WO2018184409A1 - 一种在不均匀磁场下测量质子纵向弛豫时间的方法 - Google Patents

一种在不均匀磁场下测量质子纵向弛豫时间的方法 Download PDF

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WO2018184409A1
WO2018184409A1 PCT/CN2017/118986 CN2017118986W WO2018184409A1 WO 2018184409 A1 WO2018184409 A1 WO 2018184409A1 CN 2017118986 W CN2017118986 W CN 2017118986W WO 2018184409 A1 WO2018184409 A1 WO 2018184409A1
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pulse
amplitude
dimensional
longitudinal relaxation
magnetic field
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蔡淑惠
陈浩
陈忠
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厦门大学
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/50—NMR imaging systems based on the determination of relaxation times, e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/46—NMR spectroscopy
    • G01R33/4608—RF excitation sequences for enhanced detection, e.g. NOE, polarisation transfer, selection of a coherence transfer pathway
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/448—Relaxometry, i.e. quantification of relaxation times or spin density
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/46—NMR spectroscopy
    • G01R33/4616—NMR spectroscopy using specific RF pulses or specific modulation schemes, e.g. stochastic excitation, adiabatic RF pulses, composite pulses, binomial pulses, Shinnar-le-Roux pulses, spectrally selective pulses not being used for spatial selection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/46—NMR spectroscopy
    • G01R33/4625—Processing of acquired signals, e.g. elimination of phase errors, baseline fitting, chemometric analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/46—NMR spectroscopy
    • G01R33/4633—Sequences for multi-dimensional NMR
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/5608—Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]

Definitions

  • the invention relates to a nuclear magnetic resonance (NMR) spectroscopy method, in particular to a method for recovering chemical shift information of a spectrum under an inhomogeneous magnetic field and accurately measuring the longitudinal relaxation time of a hydrogen atomic nucleus.
  • NMR nuclear magnetic resonance
  • NMR spectroscopy has been widely used in the fields of chemistry, biology and medicine.
  • each nuclear spin has a specific longitudinal relaxation time.
  • the longitudinal relaxation time reflects the kinetic information of the molecule and plays a very important role in nuclear magnetic resonance detection. Understanding the longitudinal relaxation time, the study of molecular chemical exchange [1] , accurate quantitative analysis of data and optimization of signal sampling process have important guiding significance.
  • the measured hydrogen spectrum will appear linear broadening of the peaks and overlap each other. The chemical shift information cannot be obtained, and the peaks cannot be identified. The longitudinal relaxation time cannot be accurately measured.
  • the invention comprises the following steps:
  • the conventional one-dimensional hydrogen spectrum pulse sequence is composed of a non-selective ⁇ /2 radio frequency pulse, and the one-dimensional hydrogen spectrum sampled by the conventional one-dimensional hydrogen spectrum pulse sequence can directly obtain the corresponding peak distribution. And the spectral width information, according to the obtained information, the solvent peak center is set as the pulse excitation center.
  • the calibration non-selective ⁇ /2 radio frequency pulse width can be obtained by measuring the magnetization vector from the longitudinal direction to the pulse action time corresponding to the lateral plane, thereby obtaining a non-selective ⁇ /2 radio frequency pulse width.
  • the pulse type of the conventional one-dimensional hydrogen spectrum pulse sequence described in step 2) is a Gaussian soft pulse, and the pulse width and power of the solvent selective ( ⁇ /2) I radio frequency pulse are determined.
  • the longitudinal magnetization vector inversion recovery module is composed of a solvent selective ( ⁇ ) I radio frequency pulse, a non-selective ⁇ radio frequency pulse, and an inversion recovery time ⁇ ;
  • the spatial coding module consists of two The same chirp chirped adiabatic pulse and a gradient field of opposite polarity;
  • the intermolecular two-quantum coherent selection module consists of a coherent selection gradient G 1 , a solvent selective ( ⁇ /2) I radio frequency pulse, and a coherent selective gradient G 2 and a spin echo combination ⁇ - ⁇ - ⁇ , wherein the coherent selection gradients G 1 and G 2 have the same action time but the intensity ratio is 1: (-2);
  • the spatial decoding sampling module is applied during the sampling period A pair of decoded gradient fields are constructed.
  • the setting of the nuclear magnetic resonance pulse sequence experimental parameters includes setting a non-selective ⁇ /2 radio frequency pulse width, a chirp adiabatic pulse width, a chirp pulse sweep width, a coding gradient intensity Ge, a coherent selection gradient G 1 and Its action time, coherent selection gradient G 2 and its action time, solvent selectivity ( ⁇ /2) I pulse width and power, solvent selectivity ( ⁇ ) I pulse power, echo time ⁇ , spatial decoding sampling module sampling points np1 And a module repetition number Na, a decoding gradient intensity Ga, a sequence delay time TR, a longitudinal magnetization vector inversion recovery time ⁇ ; the nuclear magnetic resonance pulse sequence experimental parameters, including a set of varying longitudinal magnetization vector inversion recovery times.
  • step 6 after the data acquisition is completed, the original data string of each ultra-fast two-dimensional spectrum is segmented into a two-dimensional matrix of np1*Na (where np1 corresponds to the spatial coding F1 dimension, and Na corresponds to direct sampling).
  • F2 dimension after Fourier transform, a two-dimensional spectrum corresponding to each longitudinal magnetization vector inversion recovery time is obtained.
  • Each of the two-dimensional spectra is rotated counterclockwise by 45°, and then cumulative projection is performed along the spatial coding dimension to obtain a set of high-resolution one-dimensional spectra, and the amplitudes of the respective peaks are measured and normalized, and the amplitude is minimized.
  • the amplitude of the data point is set to a negative value, and the peak value of the spectral peak is plotted with the longitudinal magnetization vector inversion recovery time ⁇ .
  • y is the function value corresponding to the amplitude of the peaks
  • the fitting curve is obtained a three parameters a, b, T
  • the longitudinal spin relaxation time T 1 of the hydrogen atom is the corresponding peaks.
  • the invention utilizes the intermolecular two-quantum coherence between the two components of the solvent and the solute, and accelerates the sampling by means of the spatial coding ultra-fast sampling method, and proposes an inhomogeneous magnetic field by pulse sequence design and corresponding data post-processing technology.
  • the proton longitudinal relaxation time is accurately measured.
  • the invention can effectively reduce the broadening of the peak shape of the peak under the inhomogeneous magnetic field, recover the chemical displacement information, and accurately measure the longitudinal relaxation time of each hydrogen atom group.
  • the nuclear magnetic resonance spectrum is broadened, so that the peaks overlap and cannot be identified, and the longitudinal relaxation time of the corresponding group protons cannot be accurately measured.
  • the invention adopts an intermolecular two-quantum coherent signal selection technique, combined with a spatially encoded ultra-fast sampling method, rapidly acquires a high-resolution one-dimensional spectrum under an inhomogeneous magnetic field, and recovers chemical shift information of each peak.
  • the amplitude of the spectral peak is measured by the inversion recovery time modulation, and the amplitude variation curve is fitted to obtain the corresponding longitudinal relaxation time.
  • the invention can obtain the longitudinal relaxation time under the uneven magnetic field, and is useful for understanding the dynamic information such as the molecular chemical exchange rate, and is of great significance for signal optimization and data quantification.
  • Figure 1 is a pulse sequence diagram of the present invention for measuring the longitudinal relaxation time of a hydrogen atomic nucleus under a non-uniform magnetic field.
  • FIG. 2 is a one-dimensional hydrogen spectrum sampled by a one-dimensional hydrogen spectrum sequence under a linewidth broadening of 100 Hz for an inhomogeneous magnetic field.
  • the upper right is the n-butanol structure, and each hydrogen atom group is numbered.
  • Fig. 3 is a high-resolution one-dimensional hydrogen spectrum obtained after the sampled two-dimensional spectrum is rotated and cumulatively projected when the longitudinal magnetization vector inversion recovery time is 32 s.
  • Fig. 4 is a graph showing the change of the peak amplitude of the hydrogen atom at the position of n-butanol H2 with the longitudinal magnetization vector inversion recovery time ⁇ .
  • Fig. 5 is a graph showing the relationship between the peak amplitude (absolute value) of the hydrogen atom spectrum at each position of n-butanol and the longitudinal magnetization vector inversion recovery time ⁇ .
  • Fig. 6 is a graph showing the amplitude of the data point before the minimum value of the amplitude is set to a negative value, and the obtained peak amplitude of the spectrum is inversed with the longitudinal magnetization vector inversion recovery time ⁇ .
  • the instrument used in this example is a Varian 500 MHz nuclear magnetic resonance spectroscopy, and the sample is an aqueous solution of n-butanol having a concentration of 1.0 M, wherein n-butanol is a solute and water is a solvent.
  • Designing and compiling a pulse sequence for measuring longitudinal relaxation time comprising: a longitudinal magnetization vector inversion recovery module, a spatial coding module, an intermolecular two-quantum coherent signal selection module, and a spatial decoding sampling module;
  • the vector inversion recovery module consists of a solvent selective ( ⁇ ) I radio frequency pulse, a non-selective ⁇ radio frequency pulse, and an inversion recovery time ⁇ ;
  • the spatial encoding module consists of two identical chirp chirping adiabatic pulses and polarities The opposite gradient field composition;
  • the intermolecular two quantum coherent selection module consists of a coherent selection gradient G 1 , a solvent selective ( ⁇ /2) I radio frequency pulse, a coherent selection gradient G 2 , and a spin echo combination ⁇ - A ⁇ - ⁇ configuration in which the coherent selection gradients G 1 and G 2 have the same action time but an intensity ratio of 1: (-2);
  • the spatial decoding sampling module is composed of a pair of decoded gradient fields applied during the sampling period
  • the invention provides a method for measuring proton longitudinal relaxation time under a non-uniform magnetic field, which comprises the following steps:
  • the one-dimensional hydrogen spectrum sequence is used to measure the non-selective ⁇ /2 frequency pulse width of the sample to 15 ⁇ s, and the formant distribution and spectral width information are obtained.
  • the water peak center is set as a pulse according to the obtained information.
  • Excitation center (as shown in Figure 2).
  • the Gaussian type ( ⁇ /2) I solvent selective pulse time width is 5 ms, the power is 19 dB, and the ( ⁇ ) I solvent selective pulse time width is set to 5 ms and the power is 25 dB.
  • the specific process is as follows: use the pulse generation toolbox of the nuclear magnetic resonance spectrometer to generate the chirp chirp pulse, the chirp adiabatic pulse time width is 10ms, the chirp pulse sweep width is 20000Hz, and the coding gradient intensity Ge is 3.9G/cm, coherent selection gradient G 1 intensity is 10G/cm, action time is 1.5ms, coherent selection gradient G 2 intensity is -20G/cm, its action time is 1.5ms, echo time ⁇ is 24ms, spatial decoding
  • the sampling module has np1 of 75, the module repetition number Na is 180, the decoding gradient intensity Ga is 5.9G/cm, the sequence delay time TR is 20s, and the longitudinal magnetization vector inversion recovery time ⁇ is 0.0625, 0.125, 0.25, 0.5, 1 , 1.5, 2, 2.5, 3, 4, 6, 8, 16, 32s. According to the number of preset values of ⁇ , a total of 14 two-dimensional spectra were sampled, and the data acquisition
  • the data post-processing process is as follows: (a) For an ultra-fast two-dimensional spectrum, the original data string is segmented and recomposed into a two-dimensional matrix of np1*Na (where np1 corresponds to the spatial coding F1 dimension, and Na corresponds to direct Sampling F2 dimension), after Fourier transform, a two-dimensional spectrum can be obtained, and then the two-dimensional spectrum is rotated counterclockwise by 45°, and the projection is accumulated along the F1 dimension, and a high-resolution one-dimensional similar to that shown in FIG. 3 can be obtained.
  • the spectrum, according to the recovered chemical shift information can be assigned to the position of the hydrogen atom corresponding to each peak.
  • the peak of the n-butanol H2 position changes as the inversion recovery time ⁇ increases, and the amplitude of each peak is measured.
  • the present invention provides a method for measuring the longitudinal relaxation time of a hydrogen atomic nucleus under a non-uniform magnetic field.
  • the method utilizes intermolecular two-quantum coherence to effectively reduce the broadening of the nuclear magnetic resonance line and the peak overlap caused by the magnetic field inhomogeneity, and recover the chemical shift information of the spectrum, thereby realizing the attribution of the peak.
  • the intensity of each peak can be measured with the change of the inversion recovery time.
  • the longitudinal relaxation time of the protons corresponding to each group is obtained by numerical fitting.
  • the method proposed by the invention can accurately measure the proton longitudinal relaxation time under the uneven magnetic field, and is used for suppressing the strong signal under the uneven magnetic field, thereby recovering the weak signal covered by the strong signal, and also contributing to the chemical under the uneven magnetic field. Exchange rate study.
  • the invention discloses a method for measuring proton longitudinal relaxation time under a non-uniform magnetic field, which can obtain longitudinal relaxation time under an inhomogeneous magnetic field, and is useful for understanding dynamic information such as molecular chemical exchange rate, and has the advantages of signal optimization, data quantification, etc. Important, wide range of applications, and good industrial applicability.

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Abstract

一种在不均匀磁场下测量质子纵向弛豫时间的方法，采用分子间二量子相干信号选择技术，结合空间编码超快速采样方法，在不均匀磁场下快速获取高分辨一维谱，恢复各谱峰的化学位移信息。同时利用反转恢复方法，测量谱峰的幅值受到反转恢复时间调制后的变化情况，拟合幅值变化曲线，即可得到对应的纵向弛豫时间。可以在不均匀磁场下得到纵向弛豫时间，有助于了解分子化学交换速率等动态信息，对信号优化、数据定量等具有重要意义。

Description

一种在不均匀磁场下测量质子纵向弛豫时间的方法 技术领域
本发明涉及核磁共振(NMR，Nuclear Magnetic Resonance)波谱学检测方法，尤其是涉及一种在不均匀磁场下恢复谱图的化学位移信息并准确测量氢原子核自旋纵向弛豫时间的方法。
背景技术
核磁共振波谱技术作为一种高效无损检测分析手段，已经广泛应用于化学、生物以及医学等领域。在磁场下，每个原子核自旋都有特定的纵向弛豫时间。纵向弛豫时间反映了分子的动力学信息，在核磁共振检测中有着非常重要的作用。了解纵向弛豫时间，对于分子化学交换作用的研究 [1]，数据的准确定量分析以及信号采样过程的优化，都有重要的指导意义。然而，在不均匀磁场下，使用传统的纵向弛豫时间测量方法，测得的氢谱会出现谱峰的线形展宽进而相互重叠，化学位移信息无法获取，谱峰无法辨识归属，各个谱峰的纵向弛豫时间也无法准确测量。基于分子间多量子相干的高分辨波谱技术，可以克服磁场不均匀引起的线形展宽和谱峰重叠，得到高分辨的一维氢谱，恢复化学位移信息 [2-4]。
[1]S.C.Zhang，X.Q.Zhu，Z.Chen，S.H.Cai，J.H.Zhong，Apparent longitudinal relaxation in solutions with intermolecular dipolar interactions and slow chemical exchange，Chem.Phys.Lett.，446(2007)223-227.
[2]Z.Chen，S.H.Cai，Z.W.Chen，J.H.Zhong，Fast acquisition of high-resolution NMR spectra in inhomogeneous fields via intermolecular double-quantum coherences，J.Chem.Phys.，130(2009)084504.
[3]Z.Chen，Z.W.Chen，J.H.Zhong，Quantitative characterization of intermolecular dipolar interactions of two-component systems in solution nuclear magnetic resonance，J.Chem.Phys.，115(2001)10769-10779.
[4]Z.Chen，Z.W.Chen，J.H.Zhong，Quantitative study of longitudinal relaxation related to intermolecular dipolar interactions in solution NMR，Chem.Phys.Lett.，333(2001)126-132.
发明内容
本发明的目的在于提供能够减小不均匀磁场下氢谱的谱线展宽和重叠，恢复化学位移信息，从而实现纵向弛豫时间准确测量的一种在不均匀磁场下测量质子纵向弛豫时间的方法。
本发明包括以下步骤：
1)将待测样品装入核磁管，并将装入待测样品后的核磁管送入核磁共振波谱仪的检测腔；
2)在核磁共振波谱仪的操作台上打开波谱仪控制软件，调用常规一维氢谱脉冲序列采集一维氢谱，获得谱峰分布和谱宽信息，然后进行射频线圈调谐；
3)校准非选择性π/2射频脉冲宽度以及溶剂选择性(π/2) I射频脉冲的时间宽度和射频功率；
4)在核磁共振波谱仪上导入核磁共振脉冲序列，打开核磁共振脉冲序列的纵向磁化矢量反转恢复模块、空间编码模块、分子间二量子相干信号选择模块和空间解码采样模块；
5)设置核磁共振脉冲序列实验参数，检查实验参数设置无误后，执行数据采集；
6)当数据采集完成后，进行相应的二维谱图旋转和累积投影，可得到一组幅值受到反转恢复时间调制、包含高分辨化学位移信息的一维频率谱；
7)对各谱峰的幅值变化曲线分别进行数值拟合，即可得到相应的纵向弛豫时间。
在步骤2)中，所述常规一维氢谱脉冲序列由一个非选择性π/2射频脉冲构成，由常规一维氢谱脉冲序列采样得到的一维氢谱可直接获取相应的谱峰分布和谱宽信息，根据所获信息设置溶剂峰中心为脉冲激发中心。
在步骤3)中，所述校准非选择性π/2射频脉冲宽度，可通过测量使磁化矢量由纵向方向翻转到横向平面对应的脉冲作用时间，即可得非选择性π/2射频脉冲宽度；改变步骤2)中所述常规一维氢谱脉冲序列的脉冲类型为高斯型软脉冲，测定溶剂选择性(π/2) I射频脉冲的脉冲宽度和功率。
在步骤4)中，所述纵向磁化矢量反转恢复模块由一个溶剂选择性(π) I射频脉冲、一个非选择性π射频脉冲以及反转恢复时间Δ构成；所述空间编码模块由两 个相同的chirp线性调频绝热脉冲和极性相反的梯度场组成；所述分子间二量子相干选择模块由一个相干选择梯度G 1、一个溶剂选择性(π/2) I射频脉冲、一个相干选择梯度G 2以及一个自旋回波组合δ-π-δ构成，其中相干选择梯度G 1和G 2作用时间相同但强度比为1∶(-2)；所述空间解码采样模块是由施加在采样期的一对解码梯度场构成。
在步骤5)中，所述设置核磁共振脉冲序列实验参数包括设置非选择性π/2射频脉冲脉宽、chirp绝热脉冲宽度、chirp脉冲扫频宽度、编码梯度强度Ge、相干选择梯度G 1及其作用时间、相干选择梯度G 2及其作用时间、溶剂选择性(π/2) I脉冲宽度及功率、溶剂选择性(π) I脉冲功率、回波时间δ、空间解码采样模块采样点数np1及模块重复个数Na、解码梯度强度Ga、序列延迟时间TR、纵向磁化矢量反转恢复时间Δ；所述核磁共振脉冲序列实验参数，包括一组变化的纵向磁化矢量反转恢复时间。
在步骤6)中，当数据采集完成后，将每一张超快速二维谱的原始数据串分割重组成np1*Na的二维矩阵(其中np1对应于空间编码F1维，Na对应为直接采样F2维)，经过傅里叶变换，得到与各纵向磁化矢量反转恢复时间对应的二维谱。对每一张二维谱分别逆时针旋转45°，然后沿空间编码维进行累积投影，得到一组高分辨一维谱，测量各个谱峰的幅值并进行归一化处理，将幅值最小点之前的数据点的幅值置为负值，绘制谱峰幅值随纵向磁化矢量反转恢复时间Δ变化曲线。
在步骤7)中，对步骤6)中得到的幅值随Δ变化曲线使用函数y＝a-b*exp(-x/T 1)进行计算机拟合，自变量x为纵向磁化矢量反转恢复时间Δ，函数值y为对应谱峰的幅值，拟合曲线求取a、b、T 1三个参数值，T 1即为谱峰所对应氢原子自旋的纵向弛豫时间。
本发明利用溶剂和溶质两种组分之间的分子间二量子相干，并借助空间编码超快速采样方法加速采样，通过脉冲序列设计和相应的数据后处理技术提出了一种能够在不均匀磁场下准确测量质子纵向弛豫时间。本发明能够有效减小不均匀磁场下谱峰线形的展宽，恢复出化学位移信息，准确测量出各氢原子基团的纵向弛豫时间。
在磁场强度不均匀的情况下，核磁共振氢谱谱线增宽，使谱峰相互重叠、无法辨识归属，也无法准确测量对应基团质子的纵向弛豫时间。本发明采用分子间 二量子相干信号选择技术，结合空间编码超快速采样方法，在不均匀磁场下快速获取高分辨一维谱，恢复各谱峰的化学位移信息。同时利用反转恢复方法，测量谱峰的幅值受到反转恢复时间调制后的变化情况，拟合幅值变化曲线，即可得到对应的纵向弛豫时间。利用本发明可以在不均匀磁场下得到纵向弛豫时间，有助于了解分子化学交换速率等动态信息，对信号优化、数据定量等具有重要意义。
附图说明
图1为本发明所提出的用于在不均匀磁场下测量氢原子核自旋纵向弛豫时间的脉冲序列图。
图2为在谱线展宽100Hz为不均匀磁场下用一维氢谱序列采样得到的一维氢谱。右上为正丁醇结构式，各氢原子基团用数字编号标记。
图3为纵向磁化矢量反转恢复时间为32s时，采样的二维谱经过旋转和累积投影之后得到的高分辨一维氢谱。
图4为正丁醇H2位置氢原子谱峰幅值随纵向磁化矢量反转恢复时间Δ变化示意图。
图5为正丁醇各位置氢原子谱峰幅值(绝对值)随纵向磁化矢量反转恢复时间Δ变化关系。
图6为将幅值最小值前的数据点幅值置为负值，得到的谱峰幅值随纵向磁化矢量反转恢复时间Δ变化曲线。
具体实施方式
以下结合附图和具体实施例对本发明作进一步说明。
本实施例使用的仪器为Varian 500MHz核磁共振波谱议，样品为浓度为1.0M的正丁醇水溶液，其中正丁醇为溶质，水为溶剂。
设计编译测量纵向弛豫时间的脉冲序列(如图1所示)，包括：纵向磁化矢量反转恢复模块、空间编码模块、分子间二量子相干信号选择模块和空间解码采样模块；所述纵向磁化矢量反转恢复模块由一个溶剂选择性(π) I射频脉冲、一个非选择性π射频脉冲以及反转恢复时间Δ构成；所述空间编码模块由两个相同的chirp线性调频绝热脉冲和极性相反的梯度场组成；所述分子间二量子相干选择模块由 一个相干选择梯度G 1、一个溶剂选择性(π/2) I射频脉冲、一个相干选择梯度G 2以及一个自旋回波组合δ-π-δ构成，其中相干选择梯度G 1和G 2作用时间相同但强度比为1∶(-2)；所述空间解码采样模块是由施加在采样期的一对解码梯度场构成。
本发明一种在不均匀磁场下测量质子纵向弛豫时间的方法，具体包括以下步骤：
(1)进样：将一定量的正丁醇水溶液样品(约0.6mL)装入5mm核磁管，然后放入核磁共振波谱议中。
(2)射频脉冲宽度和功率校准：调用一维氢谱序列测量样品的非选择性π/2频脉冲宽度为15μs，获得共振峰分布和谱宽信息，根据所获信息设置水峰中心为脉冲激发中心(如图2所示)。测量高斯型(π/2) I溶剂选择性脉冲时间宽度为5ms，功率为19dB，设置(π) I溶剂选择性脉冲时间宽度为5ms，功率为25dB。
(3)导入实验脉冲序列：在核磁共振波谱仪器上导入本发明所设计编译的测量纵向弛豫时间的脉冲序列(如图1所示)，打开这一脉冲序列的纵向磁化矢量反转恢复模块、空间编码模块、分子间二量子相干信号选择模块和空间解码采样模块。
(4)设置脉冲序列参数及采样，具体过程如下：使用核磁共振谱仪的脉冲生成工具箱生成线性调频chirp脉冲，chirp绝热脉冲时间宽度为10ms，chirp脉冲扫频宽度20000Hz，编码梯度强度Ge为3.9G/cm，相干选择梯度G 1强度为10G/cm，作用时间为1.5ms、相干选择梯度G 2强度为-20G/cm，其作用时间为1.5ms，回波时间δ为24ms、空间解码采样模块采样点数np1为75，模块重复次数Na为180，解码梯度强度Ga为5.9G/cm，序列延迟时间TR为20s，纵向磁化矢量反转恢复时间Δ为0.0625，0.125，0.25，0.5，1，1.5，2，2.5，3，4，6，8，16，32s。按照Δ预设数值个数，总共采样14张二维谱，整个实验过程数据采集时间约为7.5min。
(5)数据后处理过程如下：(a)对于一张超快速二维谱，将其原始数据串分割重组成np1*Na的二维矩阵(其中np1对应于空间编码F1维，Na对应为直接采样F2维)，经过傅里叶变换之后，就可以得到一张二维谱，再将二维谱逆时针旋转45°，沿F1维累积投影，即可得到类似于图3所示的高分辨一维谱，根据恢复出的化学位移信息可以归属出各谱峰对应的氢原子位置。(b)如图4所示，正丁醇H2位置的谱峰会随着反转恢复时间Δ的增加而变化，测量各个谱峰的幅值。(c) 以反转恢复时间Δ等于32s时谱峰幅值为准，进行归一化，得到如图5所示的幅值随反转恢复时间Δ变化图。(d)由于二维谱均以绝对值模式进行处理，得到一维谱的谱峰幅值均为正值，图5所示不能直接反映信号幅值的实际变化过程，因此根据时域信号的幅值关系，将幅值绝对值最小点之前的数据点幅值置为负值，得到如图6所示的幅值反转恢复时间Δ变化曲线。(e)对图6中的各条曲线使用函数y＝a-b*exp(-x/T 1)进行计算机拟合，自变量x为纵向磁化矢量反转恢复时间Δ，函数值y为对应谱峰的幅值，拟合曲线求取a、b、T 1三个参数值，T 1即为对应谱峰的纵向弛豫时间。最终测得正丁醇各氢原子基团(H2、H3、H4、H5)的纵向弛豫时间分别为2.73、2.77、3.08、3.18s。
综上所述，本发明提供了一种在不均匀磁场下测量氢原子核自旋纵向弛豫时间的方法。该方法利用分子间二量子相干有效减小磁场不均匀导致的核磁共振氢谱谱线展宽与谱峰重叠，恢复出谱图的化学位移信息，从而实现谱峰的归属。结合反转恢复方法，可以对各谱峰强度随反转恢复时间的变化进行测量，最后通过数值拟合，得到对应各基团质子的纵向弛豫时间。本发明提出的方法可以在不均匀磁场下准确测量质子纵向弛豫时间，进而用于在不均匀磁场下抑制强信号，从而恢复出被强信号掩盖的弱信号，也有助于不均匀磁场下化学交换速率的研究。
以上所述，仅为本发明较佳实施例而已，故不能依此限定本发明实施的范围，即依本发明专利范围及说明书内容所作的等效变化与修饰，皆应仍属本发明涵盖的范围内。
工业实用性
本发明一种在不均匀磁场下测量质子纵向弛豫时间的方法，可以在不均匀磁场下得到纵向弛豫时间，有助于了解分子化学交换速率等动态信息，对信号优化、数据定量等具有重要意义，应用范围广，具有良好的工业实用性。

Claims (13)

  1. 一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于包括以下步骤：
    1)将待测样品装入核磁管，并将装入待测样品后的核磁管送入核磁共振波谱仪的检测腔；
    2)在核磁共振波谱仪的操作台上打开波谱仪控制软件，调用常规一维氢谱脉冲序列采集一维氢谱，获得谱峰分布和谱宽信息，然后进行射频线圈调谐；
    3)校准非选择性π/2射频脉冲宽度以及溶剂选择性(π/2) I射频脉冲的时间宽度和射频功率；
    4)在核磁共振波谱仪上导入核磁共振脉冲序列，打开核磁共振脉冲序列的纵向磁化矢量反转恢复模块、空间编码模块、分子间二量子相干信号选择模块和空间解码采样模块；
    5)设置核磁共振脉冲序列实验参数，检查实验参数设置无误后，执行数据采集；
    6)当数据采集完成后，进行相应的数据处理、二维谱图旋转和累积投影，可得到一组幅值受到反转恢复时间调制、包含高分辨化学位移信息的一维频率谱；
    7)对各谱峰的幅值变化曲线分别进行数值拟合，即得到相应的纵向弛豫时间。
  2. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤2)中，所述常规一维氢谱脉冲序列由一个非选择性π/2射频脉冲构成，由常规一维氢谱脉冲序列采样得到的一维氢谱直接获取相应的谱峰分布和谱宽信息，根据所获信息设置溶剂峰中心为脉冲激发中心。
  3. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤3)中，所述校准非选择性π/2射频脉冲宽度，是通过测量使磁化矢量由纵向方向翻转到横向平面对应的脉冲作用时间，即得非选择性π/2射频脉冲宽度；改变步骤2)中所述常规一维氢谱脉冲序列的脉冲类型为高斯型软脉冲，测定溶剂选择性(π/2) I射频脉冲的脉冲宽度和功率。
  4. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤4)中，所述纵向磁化矢量反转恢复模块由一个溶剂选择性(π) I射 频脉冲、一个非选择性π射频脉冲以及反转恢复时间Δ构成。
  5. 如权利要求1或4所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤4)中，所述空间编码模块由两个相同的chirp线性调频绝热脉冲和极性相反的梯度场组成。
  6. 如权利要求1或4所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤4)中，所述分子间二量子相干选择模块由一个相干选择梯度G 1、一个溶剂选择性(π/2) I射频脉冲、一个相干选择梯度G 2以及一个自旋回波组合δ-π-δ构成，其中相干选择梯度G 1和G 2作用时间相同但强度比为1∶(-2)；所述空间解码采样模块是由施加在采样期的一对解码梯度场构成。
  7. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤5)中，所述设置核磁共振脉冲序列实验参数包括设置非选择性π/2射频脉冲脉宽、chirp绝热脉冲宽度、chirp脉冲扫频宽度、编码梯度强度Ge、相干选择梯度G 1及其作用时间、相干选择梯度G 2及其作用时间、溶剂选择性(π/2) I脉冲宽度及功率、溶剂选择性(π) I脉冲功率、回波时间δ、空间解码采样模块采样点数np1及模块重复个数Na、解码梯度强度Ga、序列延迟时间TR、纵向磁化矢量反转恢复时间Δ。
  8. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤5)中，所述核磁共振脉冲序列实验参数，包括一组变化的纵向磁化矢量反转恢复时间。
  9. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤6)中，当数据采集完成后，将每一张超快速二维谱的原始数据串分割重组成np1*Na的二维矩阵，经过傅里叶变换，得到与各纵向磁化矢量反转恢复时间对应的二维谱；对每一张二维谱分别逆时针旋转45°，然后沿空间编码维进行累积投影，得到一组高分辨一维谱，测量各个谱峰的幅值并进行归一化处理，将幅值最小点之前的数据点的幅值置为负值，绘制谱峰幅值随纵向磁化矢量反转恢复时间Δ变化曲线。
  10. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于在步骤7)中，对步骤6)中得到的幅值随Δ变化曲线使用函数y＝a-b*exp(-x/T 1)进行计算机拟合，自变量x为纵向磁化矢量反转恢复时间Δ，函 数值y为对应谱峰的幅值，拟合曲线求取a、b、T 1三个参数值，T 1即为谱峰所对应氢原子自旋的纵向弛豫时间。
  11. 如权利要求1所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于所述待测样品为浓度为1.0M的正丁醇水溶液，其中正丁醇为溶质，水为溶剂。
  12. 如权利要求1或11所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于测量纵向弛豫时间的脉冲序列包括纵向磁化矢量反转恢复模块、空间编码模块、分子间二量子相干信号选择模块和空间解码采样模块。
  13. 如权利要求1或11所述一种在不均匀磁场下测量质子纵向弛豫时间的方法，其特征在于所述数据后处理包括以下步骤：
    (a)对于一张超快速二维谱，将其原始数据串分割重组成np1*Na的二维矩阵，经过傅里叶变换之后，得到一张二维谱，再将二维谱逆时针旋转45°，沿F1维累积投影，即可得到高分辨一维谱，根据恢复出的化学位移信息可以归属出各谱峰对应的氢原子位置；
    (b)正丁醇H2位置的谱峰会随着反转恢复时间Δ的增加而变化，测量各个谱峰的幅值；
    (c)以反转恢复时间Δ等于32s时谱峰幅值为准，进行归一化，得到幅值随反转恢复时间Δ变化图；
    (d)由于二维谱均以绝对值模式进行处理，得到一维谱的谱峰幅值均为正值；根据时域信号的幅值关系，将幅值绝对值最小点之前的数据点幅值置为负值，得到幅值随反转恢复时间Δ变化曲线图；
    (e)对幅值随反转恢复时间Δ变化曲线图的各条曲线使用函数y＝a-b*exp(-x/T 1)进行计算机拟合，自变量x为纵向磁化矢量反转恢复时间Δ，函数值y为对应谱峰的幅值，拟合曲线求取a、b、T 1三个参数值，T 1即为对应谱峰的纵向弛豫时间；测得正丁醇各氢原子基团的纵向弛豫时间分别为2.73、2.77、3.08、3.18s。
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