JPH0141938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear magnetic resonance measurement method, and particularly to a measurement method suitable for use in measuring solid samples.

In a nuclear magnetic resonance apparatus, a sample is normally irradiated with a 90° pulse (a high-frequency pulse to tilt the magnetization of the observed nucleus by 90°) as shown in Figure 1a, and the free induction decay signal (FID signal),
The NMR spectrum of the sample is obtained by Fourier transformation. At this time, it is inevitable that some leakage L will occur at the trailing edge of the 90° pulse, and the FID signal cannot be detected (sampled) during that period. If the sample is liquid, FID
Since signal attenuation occurs relatively slowly and over a long period of time, sampling the FID signal after the leakage has subsided has little effect. However, if the sample is solid, the FID signal attenuates quickly. If the observation is performed after the leak has subsided, a large portion of the first half of the FID signal cannot be sampled, and the spectrum obtained after Fourier transform will be greatly affected by the missing data, and it is difficult to eliminate the missing data. This results in data that is greatly affected by leakage, and the spectrum obtained after Fourier transformation is extremely influenced by leakage.

Therefore, in order to solve this problem, a measurement method called the solid echo method is used. This method, as shown in Figure 1b, involves irradiating a 90° pulse, then irradiating a reimaging pulse (e.g., a 90° pulse) after a predetermined period τ determined by the sample. The echo signal generated τ after irradiation is sampled, and the echo signal is Fourier-transformed to obtain a spectrum. According to this method, a period of τ is inserted before sampling, so that the influence of leakage can be reduced.

However, even if this method is used, if τ is short, distortion of the echo signal due to leakage cannot be avoided. Therefore, recently, as shown in Figure 1c, the phase of the high frequency included in the first 90° pulse is 0°, and the phase of the high frequency wave included in the first 90° pulse is 180°, as shown in Figure 1d. It has been proposed to obtain echo signals Ec and Ed whose phases are inverted by doing this, and to obtain the difference between these two echo signals. According to this proposed method, signals due to leakage having the same phase are removed by taking the difference, so the above-mentioned problem can be solved.

However, although many nuclear magnetic resonance instruments are equipped with a function to add and integrate FID signals as standard, they also have a function to subtract, and it is not possible to add a new subtraction function. , a great deal of effort and expense is required for modifying the computer program.

The present invention has been made in view of this point, and it is an object of the present invention to provide a measurement method that can eliminate the influence of leakage by using the addition function that nuclear magnetic resonance apparatuses normally have.

The present invention irradiates a sample with a high-frequency pulse to tilt the magnetization of the observation nucleus by 90 degrees, then irradiates a reimaging pulse after a predetermined time τ, and echoes generated after τ after irradiation with the reimaging pulse. In a nuclear magnetic resonance measurement method that detects signals, the radio frequency phases of the first irradiated 90° pulse are equal, and the radio frequency phases of the subsequent reimaging pulse are equal to each other.
It is characterized by performing two types of measurements at 180° angles the same number of times, integrating the obtained echo signals, and then subjecting them to Fourier transformation. Hereinafter, one embodiment of the present invention will be explained in detail using the drawings.

FIG. 2 shows an example of a nuclear magnetic resonance apparatus for carrying out the method according to the invention. In the figure, 1 is a magnet for generating a static magnetic field, 2 is a sample tube placed in the static magnetic field, and 3 is a sample coil placed around the sample tube 2. 4 is an oscillator that generates a high frequency having the resonance frequency of the observation nucleus, and the high frequency generated by the oscillator is transmitted to the 4-phase circuit 5 at 0°,
Four types of phases differing by 90 degrees are given: 90 degrees, 180 degrees, and 270 degrees, and one of them is extracted by the selection circuit 6 and sent to the sample coil 3 as a high frequency pulse through the gate 7. irradiates the sample.

The resonance signal induced in the sample coil 3 by nuclear magnetic resonance based on the high-frequency pulse irradiation is sent to the demodulation circuit 9 via the gate 8.
Demodulation is performed based on the high frequency signal sent from the oscillator 4. FID obtained by demodulation
The signal is converted into a digital signal by an A-D converter 10 and then sent to an integration circuit 11 for integration. The integrated data obtained by integrating the data a predetermined number of times in the integrating circuit 11 is sent to the computer 12 and subjected to Fourier transform processing. 13 is a pulse programmer that controls the operations of the selection circuit 6, gates 7, 8, and A-D converter 10 according to a predetermined sequence.

In the configuration as described above, the measurement is performed an even number of times, for example, twice, and under the control of the pulse programmer 13, the measurement is performed twice.
In each measurement, the gate 7 is turned on and off at the timing shown in FIG. 3a, and the gate 8 and the A-D converter 10 are turned on and off and sampling is performed at the timing shown in FIG. 3b. Therefore, the sample is irradiated with two 90° pulses at an interval τ as shown in Fig. 1b, c, and d, but in the present invention, at this time, reimaging is performed in the first and second measurements. The high-frequency waves within the pulses have a 180° phase difference. That is, as shown in FIG. 3c, for example, the phase of the high frequency signal taken out from the selection circuit 5 is the same as that of the first pulse during the first measurement.
At 0°, the phase of the reimaging pulse is 90°, and during the second measurement, the phase of the first pulse is 90°, as shown in Figure 3d.
At 0°, the phase of the reimaging pulse is switched to 270°. Therefore, in the first measurement, the sample is irradiated with a high-frequency pulse as shown in Figure 3e,
In the second measurement, a high frequency pulse as shown in FIG. 3f is applied. It can be seen from FIGS. 3e and 3f that the phase of the leakage portion L is reversed.
However, since the phase of the first pulse is the same in the two measurements, the phase of the echo signal is the same in the two measurements. Therefore, if the echo signals obtained in two measurements are added in the integration circuit 11, the echo signal components with the same phase will be doubled, and the leakage signal whose phase is reversed in the two measurements will be doubled. The result is that signal components affected by this are canceled. Therefore, even if the sample has a small τ, it is possible to eliminate the adverse effects caused by leakage. Moreover, the integrating mechanism may be a conventional addition mechanism, and there is no need to modify it to perform subtraction.

It goes without saying that if the above two measurements are taken as one cycle and the measurements are repeated and the integration is repeated, the integration effect will be further improved. At this time, it is not necessarily necessary to alternately perform two types of measurements in which the phases of the reimaging pulses are different by 180 degrees; in short, it is sufficient to perform the two types of measurements the same number of times and integrate the echo signals obtained.

In addition, the re-imaging pulse is not limited to the 90° pulse, but can also be a 45° pulse or a 180° pulse, and even if the phases are selected to be 0° and 180° instead of 90° and 270°. In short, it is sufficient that the phases of the reimaging pulses differ by 180° in the two types of measurements.

Strictly speaking, leakage also occurs at the falling edge of the first pulse, but as shown in Figures 1 and 3,
It is omitted in the figure.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining conventional problems, FIG. 2 is a diagram showing an example of a nuclear magnetic resonance apparatus for carrying out the method according to the present invention, and FIG. 3 is an operation of the apparatus shown in FIG. 2. FIG. 1: Magnet, 2: Sample tube, 3: Sample coil, 4:
High frequency oscillator, 5: 4-phase circuit, 6: selection circuit,
7, 8: Gate, 9: Demodulation circuit, 10: A-D converter, 11: Integration circuit, 12: Computer, 1
3: Pulse programmer.

Claims (1)

[Claims] 1. After irradiating the sample with a high-frequency pulse to tilt the magnetization of the observation nucleus by 90 degrees, irradiate the re-imaging pulse after a predetermined time τ, and detect the echo signal that occurs τ after the re-imaging pulse is irradiated. In the nuclear magnetic resonance measurement method, two types of measurements are performed the same number of times, in which the radio frequency phase of the first irradiated 90° pulse is equal and the radio frequency phase of the subsequent reimaging pulse is 180° different from each other. A nuclear magnetic resonance measurement method characterized in that the echo signals obtained are integrated and then subjected to Fourier transformation.