JPH02272379A - Method and device for generating high frequency pulse and exciting nuclear magnetic resonance of sample - Google Patents

Abstract

PURPOSE:To shorten a high frequency pulse width and to narrow the frequency band by obtaining a high frequency pulse by combination of plural modulated high frequencies different in frequency. CONSTITUTION:A first high frequency generated by a high frequency oscillator 1 has the amplitude modulated in a modulator 3 by a first modulating wave generated by a modulating wave generator 2. Second and third high frequencies generated by high frequency oscillators 4 and 5 have the amplitude modulated in modulators 7 and 8 by a second modulating wave generated by a modulating wave generator 6, and second and third modulated high frequencies are added by an adder 9. The output of the adder 9 is added to the output of the modulator 3 by an adder 10. Amplitude modulation time widths and frequency bands of these high frequencies are properly selected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for generating high-frequency pulses and for excitation of nuclear magnetic resonance of a sample, and particularly the method and apparatus suitable for nuclear magnetic resonance imaging and nuclear magnetic resonance analysis. Regarding.

[Conventional technology]

To perform nuclear magnetic resonance imaging or nuclear magnetic resonance analysis, a high frequency pulse is typically applied to a sample in order to excite the sample to nuclear magnetic resonance.

According to a well-known technique, a high frequency wave (carrier wave) with a predetermined frequency is modulated by a modulating wave given by a 5 INC function limited at both ends to have time @T, thereby changing said frequency. At the center, a high frequency pulse is generated giving a frequency spectrum with a frequency band proportional to the reciprocal of the time width T.

[Problem to be solved by the invention]

However, the time width of the modulated wave and the frequency band of the frequency spectrum are inversely proportional to each other.

The time width of the modulated wave, and therefore the high frequency pulse II? (This represents the irradiation time of the sample with the high-frequency pulse) and narrowing the frequency band are difficult to satisfy at the same time.

An object of the present invention is to provide a method and apparatus for generating high-frequency pulses and for exciting nuclear magnetic resonance of a sample, which are suitable for both shortening the high-frequency pulse width and narrowing the frequency band.

[Means to solve the problem]

According to the invention, a plurality of modulated radio frequencies having mutually different frequencies are generated and these generated radio frequencies are combined to generate radio frequency pulses giving a frequency spectrum with a desired frequency band.

[Effect]

If the high frequency pulse is obtained by a combination of a plurality of modulated high frequency waves having different frequencies.

The frequency band of the frequency spectrum given by each high frequency pulse can be made wider than the frequency band of the frequency pulse given by the high frequency pulse, and therefore the high frequency pulse width can be shortened and the frequency band narrowed. It will be possible to achieve both.

〔Example〕

Referring to FIG. 1, a first high frequency wave (Wi transmission) generated by a high frequency oscillator 1 is amplitude-modulated in a modulator 3 with a first modulated wave generated by a modulated wave generator 2. The second and third high frequencies (carrier waves) generated by the high frequency oscillators 4 and 5 are transmitted to the modulated wave generator 6.
The modulated waves are amplitude-modulated in modulators 7 and 8, respectively, and the modulated second and third high-frequency waves are added in an adder 9. The output of adder 9 is further added to the output of modulator 3 in adder 10.

As the first and second modulated waves, SIN'C function waves as shown in FIGS. 2 and 3 are used. Although the polarities of the 5INC function waves in Figures 2 and 3 are opposite to each other,
5IN so that only the main lobe and its two pairs of side lobes at both ends are included within the time intervals T1 and Tz, respectively.
Both ends of the C function wave are truncated.

When the first high frequency is amplitude modulated with the 5INC function modulation wave shown in FIG. 2, a first high frequency pulse having a time width of T1 is obtained, and the second and third high frequency waves are modulated by the 5INC function modulation wave shown in FIG. When the amplitude is modulated using a function modulated wave, second and third high frequency pulses having a time width of T2 are obtained. Therefore, the second and third high frequency pulses are added in the adder 9, and the output of the adder 9 is added to the first harmonic pulse in the adder 10. 1st. A high frequency pulse having a time width T2 obtained by combining the second and third high frequency pulses is output. Therefore, for the high frequency pulse which is the output signal of the adder 1o, the first . The second and third high frequency pulses can be referred to as component high frequency pulses.

Let the frequency of the first high frequency be io, and if this high frequency is modulated by the 5INC function wave shown in Figure 2, the resulting first high frequency pulse will be fBl with fo as the center as shown in Figure 4. Provides a substantially rectangular frequency spectrum with frequency bands. Similarly, if the frequencies of the second and third high-frequency waves are set to fl and f2, and these high-frequency waves are modulated by the 5INC function wave shown in FIG. As shown in FIG. 6, a substantially rectangular frequency spectrum having a frequency band fBz centered on fl and f2 is provided. Therefore, the first. The high frequency pulse obtained by combining the second and third high frequency pulses also provides a substantially rectangular frequency spectrum.

- For example, Tz=2.5Tt+Jt=Jo-3fB.

/3. fz=io-3JBo/2. fBt=5jno
.

If f B2 = 2 f ao, the synthesized high-frequency pulse gives a frequency spectrum shown in FIG. 7, that is, a frequency spectrum with a center frequency of io and a frequency band of fao.

On the other hand, if the high-frequency pulse is obtained only by modulating the high-frequency wave of frequency fo with, for example, the 5INC function wave in FIG. The frequency band fB3 of the spectrum is proportional to 1/T2, but T2=2.
5T1 and fBx=5fso is 1/T s
Since fas is proportional to , fas becomes 2fBo.

From the above facts, according to the example of the present invention, it is possible to obtain a frequency spectrum having a frequency band fBo in time T2, whereas in the conventional method, the frequency spectrum of the frequency spectrum obtained in time T2 can be obtained. It can be seen that the band is twice as wide as that in the example of the present invention. this is,
Conversely, while the conventional example requires a time of 2T2 to obtain a frequency spectrum with a frequency band of fBo, the example of the present invention requires only half that time. , thus TI, T2
This also means that by appropriately selecting 1 jet, fB2, etc., it is possible to shorten the time and narrow the frequency band.

In the embodiment, the number of high frequencies to be combined is three: the first, second, and third high frequencies, but the number is not limited to three and may be two. Furthermore, the second and third high frequencies in the embodiment may be modulated by 5INC function waves having different time widths. Furthermore, the second
The modulated wave has a polarity opposite to that of the first modulated wave, but this polarity reversal may be performed after modulation rather than at the stage of generating the modulated wave. Also, keep the polarities the same and adder 1
A subtracter may be used instead of 0, and the difference between the surface input signals may be obtained. In addition, as a modulated wave, 5INC
In addition to function waves, Gaussian waves and rectangular waves can also be used.

Referring to FIG. 8, the static magnetic field generator 11 into which the sample is inserted may be of a superconducting type, an electromagnetic type, or a permanent magnet type. A gradient magnetic field coil 12 is disposed in the static magnetic field generator 11 so as to surround the sample.
and a magnetic field gradient control device 13 that controls the application of magnetic field gradients in two directions. High frequency pulse generator 1
4 is as shown in FIG. 1, and the amplifier 1 is configured to apply the high frequency pulse generated by this to the sample.
5 to the transmitting/receiving coil 16. A receiving device 17 is also connected to the transmitting/receiving coil 16 for receiving nuclear magnetic resonance signals obtained from the sample.

The sequence control device 18 is connected to the magnetic field gradient control device 13, the high frequency pulse generator 14, and the receiving device 17,
The timings of generation of high frequency pulses, generation of magnetic field gradients in the X, Y and Z directions, and reception of nuclear magnetic resonance signals are controlled. The sequence control device 18 also causes the data processing device 19 to perform image reconstruction based on the nuclear magnetic resonance signals received by the receiving device 17, and displays the image on the display device 21 through the operation console 20 that exchanges information. work.

Referring to FIG. 9, a selective 90' radio frequency pulse is applied in the presence of a Z-axis magnetic field gradient GS for slice selection. This selects a slice perpendicular to the Z axis. That is, the nuclear spins within that slice are knocked down by 90'. The spins thus defeated are gradually dispersed.

A selective 180° radiofrequency pulse is then applied in the presence of a magnetic field gradient O3, which inverts the nuclear spins within the slice. The dispersed nuclear spins are gradually focused, and a nuclear magnetic resonance signal called a spin echo is generated from the entire slice.

Between the selective 90° high-frequency pulse and the selective 180° high-frequency pulse, a magnetic field gradient Gp in the Y-axis direction for phase encoding is applied, and after the application of the selective 180° high-frequency pulse, a magnetic field gradient Gp in the X-axis direction for readout is applied. A magnetic field gradient GR is applied while the spin echo signal is read.

The above steps are repeated N times to generate N spin echo signals. However, GP is changed each time so that its time integral value changes at a constant rate.

N samplings are applied to each of the N spin echo signals, and a two-dimensional Fourier transform process is applied to the N spin echo signals each consisting of the N sampled signals. As a result, a two-dimensional nuclear magnetic resonance signal image in the X-Y plane of the slice is obtained.

The readout magnetic field gradient GR is also applied between the image quotient frequency pulses. This application is performed to compensate for the day phase of the nuclear spins caused by the first half of the magnetic field gradient GR applied after the selective 180° radio frequency pulse is applied.

〔Effect of the invention〕

According to the present invention, there is provided a method and apparatus for generating a high-frequency pulse and for excitation of a sample by nuclear magnetic resonance, which are suitable for both shortening the high-frequency pulse width and narrowing the frequency band.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a high-frequency pulse generation circuit according to the present invention, FIGS. 2 and 3 are diagrams showing an example of modulated waves used in the embodiment of FIG. 1, and FIG.
5, 6, and 7 are diagrams showing examples of frequency spectra given by high-frequency pulses used in the embodiment of FIG. 1, and FIG. 8 is a nuclear magnetic resonance system incorporating the embodiment of FIG. 1. FIG. 9, a block diagram of an embodiment of the imaging apparatus, is a diagram showing an example of a pulse sequence used in the embodiment of FIG. 8. 1.4.5...High frequency oscillator, 3,7.8...Modulator, 2.6...Modulated wave generator, 9,10...Adder, 11...Static magnetic field generator , 12... Magnetic field gradient coil, 13... Magnetic field gradient control device, 14... High frequency pulse generator, 16... Transmission/reception coil, 17... Receiving device, 18... Sequence control device, 19 ...Processing device, 2o...Figure 2 Figure 4 Figure 5 Figure 7

Claims (1)

[Claims] 1. Generating a plurality of modulated high frequencies having different frequencies and combining these generated high frequencies so as to generate a high frequency pulse that provides a frequency spectrum having a desired frequency band. A high-frequency pulse generation method characterized by 2. A high-frequency pulse characterized by generating a plurality of modulated high-frequency waves having mutually different frequencies and synthesizing these generated high-frequency waves so as to generate a high-frequency pulse giving a frequency spectrum having a desired frequency band. Generation method. 2. Generate a component high-frequency pulse that gives a frequency spectrum with a certain frequency band and at least one component high-frequency pulse that gives a frequency spectrum with a frequency band narrower than the certain frequency band, and combine the component high-frequency pulses with these components. A method of generating high-frequency pulses, characterized in that the combination is performed so as to generate a high-frequency pulse that provides a frequency spectrum having a narrower frequency band than any of the frequency bands of the frequency spectrum provided by the high-frequency pulses. 3. The high-frequency pulse generation method according to claim 3, wherein each of the component high-frequency pulses is obtained by modulating a high frequency with a modulated wave. 4. A first high-frequency pulse giving a frequency spectrum having a first frequency band; and a frequency band on the lower frequency side, which is wider than the central frequency band, other than the desired central frequency band in the first frequency band, and generating second and third high frequency pulses having frequency bands respectively corresponding to the frequency band on the high frequency side; combining to produce radio frequency pulses that give a frequency spectrum having substantially the same frequency band as the central frequency band of, but substantially not having substantially the same frequency bands as the frequency bands on either side thereof. High frequency pulse generation method. 5. The first high-frequency pulse is obtained by modulating the first high-frequency wave with a first modulated wave, and the second and third
The high frequency pulse is different from the frequency of the first high frequency wave and generates second and third high frequency waves having different frequencies from each other.
6. The high-frequency pulse generation method according to claim 5, which is obtained by modulating with a modulated wave of. 6. A nuclear magnetic resonance excitation method for a sample, in which a sample is placed in a static magnetic field and a high-frequency pulse is applied to the sample to excite the sample to nuclear magnetic resonance. A nuclear magnetic resonance excitation method for a sample, characterized in that high frequencies are generated and these generated high frequencies are combined to generate the high frequency pulses that give a frequency spectrum with a desired frequency band. 7. A nuclear magnetic resonance excitation method for a sample, in which the sample is placed in a static magnetic field, and a high frequency pulse is applied to the sample while applying a magnetic field gradient to the static field to excite the sample to nuclear magnetic resonance,
A core of a sample characterized in that a plurality of modulated high frequencies having different frequencies are generated and these generated high frequencies are combined to generate the high frequency pulse giving a frequency spectrum having a desired frequency band. Magnetic resonance excitation method. 8. Means for generating a plurality of modulated high frequencies having mutually different frequencies, and means for combining these generated high frequencies so as to generate a high frequency pulse giving a frequency spectrum having a desired frequency band. High frequency pulse generator. 9. means for generating a component high-frequency pulse giving a frequency spectrum having a certain frequency band and at least one component high-frequency pulse giving a frequency spectrum having a frequency band narrower than the certain frequency band; and means for combining the components of the component high frequency pulses so as to generate a high frequency pulse giving a frequency spectrum having a narrower frequency band than any of the frequency bands of the frequency spectrum provided by the high frequency pulse. 10. A first high-frequency pulse giving a frequency spectrum having a first frequency band; and a frequency band on the lower frequency side, which is wider than the central frequency band, other than a desired central frequency band in the first frequency band, and means for generating second and third high frequency pulses having frequency bands respectively corresponding to the frequency band on the high frequency side;
, second and third radio frequency pulses having a frequency band substantially the same as the desired central frequency band in the first frequency band, but substantially the same frequency bands on either side thereof. a high-frequency pulse generator comprising: means for combining to generate high-frequency pulses giving a frequency spectrum unique to that of the high-frequency pulse generator; 11. The high-frequency pulse generator according to claim 11, wherein frequency bands corresponding to frequency bands on both sides of the central frequency band in the frequency spectrum provided by the high-frequency pulse have substantially the same width. 12. The high-frequency pulse generating means generates first, second, and third high-frequency waves having different frequencies;
means for generating first and second modulated waves; and means for generating first and second modulated waves;
and means for modulating the second and third high frequency waves with the second modulation wave so as to obtain the second and third high frequency pulses. The high frequency pulse generator described above. 13. The high frequency pulse generating means, comprising means for generating a static magnetic field in which a sample is placed, means for generating a high frequency pulse, and means for applying the high frequency to the sample to excite the sample to nuclear magnetic resonance. comprises means for generating a plurality of modulated radio frequencies having mutually different frequencies, and means for combining the generated radio frequencies to produce said radio frequency pulses giving a frequency spectrum having a desired frequency band. Sample nuclear magnetic resonance excitation device. 14. means for generating static magnetism in which a sample is placed, means for applying a magnetic field gradient to the static magnetic field, means for generating a high frequency pulse, and applying the high frequency pulse to the sample in the presence of the magnetic field gradient; and means for generating nuclear magnetic resonance in the sample, and the means for generating high frequency pulses includes means for generating a plurality of modulated high frequencies having different frequencies, and converting the generated high frequency into a frequency having a desired frequency band. means for generating said radio frequency pulses giving a spectrum.