JPS61118648A - Nuclear magnetic resonance apparatus - Google Patents

Abstract

PURPOSE:To make it possible to automatically set the pulse width of a 90 deg. pulse, by repeating the measurement of the pulse width of a high frequency pulse while timewise changing said pulse width and comparing the FID signal obtained by each measurement with a reference signal. CONSTITUTION:A control circuit 16 generates a pulse at an appropriate cycle from a pulse generator 15 and increases the pulse width there of by 1mus from an initial value (e.g., 1mus). The FID signal induced in a transmitting-receiving coil 3 is taken out through a gate 10 and a demodulator 11. A reference value Vn is set to the upper limit value of noise and, if the FID signal exceeds this level even instantaneously, a comparator 17 generates a pulse and the control circuit 16 increase the pulse width of the next high frequency pulse by one step. When this pulse width becomes equal to the width of a 180 deg. pulse, the amplitude of the FID signal comes to zero and the comparator 17 generates no pulse. The control circuit 16 stops the change in the pulse width on the basis of this state and set one half of the pulse width at this time as the pulse width of a 90 deg. pulse to start final measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nuclear magnetic resonance apparatus (NMR apparatus), and particularly to an NMR apparatus that can automatically set the pulse width of a high-frequency pulse for excitation.

[Prior Art] In a nuclear magnetic resonance apparatus, an excitation high-frequency pulse (Ii
After irradiating the excitation pulse, the free induction decay signal (FID signal) induced in the transmitter/receiver coil is detected, and this FID signal, which is a signal in the time domain, is Fourier transformed into the frequency domain, and the nuclear magnetic resonance spectrum is obtained. I am getting .

[Problems to be solved by the invention] The basic excitation high-frequency pulse used for measurement is 90°.
There is a pulse (a high-frequency pulse with a pulse width that lowers the magnetization of the observation nucleus by 90"), and the setting of this pulse width is an important part of the measurement preparation procedure. Conventionally, this setting has been done, for example, by converting the FID signal to a CRT. The operator manually changes the pulse width and repeats the measurement while observing changes in the signal magnitude and phase, finds the pulse width with the highest signal strength, and uses that as the pulse width of the 90° pulse. However, this work requires skill,
If the settings are incorrect, not only will sufficient sensitivity not be obtained, but the measurement accuracy will also deteriorate, which will have a serious impact on the measurement.

Therefore, an object of the present invention is to provide an NMR apparatus that can automatically set this pulse width.

[Means for Solving the Problems] In order to achieve this objective, the present invention uses a transmitter/receiver coil disposed near a sample to be measured placed in a static magnetic field and a high frequency wave having a resonant frequency of an observation nucleus. means for pulse modulating the high frequency wave and supplying it to the transmitting and receiving coil as a high frequency pulse; means for generating a gate signal to be supplied to the gate means; In a nuclear magnetic resonance apparatus, the radio frequency pulse is repeatedly supplied to the transmitting/receiving coil. means for controlling the gate signal generating means so that the pulse width of the signal becomes longer or shorter stepwise, and comparing the FID signal induced in the transmitter/receiver coil by the high-frequency pulse irradiation or a signal obtained by processing the FID signal with a reference signal. means for stopping the change in pulse width in the control means based on the output of the comparison means, and setting the pulse width of the high-frequency pulses generated thereafter based on the pulse width at the time of stopping. It is characterized by

[Effect] The excitation pulse is a 180° pulse (the magnetization of the observation nucleus is changed by 180°).
When it comes to high-frequency pulses, the FTD signal does not appear at all in principle. Therefore, in the present invention, measurements are repeated by gradually increasing or decreasing the pulse width of the high-frequency pulse, and the FID signal obtained in each measurement is monitored, and its intensity is determined as a reference value (upper limit of noise). The pulse width when the pulse width is equal to or smaller than the 180° pulse is taken as the pulse width of the 180° pulse, and the pulse width is set to 1/2, for example.
By doing this, the pulse width of 906 pulses is obtained.

[Example] Hereinafter, one embodiment of the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing an example of a nuclear magnetic resonance apparatus embodying the present invention. In the figure, 1 is a magnet that generates a static magnetic field, 2 is a sample tube placed in the static magnetic field, 3 is a transmitter/receiver coil placed close to the sample tube, and 4 is an oscillator that generates high frequency waves to be supplied to the transmitter/receiver coil 3. It is. The high frequency generated by the oscillator 4 is transmitted to an amplifier 5, a gate 6, and a power amplifier 7.
．． The signal is sent to the transmitting/receiving coil 3 via the gate 8, and is irradiated onto the sample as a high frequency pulsed magnetic field. A resonance signal induced in the sample coil 3 after irradiation with this high-frequency pulsed magnetic field is extracted via a gate 9 and an amplifier 10 and sent to a demodulator 11. Free induction decay signal (FI
D signal) is sent to a data processing device 14 such as a computer via an amplifier 12 and an A-D converter 13.

15 is a pulse generator that generates a gate signal for turning ON/OFF the gate 6.8 to create a high frequency pulse, and 16 is a control circuit that controls the pulse width.

17 is a comparator for comparing the FID signal with a reference value vn, and its comparison output is supplied to the control circuit 16.

In the above configuration, the control circuit 16 causes the pulse generator 15 to generate pulses at appropriate intervals, and increases the pulse width from an initial value (for example, 1 μs) in 1 μs steps. Therefore, the pulse width of the excitation high-frequency pulse irradiated to the sample from the transmitting/receiving coil 3 is also 1 μs to 1 μs.
It gets longer in steps. After the high-frequency pulse irradiation, the IID signal induced in the transmitting/receiving coil 3 is transmitted to the gate 10. The reference value Vn is taken out via the demodulator 11, but the reference value Vn is set to the upper limit of noise, and if the FID signal exceeds this level even momentarily, the comparator 17 generates a pulse and sends it to the control circuit 16. , the control circuit 16 increases the pulse width of the next high frequency pulse by one step. This is repeated and the pulse width gradually becomes longer, but as the pulse width approaches the 180° pulse as shown in Figure 2 (a), the amplitude of the FTD signal increases as shown in Figure 2 (b). decreases, and when the pulse width reaches the 180° pulse width PW180, the amplitude becomes zero and there is only a noise component.

Therefore, as shown in FIG. M2 (C), no pulse is sent from the comparator 17 at that point, and based on this, the control circuit 16 stops changing the pulse width. At the same time, the control circuit 16 reduces the pulse width PW180 at that time to 1/2.
Pulse width PW of 906 pulses as PW180/2
90 is determined, and then the pulse width generated by the pulse generator 15 is set to the determined PW90, and the main measurement is started.

It goes without saying that if a 60° pulse or a 45° pulse is desired, it is sufficient to find PW180/3 or PW180/4 and set the pulse width to that value.

Further, the FID signal may be A-D converted and then compared with a reference signal, or the magnitude of the spectrum obtained by performing fast Fourier transform on the FID signal may be compared with the upper limit value of noise.

In the above example, the pulse width was lengthened stepwise, but
On the other hand, you can shorten it and find it. In particular, the pulse width PW18 of the 180° pulse obtained by increasing the length
0 and the pulse width PW 180' of the 180° pulse obtained by shortening it (PW180 + PW
If you calculate 180') / 2, you will get 180 with higher accuracy.
``The pulse width of the pulse can be determined.

[Effects of the Invention] As detailed above, the present invention provides an NMR apparatus that can automatically set the pulse width.
・It will be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a nuclear magnetic resonance apparatus embodying the present invention, and FIG. 2 is a diagram for explaining the operation of the embodiment of FIG. 1. 1...Magnet 2...Sample tube 3...Transmitting/receiving coil 4-channel oscillator 6.8.9...Gate 11...Demodulator 13...
A-D converter 14... Data processing device 15... Pulse generator 16... Control circuit 17... Comparator

Claims (1)

[Claims] A transmitter/receiver coil placed near a sample to be measured placed in a static magnetic field, a means for generating a high frequency wave having the resonant frequency of the observation nucleus, and a gate for pulse modulating the high frequency wave and supplying it as a high frequency pulse to the transmitter/receiver coil. means for generating a gate signal to be supplied to the gate means; means for detecting a free induction attenuation signal induced in the transmitter/receiver coil based on the high frequency pulse irradiation; and means for Fourier transforming the free induction attenuation signal. In a nuclear magnetic resonance apparatus comprising means for obtaining a nuclear magnetic resonance spectrum, the gate signal generating means is controlled so that the pulse width of the high-frequency pulse repeatedly supplied to the transmitting/receiving coil becomes longer or shorter in steps. and means for comparing an FID signal induced in the transmitting/receiving coil by the high-frequency pulse irradiation or a signal obtained by processing the FID signal with a reference signal, and changing the pulse width in the control means based on the output of the comparing means. What is claimed is: 1. A nuclear magnetic resonance apparatus characterized in that the pulse width of high-frequency pulses generated thereafter is set based on the pulse width at the time of stopping.