A Targeted One-Dimensional Proton Spectroscopy Extraction Method Based on Selective Two-Quantum Filtering
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-26
- Publication Date
- 2026-08-14
AI Technical Summary
[0003]1.复杂样品中存在的大量信号彼此互相拥挤重叠，谱图分辨率不足，严重影响谱图解析；
[0025]（1）本发明提及的基于选择性二量子滤波的靶向一维氢谱提取方法采用了具有选择性二量子滤波功能的双共振二自旋效应脉冲序列和层选脉冲序列相结合的方法，既精确提取了第一质子和第二质子的核磁共振信号，又消除了不均匀磁场的影响，清晰的保留了对应的偶合裂分，进一步提升了谱图分辨率。所使用的脉冲序列结构简单、易于操作、使用范围广，鲁棒性强且具有优良的选择性，能够在不均匀磁场中，针对复杂样品体系实现特定信号的高分辨率提取，并且不会对样品造成损伤。在各种不同的商用核磁共振谱仪上均可导入使用，实现复杂化学生物样品中特定信号的高分辨观测，相比于传统的方法，具有更强的选择性、抗不均匀性和更广的适用范围。
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Figure CN122567745A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of nuclear magnetic resonance spectroscopy detection, specifically to a targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering. Background Technology
[0002] Nuclear magnetic resonance spectroscopy (NMR spectroscopy), with its non-destructive and non-invasive detection characteristics, is widely used in molecular structure determination, mixture composition detection, and kinetic analysis, providing an effective tool for the identification of chemical substances and the determination of molecular structures in complex mixtures. However, in the analysis of complex sample systems in practice, NMR spectroscopy often faces two problems:
[0003] 1. In complex samples, a large number of signals are crowded and overlapping with each other, resulting in insufficient spectral resolution and severely affecting spectral interpretation;
[0004] 2. Some complex samples are difficult to homogenize, and the magnetic field inhomogeneity is large, which further aggravates the broadening and aliasing of spectral peaks, making it impossible for researchers to extract effective information from the spectrum.
[0005] Most current nuclear magnetic resonance spectroscopy methods only address one of the problems: spectral congestion or magnetic field inhomogeneity. There are no good solutions for complex samples that have both problems simultaneously. Summary of the Invention
[0006] The purpose of this application is to propose a targeted one-dimensional hydrogen spectrum extraction method based on selective two-quantum filtering to address the aforementioned technical problems.
[0007] In a first aspect, the present invention provides a targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering, comprising the following steps:
[0008] The first and second protons with J coupling were selected as the target signals. The width of the first 90° hard pulse required to excite the target signal was measured. The one-dimensional proton spectrum of the sample was obtained and the chemical shift information of the first and second protons was determined.
[0009] Based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse, a 180° two-color pulse to flip the target signal is generated, and a dual-resonance two-spin effect pulse sequence and a layer-selected pulse sequence containing the 180° two-color pulse are constructed.
[0010] The dual-resonance two-spin effect pulse sequence was applied to the sample to be tested, and the nuclear magnetic resonance signal of the target signal was extracted. The frequency point of the 180° two-color pulse was aligned with the chemical shifts of the first and second protons based on the chemical shift information of the first and second protons.
[0011] A layer-selected pulse sequence is applied to the sample to be tested, and one layer in the sample is selected to flip the direction of the NMR signal of the target signal, resulting in a single-layer flipped NMR signal. Based on the single-layer flipped NMR signal, the J coupling evolution of the first and second protons is reassembled to obtain the phase-sensitive NMR targeted filtering time-domain signal.
[0012] The phase-sensitive nuclear magnetic resonance targeted filtering time-domain signal is subjected to Fourier transform to obtain the targeted one-dimensional hydrogen spectrum of the target signal with anti-inhomogeneity.
[0013] Preferably, the dual-resonance two-spin effect pulse sequence includes a second 90° hard pulse, a first gradient field, a 180° two-color pulse, a second gradient field, a third 90° hard pulse, and a fourth 90° hard pulse arranged sequentially at intervals. The second 90° hard pulse is used to excite the NMR signals of all protons. The 180° two-color pulse is used to align two frequency points with the chemical shifts of the first and second protons, respectively, causing the directions of the NMR signals of the first and second protons to be reversed, and selecting the NMR signal at the aligned chemical shift. The third and fourth 90° hard pulses constitute a phase-cycle-based two-quantum filter to determine the coupling relationship of the NMR signal at the aligned chemical shift, and extract the NMR signal of the target signal. The first and second gradient fields are used to filter interference signals.
[0014] Preferably, the second, third, and fourth 90° hard pulses have the same duration, and the intensity, duration, and direction of the first and second gradient fields are the same.
[0015] Preferably, the phases of the second 90° hard pulse, the 180° bicolor pulse, and the third 90° hard pulse are all x, and the phase cycle of the fourth 90° hard pulse is (x, y, -x, -y), where x represents the phase in the x direction, y represents the phase in the y direction, -x represents the phase in the opposite direction of the x direction, and -y represents the phase in the opposite direction of the y direction.
[0016] Preferably, the layer-selected pulse sequence includes a selective pulse, a third gradient field, a fourth gradient field, and a fifth gradient field; the fourth gradient field coincides with the selective pulse in time, and the third and fifth gradient fields are respectively set on both sides of the fourth gradient field to filter interference signals. The fourth gradient field is used to divide the sample to be tested into different layers along the direction perpendicular to the ground, and the selective pulse is used to select one of the different layers to flip the direction of the nuclear magnetic resonance signal of the target signal.
[0017] Preferably, the width of the selective pulse duration is the same as the width of the 180° dual-color pulse duration, the intensity of the third gradient field and the fifth gradient field are the same, and the directions of the third gradient field, the fourth gradient field and the fifth gradient field are the same.
[0018] Preferably, the selective pulse is a 180° monochromatic pulse, and both the 180° monochromatic pulse and the 180° bicolor pulse use Rsnob as the basic waveform of the pulse.
[0019] Preferably, the phase of the selective pulse is x, and the receiving phase of the receiver is (x, -y, -x, y), where x represents the phase in the x direction, y represents the phase in the y direction, -x represents the phase in the opposite direction of the x direction, and -y represents the phase in the opposite direction of the y direction.
[0020] Preferably, a 180° bicolor pulse for flipping the target signal is generated based on the chemical shift information of the first and second protons, as well as the width and power of the duration of the first 90° hard pulse. Specifically, this includes:
[0021] The chemical shift information of the first and second protons is used to determine the two corresponding frequency points. The width and power of the first 90° hard pulse are used to generate two single-frequency excitation pulses corresponding to the two frequency points. The parameters of the two single-frequency excitation pulses include amplitude and phase. The amplitude and phase are used to form a vector in the polar coordinate system. The vectors formed by the parameters of the two single-frequency excitation pulses are vector-added to obtain a 180° two-color pulse.
[0022] As a preferred method, obtaining the one-dimensional proton spectrum of the sample to be tested specifically includes:
[0023] A one-dimensional proton spectrum of the sample is obtained by applying a single pulse consisting of a first 90° hard pulse and a signal sampling period to the sample.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] (1) The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering mentioned in this invention adopts a combination of dual-resonance two-spin effect pulse sequences and layer-selective pulse sequences with selective two-quantum filtering function. This method accurately extracts the NMR signals of the first and second protons, eliminates the influence of inhomogeneous magnetic fields, clearly preserves the corresponding coupling splits, and further improves the spectral resolution. The pulse sequence used is simple in structure, easy to operate, widely applicable, robust, and has excellent selectivity. It can achieve high-resolution extraction of specific signals for complex sample systems in inhomogeneous magnetic fields without damaging the sample. It can be imported and used on various commercial NMR spectrometers to achieve high-resolution observation of specific signals in complex chemical and biological samples. Compared with traditional methods, it has stronger selectivity, resistance to inhomogeneity, and a wider range of applications.
[0026] (2) The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering mentioned in this invention selects the nuclear magnetic resonance signal of the target signal through a double-resonance two-spin effect pulse sequence, which has the advantages of high selectivity and high robustness. On this basis, a layer-selected pulse sequence is added to resist the inhomogeneous magnetic field, which reduces the spectral width while retaining clear signal coupling splitting. This is of great significance for material identification, signal separation and structural observation, and provides a new solution for studying complex chemical and biological samples in an inhomogeneous field environment using magnetic resonance spectroscopy.
[0027] (3) The targeted one-dimensional hydrogen spectrum extraction method based on selective two-quantum filtering mentioned in this invention has the advantages of high experimental efficiency, accuracy and universality. It can accurately extract specific signals in complex samples under non-uniform magnetic field conditions, suppress other interference signals, and finally obtain high-resolution information of target atoms. It has important application significance for the targeted detection of chemical and biological samples under complex conditions in the field of nuclear magnetic resonance spectroscopy. Attached Figure Description
[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0029] Figure 1 This is a schematic flowchart of a targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering, as an embodiment of this application.
[0030] Figure 2 This is a schematic diagram of the pulse sequence used in the targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering, as described in an embodiment of this application.
[0031] Figure 3 This is an experimental result diagram of the targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering used in Embodiment 1 of this application to test tomato samples; wherein... Figure 3 (a) Photo of tomatoes and samples; Figure 3 (b) is the one-dimensional hydrogen spectrum of the tomato sample; Figure 3 (c) Figure 3 (e) Figure 3 (g) and Figure 3 (i) are the nuclear magnetic resonance signals of the target signals of γ-aminobutyric acid, β-D-glucose, α-D-glucose and fructose extracted by the double resonance two-spin effect pulse sequence; Figure 3 (d) Figure 3 (f) Figure 3 (h) and Figure 3 (j) is the targeted one-dimensional proton spectrum of the target signals of high-resolution γ-aminobutyric acid, β-D-glucose, α-D-glucose and fructose obtained by sampling using the method proposed in this invention. Detailed Implementation
[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0033] Figure 1 This application illustrates a targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering, comprising the following steps:
[0034] S1, select the first and second protons with J coupling relationship as target signals, measure the width of the first 90° hard pulse required to excite the target signal; obtain the one-dimensional proton spectrum of the sample to be tested and determine the chemical shift information of the first and second protons.
[0035] In a specific embodiment, obtaining the one-dimensional proton spectrum of the sample to be tested specifically includes:
[0036] A one-dimensional proton spectrum of the sample is obtained by applying a single pulse consisting of a first 90° hard pulse and a signal sampling period to the sample.
[0037] Specifically, embodiments of this application require measuring the width of the first 90° hard pulse duration needed to excite the target signal. A single pulse, consisting of the first 90° hard pulse and the signal sampling period, is applied to the sample to obtain a one-dimensional proton spectrum of the sample. The chemical shift information of the first and second protons is then determined on this one-dimensional proton spectrum. This one-dimensional proton spectrum contains the chemical shift information of all protons; from this spectrum, the chemical shift information of the first proton to be observed, as well as the chemical shift information of the second proton with which it has a J-coupling relationship, are selected.
[0038] S2 generates a 180° two-color pulse that flips the target signal based on the chemical shift information of the first and second protons and the width and power of the action time of the first 90° hard pulse, and constructs a dual-resonance two-spin effect pulse sequence and a layer-selected pulse sequence containing the 180° two-color pulse.
[0039] In a specific embodiment, a 180° bicolor pulse for flipping the target signal is generated based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse duration. Specifically, this includes:
[0040] The chemical shift information of the first and second protons is used to determine the two corresponding frequency points. The width and power of the first 90° hard pulse are used to generate two single-frequency excitation pulses corresponding to the two frequency points. The parameters of the two single-frequency excitation pulses include amplitude and phase. The amplitude and phase are used to form a vector in the polar coordinate system. The vectors formed by the parameters of the two single-frequency excitation pulses are vector-added to obtain a 180° two-color pulse.
[0041] Specifically, the two frequency points for the 180° two-color pulse are first determined based on the chemical shift information of the first and second protons. Two single-frequency excitation pulses are then constructed for each of these two frequency points, with parameters including amplitude and phase for each pulse. Based on these parameters, each single-frequency excitation pulse is represented as a vector in polar coordinates, with its magnitude representing the amplitude and its angle representing the phase. Subsequently, the vectors corresponding to these two single-frequency excitation pulses are superimposed to form a composite vector. The amplitude and phase of this composite vector are the equivalent parameters of the desired 180° two-color pulse. Further, the remaining parameters of the 180° two-color pulse are generated based on the width and power of the first 90° hard pulse's duration. The resulting 180° two-color pulse can simultaneously excite two frequency points in a single excitation, achieving efficient and selective excitation of proton pairs with a specified J-coupling relationship.
[0042] Furthermore, this 180° two-color pulse is used as part of a double-resonance two-spin effect (TSETSE) pulse sequence. In addition, it needs to be combined with an interval setting in the layer-selected pulse sequence to reduce the magnetic field inhomogeneity.
[0043] S3, the dual-resonance two-spin effect pulse sequence is applied to the sample to be tested, and the nuclear magnetic resonance signal of the target signal is extracted. The frequency point of the 180° two-color pulse is aligned with the chemical shift of the first and second protons according to the chemical shift information of the first and second protons.
[0044] In a specific embodiment, the dual-resonance two-spin effect pulse sequence includes a second 90° hard pulse, a first gradient field, a 180° two-color pulse, a second gradient field, a third 90° hard pulse, and a fourth 90° hard pulse, arranged sequentially at intervals. The second 90° hard pulse is used to excite the NMR signals of all protons. The 180° two-color pulse is used to align two frequency points with the chemical shifts of the first and second protons, respectively, causing the directions of the NMR signals of the first and second protons to be reversed, and selecting the NMR signal at the aligned chemical shift. The third and fourth 90° hard pulses constitute a phase-cycle-based two-quantum filter to determine the coupling relationship of the NMR signal at the aligned chemical shift, and extract the NMR signal of the target signal. The first and second gradient fields are used to filter interference signals.
[0045] In a specific embodiment, the second, third, and fourth 90° hard pulses have the same duration, and the intensity, duration, and direction of the first and second gradient fields are the same.
[0046] In a specific embodiment, the phases of the second 90° hard pulse, the 180° dual-color pulse, and the third 90° hard pulse are all x, and the phase cycle of the fourth 90° hard pulse is (x, y, -x, -y), where x represents the phase in the x direction, y represents the phase in the y direction, -x represents the phase in the opposite direction of the x direction, and -y represents the phase in the opposite direction of the y direction.
[0047] For details, please refer to Figure 2In the embodiments of this application, a dual-resonance two-spin effect pulse sequence is applied to the sample. Specifically, a second 90° hard pulse is used to excite the NMR signals of all protons. Then, a 180° two-color pulse is applied to the chemical shifts of the first and second protons, flipping the direction of the NMR signals corresponding to these chemical shifts. Combined with a two-quantum filter composed of a third and fourth 90° hard pulse, the J-coupling relationship in the NMR signals at the chemical shifts of the first and second protons is determined. This allows filtering out the NMR signals of the target signals exhibiting J-coupling, resulting in higher selectivity. To retain the strongest signal intensity, the embodiments of this application employ a phase-cycled approach to implement the two-quantum filter. The first and second gradient fields located on either side of the 180° two-color pulse are used to filter out interference signals. Since the first and second gradient fields are consistent in intensity, duration, width, and direction, they effectively filter out interference signals. Figure 2 All are denoted by G1. The phases of the second 90° hard pulse, the 180° bicolor pulse, and the third 90° hard pulse ( Figure 2 The values φ1, φ2, and φ3 are all x, and the phase cycle of the fourth 90° hard pulse ( Figure 2 The NMR signal of the target signal is represented as φ4 (x, y, -x, -y). Using a phase-cycle-based two-quantum filter, based on the J-coupling relationship between the first and second protons, the NMR signal of the target signal can be extracted more accurately.
[0048] S4. Apply the layer-selected pulse sequence to the sample to be tested, select one layer in the sample to flip the direction of the NMR signal of the target signal, and obtain a single-layer flipped NMR signal. Based on the single-layer flipped NMR signal, reassemble the J coupling evolution of the first and second protons to obtain the phase-sensitive NMR targeted filter time domain signal.
[0049] In a specific embodiment, the layer-selection pulse sequence includes a selective pulse, a third gradient field, a fourth gradient field, and a fifth gradient field; the fourth gradient field coincides with the selective pulse in terms of the action time, and the third and fifth gradient fields are respectively set on both sides of the fourth gradient field to filter interference signals. The fourth gradient field is used to divide the sample to be tested into different layers along the direction perpendicular to the ground, and the selective pulse is used to select one of the different layers to flip the direction of the nuclear magnetic resonance signal of the target signal.
[0050] In a specific embodiment, the width of the selective pulse duration is the same as the width of the 180° dual-color pulse duration, the intensity of the third gradient field and the fifth gradient field are the same, and the directions of the third gradient field, the fourth gradient field and the fifth gradient field are the same.
[0051] In a specific embodiment, the selective pulse is a 180° monochromatic pulse, and both the 180° monochromatic pulse and the 180° bicolor pulse use Rsnob as the basic waveform of the pulse.
[0052] In a specific embodiment, the phase of the selective pulse is x, and the receiving phase of the receiver is (x, -y, -x, y), where x represents the phase in the x direction, y represents the phase in the y direction, -x represents the phase in the opposite direction of the x direction, and -y represents the phase in the opposite direction of the y direction.
[0053] For details, please refer to Figure 2 The layer-selective pulse sequence in the embodiments of this application includes a selective pulse, a third gradient field, a fourth gradient field, and a fifth gradient field. The layer-selective pulse sequence is first applied to the sample under test, which has different layers in the z-direction perpendicular to the ground. Different layers correspond to different resonance frequencies. A low-intensity fourth gradient field, acting simultaneously with the selective pulse, divides the sample under test into different layers along the z-direction. The selective pulse selects the resonance frequency corresponding to one layer to flip the direction of the NMR signal of the target signal, while other layers are unaffected by the selective pulse, thus achieving single-layer excitation. The third and fifth gradient fields, located to the left and right of the fourth gradient field and having the same magnitude and direction, are used to filter interference signals. Due to the width of the selective pulse's duration compared to the 180° dual-color pulse's duration, the J-coupling evolution of the first and second protons is refocused, and the reverse magnetization vector is converted into a positive magnetization vector. Finally, a phase-sensitive NMR targeted filtering time-domain signal with the correct phase between the first and second protons is obtained, significantly reducing the magnetic field inhomogeneity compared to the entire sample volume. The third and fifth gradient fields are identical in intensity, duration, width, and direction, therefore... Figure 2 The middle is denoted by G2. The fourth gradient field is denoted by G3. The phase of the selective pulse ( Figure 2 (denoted as φ5) is x, and the receiving phase of the receiver is (x, -y, -x, y).
[0054] S5. The phase-sensitive nuclear magnetic resonance targeted filtering time-domain signal is subjected to Fourier transform to obtain the targeted one-dimensional hydrogen spectrum of the target signal with anti-inhomogeneity.
[0055] Specifically, the phase-sensitive NMR targeted filtering time-domain signal is subjected to a one-dimensional Fourier transform to obtain a targeted one-dimensional proton spectrum containing only the target signal. The method proposed in this invention is applicable to a variety of different sample systems, possesses strong robustness, high resolution, good operability, and good selectivity, and can be used for high-resolution extraction of specific signals from complex chemical and biological sample systems. It is of great significance for the analysis and study of material composition in NMR spectroscopy.
[0056] The technical effects of the present invention will be illustrated below through specific embodiments.
[0057] Example 1
[0058] Tomatoes, a common vegetable, contain numerous important components beneficial to the human body. This sample, a solid-liquid mixture, exhibited a significant non-uniform magnetic field and contained various complex molecules. Under these unfavorable conditions, the sample's spectrum was dominated by the non-uniform magnetic field and spectral congestion, making it impossible to identify any signal in the one-dimensional proton spectrum. This problem limits the widespread application of nuclear magnetic resonance spectroscopy in complex samples. Therefore, this method extracts typical signals of four substances from the tomato sample and derives their corresponding high-resolution spectra, which is of great significance for the compositional analysis of complex samples. The instrument used in this embodiment is a Varian 500MHz nuclear magnetic resonance spectrometer.
[0059] The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering proposed in the embodiments of this application is applied to tomato samples. The specific process is as follows:
[0060] Step 1: As Figure 3 As shown in (a), tomato tissue was placed inside a 5 mm NMR tube as the sample to be tested. The sample was then placed into the NMR cavity. After performing tuning, field locking, and shimming operations in the NMR spectrometer software interface, a first 90° hard pulse was applied to obtain... Figure 3 (b) shows the one-dimensional proton spectrum. The first and second protons are selected on the one-dimensional proton spectrum and their chemical shift information is recorded.
[0061] Step 2: Using the targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering proposed in the embodiments of this application, after setting the chemical shifts, spectral widths, and number of sampling points for the first and second protons, the experiment was conducted. The results after applying the double-resonance two-spin effect pulse sequence are as follows: Figure 3 As shown in (c), 3(e), 3(g), and 3(i), it can be seen that in the dual-resonance two-spin effect pulse sequence, although the NMR signal of the target signal can be filtered and extracted, due to the effect of the inhomogeneous magnetic field, the NMR signal of the target signal is severely broadened and the splitting cannot be observed, making it difficult to identify. The results after further applying the layer-selective pulse sequence are as follows. Figure 3 As shown in (d), 3(f), 3(h), and 3(j), compared to the targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering proposed in the embodiments of this application, the targeted one-dimensional proton spectrum of the target signal is not only completely extracted, but also exhibits a high-resolution signal. The splitting of the targeted one-dimensional proton spectrum of the target signal is clearly visible, and the J-coupling constant of the target signal can be directly measured, such as... Figure 3 The comparison of the magnified regions in (c) and 3(d) is shown.
[0062] The specific parameters of the pulse sequence used in the embodiments of this application are as follows: the power of the 90° hard pulse is 58dB, the duration is 13.5μs, the spectral width is 3000Hz, and the number of sampling points is 3000.
[0063] In summary, the sample used in Example 1 is a representative sample selected by the present invention. Using other samples, the method proposed in the embodiments of this application can also yield targeted high-resolution one-dimensional proton spectra.
[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering, characterized in that, Includes the following steps: Select the first and second protons with J coupling as the target signal, and measure the width of the first 90° hard pulse duration required to excite the target signal; Obtain the one-dimensional proton spectrum of the sample to be tested and determine the chemical shift information of the first and second protons; Based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse, a 180° two-color pulse to flip the target signal is generated, and a dual-resonance two-spin effect pulse sequence and a layer-selected pulse sequence containing the 180° two-color pulse are constructed. The dual-resonance two-spin effect pulse sequence is applied to the sample to be tested, and the nuclear magnetic resonance signal of the target signal is extracted. The frequency point of the 180° two-color pulse is aligned with the chemical shifts of the first and second protons according to the chemical shift information of the first and second protons. The layer-selected pulse sequence is applied to the sample to be tested, and one layer of the sample to be tested is selected to flip the direction of the NMR signal of the target signal, so as to obtain a single-layer flipped NMR signal. Based on the single-layer flipped NMR signal, the J coupling evolution of the first proton and the second proton is reassembled to obtain the phase-sensitive NMR targeted filtering time domain signal. The phase-sensitive nuclear magnetic resonance targeted filtering time-domain signal is subjected to Fourier transform to obtain a targeted one-dimensional hydrogen spectrum of the target signal with anti-inhomogeneity.
2. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 1, characterized in that, The dual-resonance two-spin effect pulse sequence includes a second 90° hard pulse, a first gradient field, a 180° two-color pulse, a second gradient field, a third 90° hard pulse, and a fourth 90° hard pulse, arranged sequentially at intervals. The second 90° hard pulse is used to excite the NMR signals of all protons. The 180° two-color pulse is used to align two frequency points with the chemical shifts of the first and second protons, respectively, causing a reversal in the direction of the NMR signals of the first and second protons, and selecting the NMR signal at the aligned chemical shift. The third and fourth 90° hard pulses constitute a phase-cycle-based two-quantum filter to determine the coupling relationship of the NMR signal at the aligned chemical shift, thereby extracting the NMR signal of the target signal. The first and second gradient fields are used to filter interference signals.
3. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 2, characterized in that, The second, third, and fourth 90° hard pulses have the same duration, and the intensity, duration, and direction of the first and second gradient fields are also the same.
4. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 2, characterized in that, The phases of the second 90° hard pulse, the 180° dual-color pulse, and the third 90° hard pulse are all x. The phase cycle of the fourth 90° hard pulse is (x, y, -x, -y), where x represents the phase in the x direction, y represents the phase in the y direction, -x represents the phase in the opposite direction of the x direction, and -y represents the phase in the opposite direction of the y direction.
5. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 1, characterized in that, The layer-selected pulse sequence includes a selective pulse, a third gradient field, a fourth gradient field, and a fifth gradient field. The fourth gradient field coincides with the selective pulse in time. The third and fifth gradient fields are respectively spaced on both sides of the fourth gradient field to filter interference signals. The fourth gradient field is used to divide the sample under test into different layers along the direction perpendicular to the ground. The selective pulse is used to select one of the different layers to flip the direction of the nuclear magnetic resonance signal of the target signal.
6. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 5, characterized in that, The width of the selective pulse duration is the same as the width of the 180° dual-color pulse duration, the intensity of the third gradient field and the fifth gradient field are the same, and the directions of the third gradient field, the fourth gradient field and the fifth gradient field are the same.
7. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 5, characterized in that, The selective pulse has a phase of x, and the receiver's receiving phase is (x, -y, -x, y), where x represents the phase in the x-direction, y represents the phase in the y-direction, -x represents the phase in the opposite direction of the x-direction, and -y represents the phase in the opposite direction of the y-direction.
8. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 5, characterized in that, The selective pulse is a 180° monochromatic pulse, and both the 180° monochromatic pulse and the 180° bicolor pulse use Rsnob as the basic waveform of the pulse.
9. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 1, characterized in that, Based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse, a 180° bicolor pulse to flip the target signal is generated, specifically including: Two corresponding frequency points are determined using the chemical shift information of the first and second protons. Two single-frequency excitation pulses corresponding to the two frequency points are generated with reference to the width and power of the action time of the first 90° hard pulse. The parameters of the two single-frequency excitation pulses include amplitude and phase. A vector is formed on the polar coordinate system based on the amplitude and phase. The vectors formed by the parameters of the two single-frequency excitation pulses are vector-added to obtain a 180° bicolor pulse.
10. The targeted one-dimensional proton spectrum extraction method based on selective two-quantum filtering according to claim 1, characterized in that, Obtaining the one-dimensional proton spectrum of the sample to be tested specifically includes: A one-dimensional hydrogen spectrum of the sample is obtained by applying a single pulse consisting of the first 90° hard pulse and the signal sampling period to the sample.