JPH04174380A - Nuclear magnetizing and exciting method - Google Patents

Abstract

PURPOSE:To excite a wide frequency band by low radio wave intensity by constituting each of the first and second pulses of a composite pulse consisting of the same number of pulse trains and setting the pulses positioned in the same order of both pulses so that pulse width is equal but the phases thereof are mutually different by about 90 deg. and the phases of the pulses adjacent in the composite pulse are mutually different by 180 deg.. CONSTITUTION:At first, the first pulse 10 is applied and the second pulse 11 is applied after a predetermined time tau1 from the falling of the pulse 10 and data is taken in after a predetermined time tau2 from the falling of the pulse 11. Herein, each of the pulses is a composite pulse wherein a plurality of pulses are combined without providing a time interval and the number of the pulses is same. The pulses positioned in the same order of the pulses 10, 11, that is, the N-th pulse of the pulse 10 and the N-th pulse of the pulse 11 are equal in pulse width and mutually different by 90 deg. in phase. Further, the phases of the pulses adjacent in the composite pulse are made mutually different by 180 deg..

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a nuclear magnetization excitation method suitable for use in a system with a spin quantum number of 1. Concerning configuration.

[Prior Art] Conventionally, when measuring a system in which the spin quantum number is 1, such as deuterium and its isotopes, using a nuclear magnetic resonance apparatus (NMR), when the direction of the static magnetic field is the Z direction, first a first pulse is detected. 1
A 90'''X pulse is applied in the X-axis direction, and then a second pulse 2 of 30° is applied in the Y-axis direction after a predetermined time τ, and then, after a predetermined time τ2, the data is Then, by Fourier transforming the captured data, a spectrum as shown in Figure 5B is obtained, which allows us to know the structure and motion of the molecules that make up the sample. 5B is a diagram showing a spectrum obtained by applying a 90'' pulse to d, -PMMA as a sample and measuring it by the quadrupole echo method, and the 2H1 resonance frequency of the nucleus is 41.5.
MHZ, radio wave intensity is γB, /2z=83kHz
It is z.

[Problems to be Solved by the Invention] However, when using a 90° pulse as shown in Fig. 5, the frequency band that can be excited with a constant radio wave intensity is narrow, and therefore the frequency band must be excited over a wide frequency band. This required extremely strong radio waves. For example, in order to excite a frequency band of about 250kHz,
For both the first pulse and the second pulse, γB, which is a parameter indicating the intensity of radio waves, was required to be about 20 kHz.

In contrast, the first and second pulses are combined into a single 90°
In place of the @pulse, a composite pulse that combines multiple pulses has also been used, and according to this, the sO
Compared to the case where @pulses are used, a wider frequency band can be excited with the same radio wave intensity, but conventional composite pulses have a similar effect between a system with a spin quantum number of 1 and a system with a spin quantum number of 1/2. For example, 18G
``This is an inversion pulse for a system with a spin quantum number of 1/2 that has only an RF phase shift, and a pulse width of 1/2 was used, so it is optimal for a system with a spin quantum number of 1. This required relatively high radio wave intensity.

The present invention solves the above problems, and aims to provide a nuclear magnetization excitation method that can excite a sufficiently wide frequency band with low radio wave intensity.

[Means for Solving the Problems] In order to achieve the above object, the nuclear magnetization excitation method of the present invention applies a first pulse and a second pulse at a predetermined time interval. The first pulse and the second pulse are both composed of a composite pulse consisting of the same number of pulse trains, and the pulses located in the same order of the first pulse and the second pulse have the same pulse width and a phase difference of about 9 G° from each other, and It is characterized in that the phases of adjacent pulses within a composite pulse differ from each other by approximately 180@.

[Function] According to the present invention, for example, as the first pulse, a pulse with a pulse width of approximately 3G@ and a phase of approximately 270', a pulse with a pulse width of approximately 148' and a phase of approximately 90@; about 6
2″ and a pulse with a phase of approximately 270 @ and a pulse width of approximately 37
When a composite pulse is used in which a pulse with a pulse width of approximately 3B'' and a phase of approximately 90° is combined in this order, the second pulse is a pulse with a pulse width of approximately 3B'' and a phase of approximately 0°, These are a pulse with a pulse width of approximately 148' and a phase of approximately 180'', a pulse with a pulse width of approximately 62# and a phase of approximately O'', and a pulse with a pulse width of approximately 37'' and a phase of approximately 180''. Composite pulses that are combined in sequence are used.

Note that the time τ1 from the fall of the first pulse to the rise of the second pulse is about 10 to 209 seconds. Also, the pulse width of each pulse that makes up the composite pulse is
As a whole, a range of about ±5'' is acceptable for the composite pulse.

Unlike conventionally used composite pulses, this type of composite pulse is optimally designed for a system with a spin quantum number of 1, so it is possible to excite a wide frequency band with low radio wave intensity. It is possible.

[Example code] Examples will be described below with reference to the drawings.

In the nuclear magnetization excitation method according to the present invention, as shown in FIG. 2 Predetermined time τ2 from the falling edge of pulse 11
After that, import the data. Here, the first pulse 1
The 0 and second pulses 11 are each a composite pulse in which a plurality of pulses are combined without any time interval, and the number of pulses thereof is the same. Then, the pulses located in the same order of the first pulse 10 and the second pulse 11, that is, the first pulse 1
The Nth pulse of 0 and the Nth pulse of second pulse 11 have the same pulse width, and their phases differ from each other by approximately 90°.

The reason why the pulse widths of the first pulse 10 and the second pulse 11 are made equal is as follows. The effective band, that is, the band in which phase-aligned magnetization components are observed with an intensity of 98% or more, is determined by the narrower of the bandwidths of the first pulse 10 and the second pulse 11. In other words, it goes without saying that the pulse widths of the first pulse 10 and the second pulse 11 can be made different;
In that case, the pulse with the wider effective band will not be used effectively. Therefore, in order to make the effective bands of the first pulse 10 and the second pulse 11 the same, the pulse widths of the pulses at the corresponding positions are made the same.

Furthermore, the phases of adjacent pulses within a composite pulse are 1 relative to each other.
80' are made differently.

FIG. 2 shows an example of a composite pulse that can be used as the first pulse 10 or the second pulse 11. In addition, in the numerical value written for each pulse in the figure, the upper part indicates the pulse width, and the lower part in parentheses indicates the phase.

The composite pulse in Figure 2A consists of a pulse with a pulse width of 36.0' and a phase of 270'', a pulse with a pulse width of 147.8@ and a phase of 30'', and a pulse with a pulse width of 62.0' and a phase of 270''. is 2
70" pulse with pulse width of 38.9° and phase of 90"
Similarly, the composite pulse shown in Figure B is composed of 8 pulses combined, and the composite pulse shown in Figure C is composed of 10 pulses. It is made up of a combination of pulses. The pulse width and phase of each pulse constituting each composite pulse are as shown in the figure.

The effective bands when using the composite pulses shown in Fig. 2 A, B, and C are mainly 1°5γB1 and 1°5γB1, respectively.
Main 2゜9γB8. ±3.7γB. On the other hand, the conventional one is about ±0.5γB, so Fig. 2A
The composite pulse shown in Figure 2A has approximately three times the voltage and approximately three times the power. Therefore, when the composite pulse shown in Figure 2A is used, the excitation is greater than that of the conventional method when the radio wave intensity is the same. The possible frequency band is tripled, and to excite the same frequency band, 1/9th the power of the conventional method is required.

Although the composite pulses shown in FIGS. 2A, B, and C can be used as the first pulse 10 or the second pulse as they are, the pulse arrangement shown in FIG. 2 may be reversed.

For example, taking the composite pulse shown in FIG. is 147.8', the phase is 80'', and the pulse width is 3.
A composite pulse in which four pulses of 8.0@ and a phase of 270'' are arranged in this order can also be used as the first pulse 10 or the second pulse 11.

When the composite pulses shown in FIG. 2 A, B, and C are used as the first pulse 10, the second pulse 11 has the same pulse width and phase as each pulse constituting the composite pulse of the first pulse 10. A composite pulse consisting of 906 pulses is used. For example, when the composite pulse shown in FIG. 2A is used as the first pulse 10 or the second pulse 11, the second pulse 11 or the first pulse 10
is a pulse with a pulse width of 38.0° and a phase of θ°, a pulse with a pulse width of 147.8@ and a phase of 180@, and a pulse with a pulse width of 62.0'' and a phase of 0@. , a pulse width of 36.9'' and a phase of 180''. The same applies to the composite pulses shown in FIGS. 2B and 2C.

Note that the pulse width of each pulse constituting the composite pulse is not limited to the above numerical value, and there is a tolerance range of approximately ±5° for the composite pulse as a whole.

The first pulse 10 consisting of the above-described composite pulse tilts the thermal equilibrium magnetization in the X-Y plane perpendicular to the thermal equilibrium magnetization so that it can be refocused by the second pulse 11. In addition, the second pulse 11 is applied at x
- Change the sign of magnetization in the y-plane.

τ1 and τ2 in FIG. 1 vary depending on the composite pulse used as the first pulse 10 and second pulse 11, but approximately l
It is about 0 to 20 μsec.

Next, a method for designing the above-mentioned composite pulse will be explained.

First, the following pulse train with a pulse width of 45'' and different phases is created.

45@I+ + 45@12 H45@ii-+...
・・・・・・・・・45°i.

However, 2≦n: 51B, and the RF phase 11 is 0″.

It is either 90', 180', or 27G'.

The reason why the pulse width was set at 45@ is because many conventionally used pulses have a pulse width that is a multiple of 45'', and the simulation 2 method has been established, so This is because the time required can be minimized.Also, the number of pulses is set to 16 at maximum because
It is estimated that the frequency band that can be excited is approximately proportional to the overall pulse width of the composite pulse, and therefore, it is possible to excite a wider frequency band than before by using a composite pulse consisting of a maximum of about 18 pulse trains; This is because if the number is larger than that, it is presumed that a relaxation phenomenon will occur and the practicality will be lost.

There are about 101e combinations of the above pulse trains, and from among them, for example, a simulation is performed such as multiplying by a rotation matrix to find the direction of magnetization, and the quadrupole coupling constant Δω is determined. When =0, about tOW pulse trains that can obtain the same effect as the 90'' pulse are extracted.

Next, using the pulse train extracted in this manner as an initial pulse, optimization is performed using the pulse width and RF phase as variables.

Examples of composite pulses obtained by such a method are shown in FIGS. 2A, B, and C, and many composite pulses having effects equivalent to these composite pulses have been confirmed.

FIG. 3 shows a comparison between the case where the composite pulse according to the present invention is used and the conventional example. Figure 3 is a graph obtained as a result of the above-mentioned Siminireshiron, and is a graph showing the state of magnetization with respect to the frequency normalized by ω0/2ω1, and rlJ on the vertical axis indicates the completely excited state. , "O" indicates a non-magnetized state, and r-IJ indicates a state where the magnetization is reversed. Figure 3A shows the case where a conventional 90° pulse is used (τ1=200", t@=245"),
Figure B shows the case (τI=200@, τ2
:474'), and C in the same figure shows the case where the composite pulse shown in Fig. 2B is used (τ+"2000, τ2:sos'),
The same diagram shows the case where the composite pulse shown in Figure 2C is used (τ
+=200', τ2=883').

As is clear from FIG. 3, it can be seen that according to the present invention, magnetization is achieved satisfactorily over a wide frequency band.

Figure 4 is a comparison of spectra measured by the quadrupole echo method, in which the samples are da-P M M
A. The 2H1 resonance frequency of the nucleus is 41.5MHz.

Figure 4A shows the spectrum when the composite pulse shown in Figure 2C is used, and the radio wave intensity γB+/2π=21k
It is H2. Figure B is the same as that shown in Figure 5B, and is the spectrum when a conventional 90'' pulse is used, and the radio wave intensity γB +/2π = 83kHz. Figure C is based on Rale1gh et al. This is the spectrum when using the proposed conventional composite pulse, and the radio wave intensity γB1/2π = 21kHz.
'This is the spectrum when pulses are used, and the radio wave intensity is γB+/2π=21 kHz.

Comparing FIGS. 4A, B, C, and D, it can be seen that the use of the composite pulse according to the present invention can excite a wide frequency band with low radio wave intensity, and is therefore the best. The spectrum in Figure 4B is almost the same as the spectrum in Figure 4A, but the radio wave intensity is three times that of Figure A, and the peak at ±62kHz is 70% of the original intensity. It has been confirmed by calculation that there is.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, it is possible to obtain an optimal composite pulse for a system with a spin quantum number of 1 through simulation, so that it is possible to obtain a composite pulse that is optimal for a system with a spin quantum number of 1. can be excited by canceling out the effects of quadrupolar coupling across the range.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating pulses used in the nuclear magnetization excitation method according to the present invention, FIG. 2 is a diagram illustrating an example of the configuration of a composite pulse,
Fig. 3 is a diagram for comparing the present invention and the conventional example in terms of the state of magnetization, Fig. 4 is a diagram for comparing the present invention and the conventional example in terms of spectra, and Fig. 5 is a diagram showing the conventional example. . 10...1st pulse, 11...2nd)<)Response. Applicant JEOL Ltd. Agent Patent Attorney Hideo Sugai (7 others) Figure 1 Figure 3 0 1 2 ωG/2ω
1ku ω Fig. 3 0 1 2 ωQ/2ω1 Fig. 5'. 'o,,,,.

Claims (4)

[Claims] (1) In a nuclear magnetization excitation method in which a first pulse and a second pulse are applied at a predetermined time interval, the first pulse and the second pulse are
The pulses are composed of composite pulses each consisting of the same number of pulse trains, and the pulses located in the same order of the first pulse and the second pulse have the same pulse width, differ in phase from each other by approximately 90°, and are adjacent to each other within the composite pulse. A nuclear magnetization excitation method characterized in that the phases of the pulses differ by approximately 180 degrees from each other. (2) The composite pulse used for either the first or second pulse is a pulse with a pulse width of approximately 36° and a phase of approximately 270°, and a pulse with a pulse width of approximately 148° and a phase of approximately 90°. A pulse having a pulse width of approximately 62 degrees and a phase of approximately 270 degrees, and a pulse having a pulse width of approximately 37 degrees and a phase of approximately 90 degrees are combined in this order or in the reverse order. The nuclear magnetization excitation method according to claim 1. (3) The composite pulse used for either the first or second pulse is a pulse with a pulse width of approximately 31° and a phase of approximately 90°, and a pulse with a pulse width of approximately 61° and a phase of approximately 270°. , a pulse with a pulse width of approximately 74 degrees and a phase of approximately 90 degrees, a pulse with a pulse width of approximately 73 degrees and a phase of approximately 270 degrees, a pulse with a pulse width of approximately 155 degrees and a phase of approximately 90 degrees, and a pulse with a pulse width of approximately 155 degrees and a phase of approximately 90 degrees. A pulse with a width of approximately 75 degrees and a phase of approximately 270 degrees, a pulse with a pulse width of approximately 65 degrees and a phase of approximately 90 degrees, and a pulse with a pulse width of approximately 31 degrees and a phase of approximately 270 degrees in this order or 2. The nuclear magnetization excitation method according to claim 1, wherein the nuclear magnetization excitation method is combined in a reverse order. (4) The composite pulse used for either the first or second pulse includes a pulse with a pulse width of approximately 83° and a phase of approximately 90°, and a pulse with a pulse width of approximately 75° and a phase of approximately 270°. A pulse with a pulse width of approximately 158 degrees and a phase of approximately 90 degrees, a pulse with a pulse width of approximately 66 degrees and a phase of approximately 270 degrees, a pulse with a pulse width of approximately 117 degrees and a phase of approximately 90 degrees, and a pulse with a pulse width of approximately 117 degrees and a phase of approximately 90 degrees. A pulse with a pulse width of approximately 42 degrees and a phase of approximately 270 degrees, a pulse with a pulse width of approximately 66 degrees and a phase of approximately 90 degrees, a pulse with a pulse width of approximately 158 degrees and a phase of approximately 270 degrees, and a pulse with a pulse width of approximately 270 degrees. A pulse with a phase of approximately 90° at 75° and a pulse width of approximately 6
6° and a phase of approximately 270°, which are combined in this order or in the reverse order.
The nuclear magnetization excitation method described.