JPS62298344A - Inspection device 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] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention measures the nuclear magnetic resonance signals of various atomic nuclei in a specimen, and determines the density distribution, relaxation time distribution, and chemical shift of the nuclei. The present invention relates to a device for visualizing distribution, etc., and particularly to a device suitable for obtaining highly accurate images.

[Conventional technology]

Conventionally, a circuit that blocks the induced current flowing through the signal detection coil by connecting the coil in parallel with a crossed diode connected in series to the tuning capacitor of the signal detection coil is described by the Society of Magnetic Resonance in Medicine. Book of Abstracts 4th Annual Meeting (1985) pp. 1082-10
83 pages.

and pages 1085 to 1086 (Society
ot Magnetic Re5onance in
Medicine Book of Abstracts
4th Annual Meeting (1985)
) pp1082-1083and pp1085-1
086).

[Problem that the invention seeks to solve]

The purpose of the above conventional technology is to prevent an induced current from flowing in a signal detection coil when a high-frequency magnetic field is generated, and to prevent the generation of a magnetic field that cancels the high-frequency magnetic field.However, when detecting a signal, the off resistance of the crossed diode is No consideration was given to the fact that a loss would occur and the Q value of the signal detection coil would decrease, resulting in a problem of a decrease in S/N.

That is, FIG. 4 shows an example of a conventional signal detection coil tuning and impedance matching circuit.

1 is a signal detection coil, 2 is a tuning capacitor, 3 is an impedance matching capacitor, 4 is a crossing diode, 5
is an inductance element that satisfies resonance conditions at the resonance frequency of the capacitor 2, that is, the frequency of the high-frequency magnetic field. Fourth
FIG. 5 shows an equivalent circuit at the time of signal detection of the tuned circuit of the signal detection coil shown in the figure. re is the loss of the coil 1, Ll is the inductance of the coil 1, Cr is the capacitance of the tuning capacitor 2, r4 is the off resistance of the crossover diode,
L2 indicates the inductance of the inductance cord 5,
Since Lz=Lz=L, the impedance of the equivalent circuit shown in FIG. 3 is expressed by a linear equation, where ω is the resonance frequency.

Z=r c + jωL+□ Therefore, since the Q value of the circuit is 1 reactance/1/resistance, the Q value of the equivalent circuit shown in FIG. 2 is expressed by the following equation.

Ctr ll That is, by inserting the crossing diode 4 and the inductance element 5, the Q value is reduced.

An object of the present invention is to magnetically decouple a high-frequency magnetic field generation coil and a signal detection coil while preventing the Q value of the signal detection coil from decreasing.

[Means for solving problems]

The present invention is characterized by a configuration in which the tuning capacitor of the signal detection coil is divided by series connection, and a cross-over diode and an inductance element connected in series are connected in parallel with one of the divided tuning capacitors.

[Effect]

According to the above-mentioned gutter bottom, the capacitance of the tuning capacitor becomes large, and therefore the inductance of the inductance element becomes small, so the loss due to the crossed diode is equivalently reduced, and therefore the high-frequency magnetic field generation coil and the signal detection coil are It is possible to prevent the coil Q value from decreasing while magnetically decoupling.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on one drawing. FIG. 3 shows the configuration of an inspection device that is an embodiment of the present invention. In FIG. 3, 6 is a control device, 7 is a high-frequency pulse generator, 8 is a power amplifier, 10 is a coil for generating a high-frequency magnetic field, 9 is a coil for detecting a signal generated from a target object 22, 11 is an amplifier, 12 13 is a wave detector, and 13 is a signal processing device. Further, 14, 15, and 16 are coils that generate gradient magnetic fields in two directions and in a direction perpendicular to these, respectively, and 17, 18, and 19 are power supply units that drive the coils 14, 15, and 16, respectively.

The gradient magnetic fields generated by these coils cause the magnetic field distribution in the space where the inspection object is placed to have a desired gradient.

The control device 6 has a function of outputting various commands to each device at a constant timing. The output of the high frequency pulse generator 7 is amplified by a power amplifier 8 and excites the coil 10. The coil 9 is a receiving coil, and the received signal component passes through an amplifier 11 and is detected by a detector 12, and then converted into an image and a spectrum by a signal processing device 13.

Note that the static magnetic field is generated by a coil 20 driven by a power source 21. The human body 22, which is the object to be inspected, is on the bed 2.
3, and the bed 23 is configured to be movable on a support base 24.

FIG. 1 shows an example of the configuration of a tuning and impedance matching circuit for a signal detection coil 9 to reduce a drop in Q value and reduce coupling with a high frequency magnetic field generation coil 10. Capacitors 25 and 26 are tuning capacitors, capacitor 27 is an impedance matching capacitor, and 28 is a crossed diode 29, which is an inductance element that satisfies resonance conditions at a resonance frequency with capacitor 26. FIG. 2 shows an equivalent circuit during signal detection of the tuned circuit of the signal detection coil shown in FIG. The capacitance Crt is the capacitance of the capacitor 26, r is the off resistance of the crossed diode, and La is the inductance of the inductance element 29. The conditions at this time are as follows.

Cr 1 = −Cr −(3)C
rz= a Cr ・= (
4) Cr At this time, the impedance of the equivalent circuit shown in FIG. 5 is expressed by the following equation.

r4+jω- Therefore, the Q value of the equivalent circuit shown in FIG. 5 is expressed by the following equation.

ωL Q　z　=□　　　　　...(8) rc+□ a”crrt Here, if we assume a1, a2crra　　　Crra Next door.

Q2>Qt becomes. Also, as we increase a, □〜　O 2crra Then, ωL Q2~□=Q c. It becomes ゛　.

Therefore, by dividing the tuning capacitor in series as shown in Figure 1, even if a series connection of a crossed diode and an inductance element is connected in parallel with one of the divided tuning capacitors, it will not work when transmitting a high frequency magnetic field. Reduces coupling with the high frequency magnetic field generating coil 10,
At the time of signal detection, it has become possible to reduce the decrease in the Q value of the signal detection coil 4.

〔Effect of the invention〕

According to the present invention, it is possible to block induced current from flowing in the signal detection coil when a high frequency magnetic field is generated, and to prevent the Q value of the signal detection coil from decreasing significantly during signal detection.

That is, by dividing the tuning capacitor as described above, the Q (if) of the tuning circuit according to the present invention can be made larger than the Q value of the conventional tuning circuit by the amount shown in the following equation.

z-Q ωL ωL a 2Cr r a Cr r a (however, a
〉1)

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a conventional signal detection coil tuning and impedance matching circuit including a decoupling circuit with a high-frequency magnetic field generation coil, FIG. 2 is a diagram showing its equivalent circuit, and FIG. The figure shows the configuration of an inspection device that is an embodiment of the present invention. FIG. 4 is a diagram showing an example of a conventional signal detection coil tuning and impedance matching circuit, and FIG. 5 is a diagram showing its equivalent circuit. Straw 1 Figure Z Figure 14 Figure 75

Claims (1)

[Scope of Claims] 1. A means for generating a static magnetic field and a gradient magnetic field to create a desired magnetic field distribution in a space where an inspection target is placed, and a means for generating a high-frequency magnetic field to generate a high-frequency magnetic field via a high-frequency magnetic field generating coil. , in an inspection apparatus using nuclear magnetic resonance that includes a signal detection means for detecting a nuclear magnetic resonance signal from the inspection object via a signal detection coil, the tuning capacitor of the signal detection coil being divided by series connection. A crossed diode and an inductance element are connected in series, and this is connected in parallel with one of the divided capacitors of the tuning capacitor, and a load consisting of the off resistance of the crossed diode and the inductance element, which is turned off when a signal is detected, is connected in series. When the high-frequency magnetic field generating coil generates a high-frequency magnetic field, the crossed diode is turned on by an induced current without significantly reducing the Q value of the signal detecting coil during signal detection.
An inspection apparatus using nuclear magnetic resonance, characterized in that the inductance element and one of the divided parts of the tuning capacitor form a resonant circuit to reduce an induced current flowing through the signal detection coil.