JPS63197440A - Examination apparatus using nuclear magnetic resonance - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device that measures information inside an object using nuclear magnetic resonance (NMR), and particularly relates to a device that measures information inside an object using nuclear magnetic resonance (NMR). This invention relates to an inspection device using NMR suitable for.

[Conventional technology]

For conventional devices, see Journal of Magnetic Resonance, 60 (1984), pp. 397-404.
Resonance, 60 (1984) pp, 3
97-404).

As stated in the above-mentioned literature, the noise in NMR is almost determined by the thermal noise from the detection coil and preamplifier, and this is a cause that prevents high sensitivity of NMR. Therefore, attempts have been made to cool the detection coil and preamplifier in order to reduce this thermal noise.

In NMR, S/N (signal-to-noise ratio) is given by: Here, a is the radius of the coil, p is the circumference and length of the conductor constituting the coil, ξ is the proximity coefficient of the coil, Ta is the equivalent noise temperature of the preamplifier, Tc is the temperature of the coil, and ρ( Tc) is the resistivity of the coil and ω0 is the resonant refrequency. Here, ω0 is generally a high frequency. (For example, at a static magnetic field strength of 0.15 Tesla, the resonant frequency is about 6 MHz.) As stated in the above literature, by cooling (Ta+
Since Tc) and ρ(TC) decrease, the S/N can be increased. This analytical NMR noise reduction method is
If applied to an R imaging device, it is possible to improve image quality and shorten imaging time by improving S/N.

[Problem that the invention seeks to solve]

In the prior art described above, the detection coil and the preamplifier are immersed in a coolant (liquid He) to reduce thermal noise generated from both. In this conventional analytical NMR, the diameter of the detection coil is small and the diameter of the constituting conductor is made of a thin silver tube, so there is no need to take into account heat intrusion from the outside. In addition, since the amount of refrigerant consumed is low, the refrigerant reservoir can also be small. However, if this method is applied to a device that has a detection coil into which a human body can enter, the diameter of the detection coil will increase, and the diameter of the conductor that makes up the system will increase. If it is not made thicker, there will be a large loss due to the skin effect, and the cooling effect will be lost. In the above conventional example, sufficient consideration has not been given to the problem that as the detection coil becomes larger and the diameter of the conductor becomes thicker, heat intrusion increases, refrigerant consumption increases, and equipment maintenance costs increase. There wasn't. Furthermore, there remains the problem that the operation is unstable if the detection coil and preamplifier do not reach thermal equilibrium.

The purpose of the present invention is to effectively prevent heat intrusion, which becomes a problem when the detection coil becomes large, and to reduce refrigerant consumption while electrically connecting the NM to the outside in a substantially direct current or alternating current manner.
The purpose of the present invention is to provide an R device.

[Means for solving problems]

The above object is achieved by completely immersing the detection coil and preamplifier in a refrigerant, sealing and insulating them to prevent heat from entering, and making electrical connection to the outside by electromagnetic induction. Note that various methods can be used to prevent the intrusion of heat depending on the amount of refrigerant consumed. For example, known methods such as vacuum insulation can be used.

[Effect]

Prevention of heat intrusion can be achieved by completely separating the detection coil and preamplifier immersed in the coolant from the outside (for example, by vacuum insulation, etc.).

Electrical connection can be achieved by noting that the output signal component of the preamplifier is a high frequency signal and causing a distance change using electromagnetic induction. Further, direct current is supplied to the preamplifier in the refrigerant at a high frequency by causing a magnetic flux change using electromagnetic induction from the outside, and rectification is performed on the preamplifier side in the refrigerant.

〔Example〕

An embodiment of the present invention will be described below.

FIG. 1 is a block diagram of an embodiment in which NMR signals received by a detection coil into which a human body or the like is inserted are thermally separated and electrically connected (AC connection).

A high-frequency NMR signal is received by an LC resonant circuit consisting of a detection coil 1 immersed in a coolant and capacitors Ch and Cx by generating nuclear magnetic resonance in a target object using a known method.

This NMR signal is amplified by a preamplifier 2 immersed in the refrigerant. This amplified high frequency signal is electrically connected to the outside of the refrigerant in a thermally isolated state in a coupling circuit 3. In this embodiment, the coupling circuit 3 uses electromagnetic induction to connect the input side coil 7 in the refrigerant. The high frequency signal is converted into a magnetic flux change, and this magnetic flux change is detected by the output side coil 8 outside the refrigerant.

Convert to electrical signal.

FIG. 2 is a block diagram of an embodiment in which direct current supplied to the preamplifier 2 is electrically connected while being thermally separated. An alternating current is supplied to the coupling circuit 3' from outside the refrigerant, and the alternating current is sent into the refrigerant. This alternating current signal is rectified by a rectifier circuit 4 and converted into direct current. The operation of the coupling circuit 3' can be performed in the same way as the connection of the NMR signal described above, and the most basic configuration of rectification in the rectifier circuit 4 is a low voltage configuration consisting of a diode, a resistor, and a capacitor, as shown in FIG. AC coupling using zero or more coils that can be realized by a bandpass filter.

The rectification method can be realized using various known configurations.

In Fig. 3, frequency conversion is performed on the output signal of the preamplifier 2 to prevent coupling between the detection coil 1 and the input coil 7.
A block diagram is shown below. @1 In the configuration shown in Figure 1, since the detection coil 1 and the input side coil of the coupling circuit operate at the same frequency, coupling between the coils may occur. Therefore, after the high frequency detection signal from the detection coil 1 is amplified by the amplifier 2, the frequency of the signal is converted to a frequency that does not interfere with the frequency converter 5, and the signal of this converted frequency is used to coil the input side coil in the refrigerant of the coupling circuit 3. Drive 7. This magnetic flux conversion by the input side coil 7 is detected by the output side coil 8 outside the refrigerant, and is converted back to the original frequency signal by the frequency converter 5.

FIG. 4 shows an embodiment of the coupling circuit portion of the preamplifier 2.
A high frequency signal from the input coil 7 is input to the input coil 7 placed in a vacuum, causing a change in magnetic flux. This magnetic flux change is detected by the output coil 8. At this time, the output side coil 8
, the input side coils 7 are both wound in a vacuum so as not to touch each other, and from the input side coil 7 to the output side coil 8.
It can prevent cold heat from entering. At this time, the surface of the coil may be plated with a material having a high reflectance in order to prevent heat intrusion due to thermal radiation.

Further, in the embodiment shown in FIG. 4, there is a portion connecting the inside of the refrigerant and the inside of the vacuum, and the mechanical strength may be insufficient. In such a case, as shown in Fig. 5, the input side coil 7 is completely immersed in the refrigerant, and the output side coil 8 is completely taken out of the refrigerant, so that the input side coil 7 and the output side coil 8 face each other. By installing the refrigerant, the heat insulating layer (e.g. vacuum) can be made independent, and the part inside the refrigerant can be completely sealed.

Although the above method is a coupling based on a change in magnetic flux, the coupling circuit 3 may also be electrically connected via a change in an electric field, such as electrostatic coupling.

FIGS. 6(a) and 6(b) show a perspective view and a side sectional view of an embodiment of the coupling circuit 3 in the case of capacitive coupling.

In Figure 6, horizontal plates 90 and 92 inside the refrigerant and horizontal plates 91 outside the refrigerant.
．． 93 is thermally insulated with a heat insulating layer (e.g. vacuum), and electrical current is generated between the electrode plates 90 and 91, and between the electrode plates 92 and 93 through electric field changes caused by high frequency signals. Achieve connectivity. As for the arrangement of the electrode plates, it is also possible that the electrode plates 90, 91, 92, 93 are located in the heat insulating layer as in FIG.

According to this embodiment, it is possible to prevent heat infiltration with a simple configuration, reduce the amount of refrigerant consumed while reducing noise due to cooling, and reduce the maintenance cost of the apparatus.

Further, since thermal separation can be performed, thermal balance can be maintained, and operation can be stabilized while reducing noise through cooling.

Further, in this embodiment, a large detection coil is used as an example, but it goes without saying that even if a small detection coil is used, a corresponding effect can be achieved in reducing the amount of refrigerant consumed.

〔Effect of the invention〕

According to the present invention, since thermal separation is possible, the consumption of refrigerant can be reduced, and the amount of refrigerant is also small, making it possible to reduce thermal noise through cooling. Furthermore, since it operates in a state of thermal equilibrium, it has the effect of reducing thermal noise while operating stably.

[Brief explanation of the drawing]

1 and 3 are block diagrams of an AC connection section according to an embodiment of the present invention, FIG. 2 is a block diagram of a DC connection section according to an embodiment of the present invention, and FIGS. 4 and 5 are block diagrams of an AC connection section according to an embodiment of the present invention. FIG. 6 is a side sectional view of a coupling circuit section according to one embodiment, and FIG. 6 is a perspective view and a side sectional view of a coupling circuit section according to another embodiment. 1...Detection coil, 2...Preamplifier, 3...Coupling circuit. 4... Rectifier circuit, 5... Frequency converter, 6... Glass, 7... Input side coil, 8... Output side coil,
9... Pole plate. Figure 4 'IE, 51! ] Cb) 9 Saiita

Claims (1)

[Claims] 1. The nuclear magnetic resonance signal detection coil and the means for amplifying the nuclear magnetic resonance signal detected by the coil are thermally separated from another amplifying means following the amplifying means, and there is an electromagnetic connection between the two amplifying means. An inspection device using nuclear magnetic resonance characterized by being provided with an electrical connection means using induction.