JP2824765B2 - Nuclear magnetic resonance equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear magnetic resonance apparatus. 2. Description of the Related Art In this nuclear magnetic resonance apparatus, for example, one disclosed in Japanese Patent Publication No. 62-9856 is known in order to homogenize a magnetic field. The magnetic field homogeneity is automatically corrected by using a nuclear magnetic resonance signal which is constantly in a resonance state as a monitor signal. However, a magnetic field locking means is required to constantly maintain nuclear magnetic resonance. A nuclide other than the measured nucleus, typically a deuterium nucleus, is used as a monitor signal. [0004] However, since the conventional device is provided with the magnetic field locking means, the device itself becomes complicated and its operation becomes complicated. [0005] Further, the deuterium nucleus used as a monitor signal is present in a very small amount in nature (natural abundance ratio 0.015%), and it is difficult to observe a nuclear magnetic resonance signal as it is. In particular, addition of a deuterium-enriched material was required, and contamination of the sample to be measured could not be prevented. SUMMARY OF THE INVENTION Therefore, an object of the present invention has been made in view of such circumstances, and has been provided with a simple and operable magnetic field uniformity automatic correction mechanism without a magnetic field locking means. It is to provide a resonance device. [0007] In order to achieve the above object, the present invention comprises a coil for correcting the uniformity of the spatial distribution of the DC magnetic field intensity, and controls a current value flowing through the coil. In such a nuclear magnetic resonance apparatus, a wiggle beat signal, which is one of the non-stationary nuclear magnetic resonance signals, is monitored, and the area within the envelope of the wiggle beat signal or a value corresponding to this area is maximized. A control means for controlling the current value is provided. That is, the area under the attenuation envelope of the wiggle beat signal is proportional to the attenuation time constant. The decay time constant is inversely proportional to the resolution of the spectrum.
Therefore, the condition for maximizing the area corresponds to the condition for maximizing the resolution of the spectrum. Therefore, if the value of the current flowing through the magnetic field correction coil is set so as to maximize the area or the value corresponding to this area, the magnetic field can be made uniform. The wiggle beat signal is a signal whose frequency starts from direct current and gradually increases in frequency as the magnetic field is swept, and can be obtained by sequentially exciting a narrow band component (single frequency component). Observing the wiggle beat signal has the advantage that the resolution can be adjusted by selecting a single peak even for a sample having many peaks in the spectrum. FIG. 1 is a block diagram showing an embodiment of a nuclear magnetic resonance apparatus to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a magnet for generating a static magnetic field,
2 is a magnetic field correction coil for uniformly correcting the magnetic field circle, 3 is a high frequency transmitter, 4 is a nuclear magnetic resonance detector, 5 is a nuclear magnetic resonance receiving circuit, 6 is an A / D converter, 7 is a digital single processor, 8 Is a magnetic field correction current controller, and 9 is a central controller. The nuclear magnetic resonance inspection apparatus 4 is arranged in a magnetic field between the magnets 1 and holds a sample to be measured therein. The high-frequency transmitter 3 sends a high-frequency pulse to the nuclear magnetic resonance detector 4 in accordance with an instruction from the central control unit 9. Thereby, the nuclear magnetic resonance detector 4
Nuclear magnetic resonance is induced in the sample to be measured. A nuclear magnetic resonance signal obtained by the nuclear magnetic resonance is digitized by an A / D converter 6 via a nuclear magnetic resonance receiving circuit 5. And
The digitized signal is sent to the digital single processor 7. Here, the nuclear magnetic resonance signal detected in the above process is called a free induction decay signal (FID), and is a non-stationary signal that gradually attenuates. FIG. 2 (a) shows an example of the waveform of the free induction decay signal, and FIG. 2 (b) shows the waveform subjected to the Fourier transform. The free induction decay signal generally decays exponentially, and its Fourier transform shows a Lorentzian shape. In this case, if the decay time constant of the free induction decay signal is T and the half width of the Fourier transform spectrum is (Δf), the following relational expression (1) is established. ## EQU1 ## As is apparent from the equation (1), as T increases, (Δf) decreases. That is, it indicates that the spectral resolution is improved and the magnetic field uniformity is improved. Also, the envelope g (t) of the free induction attenuation signal
Satisfies the following relational expression (2) as a function of T. [Equation 2] Here, A is a proportional constant. And g
The area s (t) surrounded by (t) is expressed by the following relational expression (3). [Equation 3] That is, the area under the envelope of the free induction decay signal is proportional to the time constant T, and as T increases, S
(T) also increases. Conversely, when S (T) increases, T also increases. From this, S (T) is monitored,
The magnetic field can be made uniform by controlling the current value of the correction coil so as to increase S (T). Referring again to FIG. 1, the digital single processor 7 obtains the S (T) from a series of time-series data output from the A / D converter 6. The value of S (T) obtained in this way is
The central control unit 9 repeats the measurement of the free induction decay signal while sequentially changing the correction coil current value via the correction current controller 8, and the measurement is performed as a function of the correction coil current value I. S (T), that is, S _T (I) is obtained. Figure 2 (c) are those showing an example of a measurement curve of _{S T (I), S T} (I) is the value I ₀ is the most uniform magnetic field of high current value I when the increase (corrected Shim current value). FIG. 3 is a diagram showing the above processing procedure.
In the figure, an initial set for determining parameters is performed in step 101. Then successively increasing the current I ₁ flowing in the step 102 to the magnetic field correction coil, Step 1
At 03, the signal shown in FIG. 2 (a) is measured.
Then, the area within the envelope of the signal calculated in step 104, at the next step 105, and registers the area value for said current I _1. The above process sequentially performed in increasing the course of the current values I _1, after completion of the entire measurement at step 106, at step 107, the current value I ₁ That correction Jim current value I _M of maximum area step 108
As specified in. According to the configuration described above, by monitoring the area of the envelope of the damped oscillation waveform, the magnetic field can be easily and automatically made uniform using the unsteady signal. . In the above-described embodiment, the area under the envelope of the free induction attenuation signal is used. However, the present invention is not limited to this.
Any parameter that corresponds to the area one-to-one can be used in the same manner. For example, the same effect can be obtained by using the area of the hatched portion of the damped vibration waveform shown in FIG. 2 (d). The non-stationary signal may be a signal other than the free induction decay signal, such as a wiggle beat in a magnetic field sweeping method. And since the wiggle beat signal is obtained by sequentially exciting narrow band components, even for a sample that has many peaks in the spectrum, it is easy to adjust the resolution by selecting a single peak from the peak. Can be performed. As is apparent from the above description,
According to the nuclear magnetic resonance apparatus of the present invention, it is possible to provide a simple and operable magnetic field uniformity automatic correction mechanism without a magnetic field locking means. Further, the contamination of the sample to be measured can be prevented without adding a deuterated concentrated sample or the like. Further, since the present invention uses a wiggle beat signal, even for a sample having many peaks in the spectrum, there is an effect that the resolution can be easily adjusted by selecting a single peak. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of a nuclear magnetic resonance apparatus to which the present invention is applied. 2 (a) to 2 (c) are explanatory diagrams showing the operation of FIG. 2 of the present invention, and FIG. 2 (d) is an explanatory diagram showing another embodiment of the present invention. FIG. 3 is a diagram showing a processing procedure according to an embodiment of the present invention. [Description of Signs] 1 Magnet 2 Magnetic field uniformity correction coil 3 High frequency transmitter 4 Nuclear magnetic resonance detector 5 Nuclear magnetic resonance receiving circuit 6 A / D converter 7 Digital signal processor 8 Current controller 9 for magnetic field uniformity correction coil Central control unit

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 24/00-24/12

Claims (1)

(57) [Claims] A nuclear magnetic resonance apparatus that includes a coil that corrects the uniformity of the spatial distribution of the DC magnetic field intensity, and controls a current value flowing through the coil. In the nuclear magnetic resonance apparatus, a wiggle beat signal, which is one of non-stationary nuclear magnetic resonance signals, A nuclear magnetic resonance apparatus having a control means for monitoring and controlling the current value so as to maximize an area within an envelope of the wiggle beat signal or a value corresponding to the area. 2. 2. The nuclear magnetic resonance apparatus according to claim 1, wherein the value corresponding to the area is the wiggle beat signal.
A nuclear magnetic resonance apparatus characterized by having an area of a signal waveform.