JPS6040972A - Nuclear magnetic resonance apparatus - Google Patents

Abstract

PURPOSE:To remove a spurious peak, in a Fourier transform type nuclear magnetic resonance apparatus, by subtracting the time average value of time data, in which no separately sampled resonance signal is present, from measuring data containing a resonance signal. CONSTITUTION:A high frequency pulse is applied to a probe 4 which is placed to the side of a DC static magnetic field 3 through a phase inversion controller 2 and filled with a specimen to be measured, from a transmitter 1. By this pulse application, the specimen to be measured is excited and a resonance signal is detected by the probe 4 to be sent to phase detectors 6, 10 through a high frequency amplifier 5 while reference signals of the detectors 6, 10 are supplied from a phase controller 16. A central processing apparatus 14 samples the detected resonance signal and performs sampling at time when no resonance signal is present and also performs Fourier transform so as to subtract the time average value of the sampling data from the resonance signal to obtain a frequency spectrum. By this method, the spurious peak in the frequency spectrum due to a DC offset component can be removed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a Fourier transform type nuclear magnetic resonance apparatus, and more specifically to a nuclear magnetic resonance apparatus which aims to remove the tin-tin peak in the frequency spectrum due to a DC offset component. Relating to a resonator.

[Background of the invention]

A Fourier transform nuclear magnetic resonance apparatus irradiates a sample placed in a DC static magnetic field with a high-frequency component close to the resonance frequency in a pulsed manner for a short period of several microseconds, and samples the resulting resonance signal. Then, a frequency spectrum is obtained by Fourier transforming the sampling take. The following will explain based on the drawings. Figure 1 shows the system configuration of the Fourier conversion type Sugi magnetic resonance apparatus. In the figure, a high-frequency pulse is applied from a transmitter 1 via a phase inversion controller 2 to a probe 4 which is set across the width of a DC static magnetic field 3. As a result, the sample to be measured hidden in the glove 4 is excited. After the resonance signal is detected by the globe 4, it is sent to the phase detector 6 via the high frequency amplifier 5, where it is converted into a low frequency component of about 0 to several tens of kilohertz. This signal component is transmitted to the central control unit 1 via a low frequency amplifier 7, a low pass filter 8, and an A/D converter 9.
Sampled at 4. On the other hand, the output signal of the high frequency amplifier 5 is also sent to the phase detector 10, and the output signal is sent to the low frequency amplifier 11, the low pass filter 12, and the A/D converter 13.
The data are sampled by the central controller 14 via the central controller 14.

- On the other hand, the reference signals of the phase detectors 6 and 10 are supplied to the phase controller 16.
Therefore, the output signals of the phase detector 6.10 also differ in phase by 90°. This corresponds to the complex 1 (real part and imaginary part as self-signs), and the output signal of the A/D converter 9.13 is the central control unit.
The signal is subjected to a complex Fourier transform and converted into a frequency spectrum, and this frequency spectrum is displayed on a display device 15.

In the nuclear magnetic resonance apparatus having the above-mentioned configuration, when a direct current offset component is heavily present in the resonance signal, spurious peaks B occur in the frequency spectrum in addition to the resonance signal A, as shown in FIG.

One method for removing this DC offset component is to reduce the offset appearing at the output end by superimposing an offset current on a low frequency amplifier with an opposite phase, as shown in FIG. The limit of the offset that can be reduced by this method is about one-tenth to one-tenth of the noise.

Fourier transform corresponds to taking the time average of a time-series signal seen in a rotating zagura system that rotates at the frequency of interest. In particular, the DC component is a simple time average in the experimental coordinate system. Therefore, the S/N ratio of the resonance signal of the DC component is improved by Fourier transformation, and the improvement is proportional to the square root of the number of sampling data points. For example, the number of data points is 1
In the case of 6384 points, there is an S/N improvement effect of 128 times.

In other words, 1/1 of the noise level in time domain data.
If there is a DC offset component of 128, it appears in the frequency domain spectrum with a magnitude comparable to the noise level. Therefore, the above-described method of supplying offset currents in opposite phases to the low frequency amplifier is insufficient.

A second method for removing the DC offset component is to alternately invert the phase of the high-frequency pulse when integrating the resonance signal multiple times.

For example, when the phase of the high-frequency pulse in the first measurement is inverted by a phase inversion controller, the phase of the resonance signal follows the phase of the high-frequency pulse, whereas the polarity of the DC offset component is not affected. In many cases, it becomes possible to separate the resonance signal and the DC offset component. This state is shown in FIG. That is, the first 1llll
By inverting the phase of the + constant resonance signal (Figure 4(a)) as shown in Figure 4(Φ) and subtracting these two resonance signals, the spurious peak B becomes as shown in Figure 4(C). ,
will be deleted.

However, this method can only be used for multiple integrations such as low concentration sampling measurements and carbon nucleus measurements, and cannot be used for single measurements such as sb and hydrogen nucleus measurements.

[Purpose of the invention]

An object of the present invention is to provide a nuclear magnetic resonance apparatus that efficiently detects minute DC offset components and removes the DC offset components from the frequency spectrum of resonance signals.

[Summary of the invention]

In a Fourier transform type nuclear magnetic resonance apparatus, the present invention subtracts the time average value of separately sampled data at a time when no resonance signal exists from measurement data including a resonance signal, thereby eliminating spurious signals caused by DC offset components in the frequency spectrum. It removes peaks.

[Embodiment of the Invention] In this embodiment, in order to accurately detect the DC offset component, the central control unit fR14 samples a time-series signal that includes only the DC offset signal and the noise that does not include the resonance signal. By calculating the average value, the magnitude of the spurious peak due to the DC offset component on the frequency spectrum is calculated.

FIG. 5 shows a schematic flow of the program executed by the central controller 14 in this embodiment.

In the same figure, when the program is started in step 50, device parameters such as gain on the receiving side and filter bandwidth are set in step 52, and then in step 54, the signal is transmitted from the transmitter 1 to the probe 4 via the phase controller 2. A high frequency pulse is applied.

Further, in step 56, sampling of the resonance signal detected by the probe 4 is performed. In step 58, a signal containing only noise and a DC offset signal at a time when no resonance signal is present is sampled. Next, in step 60, a time average value of the sampling data obtained in step 58 is calculated, and in step 62, a Fourier transform operation is performed on the sampling data obtained in step 56.

Further, in step 64, the time average value obtained in step 60, that is, the DC offset value, is subtracted by 3+2 from the frequency spectrum obtained in step 62, and in step 66, a frequency spectrum is obtained from which spurious peaks due to the DC offset l' have been removed, Execution of the program ends at step 68.

Here, the sampling of the signal containing only the noise and the DC offset signal in step 58 may be performed under exactly the same conditions after the normal measurement data has been taken in, without emitting only the high-frequency pulse.

In this case, there is no need to store data for a predetermined number of points on the horizontal axis, so the storage capacity of the memory can be reduced, and the measurement time can be shortened.

In the above sampling, when the normal one-time measurement data (time domain) is taken in, the first half of the data contains resonance signals, and the second half of the data contains only noise and DC offset components, so the second half of the measurement is performed in step 58. Alternatively, only the data may be captured, and the entire captured measurement data may be corrected by detecting the DC offset component using the time average value determined in step 60.

In this case, the measurement time can be further shortened.

As explained above, according to this embodiment, spurious beaters caused by DC offset can be effectively eliminated from the frequency spectrum without affecting the nuclear spin system even in a single measurement like in the case of hydrogen nuclear measurements. can be removed from

〔Effect of the invention〕

In the present invention, the Fourier transform nuclear magnetic resonance apparatus is configured to subtract the time average value of separately sampled data at a time when no resonance signal exists from the measurement data including the resonance signal. Spurious peaks caused by direct current offset components can be effectively removed from the frequency spectrum.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the Fourier transform nuclear magnetic resonance apparatus, Figure 2 is a diagram showing spurious peaks caused by DC offset components appearing on the frequency spectrum, and Figure 3 is the configuration of the offset compensation circuit. The circuit diagram, FIG. 4 is a diagram showing the process in which spurious speakers are removed when +1111 constant data is integrated the first number of times, and FIG. It is a flowchart showing the contents. ...Transmitter, 2.16...Phase controller, 3
...Magnet, 4...Glove, 5...High frequency amplifier, 6゜10...Phase detector, 7.11...Low frequency increase 1 [scary, 8゜12...Low pass Filter, 9.13・
... A/D converter, 14... Central control unit, 15...
・Display device. Agent Patent Attorney Tatsuyuki Unuma Figure 1! 20th 312th] 4th - Exit (I7)

Claims (1)

[Claims] 1. Applying a high frequency pulse to a probe placed in a DC static magnetic field and filled with a sample to be measured, sampling the resonance signal detected by the globe, and Fourier transforming the sampling data. In a nuclear magnetic resonance apparatus configured to obtain a two-frequency vector by sampling separately at a time when the resonance signal does not exist,
A nuclear magnetic resonance apparatus characterized in that a time average value of the sampling data is subtracted from the resonance signal. 2. Claim 1, characterized in that the time average value of the sampling take at a time when no resonance signal exists is subtracted from the frequency spectrum obtained by Fourier transforming the sampling take containing the resonance signal. The nuclear magnetic resonance apparatus described in .