CN110850348B - Shape pulse editing and controlling method for nuclear magnetic resonance multimodal excitation - Google Patents

Abstract

The invention provides a shape pulse editing and controlling method for nuclear magnetic resonance multimodal excitation, which comprises the following steps: s1, specifying a pulse excitation mode and calculating an integral factor IR and a bandwidth factor BF of a pulse shape; s2, selecting a multi-peak range to be excited on a map, and calculating the frequency offset and the excitation bandwidth of an excitation peak; s3, synthesizing multi-peak excited shape pulses through frequency offset, excitation bandwidth and pulse excitation of N peaks; and S4, verifying the self-rotation excitation position and the self-rotation excitation range corresponding to the N peaks through simulation. According to the invention, the frequency information of different excitation peaks is subjected to fitting calculation through a pulse excitation time-varying evolution model to obtain a shape pulse with the amplitude and the phase of the pulse modulated at the same time, the excitation range and the excitation position of spins corresponding to a plurality of peaks are verified through simulation, and finally the pulse is edited and the multi-peak excitation is realized.

Description

Shape pulse editing and controlling method for nuclear magnetic resonance multimodal excitation

Technical Field

The invention relates to a pulse sequence control technology of a nuclear magnetic resonance spectrometer, in particular to a shape pulse editing and control method for multimodal excitation of nuclear magnetic resonance.

Background

Modern high resolution nuclear magnetic resonance spectroscopy (NMR) technology has the ability to detect and analyze various weak interactions between nuclei, and the development of one-, two-, and multi-dimensional NMR pulse sequence experimental methods establishes a rich information base of molecular conformation. The design and control of the pulse sequence are the core components of the nuclear magnetic resonance spectrometer technology, and various target experiments are completed through a certain number of Radio Frequency (RF) pulses and time delay.

The square wave pulses realized by the commonly used narrow pulse width editing have the characteristics of short duration and high action power and are generally called hard pulses or nonselective pulses. The hard pulse realizes equivalent excitation in a wide frequency range, and solves the inconvenience brought by an early-stage field-sweeping spectrometer. However, the natural influence of the inhomogeneity of the radio frequency field of the nuclear magnetic resonance probe can cause the excitation efficiency of the spin at the off-resonance position to be reduced, and brings adverse factors such as 'edge effect', and meanwhile, the extraction of useful structural information can be interfered by the overlapping of complex spectral peaks caused by insufficient resolution. Thus, the disadvantages of hard pulses are apparent from the advanced experimental requirements of selective excitation of signals in specific regions, or broadband decoupling of high field spectrometers.

Shaped pulses (also called "soft pulses" or "selective pulses") are a general term for a class of pulses of long duration and low applied power, either as square waves or as shaped pulses. By editing amplitude (amplitude), phase (phase) or both modulation of the control rf pulse, the shape pulse achieves excitation bandwidth selection from tens to hundreds of hertz (Hz) (relative hard pulses are typically on the kHz level), and selective excitation, inversion and decoupling experiments can be performed on signals in a specific region. The selectivity experiments are classified into a band selectivity experiment, a line selectivity experiment, and a multiple peak selectivity experiment according to the type of the selected shape pulse. Band-selective experiments larger-area excitation can be performed, such as band-selective HMBC experiments; line selectivity experiments are also known as unimodal excitation experiments, such as one-dimensional selectivity COSY, TOCSY, NOESY, etc.; the multi-peak selectivity experiment is an experiment for exciting a plurality of peaks (spectral lines) at different positions in a spectrum, which requires that an instrument simultaneously excites a plurality of preset spins with different resonance frequencies and satisfies the narrow excitation range of each spin, and the implementation difficulty is higher compared with other two kinds of experiments. Whether a single shaped pulse of one transmit channel is used to sequentially tune to selected frequencies and perform a series of sequential excitation modes, or multiple rf channels are used to simultaneously excite shaped pulses of different tuned frequencies, significant challenges are presented to the hardware and software of the nmr spectrometer.

Disclosure of Invention

The invention provides a shape pulse editing and controlling method for nuclear magnetic resonance multimodal excitation, which includes the steps of calculating frequency information of different excitation peaks through pulse excitation time-varying evolution model fitting to obtain a shape pulse with the amplitude and the phase of the pulse modulated at the same time, verifying the excitation range and the excitation position of spins corresponding to a plurality of peaks through simulation, finally editing the pulse and realizing multimodal excitation.

The technical scheme of the invention is realized as follows:

a shape pulse editing and control method for multi-peak nuclear magnetic resonance excitation comprises the following steps:

s1, specifying a pulse excitation mode and calculating an integral factor IR and a bandwidth factor BF of a pulse shape;

s2, selecting a multi-peak range to be excited on a map, and calculating the frequency offset and the excitation bandwidth of an excitation peak;

s3, synthesizing multi-peak excited shape pulses through frequency offset, excitation bandwidth and pulse excitation of N peaks;

and S4, verifying the self-rotation excitation position and the self-rotation excitation range corresponding to the N peaks through simulation.

Preferably, in step S1, the method specifically includes:

step 1.1, selecting an excitation mode: the method comprises the shape of the pulse and the executed excitation angle, adopts Gaussian-shaped pulse to execute excitation with the flip angle of 90 degrees, is called Gauss90 for short, and the distribution expression of the shaped pulse along with the time t is as follows:

the pulse width Tp and the time t are changed by M +1 points, and the time step taup is Tp/M;

step 1.2, calculate the integral factor IR of Gauss 90:

wherein S is_gaussIs the area of the Gauss pulse, S_squareThe integration factor IR of Gauss90 is the area of the square wave of the same pulse length.

Step 1.3, calculating the maximum power value PM of the shape pulse:

PM＝1/Tp·(360/ang)/IR

wherein ang is the excitation angle;

step 1.4, calculating the variation A of the amplitude and the phase of the shape pulse along with the time t₀(t) and phi₀(t)：

A₀(t)＝F_gauss(t,Tp)·PM

φ₀(t)＝0

Step 1.5, calculating the effective field Q from Gauss90 single-peak excitation^r(t, Ω) change amount over time t, including: θ (t, Ω), α (t, Ω), and φ (t):

θ(t，Ω)＝arctan(A₀(t)/Ω)

α(t，Ω)＝A₀(t)·τp/sin(θ(t，Ω))

φ(t)＝φ₀(t)

where Ω is the frequency offset of the spins, and θ (t, Ω) is the effective field Q^r(t, omega) and the variation of the included angle of the main magnetic field direction along with the time t, alpha (t, omega) is the variation of the flip angle of the effective field along with the time t, and both are influenced by omega; phi (t) is the variation of the pulse phase over time t.

Step 1.6, calculating the spin magnetization distribution after loading the shape pulse

[MF_x(Ω),MF_y(Ω),MF_z(Ω)]：

Wherein the content of the first and second substances,

the rotation matrix form in the above formula is as follows:

and (1).7. According to transverse magnetization vector

The excitation range with a 3dB signal intensity attenuation was calculated and set to the excitation bandwidth Δ ω of the Gauss90 unimodal excitation shape pulse, i.e.

Not less than 70.8% of the maximum signal intensity.

Step 1.8, calculating a bandwidth factor BF of the shape pulse: BF is Tp.DELTA.omega

Preferably, in step S2, the method specifically includes:

step 2.1, opening a spectrogram of a nuclear magnetic resonance spectrum experiment needing selective excitation, and assuming that N peaks need to be excited and the excitation range of the kth peak is [ L ]_k,R_k],k＝1,2,...N；

Step 2.2, calculating the frequency offset omega corresponding to the kth peak_RF,kAnd the required excitation bandwidth Δ ω_k

ω_RF,k＝ω₀*(L_k+R_k)/2-O1

Δω_k＝ω₀*(L_k-R_k),k＝1,2,...N

Wherein ω is₀The reference frequency is O1, which is the excitation frequency of the nmr experiment pulse, and specifically the offset from the reference frequency.

Preferably, in step S3, the method specifically includes:

step 3.1 excitation Bandwidth Δ ω required by the kth Peak_kCalculating the pulse width Tp of the corresponding pulse of independent shape_k：

Tp_k＝BF/Δω_k,k＝1,2,...,N；

Step 3.2, from N pulse widths Tp_kN, the largest value is selected as the shape pulse width Tp of the synthetic multi-peak excitation_s：Tp_s＝max(Tp₁,Tp₂,...Tp_N)；

Step 3.3 excitation Bandwidth Δ ω required by the kth Peak_kComputingCorresponding shape pulse scale factor scalingfactor_k：

Step 3.4, calculating the amplitude of the shape pulse of the kth peak along with the time t by a Gauss90 shape pulse excitation mode_sAmount of change A of_k(t_s)：

Pulse width Tp_sTime t_sVariation M_s+1 point,. tau.p_sRepresenting time step τ ps ═ Tp_s/M_s；

Step 3.5, according to the frequency offset omega corresponding to the kth peak_RF,kCalculating phase over time t_sVariation phi of_k(t_s)：

φ_k(t_s)＝2π·ω_RF,k·t_s+φ_k,0,k＝1,2,...,N

Wherein phi_k,0Initial phase of kth peak;

step 3.6, calculate the maximum power value PM of the shape pulse for synthesizing the multimodal excitation_s：

Wherein ang is the excitation angle;

step 3.7, utilizing the amplitude A of the shape pulse corresponding to the N peaks_k(t_s) And phase phi_k(t_s) The shape pulse of the multimodal excitation is synthesized and expressed as time t_sVariation Q of_sum(t_s)：

Wherein i is an imaginary number, and wherein i is an imaginary number,

step 3.8, for the edited multi-peak excited shape pulse Q_sum(t_s) Solving the variable quantity A of the amplitude and the phase which can be realized by the nuclear magnetic resonance instrument_s(t_s) And phi_s(t_s)：

φ_s(t_s)＝arctan(imag(Q_sum(t_s))/real(Q_sum(t_s)))

Wherein real and imag represent Q for complex numbers_sum(t_s) And solving the real part and the imaginary part.

Calculating to obtain the amplitude A of the multi-peak excited shape pulse_s(t_s) And phase phi_s(t_s) Over time t_sThe amount of change in (c).

Preferably, in step S4, the method specifically includes:

step 4.1, calculating the shape pulse effective field of multimodal excitation

Over time t_sThe amount of change of (c) includes: theta_s(t_s，Ω)、α_s(t_s，Ω)：

θ_s(t_s，Ω)＝arctan(A_s(t_s)/Ω)

α_s(t_s，Ω)＝A_s(t_s)·τp_s/sinθ_s(t_s，Ω)

Where Ω is the frequency offset of the spins, θ_s(t_sOmega) as effective field

And a main magnetAngle of field direction over time t_sAmount of change of (a)_s(t_sOmega) is the flip angle of the effective field over time t_sBoth of which are affected by Ω;

step 4.2 shape pulsed effective field by multimodal excitation over time t_sAmount of change of (theta)_s(t_s，Ω)、α_s(t_sOmega) and phi_s(t_s) Calculating spin magnetization distribution after Loading pulse [ MF_s,x(Ω),MF_s,y(Ω),MF_s,z(Ω)]；

Step 4.3, plotting and representing transverse magnetization vector

Sequentially verifying the excitation site and the excitation range corresponding to the kth peak, intercepting the area range not less than 70.8% of the maximum signal intensity in the excitation range, and judging whether to offset omega with the frequency_RF,kAnd excitation bandwidth Δ ω_kAnd (4) according to the shape, pulse reasonableness of the computed nuclear magnetic resonance multimodal excitation.

The invention has the following beneficial effects: the invention carries out optimization calculation aiming at nuclear magnetic resonance pulse excitation and a change model of an effective field along with time, can realize the excitation of a plurality of preset spins with different resonance frequencies by editing the amplitude and the phase of the modulation-shaped pulse and meet the narrow excitation range of each spin, so that a single radio frequency emission channel of a conventional nuclear magnetic resonance instrument can realize a complex multimodal selectivity experiment, the experiment robustness is improved, and the dependence on instrument hardware is reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a flow chart of the present invention.

Fig. 2 is a shape of a gaussian (Gauss) pulse and a corresponding square wave pulse.

Fig. 3 is a shape pulse editing diagram: (1) and (2) the amplitude A of Gauss90, respectively₀(t) amount of change and phase phi with time t₀(t) the amount of change over time t; (3) and (4) the amplitude A of the composite shape pulse used in this example for multimodal excitation, respectively_s(t_s) Over time t_sVariation and phase of (2)_s(t_s) Over time t_sThe amount of change in (c).

FIG. 4 is an effective field Q^r(t, Ω), frequency offset Ω of the spins, amplitude a (t) and phase Φ (t) of the radio-frequency pulses in the same coordinate system.

FIG. 5 is a nuclear magnetic resonance spectrum in which three peaks are selected and the excitation ranges of the three peaks are set.

FIG. 6 is a graph showing the transverse magnetization vector plotted in this example

And (3) sequentially verifying whether each excitation site and excitation range are consistent with the excitation peak corresponding to the spectrogram of the graph in fig. 5.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

1. The manner of pulse firing is specified and an integration factor IR and a bandwidth factor BF of the pulse shape are calculated.

Step 1.1, selecting an excitation mode: including the shape of pulse and the excitation angle of execution, this example adopts gaussian (Gauss) shape pulse to carry out the excitation that flip angle is 90, abbreviated as Gauss90, and shape pulse is along with time t distribution expression is:

in this example, the pulse width Tp is 1000 μ s, the time t is changed by M +1 points, M is 1000, and the time step τ p is set to 1 μ s when Tp/M.

Step 1.2, calculate the integral factor IR of Gauss 90:

as shown in FIG. 2, S_gaussIs the area of the Gauss pulse, S_squareThe integral factor IR of Gauss90 is 0.4116 for the area of the square wave of the same pulse length.

Step 1.3, calculating the maximum power value PM of the shape pulse:

PM＝1/Tp·(360/ang)/IR

where ang is the excitation angle and the excitation angle of the excitation pulse in this example is 90.

Step 1.4, calculating the variation A of the amplitude and the phase of the shape pulse along with the time t₀(t) and phi₀(t)：

A₀(t)＝F_gauss(t,Tp)·PM

φ₀(t)＝0

Where the pulse width Tp is 1000 mus in this example.

As shown in FIG. 3(1) and FIG. 3(2), the amplitude A of the shape pulse is shown when Gauss90 is excited in a single peak₀(t) and phase phi₀(t) as a function of time t.

Step 1.5, calculating the effective field Q from Gauss90 single-peak excitation^r(t, Ω) change amount over time t, including: θ (t, Ω), α (t, Ω), and φ (t):

θ(t，Ω)＝arctan(A₀(t)/Ω)

α(t，Ω)＝A₀(t)·τp/sin(θ(t，Ω))

φ(t)＝φ₀(t)

where Ω is the frequency offset of the spins, and θ (t, Ω) is the effective field Q^r(t, Ω) and main magnetic fieldThe variation of the angle of the direction with the time t, and alpha (t, omega) is the variation of the flip angle of the effective field with the time t, and both are influenced by omega. Phi (t) is the variation of the pulse phase over time t. The relationship of the effective fields is shown in fig. 4.

Step 1.6, calculating the spin magnetization distribution after loading the shape pulse

[MF_x(Ω),MF_y(Ω),MF_z(Ω)]：

Wherein the content of the first and second substances,

the rotation matrix form in the above formula is as follows:

step 1.7, according to transverse magnetization vector

The excitation range with a 3dB signal intensity attenuation was calculated and set to the excitation bandwidth Δ ω of the Gauss90 unimodal excitation shape pulse, i.e.

Not less than 70.8% of the maximum signal intensity. This example gives its excitation bandwidth Δ ω 2122 Hz.

Step 1.8, calculating a bandwidth factor BF of the shape pulse: BF is Tp.DELTA.omega

Here, the pulse width Tp of Gauss90 in this example is 1000 μ s, and the excitation bandwidth Δ ω is 2122Hz in step 1.7, so that the bandwidth factor BF of Guass90 is calculated to be 2.122.

2. Selecting a multi-peak range needing excitation on a spectrum: introducing a spectrogram of a nuclear magnetic resonance spectrum experiment needing selective excitation, selecting excitation ranges of a plurality of peaks needing excitation on the spectrogram, and calculating frequency offset and excitation bandwidth of the excitation peaks, wherein the method specifically comprises the following steps:

step 2.1, opening a spectrogram of a nuclear magnetic resonance spectrum experiment needing selective excitation, and assuming that N peaks need to be excited and the excitation range of the kth peak is [ L ]_k,R_k]N, in ppm. In this example, the imported spectrum is shown in fig. 5, and 3 peaks are selected and the excitation ranges are calibrated as follows:

[L₁,R₁]＝[6.125,5.595]

[L₂,R₂]＝[4.40,3.98]

[L₃,R₃]＝[1.47,1.11]

step 2.2, calculating the frequency offset omega corresponding to the kth peak_RF,kAnd the required excitation bandwidth Δ ω_k

ω_RF,k＝ω₀*(L_k+R_k)/2-O1

Δω_k＝ω₀*(L_k-R_k),k＝1,2,...N

Wherein ω is₀For fundamental frequency, the nuclear magnetic resonance experiment of the example uses¹H proton frequency of 400.0MHz, omega₀The value is 400.0 MHz. O1 is the excitation frequency of the pulse in the NMR experiment, specifically the offset relative to the fundamental frequency. In this example, O1-1676 Hz, the frequency offset of the three peaks is calculated as ω_RF,1,ω_RF,2,ω_RF,3]＝[668,0,-1160]In Hz; and the excitation bandwidth required for the three peaks is [ Δ ω [ ]₁,Δω₂,Δω₃]＝[212,168,144]In Hz.

3. Synthesizing multi-peak excited shape pulses by means of frequency offset, excitation bandwidth and pulse excitation of the N peaks, specifically including the following calculations:

step 3.1, obtaining the excitation bandwidth delta omega needed by the kth peak according to the step 2.2_kCalculating the pulse width Tp of the corresponding pulse of independent shape_k：

Tp_k＝BF/Δω_k,k＝1,2,...,N

Wherein BF is the bandwidth factor obtained in step 1.8, and Tp can be obtained₁,Tp₂,Tp₃]＝[10009,12631,14736]In μ s.

Step 3.2, from N pulse widths Tp_kN, the largest value is selected as the shape pulse width Tp of the synthetic multi-peak excitation_s：Tp_s＝max(Tp₁,Tp₂,...Tp_N) In this example Tp is obtained_s＝14736μs。

Step 3.3, excitation bandwidth Δ ω required according to kth peak of step 2.2_kCalculating a corresponding shape pulse scale factor scalingfactor_k：

Step 3.4, calculating the amplitude of the shape pulse of the kth peak along with the time t by the Gauss90 shape pulse excitation mode selected in the step 1.1_sAmount of change A of_k(t_s)：

Wherein the pulse width Tp of the shape of the synthetic multimodal excitation is obtained from step 3.2_s14736 mus, time t_sVariation M_s+1 points, M_s3000, time step τ p_s＝Tp_s/M_sSet to 4.912 μ s.

Step 3.5, according to the frequency offset omega corresponding to the kth peak in the step 2.2_RF,kCalculating phase over time t_sAmount of change ofφ_k(t_s)：

φ_k(t_s)＝2π·ω_RF,k·t_s+φ_k,0,k＝1,2,...,N

Wherein phi_k,0The initial phase of the kth peak is assumed to be 0 in this example.

Step 3.6, calculate the maximum power value PM of the shape pulse for synthesizing the multimodal excitation_s：

Where ang is the excitation angle and the excitation angle of the excitation pulse in this example is 90.

Step 3.7, utilizing the amplitude A of the shape pulse corresponding to the N peaks_k(t_s) And phase phi_k(t_s) The shape pulse of the multimodal excitation is synthesized and expressed as time t_sVariation Q of_sum(t_s)：

Wherein i is an imaginary number, and wherein i is an imaginary number,

step 3.8, for the edited multi-peak excited shape pulse Q_sum(t_s) Solving the variable quantity A of the amplitude and the phase which can be realized by the nuclear magnetic resonance instrument_s(t_s) And phi_s(t_s)：

φ_s(t_s)＝arctan(imag(Q_sum(t_s))/real(Q_sum(t_s)))

Wherein real and imag represent Q for complex numbers_sum(t_s) To findThe real part and the imaginary part are solved.

In this example, the amplitude A of the multi-modal excited shape pulse is calculated_s(t_s) And phase phi_s(t_s) Over time t_sThe variation amounts of (a) are shown in fig. 3(3) and fig. 3(4), respectively.

4. The excitation positions and the excitation ranges of the spins corresponding to the N peaks are verified through simulation.

Step 4.1, calculating the shape pulse effective field of multimodal excitation

Over time t_sThe amount of change of (c) includes: theta_s(t_s，Ω)、α_s(t_s，Ω)：

θ_s(t_s，Ω)＝arctan(A_s(t_s)/Ω)

α_s(t_s，Ω)＝A_s(t_s)·τp_s/sinθ_s(t_s，Ω)

Where Ω is the frequency offset of the spins, θ_s(t_sOmega) as effective field

Angle with main magnetic field direction over time t_sAmount of change of (a)_s(t_sOmega) is the flip angle of the effective field over time t_sBoth are affected by omega.

Step 4.2, synchronous step 1.6, shape pulsed effective field by multimodal excitation over time t_sAmount of change of (theta)_s(t_s，Ω)、α_s(t_sOmega) and phi_s(t_s) Calculating spin magnetization distribution after Loading pulse [ MF_s,x(Ω),MF_s,y(Ω),MF_s,z(Ω)]。

Step 4.3, plotting and representing transverse magnetization vector

As shown in FIG. 6, the k-th peak pair is verified in turnThe corresponding excitation site and excitation range (the range of the excitation range is intercepted to be not less than 70.8 percent of the maximum signal intensity), and whether the frequency deviation omega is obtained from the step 2.2 or not is judged_RF,kAnd excitation bandwidth Δ ω_kAnd (3) according to the result, verifying the pulse reasonableness of the shape of the nuclear magnetic resonance multi-peak excitation calculated in the step 3.8.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (3)

1. A shape pulse editing and control method for multi-peak nuclear magnetic resonance excitation is characterized by comprising the following steps:

s1, specifying a pulse excitation mode and calculating an integral factor IR and a bandwidth factor BF of a pulse shape;

s2, selecting a multi-peak range to be excited on a map, and calculating the frequency offset and the excitation bandwidth of an excitation peak;

s3, synthesizing multi-peak excited shape pulses through frequency offset, excitation bandwidth and pulse excitation of N peaks;

s4, verifying the self-rotation excitation position and the self-rotation excitation range corresponding to the N peaks through simulation;

in step S1, the method specifically includes:

step 1.1, selecting an excitation mode: the method comprises the shape of the pulse and the executed excitation angle, adopts Gaussian-shaped pulse to execute excitation with the flip angle of 90 degrees, is called Gauss90 for short, and the distribution expression of the shaped pulse along with the time t is as follows:

the pulse width Tp and the time t are changed by M +1 points, and the time step taup is Tp/M;

step 1.2, calculate the integral factor IR of Gauss 90:

wherein S is_gaussIs the area of the Gauss pulse, S_squareThe area of the square wave of the same pulse length, the integration factor IR of Gauss 90;

step 1.3, calculating the maximum power value PM of the shape pulse:

PM＝1/Tp·(360/ang)/IR

wherein ang is the excitation angle;

step 1.4, calculating the variation A of the amplitude and the phase of the shape pulse along with the time t₀(t) and phi₀(t)：

A₀(t)＝F_gauss(t,Tp)·PM

φ₀(t)＝0

Step 1.5, calculating the effective field Q from Gauss90 single-peak excitation^r(t, Ω) change amount over time t, including: θ (t, Ω), α (t, Ω), and φ (t):

θ(t，Ω)＝arctan(A₀(t)/Ω)

α(t，Ω)＝A₀(t)·τp/sin(θ(t，Ω))

φ(t)＝φ₀(t)

where Ω is the frequency offset of the spins, and θ (t, Ω) is the effective field Q^r(t, omega) and the variation of the included angle of the main magnetic field direction along with the time t, alpha (t, omega) is the variation of the flip angle of the effective field along with the time t, and both are influenced by omega; phi (t) is the variation of the pulse phase with time t;

step 1.6, calculating spin magnetization distribution [ MF ] after loading shape pulse_x(Ω),MF_y(Ω),MF_z(Ω)]：

Wherein the content of the first and second substances,

the rotation matrix form in the above formula is as follows:

step 1.7, according to transverse magnetization vector

The excitation range with a 3dB signal intensity attenuation was calculated and set to the excitation bandwidth Δ ω of the Gauss90 unimodal excitation shape pulse, i.e.

A range of the region not less than 70.8% of the maximum signal intensity;

step 1.8, calculating a bandwidth factor BF of the shape pulse: BF ═ Tp × Δ ω;

in step S3, the method specifically includes:

step 3.1 excitation Bandwidth Δ ω required by the kth Peak_kCalculating the pulse width Tp of the corresponding pulse of independent shape_k：

Tp_k＝BF/Δω_k,k＝1,2,...,N；

Step 3.2, from N pulse widths Tp_kN, the largest value is selected as the shape pulse width Tp of the synthetic multi-peak excitation_s：Tp_s＝max(Tp₁,Tp₂,...Tp_N)；

Step 3.3 excitation Bandwidth Δ ω required by the kth Peak_kComputing correspondencesThe shape pulse scale factor scaling factor of_k：

Step 3.4, calculating the amplitude of the shape pulse of the kth peak along with the time t by a Gauss90 shape pulse excitation mode_sAmount of change A of_k(t_s)：

Pulse width Tp_sTime t_sVariation M_s+1 point,. tau.p_sRepresenting time step τ ps ═ Tp_s/M_s；

Step 3.5, according to the frequency offset omega corresponding to the kth peak_RF,kCalculating phase over time t_sVariation phi of_k(t_s)：

φ_k(t_s)＝2π·ω_RF,k·t_s+φ_k,0,k＝1,2,...,N

Wherein phi_k,0Initial phase of kth peak;

step 3.6, calculate the maximum power value PM of the shape pulse for synthesizing the multimodal excitation_s：

Wherein ang is the excitation angle;

step 3.7, utilizing the amplitude A of the shape pulse corresponding to the N peaks_k(t_s) And phase phi_k(t_s) The shape pulse of the multimodal excitation is synthesized and expressed as time t_sVariation Q of_sum(t_s)：

Wherein i is an imaginary number, and wherein i is an imaginary number,

step 3.8, for the edited multi-peak excited shape pulse Q_sum(t_s) Solving the variable quantity A of the amplitude and the phase which can be realized by the nuclear magnetic resonance instrument_s(t_s) And phi_s(t_s)：

φ_s(t_s)＝arctan(imag(Q_sum(t_s))/real(Q_sum(t_s)))

Wherein real and imag represent Q for complex numbers_sum(t_s) Solving a real part and an imaginary part;

calculating to obtain the amplitude A of the multi-peak excited shape pulse_s(t_s) And phase phi_s(t_s) Over time t_sThe amount of change in (c).

2. The method for shape pulse editing and control of nmr multimodal excitation according to claim 1, wherein step S2 specifically comprises:

step 2.1, opening a spectrogram of a nuclear magnetic resonance spectrum experiment needing selective excitation, and assuming that N peaks need to be excited and the excitation range of the kth peak is [ L ]_k,R_k],k＝1,2,...N；

Step 2.2, calculating the frequency offset omega corresponding to the kth peak_RF,kAnd the required excitation bandwidth Δ ω_k

ω_RF,k＝ω₀*(L_k+R_k)/2-O1

Δω_k＝ω₀*(L_k-R_k),k＝1,2,...N

Wherein ω is₀At fundamental frequency, O1The pulse excitation frequency for nuclear magnetic resonance experiment specifically refers to the offset relative to the fundamental frequency;

calculating to obtain the amplitude A of the multi-peak excited shape pulse_s(t_s) And phase phi_s(t_s) Over time t_sThe amount of change in (c).

3. The method for shape pulse editing and control of nmr multimodal excitation according to claim 1, wherein step S4 specifically comprises:

step 4.1, calculating the shape pulse effective field of multimodal excitation

Over time t_sThe amount of change of (c) includes: theta_s(t_s，Ω)、α_s(t_s，Ω)：

θ_s(t_s，Ω)＝arctan(A_s(t_s)/Ω)

α_s(t_s，Ω)＝A_s(t_s)·τp_s/sinθ_s(t_s，Ω)

Where Ω is the frequency offset of the spins, θ_s(t_sOmega) as effective field

Angle with main magnetic field direction over time t_sAmount of change of (a)_s(t_sOmega) is the flip angle of the effective field over time t_sBoth of which are affected by Ω;

step 4.2 shape pulsed effective field by multimodal excitation over time t_sAmount of change of (theta)_s(t_s，Ω)、α_s(t_sOmega) and phi_s(t_s) Calculating spin magnetization distribution after Loading pulse [ MF_s,x(Ω),MF_s,y(Ω),MF_s,z(Ω)]；

Step 4.3, plotting and representing transverse magnetization vector

Sequentially verifying the excitation site and the excitation range corresponding to the kth peak, intercepting the area range not less than 70.8% of the maximum signal intensity in the excitation range, and judging whether to offset omega with the frequency_RF,kAnd excitation bandwidth Δ ω_kAnd (4) according to the shape, pulse reasonableness of the computed nuclear magnetic resonance multimodal excitation.

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