging a narrow area with high sensitivity. However, if the surface coil is made large, the sensitivity is lowered, so that a surface coil having a high sensitivity capable of simultaneously capturing a wide area cannot be formed. On the other hand, Roemer et al. Proposed a new shape surface coil (referred to as "NMR phased array") to solve the above problems. This surface coil is a method that introduces the same idea as the phased array used in radar and ultrasonic waves, and arranges many small surface coils to image a wide area with the same sensitivity as each small surface coil. Is the way. This coil is described in Magnetic Resonance in Medicine (Magn. Reson. Med.) Vol. 16, No. 19.
A detailed description can be found on pages 2 to 225 (1990).

[0014]

The above-mentioned prior art is an effective coil configuration for the problem of simultaneously imaging a large area with the same sensitivity as a small surface coil.

However, the QD (Quad
rature detection) No consideration is given to the coil configuration.

An object of the present invention is to provide a surface coil having a QD coil structure capable of further improving the sensitivity in addition to the advantage that a small surface coil of the prior art can be imaged in a wide area at the same time with the same sensitivity. It is in.

[0017]

In order to achieve the above object, the signal detecting means is composed of a plurality of conductive loops, and the conductive loops are connected so that the currents flowing through the conductive loops are in opposite directions. It is composed of a first coil and a second coil composed of a conductive loop in which the sensitivity directions in the region of interest of the first coil are orthogonal to each other, and a plurality of sets of the first and second coils are formed on the same plane. I placed it.

[0018]

[Function] First and second magnetic flux directions orthogonal to each other in the imaging region
QD that can receive the rotating magnetic field by combining the coils of
Coil (also called CIRCULAR POLARIZATION COIL) configuration is possible. Therefore, since the magnetic flux passing through the imaging region can be efficiently captured, the magnetic flux can be received with higher sensitivity than a single coil. By arranging a plurality of sets of these coils, a wide area can be simultaneously imaged with high sensitivity.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an inspection apparatus using NMR which is an embodiment of the present invention. In FIG. 1, 5
Is a control device, 6 is a high frequency pulse generator, 7 is a power amplifier, 8 is a transmission / reception coil for generating a high frequency magnetic field and detecting a signal generated from the target object 20, 9 is an amplifier, 10 is a detector, and 11 is a detector. 1 shows a signal processing device. In this embodiment, the coil 8 is used as a transmission / reception coil, but transmission and reception may be performed by separate coils. Further, reference numerals 12, 13, 14 denote coils for generating a gradient magnetic field in the z direction and directions (x direction and y direction) perpendicular thereto, and 15, 16, 17 respectively denote the coils 12, 13, 14 respectively. It shows a power supply unit for driving the. The gradient magnetic field generated by these coils causes the magnetic field distribution in the space in which the inspection object is placed to have a desired gradient. In FIG. 1, the coils 13, 14 and 8 are drawn in order of decreasing size, but this is for convenience of showing the overall configuration, and it is not necessary to stick to this size and order.

The control device 5 has a function of outputting various commands to each device at a constant timing. The output of the high frequency pulse generator 6 is amplified by the power amplifier 7,
The coil 8 is excited. The signal component received by the coil 8 passes through the amplifier 9, is detected by the wave detector 10, and is then converted into an image by the signal processing device 11.

The static magnetic field is generated by the coil 18 driven by the power supply 19. In the present embodiment, the static magnetic field is generated by the normal conducting method using the coil 18, but it may be a superconducting method that does not require the power source 19 except during excitation. The subject 20 to be inspected is placed on the bed 21 and
Is configured to be movable on the support base 22.

FIG. 2 is an example showing the structure of the gradient magnetic field coil shown in FIG. 1 and the direction of the current to flow. An example is shown in which the coil 12 generates a z-direction gradient magnetic field, the coil 13 generates an x-direction gradient magnetic field, and the coil 14 generates a y-direction gradient magnetic field.
The coil 13 and the coil 14 have the same shape and are rotated by 90 degrees around the z axis. Actually, the coils 12, 13, and 14 are used by being wound on one cylindrical bobbin. These gradient coils have the same direction (z
A magnetic field is generated in the axial direction, and a magnetic field having a linear gradient (gradient) is generated along the z, x, and y axes, respectively.

The present invention relates to the improvement of the coil 8. Here, the coil 8 has a size of about 300 mm in diameter and about 300 mm in length for a head coil, for example. The present invention relates to a surface coil, and in the case of a coil intended for the spine, it has a size of, for example, a width of 150 mm and a length of 450 mm (depending on the configuration).

In the present embodiment, the coil shape is described as a rectangular flat plate type, but it is possible to change the shape of the coil into a circular shape or to bend it according to the body, and the present invention is not restricted.

Further, although the following examples show the case where the wire is made of a copper wire, it may be made of a copper pipe, a copper foil, a copper plate or the like.

The embodiment shown in FIG. 4 is an example of a surface coil composed of a rectangular coil 820 consisting of electrodes 321 to 324, a coil 830 in which currents flow in opposite directions through electrodes 331 to 334 and electrodes 335 to 338. Is. The coil 820 and the coil 830 are arranged so as to overlap with each other, and are configured so that the same imaging region can be imaged. FIG. 4B is a cross-sectional view showing the AA ′ cross section of FIG. Figure 4
In (b), the cross sections of the electrodes 321 and 323 of the rectangular coil 820 and the electrodes 332, 338 and 334, 336 of the coil 830 are shown.

FIG. 5 is an explanatory view showing the sensitivity direction of the embodiment shown in FIG. FIG. 5 shows a cross section taken along the line AA ′ of FIG. 4A, and the coils 820 and 830 of the embodiment shown in FIG.
6 schematically shows the sensitivity direction when a current flows in the direction shown in FIG. As shown in FIG. 5, the sensitivity directions of the coils 820 (electrodes 321 and 323) and 830 (electrodes 332, 334 and 336, 338) are orthogonal to each other in the imaging region. Further, the coils 820 and 830 are arranged so that the plane shown in FIG. 5 is orthogonal to the direction of the static magnetic field. Therefore,
The coils 820 and 830 can form a QD coil and can receive signals with high sensitivity.

The embodiment shown in FIG. 6 has a coil 82 shown in FIG.
It is a block diagram shown about the case where many surface coils which consist of 0,830 are arranged. In the embodiment shown in FIG. 6, four coils of the embodiment shown in FIG. 4 are arranged side by side. The first 3 digits of the electrode correspond to the electrode shown in Fig. 4, and the last 1
The digits represent the surface coil number. In the embodiment shown in FIG. 6, it is possible to widen the image capturing range as compared with the case of only one set of surface coils shown in FIG.

The embodiment shown in FIG. 7 is an illustration of a method for adjusting the interference between the coils of the embodiment shown in FIG. Figure 7
For simplicity, only the first two adjacent coils shown in FIG. 6 are shown. This is an embodiment showing a method for eliminating interference by adjusting the distance (L1, L2, L3) between the coils as shown in FIG. For example, L1 = L
Interference can be eliminated by setting 3 = 10 * L2.

The embodiment shown in FIG. 8 has coils 820 and 830.
An example of a method for extracting a signal from a surface coil made of In the embodiment shown in FIG. 8, electrodes 323 and 336 are divided into electrodes 32301, 32302 and 33601, 33602, capacitors 821, 831 are inserted and signals are taken out from both ends of the capacitors 821, 831. The coil 820 forms a resonance circuit with the inductance of the electrodes 321 to 324 and the capacitor 821, and is tuned to the resonance frequency of the target nuclide. The coil 830 forms a resonance circuit with the inductance of the electrodes 331 to 338 and the capacitor 831, and is tuned to the resonance frequency of the target nuclide. Actually H,
Capacitor 84 as shown in FIG. 9 is provided at points G and H ', G'.
A tuning / matching circuit composed of 0,841 is connected.

FIG. 10 shows a coil 820 composed of electrodes 320 to 324 and a coil 83 composed of electrodes 331 to 338.
An example of connection between 0 and the power amplifier 7 and the amplifier 9 will be shown. Although the single coil system in which transmission and reception are performed by the same coil is shown in FIG. 10, it goes without saying that a cross coil system in which transmission and reception are performed by different coils is also possible. In this case, it can be considered that the connection of the irradiation signal from the power amplifier 7 is lost, but it is necessary to separately provide an irradiation system that functions equivalently to this connection. In FIG. 10, the main purpose is to show the connection, and therefore the coils 820 and 830 are shown in a simplified manner. Further, in this embodiment, two sets of power amplifiers and amplifiers (power amplifiers 71 and 72, amplifiers 91 and 9) are used.
2) It shows the case of using it. The embodiment shown in FIG. 10 shows the case where the direction of the rotating magnetic field is the direction shown in the figure (clockwise). At the time of irradiation, the irradiation signal is separated into two systems, one is input to the power amplifier 71, and the other is input to the power amplifier 72 after delaying the phase of the irradiation signal by 90 degrees by the phase shifter 701. The signals amplified by the power amplifiers 71 and 72 drive the coils 820 and 830. Next, at the time of reception, the signals received by the coils 820 and 830 are amplified by the amplifiers 91 and 92, respectively, and then the coil 820
The phase shifter 901 shifts the phase of the signal received in step 90 by 90 degrees, and the combiner 100 combines the signals. When the direction of the rotating magnetic field is in the opposite direction (counterclockwise), the insertion positions of the phase shifters 701 and 901 are changed to the other channel as shown in FIG. 11, and the basic configuration is the same. is there. Although the separation of signals between the power amplifiers 71 and 72 and the amplifiers 91 and 92 is not shown in FIG. 10, they can be separated by a known method using a λ / 4 cable and a cross diode. Further, in addition to the present embodiment, there are various configuration methods such as a method of actively performing with a signal from the outside as a configuration method of driving and receiving when exciting and receiving with a rotating magnetic field.
Any configuration other than the configuration shown in is also possible.

Further, it goes without saying that the configuration shown in FIG. 10 is shown only for one set of coils and is actually required for all sets of coils to be arranged.

In the embodiments shown in FIGS. 4, 6, 7 and 8, the case where the coil is not divided by the capacitor is shown. However, when the resonance frequency becomes high and the coil cannot be tuned, or when the coil is not tuned. When the influence of the sample is large, these problems can be avoided by dividing the coil with a capacitor. An example of such a configuration is shown in FIG.
The electrodes of the coils 3310 to 3360 of the coil 830 are divided by the capacitors 831 to 836, and 3210 to 3 of the coil 820 are divided.
240 electrodes are divided by capacitors 821 to 824. In this embodiment, the capacitors are not divided so that the electrodes have the same length, but the capacitors may be divided so that the electrodes have the same length. If the electrodes are divided by capacitors so that the electrodes have the same length, the increase in the potential due to the inductance and the decrease in the potential due to the capacitance cancel each other out, and the potential can be kept low, so that the influence of the subject can be further reduced. It is necessary to appropriately change the number of divisions by the capacitor depending on the resonance frequency and the degree of influence by the subject.

Although the individual explanations have been given in the above description,
It goes without saying that these may be combined.

[0036]

According to the present invention, it is possible to provide a surface coil having a QD coil structure capable of simultaneously imaging a wide area with the same sensitivity as a small surface coil and further improving the sensitivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an inspection apparatus using NMR which is an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a gradient magnetic field coil and a direction of a flowing current.

FIG. 3 is an explanatory diagram of a spin echo method sequence.

FIG. 4 is a configuration diagram of a pair of surface coils according to an embodiment of the present invention.

5 is an explanatory diagram of a sensitivity direction in the embodiment shown in FIG.

6 is a configuration diagram of an embodiment in which a plurality of the embodiments shown in FIG. 4 are arranged.

FIG. 7 is a configuration diagram of an embodiment for preventing mutual interference in the embodiment shown in FIG.

FIG. 8 is a configuration diagram showing how to extract a signal in the embodiment shown in FIG.

FIG. 9 is a circuit diagram of a tuning / matching circuit.

FIG. 10 is a connection explanatory diagram of a coil, a power amplifier, and an amplifier.

FIG. 11 is a connection explanatory diagram of the same.

FIG. 12 is an equivalent circuit diagram when division is performed by capacitors.

[Explanation of symbols]

5 ... Control device, 6 ... High frequency pulse generator, 7, 71, 7
2 ... Power amplifier, 8 ... Transmission / reception coil, 9, 91, 9
2 ... Amplifier, 10 ... Detector, 11 ... Signal processing device, 1
2, 13, 14 ... Coil for generating gradient magnetic field, 15,
16, 17, 19 ... Power supply unit, 18 ... Coil for generating static magnetic field, 20 ... Subject, 21 ... Bed, 22 ... Supporting base,
701, 901 ... Phase shifter.

Claims (7)

[Claims] 1. A magnetic field generating means for a static magnetic field, a gradient magnetic field and a high frequency magnetic field, a signal detecting means for detecting a nuclear magnetic resonance signal from an inspection target, a computer for calculating a detection signal of the signal detecting means, and In an inspection apparatus using nuclear magnetic resonance having an output means for calculation by a computer, the signal detecting means is composed of a plurality of conductive loops, and the currents flowing through the conductive loops are conducted in opposite directions. Inspection using nuclear magnetic resonance, comprising a first coil connected to a loop and a second coil formed of a conductive loop, wherein the first and second coils are arranged on the same plane. apparatus. 2. The inspection apparatus using nuclear magnetic resonance according to claim 1, wherein in the region of interest, the sensitivity direction of the first coil and the sensitivity direction of the second coil are orthogonal to each other. 3. An inspection apparatus using nuclear magnetic resonance according to claim 2, wherein a plurality of signal detecting means each composed of the first coil and the second coil are used. 4. The inspection apparatus using nuclear magnetic resonance according to claim 3, wherein the plurality of signal detecting means are configured so that interference between them is eliminated. 5. The phase of signals from the first coil and the second coil are matched and added.
An inspection apparatus using the described nuclear magnetic resonance. 6. The inspection apparatus using nuclear magnetic resonance according to claim 3, wherein the plurality of signal detecting means are configured to be simultaneously operable. 7. An inspection apparatus using nuclear magnetic resonance according to claim 2, wherein one or both of the first and second coils has a conductive loop divided by a capacitive element.