JPH04361738A - Inspection device using nuclear magnetism resonance - Google Patents

Abstract

PURPOSE:To make image photographing with high sensitivity and high resolution and perform inspection noninvasively by using a solenoid in the form admitting a hand or wrist, and furnishing if necessary a mechanism to press this hand or wrist. CONSTITUTION:An electrode consisting of a Cu wire is enwrapped on a cylindrical bobbin 300, and a solenoid is fabricated. Fabrication will be easier if circular electrodes 320, 321, 322 are enwrapped on the bobbin 300 and connected aslant using electrodes 323, 324, because it eliminates need for forming spirally. The bobbin 300 is embodied in such a form that its side faces are open so as to admit the hand or wrist 201 of the person to undergo inspection. The bobbin 300 is equipped in its inside with airtight sacks for pressing 601, 602 made of a material with possibility of expansion and contraction, and air, etc., of an appropriate pressure is injected externally into these sacks so as to generate pressing. Thereby image photographing can be made with high sensitivity and high resolution, and inspection can noninvasively be conducted.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention measures nuclear magnetic resonance (hereinafter referred to as "NMR") signals from hydrogen, phosphorus, etc. in living organisms, and visualizes nuclear density distribution, relaxation time distribution, etc. N.M.
This 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 non-destructively inspecting internal structures such as the head and abdomen of a human body. In recent years, attempts to perform similar inspections using NMR phenomena have been successful, and it has become possible to obtain a wide variety of information that could not be obtained with X-ray CT or ultrasonic imaging devices.

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

[0004] Let us now consider the hydrogen nucleus. The hydrogen nucleus consists of one proton and rotates as represented by the spin quantum number 1/2. Protons have a positive charge, so as the nucleus rotates, the magnetic moment μ
occurs, and each atomic nucleus can be thought of as a very small magnet. (For example, in a ferromagnetic material such as iron, magnetization occurs as a whole because the directions of the magnets mentioned above are aligned. On the other hand, in hydrogen etc., the directions of the magnets mentioned above are different and no magnetization occurs as a whole.However, Even in this case, if a static magnetic field H is applied, each atomic nucleus will align in the direction of the static magnetic field.) In the case of hydrogen nuclei, the spin quantum number is 1/2, so it is divided into -1/2 and +1/2. It is divided into two energy levels. This difference ΔE between energy levels is generally expressed by the following equation.

[0005]

[Equation 1] ΔE=γhH/2π Here, γ: gyromagnetic ratio, h: Planck's constant, H: static magnetic field strength.

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

[0007]

[Equation 2] ω = γH When an electromagnetic wave (radio wave) with a frequency of ω is applied to a system in this state, a nuclear magnetic resonance phenomenon occurs, and the atomic nucleus generally absorbs energy corresponding to the energy difference ΔE expressed by the equation 1. and transitions to a higher energy level. At this time, even if a large number of various atomic nuclei exist, not all of them cause nuclear magnetic resonance phenomena. This is because the gyromagnetic ratio γ differs for each atomic nucleus, so that the resonance frequency shown by Equation 2 differs for each atomic nucleus, and only a certain atomic nucleus corresponding to the applied frequency resonates.

[0008]Next, the atomic nucleus that has been transitioned to a higher level by radio waves returns to its original level after a time determined by a certain time constant (called relaxation time). At this time, the angular frequency ω from the atomic nucleus transitioned to a higher level by the radio waves
A nuclear magnetic resonance signal is emitted.

[0009] Here, the above-mentioned relaxation time is further changed to spin-
It is divided into lattice relaxation time (longitudinal relaxation time) T1 and spin-spin relaxation time (transverse relaxation time) T2. Generally, in the case of a solid, interaction between spins is likely to occur, so the spin-spin relaxation time T2 becomes short. Furthermore, since the absorbed energy is first transferred to the spin system and then to the lattice system, the spin-lattice relaxation time T1 has a much larger value than the spin-spin relaxation time T2. However, in the case of a liquid, the molecules move freely, so the ease with which spin-spin and spin-lattice energy exchange occurs is about the same.

The above-mentioned phenomenon is the same for phosphorus, carbon, sodium, fluorine, oxygen, and the like in addition to hydrogen nuclei.

[0011] In an inspection device using the NMR phenomenon based on the basic principle described above, the signal from the inspection object is separated and
One way to do this is to apply a gradient magnetic field to the object to be inspected, to vary the magnetic field placed on each part of the object, and then to vary the resonant frequency or phase encode amount of each part to obtain position information. There is a way to get it. The basic principle of this method is described in Japanese Patent Application Laid-Open No. 55-20495, Journal of Magnetic Resonance (J.
Magn. Reason. ) Volume 18, pages 69-83 (
(1975), Physics of Medicine and Biology (Phys. Med. & Biol.
) Vol. 25, pp. 751-756 (1980), so a detailed explanation will be omitted, but the principle of the most commonly used spin echo technique will be briefly explained below.

As shown in the overall configuration diagram of FIG.
A coil 18 that generates a static magnetic field H and an X, Y, and Z gradient magnetic field coil 1 that generates gradient magnetic fields in three directions orthogonal to each other.
6, 17, and 15 (see FIG. 5), and are installed in a high-frequency magnetic field coil 8 that generates a high-frequency magnetic field. Here, since the direction of the static magnetic field is generally set as the Z axis, the X and Y axes are as shown in FIGS. 4 and 5. Here, subject 20
To image a cross section (X-Y plane) of , a gradient magnetic field and a high-frequency magnetic field are driven according to the spin echo sequence shown in FIG. To explain below using FIG. 10, in period A, amplitude-modulated high-frequency power is applied to the high-frequency coil 8 while a gradient magnetic field Gz is applied to the subject 20. The magnetic field strength in the cross section is expressed as the sum H+zGz of the static magnetic field H and the gradient magnetic field strength zGz at position z. On the other hand, since the amplitude modulated high frequency power of frequency ω has a specific frequency band ω±Δω,

[0013]

[Equation 3] The frequency ω or the gradient magnetic field strength Gz is adjusted to satisfy ω±Δω=γ(H+zGz)
By choosing , the hydrogen nuclear spin in the cross section will be excited. Here, γ indicates the gyromagnetic ratio of the hydrogen nucleus. In period B, by applying a gradient magnetic field Gy for a period of Δt, the previously excited nuclear spins change depending on the position of y.

[0014]

A frequency shift of Δω'=γyGyΔt is caused in the resonance signal. Period D
Resonant signals are collected while applying a gradient magnetic field Gx. At this time, the nuclear spin excited during period A is

[0015]

[Equation 5] There will be a frequency difference represented by Δω"=γxGx. During period C, a 180 degree high frequency magnetic field and a gradient magnetic field Gz are applied to obtain spin echoes of excited nuclear spins. Period E is the waiting time until the nuclear spin returns to equilibrium.If the amplitude value of the gradient magnetic field Gy in period B is changed by 256 steps and resonance signals are repeatedly collected, 256 x 256 data can be obtained. An image can be obtained by performing two-dimensional Fourier transformation.

[0016] In imaging using an inspection device that uses the NMR phenomenon as described above, improving the efficiency of the coil that generates or receives a high-frequency magnetic field is an important issue that will lead to improved image quality and shortened imaging time. .

By the way, the S/N ratio in an inspection device using the NMR phenomenon increases in proportion to the 1st to 1.5th power of the static magnetic field strength H. Therefore, by increasing the static magnetic field strength as much as possible, the S/N
Efforts are being made to improve the ratio. Transmitting/receiving coils that have been used so far (hereinafter simply referred to as "coils")
is a saddle-shaped coil. However, as the static magnetic field strength increases, the resonance frequency of the atomic nucleus also increases, resulting in a situation where the self-resonance frequency of the coil approaches or reverses the NMR frequency, resulting in a decrease in sensitivity during reception or an increase in the high-frequency magnetic field during transmission. This has led to the problem of reduced generation efficiency. In response, Alderman et al. proposed a coil with a new shape (referred to as an "Alderman coil"), which solved the above problems. This coil is described in the Journal of Magnetic Resonance (J. Magn. Resonance).
n. ) Vol. 36, pp. 447-451 (1979) has a detailed description. As shown in FIGS. 6 and 7, the Alderman type coil has guard ring electrodes 131, 132 and arm electrodes 111, 112.
, a wing electrode 121 connected to the arm electrode 111,
122, 125, 126, wing electrodes 123, 124, 127, 128 connected to the arm electrode 112, and a capacitor 14 provided between the wing electrodes 121, 124.
1, a capacitor 142 provided between wing electrodes 122 and 123, a capacitor 143 provided between wing electrodes 125 and 128, and a capacitor 144 provided between wing electrodes 126 and 127. The tuning/matching circuit shown in FIG. 8 is composed of capacitors 201 and 202, and is connected to points H and G in FIG. Figure 9 is Figure 6,
FIG. 8 is a plan view of the outer portion of FIG. 7 that includes arm electrodes 111, 112, wing electrodes 121-128, and capacitors 141-144.

[0018]

[Problems to be Solved by the Invention] In the above-mentioned prior art, in the horizontal magnetic field method in which the static magnetic field H is horizontal and the subject is inserted in the direction of the static magnetic field, there is a decrease in reception sensitivity in high magnetic fields, that is, high frequencies, and a decrease in the generation efficiency of the high-frequency magnetic field. Regarding the problem, it is an effective coil configuration.

However, no consideration is given to the case where a local location (hand or wrist of a subject) is imaged with high sensitivity.

[0020] The purpose of the present invention is to image with high sensitivity and high resolution when targeting a local location (hand or wrist of a subject) that the above-mentioned conventional technology does not take into consideration in the horizontal magnetic field method, thereby eliminating the need for examination. The purpose of this invention is to provide a coil that can be used invasively.

[0021]

[Means for Solving the Problems] In order to achieve the above object, a solenoid coil shaped to accommodate the hand or wrist is used, and a mechanism for compressing the hand or wrist as necessary is provided.

[0022]

[Operation] Generally, in an inspection apparatus using nuclear magnetic resonance, the direction of the static magnetic field and the direction of sensitivity of the coil must be perpendicular to each other. In an examination apparatus using horizontal magnetic field nuclear magnetic resonance, the direction of insertion of the subject and the direction of the static magnetic field coincide, so saddle-shaped coils have been devised and used as coils for the head and abdomen. However, when imaging a hand or wrist, a solenoid coil that can efficiently convert changes in magnetic flux from a target region into electrical signals based on the principle of nuclear magnetic resonance is applicable. That is, since the hand or wrist is not very thick, it is possible to adopt a configuration in which the imaging region is accommodated within the coil. Further, by providing a mechanism for expanding and contracting inside the coil, it is possible to fix the hand or wrist so as not to compress or move it, and it is possible to obtain an image with good resolution.

[0023]

Embodiments 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 FIG. 4, 5 is a control device, 6 is a high-frequency pulse generator, 7 is a power amplifier, and 8
9 is a transmitting/receiving 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 signal processing device. Further, 12, 13, and 14 are coils that generate gradient magnetic fields in the z direction and the directions perpendicular to this (x direction and y direction), respectively, and 15, 16, and 17 are the coils 12, respectively.
, 13, 14 is shown. The gradient magnetic field generated by these coils is used to make the magnetic field distribution in the space where the inspection object is placed to have a desired gradient. In FIG. 4, the coils 8, 13, and 14 are depicted as decreasing in size in this order, but this is for convenience in showing the overall configuration, and it is not necessary that the coils be in this 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 a power amplifier 7,
The coil 8 is excited. The signal component received by the coil 8 passes through an amplifier 9, is detected by a detector 10, and is converted into an image by a signal processing device 11.

Note that the static magnetic field is generated by a coil 18 driven by a power source 19. Subject 20 to be tested
is placed on a bed 21, and the bed 21 is placed on a support stand 2.
It is configured to be movable on 2.

FIG. 5 is an example showing the configuration of the gradient magnetic field coil in FIG. 4 and the direction of the current flowing therein. 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 90 degrees around the z-axis. In reality, the coils 12, 13, and 14 are wound around a single cylindrical bobbin. These gradient coils are aligned in the same direction as the static magnetic field (z
It generates a magnetic field (in the axial direction) and has a linear gradient (inclination) along the z, x, and y axes, respectively.

The present invention relates to an improvement of the coil 8 described above. Here, the coil 8, if it is a head coil, has a diameter of about 300 mm and a length of about 300 mm.

In this embodiment, the coil shape will be described as a cylindrical shape, but it is possible to change the shape to an ellipse or the like, and this does not limit the scope of the present invention.

FIG. 1(a) is a bird's eye view schematically showing one embodiment of a hand or wrist coil. Figure 1(b) is different from Figure 1(b).
FIG. 4 is an equivalent circuit diagram of the hand or wrist coil shown in a). Although FIG. 1 shows the case where only one hand is targeted, it is also possible to use two sets to image both hands at the same time. Figure 1 (a
) has a configuration in which an electrode 310 made of copper wire is wound around a cylindrical bobbin 300. Although the embodiment shown in FIG. 1A shows the case where the electrode 310 is made of copper wire, it may be made of a copper pipe, copper foil, or copper plate. In FIG. 1, the coil is a three-turn solenoid coil, but the present invention does not limit the number of turns to three. The number of turns may need to be varied depending on the resonant frequency and sensitivity.

Furthermore, although FIG. 1 shows a configuration in which the electrode 310 is spirally wound, as shown in FIG. The electrodes of electrodes 323, 32
Make sure to connect diagonally with step 4. By doing so, it is not necessary to wind the electrode 310 around the bobbin 300 at a certain angle to form a spiral shape, which facilitates production.

FIG. 3 schematically shows a cross-sectional view of the hand or wrist 201 of the subject 20 inserted into the hand or wrist coil shown in FIG. The cylindrical bobbin 300 has a structure in which the side surface of the bobbin is open so that the hand or wrist 201 of the subject 20 can be inserted therein. As is clear from FIG. 3, there are electrodes 320, 321, 322 on the outside of the cylindrical bobbin 300.
Because of the configuration in which the electrodes 320 and 32 are wrapped around the
There is no need to worry about getting an electric shock by directly touching 1,322. At this time, by attaching a cushioning material such as a cushion to the inside of the cylindrical bobbin 300, the subject 20 can be examined comfortably. Furthermore, by using a material that is soft to the touch for the cushioning material, it is possible to make the examination more comfortable. In addition, although Figure 1 shows the case where the coil is not divided by capacitors, if the resonant frequency becomes high and the coil cannot be tuned, or if the influence of the test object is large, it is possible to divide the coil by capacitors. These problems can be avoided. An example of such a configuration is shown in FIG. In the embodiment shown in FIG. 11(a), spiral coils 3101 to 3107 are used, and in the embodiment shown in FIG. 11(b), circular coils 3201 to 3203, 3211 to 321 are used.
3, capacitor 4 for each of 3221 to 3223
The case where the data is divided into 01 to 406 and 421 to 426 is shown. The embodiment shown in FIG. 11(b) is a case where the structure shown in FIG. 11(a) is rotated by 90 degrees so that the entire structure can be easily seen. In this embodiment, the electrodes are not divided by capacitors so that the lengths of the electrodes are equal, but the electrodes may be divided by capacitors so that the lengths of the electrodes are equal. If the electrodes are divided by a capacitor so that their lengths are equal, the increase in potential due to inductance and the decrease in potential due to capacitance cancel each other out, keeping the potential low, and the influence of the subject can be further reduced. The number of divisions by capacitors needs to be changed as appropriate depending on the resonance frequency and the degree of influence by the object.

FIG. 12 shows an embodiment showing a method of connecting two sets of coils when images of the left and right hands are taken simultaneously. Figure 1
2, the purpose is to show how to connect two sets of coils, so the coils are shown as one turn (500, 501). The specific configuration is as shown in FIGS. 1, 2, and 11. FIG. 12(a) shows a case where two sets of coils are connected in series, and FIG. 12(b) shows a case where two sets of coils are connected in parallel. In each case, two connections are shown for each coil 500, 501.
When the direction of magnetic flux is the same direction and when it is opposite. As in the conventional case, tuning and matching can be achieved by connecting the tuning/matching circuit shown in FIG. 8 to points H and G in FIG. 12.

FIG. 13 is a sectional view showing a schematic configuration of a mechanism for compressing a hand or wrist, and corresponds to the sectional view shown in FIG. 3. FIG. 13 shows a schematic cross-sectional view of a mechanism for compressing with fluid such as air. In the embodiment shown in FIG. 13, pressure airtight bags 601 and 602 made of an expandable material are provided inside a cylindrical bobbin 300, and a fluid 650 such as air at an appropriate pressure is applied from outside to each bag (for simplicity, FIG.
3 shows a configuration in which compression is performed by injecting (not shown). In this embodiment, for the sake of explanation, a case is shown in which the compression airtight bag is composed of two bags. By increasing or decreasing the number of airtight bags, it becomes possible to freely set pressure points such as partial pressure. Furthermore, by dividing this airtight bag into several parts, more delicate compression is possible. Furthermore,
By using an airtight bag that wraps around the entire hand, the pressure applied to the entire hand can be evened out, and air can also be injected.
It only takes one place, and the configuration can be made simple. By doing this, movement is suppressed and an image with good resolution can be obtained. Various modifications other than those described above are possible, and do not limit the present invention.

In the above explanation, the method of fixing the bobbin 300 into which the hand or wrist is inserted was not shown to the bed 21 or the like, but if the bobbin 300 is fixed to the bed 21 or other object that does not move during imaging.
If it is fixed, the movement of the subject 20 can be more completely suppressed and images can be taken with good resolution.

[0036] In the above explanation, each individual was explained, but
It goes without saying that these may be combined.

[0037]

[Effects of the Invention] According to the present invention, images can be obtained with high sensitivity and high resolution when a local location (hand or wrist of a subject) is targeted in an examination device using horizontal magnetic field type nuclear magnetic resonance. Tests can be performed non-invasively.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a configuration diagram of an embodiment of the present invention.

FIG. 4 is a configuration diagram of an inspection apparatus using NMR, which is an embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of a gradient magnetic field coil and the direction of flowing current.

FIG. 6 is a configuration diagram of an Alderman coil.

FIG. 7 is a configuration diagram of an Alderman coil.

FIG. 8 is a circuit diagram of a tuning/matching circuit.

FIG. 9 is a configuration diagram of an Alderman coil.

FIG. 10 is an explanatory diagram of a spin echo method sequence.

FIG. 11 is an equivalent circuit diagram when division is performed using capacitors.

FIG. 12 is a series and parallel connection diagram of two sets of coils.

FIG. 13 is a schematic configuration diagram of a mechanism for compressing a hand or wrist.

[Explanation of symbols]

5... Control device, 6... High frequency pulse generator, 7... Power amplifier, 8... Transmitting/receiving coil, 9... Amplifier, 10... Detector, 11... Signal processing device, 12, 13, 14... Coil that generates a gradient magnetic field , 18... Coil that generates a static magnetic field,
15, 16, 17, 19...power supply section, 20...subject, 20
1...hand and wrist, 21...bed, 22...support stand, 131
, 132... Guard ring electrode, 111, 112... Arm electrode, 121-128... Wing electrode, 141-144
, 201, 202, 421-426, 401-406...
Capacitor, 310, 3101~3107, 3201~
3203, 3211-3213, 3221-3223,
323,324,330-332,334,335...electrode, 601,602...airtight bag for compression.

Claims (8)

[Claims] 1. 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 object to be examined, a computer for calculating a detection signal of the signal detecting means, and a computer for calculating a detection signal of the signal detecting means. A nuclear magnetic resonance inspection apparatus using nuclear magnetic resonance having a means for outputting calculations by a computer, characterized in that a hand or wrist is placed inside the signal detecting means when the static magnetic field is in a horizontal direction. An inspection device using 2. Inspection using nuclear magnetic resonance according to claim 1, characterized in that the signal detection means uses magnetic flux/electricity conversion means consisting of a current path spirally provided along a cylindrical surface. Device. 3. The signal detecting means comprises a plurality of current paths provided spirally or concentrically along a cylindrical surface, and the tip of each current path is capacitively coupled. 2. An inspection apparatus using nuclear magnetic resonance according to claim 1, characterized in that magnetic flux/electricity conversion means is used. 4. Claim 1, characterized in that a plurality of the signal detection means are provided and each is connected in series or in parallel.
An inspection device using the described nuclear magnetic resonance. 5. An examination apparatus using nuclear magnetic resonance according to claim 1, further comprising hand or wrist compression means provided inside said signal detection means. 6. An examination apparatus using nuclear magnetic resonance according to claim 5, wherein a fluid is used as the compression means. 7. An inspection apparatus using nuclear magnetic resonance according to claim 1, further comprising a buffer material provided inside said signal detection means. 8. An inspection apparatus using nuclear magnetic resonance according to claim 1, wherein the inside of said signal detection means is made of a material that is soft to the touch.