JPS59136642A - Nuclear magnetic resonance apparatus - Google Patents

Abstract

PURPOSE:To detect exactly a nuclear magnetic resonance point independently of the phase of a detection system by detecting a resonance signal for controlling magnetic field by two detectors different in the phases by 90 deg., performing the addition, etc. after squaring to determine the resonance information. CONSTITUTION:The nuclear magnetic resonance detecting signal through a transmitting and receiving coil 3 for controlling magnetic field is detected by the detectors 11, 12 different by 90 deg. in the phases, wherein oscillating outputs different by 90 deg. in the phases are impressed respectively from an oscilltor 5. The detected result is processed by a square-low detectors 15, 16, an adder 18, a square rooter 19, etc. to determine the nuclear magnetic resonance information. By this constitution, the nuclear magnetic resonance point is detected exactly and independently of the phase shift of the detection system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nuclear magnetic resonance apparatus, and more particularly to a nuclear magnetic resonance apparatus equipped with a magnetic field control device to keep the magnetic field stable.

[Prior Art] Generally, the polarization magnetic field used in a nuclear magnetic resonance apparatus is required to have a stability of about 10 (~10-3) over a long period of time.
To this end, conventional magnetic field control devices have been used that detect magnetic field fluctuations based on nuclear magnetic resonance signals and cancel them. In nuclear magnetic resonance, this is the resonance frequency of the nucleus (
Focusing on the fact that the relationship ω0-γHo is established between ω0) and the external magnetic field (l-1o) using the gyromagnetic ratio (γ), which is a constant unique to the nucleus, we calculate the variation in the magnetic field as a change in the resonant frequency. The system detects the fluctuations as follows and corrects the fluctuations.

In such a magnetic field control device, a control sample containing a specific nucleus, for example, a deuterium nucleus 2D, is mixed into a measurement sample, and the high frequency of the resonance frequency of the deuterium nucleus is focused on, and the resulting 2D resonance signal (
The magnetic field is stabilized by using the U mode waveform as a magnetic field control signal and passing it negatively to the magnetic field strength control means of the magnet to form an automatic control loop. However, since the range in which this control loop operates is relatively narrow, it is necessary to preset the strength of the magnetic field within the operating range, which is a burden on the operator.

In this operation, the magnetic field strength is changed while observing the resonance signal, and the control loop is activated after confirming that the resonance signal level is high and the magnetic field strength is close to the resonance point. If the detection system is out of phase, the resonance signal may become zero even though it is at the resonance point, and the operator must adjust the phase relationship in advance, making it difficult to automate this operation.

[Object of the Invention] The present invention has been made in view of this point, and is an IC device that uses two detectors with a 90° phase difference to adjust the phase relationship as a means for detecting the nuclear resonance signal for control. It is an object of the present invention to provide a nuclear magnetic resonance apparatus that can automatically set the magnetic field strength near the resonance point without the need for the magnetic field strength.

[Structure of the Invention] A nuclear magnetic resonance apparatus according to the present invention includes means for sweeping a polarized magnetic field, an irradiation coil for irradiating a control sample placed in the polarized magnetic field with a high-frequency magnetic field, and a high-frequency wave supplied to the coil. an oscillator for generating the resonance signal, a detection coil for detecting the resonance signal from the control coil, and two oscillators with a 90° phase difference to which the detection signal 1q from the detection coil is supplied.
an arithmetic means for squaring and adding the respective output signals from the two wave detectors; and a discriminating means for generating a signal to stop the magnetic field sweeping by the sweeping means based on the output of the arithmetic means. It is characterized by being configured.

[Example] An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1 is a sample tube in which a measurement sample and a control sample are placed. 2 is a coil for varying magnetic field strength; 3 is a transmitting/receiving coil for magnetic field control; and 4 is a transmitting/receiving switch for switching between a transmitting state and a receiving state at appropriate intervals. The high frequency generated from the oscillator 5 is mixed with the high frequency from the local oscillator 7 in the mixer 6, and the mixed output is sent to the amplifier 8 during the transmission period.
It is supplied to the transmitting/receiving coil 3 via the ° changeover switch 4. The detection signal induced in the transmitter/receiver coil 3 by the high frequency irradiation is transmitted to the mixer 1 which is supplied with the high frequency from the local excavator via the switch 4 and the amplifier 9 during the reception period.
Sent to 0. The output of the mixer 10 is sent to a detector 11.1.
2, but the detector 11 receives the O° signal from the oscillator 5.
A high frequency wave with a phase of 90° is supplied to the detector 12.
Phase high frequency is supplied. The resonance signals obtained as outputs of the two detectors are filtered through a low-pass filter 13.1.
4, and sent to the adder 17 via the two-way registers 15 and 16. 18 is a 1z square circuit that detects the square root of the output signal of the adder 17; 19 is the 1z square circuit 18;
The output pulse of the discriminator 19 is sent to the magnetic field sweep circuit 20.

21 adds the sweep signal from the magnetic field sweep circuit, the magnetic field correction signal from the magnetic field correction circuit 22, and the resonance signal sent via the switch 23, and sends the resultant signal to the magnetic field strength variable coil 2 via the amplifier 24. This is an adder for sending. Furthermore, 2
5 is a mask oscillator, and the other oscillators 5.7 are the oscillators 2
5 and generates a signal of a predetermined frequency in a phase-synchronized state.

In the above-described configuration d3, the magnetic field control nucleus is, for example, a deuterium nucleus 2D, and its resonance frequency is 61.3M+-IZ ("
Near I, the frequency of the oscillator 5 is 10.7Mt-1z and the frequency of the oscillator 7 is 72M1-1z, and both are mixed in the mixer 6 to obtain a high frequency for irradiation of 61.3M1-IZ as the difference frequency. shall be taken as a thing. The high frequency is sent to the coil 3 via the switch 4 during the transmission period and is irradiated onto the control sample. The detection signal generated in the coil 3 during the reception period has a resonance signal superimposed on its 61.3 MHz, and the detection signal is sent to the mixer 10 via the switch 4, and the oscillator 7
is mixed with the 72 MHz signal from , and converted to a difference frequency of 10.7M1-1z. This converted detection signal is sent to detectors 11 and 12 with a 90' phase difference,
Since detection is performed based on the reference signal of 10.7M1-1z, resonance signals having a phase difference of 90° are obtained as the output of the filter 13.14. At this time, the magnetic field strength is subtracted by 4iil by the sweep circuit 20, so if the phase of the detection system is adjusted correctly, the detectors 11 and 12
For example, as shown in Fig. 2 (a) and (b), as the magnetic field sweeps,
V-mode and U-mode NMR signals as shown in FIG. 1 are obtained.

These two types of NMR signals are the magnetic resonance of the 2D nucleus captured by two detection systems with a 90° phase difference. It can be easily understood by thinking of it as a projection onto a plane.

In other words, if the trajectory of the magnetization vector M of the 2D nucleus in a helical motion near the resonance point Go as the magnetic field G sweeps is three-dimensionally expressed as a helix L, then the projection of it onto the X plane is V. This is a mode NMR signal, and the one projected onto the Y plane is a U-mode NMR signal. In FIG. 3, the helix L is drawn away from the G-axis for ease of viewing, but more accurately, the straight line portion of the helix L coincides with the G-axis. Therefore, both the V and U mode 1'NMR signals have a flat portion other than the peak or a zero level.

At this time, if there is a phase shift in the detection system, X.

The Y plane rotates with respect to the helix L, for example, like the X' and Y' planes shown by broken lines in FIG. For this reason, X'
, the projection onto the Y' plane is shown in Figure 2 (C).

The signal changes as shown in (d), and the signal level reaches its maximum at a location other than the resonance point. Therefore, with conventional devices that had only one detection system and could only observe either one of Figures 2 (c) and (d), it was necessary to simply find the resonance point from the No. 11 level and automate the magnetic field setting. It was not possible to do so, and it was only possible to determine whether or not it was a resonance point until the operator manually adjusted the phase of the detection system.

By the way, the point P on the center L and the axis G (coinciding with the straight line part of the spiral), which is given as the locus when the C magnetization vector moves in a helical manner near the resonance point A as the magnetic field G sweeps. Focusing on the distance (A in Fig. 3), the value of A is zero when P is on the straight line part of helix L as shown in Fig. 4, and the value of A is zero when P is on the straight line part of helix L as the magnetic field sweeps. It can be seen that the magnetic field strength increases and decreases as it moves along the curved part, and shows a maximum value when it is at the resonance point Go, that is, at the position d'3 (Po in Figure 3). Place point P on the X plane as shown.

A from signal levels a and b of px and py projected onto the Y plane
= (a2+b2) By finding V2, no matter what the phase of the detection system is, the position where A is maximum, that is, the resonance point Go
The position of can be found. Therefore, in the present invention, the resonance signals having a 90° phase difference extracted from the detectors 11 and 12 via the filters 13 and 14 are respectively squared by the doublers 15 and 16, and then tightened by the adder 17. Furthermore, by passing through the 1/2 power circuit 18, the above-mentioned 8-(a
2+1)2) Obtaining the value of V2. Therefore, if a pulse is generated from one discriminator when the output of the 1/2 power circuit 18 reaches a preset level, and the magnetic field sweep by the magnetic field sweep circuit 20 is stopped by this pulse, the magnetic field is If the operator closes the switch 23 in synchronization with the resonance point (stops) or after that, the resonance signal obtained from the detector 11 is fed back to the magnetic field strength variable coil 2, and automatic control is performed. Because a loop is formed,
The magnetic field strength will be held fixed at its resonance point.

In the above-described embodiment, the calculation was performed using a combination of the 2D detectors 15 and 16, the adder 17, and the 1/2 power circuit 1B, but as shown in FIG. ．．
The two resonance signals taken out through the AD converter 2
6.27, it goes without saying that each signal may be AD converted into a digital signal, and the value of A may be determined using the digital arithmetic unit 28. A clock oscillator 32 generates a clock signal for specifying the timing of Δ1 conversion and calculation.

FIG. 6 does not show any further embodiments. In this embodiment, two resonance signals taken out through filters 13 and 14 are mixed in a time division manner by a time division synthesis circuit 29, the mixed resonance signal is converted into a digital signal by an AD converter 30, and the digital The composite signal is led to the arithmetic unit 28 to obtain the value of A, and in this way, only one expensive AD converter is required. In FIG. 6, numeral 31 is a clock oscillator that generates a tarok signal for specifying the timing of time division and calculation.

Also, in reality, there is no need to find the value of in the calculation,
The magnitude of the value of Δ can be determined at the stage of A2 = a2 + 112. Therefore, the 1/2 power circuit 18 is not necessarily necessary, and even when digital calculation means are used, it is not necessary to find the square root.

[Effect] As described in detail above, according to the present invention, resonance signals for magnetic field control are generated at 141° by two detectors with different 90°
Information on the resonance point is obtained by squaring the two resonance signals and adding them, so the resonance point can be detected accurately regardless of the phase shift of the detection system, making it possible to automate magnetic field settings. becomes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIGS. 2 and 4 are waveform diagrams for explaining its operation, FIG. 3 is a schematic diagram, and FIGS. 5 and 6 are It is a figure which shows the principal part of another Example. 1: Sample tube, 2: Magnetic field strength variable coil, 3:! 1 Field control transmitting/receiving coil, 4.23: Switch, 5.7.25: Oscillator, 11.1
2: Detector, 15.16: Square generator, 17.21: Calculator, 18: 1/2 power circuit, 19 Two-level discriminator, 20: Magnetic lift circuit. Patent No. 8' [Applicant JEOL Co., Ltd. Representative: Mr. Ito

Claims (1)

[Claims] a means for drawing a polarized magnetic field; an irradiation coil for irradiating a control sample placed in the polarized magnetic field with a high-frequency magnetic field;
an oscillator for generating a high frequency to be supplied to the coil;
A detection coil for detecting a resonance signal from a control coil, two detectors with different 90' phases to which detection signals obtained from the detection coil are supplied, and respective output signals from the two detectors. What is claimed is: 1. A nuclear magnetic resonance apparatus comprising: a calculation means for squaring and adding the squared values; and a determination means for generating a signal for stopping magnetic field sweeping by the sweeping means based on the output of the calculation means.