JPS6013463B2 - Magnetic field control device in nuclear magnetic resonance equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic field control device in a nuclear magnetic resonance apparatus.

Generally, the magnetic field used in a nuclear magnetic resonance apparatus is required to have a stability of about 10-8 to 10-8 over a long period of time, and for this reason, magnetic field fluctuations are studied based on the subordinate magnetic resonance signals.
Magnetic field control devices are used to counteract this.

In other words, in such a magnetic field control device, for example, a control sample is mixed into the sample to be observed, or a control sample is placed near the observation sample, and the resonance signal (dispersion waveform) obtained from this control sample is transferred to the magnetic field. The magnetic field is stabilized by negative feedback to the magnet excitation current control means as a control signal. In particular, with the magnetic field control device that has been used recently, the control sample is irradiated with control high frequency waves intermittently at a fixed period as shown in Figure 4, and the detection of resonance signals from the control sample is performed during the non-irradiation period. A so-called time sharing method is adopted. This method has many advantages, such as being able to use a single coil as both the irradiation coil and the detection coil, and eliminating the need for a complicated modulation mechanism. However, with this method, spurious signals occur in the control high frequency due to time sharing.
Since this is detected by the observation detection coil and sent to the observation detection system, there is a problem in that an abnormal peak due to the above spurious occurs in the obtained NMR spectrum. In particular, this has been a big problem when the resonant frequency of the control sample and the resonant frequency of the observation sample are close to each other. This point will be explained below using FIGS. 5 and 6.

Assuming that the frequency of the high-frequency control wave shown in Fig. 4 is T, and the period of time sharing is T, the high-frequency control magnetic field generated thereby has a 5th wave in the frequency domain.
As shown in the figure, a side band (spurious) is generated at an interval of 1/T around that point. Species that deviate from the sideband intensities are reduced, so there is no problem as long as the resonant frequency of the control sample and the resonant frequency of the observation sample are far apart. However, the two are close to each other, and for example, as shown in Figure 5, the resonant frequency of the observed sample is f, and f2, which includes it,
When observing the region f3 from f2 to f
There is a sideband in the region 3, which is detected by the observation detection coil, so the spectrum obtained is as shown in FIG. In FIG. 6, a and b are the NMR spectra of the sample, and c, d, and e are abnormal peaks due to sidebands (spurious) that existed between the two, which causes a big problem in spectrum analysis. The present invention has been made in view of the above points, and an object of the present invention is to provide a magnetic field control device that can diffuse the above-mentioned spurious and reduce its level to an extremely low level by randomly changing the time-sharing period. shall be.

The present invention will be explained in detail below using the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, 1 and 2 are magnetic poles arranged to face each other, 3 is an excitation coil, 4 is an excitation power source that supplies excitation current to the nuclear excitation coil, and 5 is an NMP probe arranged between the magnetic poles. In addition to the measurement coil, a magnetic field fixing (locking) coil is provided inside the NMP probe, and the locking coil receives a locking high frequency generated from a high frequency oscillator 6 via a gate circuit 7 in a time-sharing manner. The gate circuit 7 is sent by
are opened and closed based on a timing signal obtained from a timing circuit 9 to which random pulses generated from a pseudorandom pulse generator 8 are supplied. A detection signal obtained from the NMP probe 5 by irradiation with the locking high frequency wave is sent to a detection circuit. The detection circuit 1 is supplied with a timing signal from the timing circuit 9 and a reference signal from the oscillator 6, and performs a detection operation only during the period when the timing signal is supplied. The self-excitation power supply controls the excitation current based on the resonance signal obtained by detection. In such a configuration, when the nucleus for controlling the magnetic field is selected as deuterium (phantom), the oscillator 6 generates a high frequency of, for example, 13.9 MHz to make the 20 resonate.

On the other hand, the random pulse generator 8 generates pulses at random time intervals as shown in FIG. 2 {a).

The timing circuit 9 generates a first timing signal (FIG. 2 {b-) which is synchronized with the pulse and has a constant pulse width,
The second timing signal (Fig. 2c) rises after a certain period of time from the fall of the timing signal of
), the first timing signal is sent to the gate circuit 7, and the second timing signal is sent to the detection circuit 10, respectively. Therefore, as shown in FIG. 2d, the locking high-frequency wave is irradiated during the second period, and during the period t and after t2, the detection circuit 1 is used to detect the resonance signal ( A dispersive waveform) is obtained. Based on the resonance signal, the excitation power supply 4 controls the current to the excitation coil 3 so that the magnetic field is fixed at the resonance point M of the distributed waveform shown in FIG. By the way, observation of resonance signals from observation samples is carried out over a period of one second to several minutes to several minutes. 13.9
The high frequency for controlling the M ratio is set to a constant repetition frequency, for example, Hinamachi z
When intermittent with continues to be superimposed on the resonance signal from.

Therefore, in the spectrum obtained by Fourier transformation after observation, sharp spurious signals that are accumulated during the observation period appear at the fixed frequency positions. However, in the present invention, the control high frequency is intermittent at random time intervals during the observation period ranging from one second to several minutes, so the sideband is centered around the 13.8M ratio and is The result is that its frequency position changes randomly.

Therefore, although the sideband is superimposed on the resonance signal from the observation sample, the frequency of the sideband changes randomly thousands of times, tens of thousands of times, or more during the observation period from one second to several minutes, so the Fourier When converted, the sidebands are not concentrated at a specific frequency but are spread over a wide range, and their intensity becomes extremely small. Therefore, the obtained N
No abnormal peaks due to sidebands (spurious) occur on the MR spectrum. As described in detail above, according to the present invention, it is possible to eliminate the adverse effects of the magnetic field control device on the NMR spectrum.

In addition to the above, if t, , t2 are also randomly varied, the spurious can be diffused more effectively.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining its operation, FIG. 3 is a diagram showing a resonance signal (dispersion waveform), and FIG. The figure shows the high frequency irradiated to the control sample using the time sharing method, Figure 5 is a diagram to explain spurious, and Figure 6 is N
It is a figure showing the spurious which appeared in the MR spectrum.

3... Excitation coil, 4... Excitation power supply, 5... NM
R probe, 6... High frequency oscillator, 7... Gate circuit, 8... Pseudo random pulse generator, 9... Timing circuit, 10... Detection circuit.

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A magnetic field control device in a nuclear magnetic resonance apparatus, characterized in that a sample is intermittently irradiated with magnetic field control high frequency waves at random time intervals.