CN114002258A - Method for rapidly measuring two-dimensional relaxation by using dynamic nuclear polarization enhancement build time - Google Patents

Method for rapidly measuring two-dimensional relaxation by using dynamic nuclear polarization enhancement build time Download PDF

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CN114002258A
CN114002258A CN202111278683.3A CN202111278683A CN114002258A CN 114002258 A CN114002258 A CN 114002258A CN 202111278683 A CN202111278683 A CN 202111278683A CN 114002258 A CN114002258 A CN 114002258A
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刘朝阳
张震
陈俊飞
冯继文
刘买利
陈方
杨春升
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Hubei Optics Valley Laboratory
Institute of Precision Measurement Science and Technology Innovation of CAS
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Abstract

The invention discloses a method for rapidly measuring two-dimensional relaxation by utilizing dynamic nuclear polarization enhancement build time, which aims at the conventional two-dimensional T based on inversion recovery1‑T2The method, the problem of long experimental time caused by low signal-to-noise ratio, uses variable-time microwave pulse to irradiate a solution sample system containing free radicals, transfers the polarization of electrons to atomic nuclei based on Overhauser effect, changes the irradiation time of the microwave pulse, the atomic nuclei can reach different polarization degrees, and the polarization degree of the nuclei reaches the maximum along with the gradual increase of the microwave time. By encoding the polarization build-up time of the nuclei, T is obtained by inversion1Dimensional relaxation distribution combined with CPMG to form T based on dynamic nuclear polarization enhanced polarization establishment time1‑T2Sequence, capable of rapidly obtaining accurate two-dimensional T in a short time in a single time1‑T2Spectra.

Description

Method for rapidly measuring two-dimensional relaxation by using dynamic nuclear polarization enhancement build time
Technical Field
The invention relates to the technical field of magnetic resonance, in particular to a method for measuring two-dimensional T1-T2 by utilizing dynamic nuclear polarization enhancement establishing time.
Background
Porous media are ubiquitous in the environment, and it is important to know their physical information, such as porosity, pore size distribution, bound water, and permeability, for their applications. Nuclear Magnetic Resonance (NMR) is a non-invasive, in-situ detection means that can accurately obtain such information, and is widely used in the research of porous media such as cement, wood, high polymers, and rock. NMR detection to obtain transverse relaxation time T2Longitudinal relaxation time T1And a diffusion coefficient D, which is related to a plurality of physical property parameters (fluid viscosity, crystallinity, ion concentration in a solution, and chain length of a polymer compound), etc., and physical property analysis can be performed based on these three parameters, which are called time domain spectra corresponding to a frequency domain spectrum (chemical shift spectrum) used by MRS, the abscissa of the time domain spectrum being T2、T1D, the abscissa of the frequency domain spectrum is frequency scale, the NMR technology of component detection by means of the time domain spectrum is also called time domain nuclear magnetic resonance, a sample with magnetic substances in the interior can only be sampled in a low field, the internal gradient field can even be used as a parameter to be measured in a low field environment, and the influence of the internal inherent gradient field of the porous medium can be avoided by utilizing low-resolution time domain NMR relaxation analysis.
The moisture state is generally classified into: the relaxation time of the free water, the water which is difficult to flow and the bound water is generally reduced in sequence, so that the water state and the content can be judged from the position and the amplitude of a peak in a relaxation spectrum, most foods are porous media mixed by water and oil, the relaxation rate of the foods is influenced by the size of pores where the oil and the water are located, and the oil-water separation and the pore distribution measurement can be carried out by utilizing low-field nuclear magnetic resonance,
however in different regions of the porous medium, as shown in FIG. 1, one-dimensional relaxation (T)1Or T2) The time is very close to each other in some cases and cannot be distinguished, when the positions of different peaks are close to each other, the overlapping condition of the peaks is serious, the definition cannot be clearly defined, a two-dimensional relaxation method is needed for analysis, and the two-dimensional T in the figure 2 is shown in the specification1-T2In the spectra, three components can be clearly distinguished. In both the one-dimensional experiment and the two-dimensional experiment, the raw data acquired by the NMR apparatus is difficult to be used as a direct decision basis, and a one-dimensional spectrum or a two-dimensional spectrum needs to be calculated according to the raw data, which is called nuclear magnetic resonance inversion.
Two-dimensional T1-T2Relaxation methods have wide application in many fields such as food, cement-based mixtures, oil recovery, etc. The main problems to be solved by the current two-dimensional inversion are as follows: the signal-to-noise ratio of low-field NMR is low, the SNR of the sampling is generally low due to the use of a low-field-strength main magnet, and the inversion is very sensitive to noise, resulting in large inversion errors of the two-dimensional relaxation spectrum. By accumulating experiments for multiple times, the signal-to-noise ratio can be improved, but the experiment is time-consuming at the same time. These disadvantages limit the conventional T1-T2The method is further developed in rapid detection and dynamic process observation.
Disclosure of Invention
Two-dimensional T for conventional inversion recovery based1-T2Method, problem of long experimental time due to low signal-to-noise ratio, the invention provides a method for measuring two-dimensional T by using dynamic nuclear polarization enhancement establishment time1-T2The method comprises the steps of irradiating a solution sample system containing free radicals by using a microwave pulse with variable time, transferring the polarization of electrons to atomic nuclei based on an Overhauser effect, changing the irradiation time of the microwave pulse, enabling the atomic nuclei to reach different polarization degrees, and enabling the polarization degree of the nuclei to reach the maximum degree along with the gradual increase of the microwave time. By encoding the polarization build-up time of the nuclei, T is obtained by inversion1Dimensional relaxation distribution combined with CPMG to form T based on dynamic nuclear polarization enhanced polarization establishment time1-T2Sequence, can be rapidly obtained in a short time in a single timeAccurate two-dimensional T1-T2Spectra.
The above object of the present invention is achieved by the following technical solutions:
method for rapid measurement of two-dimensional relaxation by dynamic nuclear polarization enhancement build-up time by letting the radio frequency channel, gradient channel and microwave channel perform a two-dimensional T1-T2Scanning a sample in a target area, and performing two-dimensional inverse Laplace transform on the change data of the longitudinal magnetization vector of the sample along with the microwave pulse time d1 and the spin echo signal data to obtain T1-T2Relaxation of S (T)1,T2) Are distributed to obtain two-dimensional T1-T2Spectrum, performing two-dimensional T1-T2The sequence of steps includes:
a) applying a non-zero small-angle pulse, namely (0 DEG and 180 DEG), to the sample at the radio frequency channel;
b) then applying a destructive gradient to the sample in the gradient channel;
c) repeating steps a) → b) or b) → a), stopping the repeating cycle after the application of the wavefront detection macroscopic magnetization vector 0;
d) applying a microwave pulse with variable time length and constant power to the microwave channel to irradiate the sample, wherein the time length of the microwave pulse is recorded as d 1; the frequency omega of the microwave pulses being equal to or close to the electronic lamor frequency omegae；
e) Applying a 90-degree hard pulse to the sample in a radio frequency channel after the microwave pulse, and waiting for te/2 time;
f) applying M2 times of 180-degree hard pulses to a sample in a radio frequency channel, taking echo time te as a time interval between two adjacent 180-degree pulses, and taking te/2 time after the 180-degree pulses as the central maximum time of an echo to obtain M2 echo signals, so as to form a CPMG sequence and obtain spin echo signal data; latency d2 is set to 0;
g) increasing the length of the microwave pulse time d1, repeating the steps a) to f) M1 times, and enabling d1 to be d1nN is the number of repetitions, 3T1≤d1M1≤5T1M1 is more than or equal to 16, M1 longitudinal magnetization vectors are obtained along with microwave pulseData varying at time d 1;
the magnetization vectors evolve over time in steps a) to g) as follows:
Figure BDA0003330506890000031
wherein f is a leakage factor, xi is a coupling factor, s is a saturation factor, and the parameters are related to the dynamic nuclear polarization process and are constants in an experiment under the condition of determining power and the same sample system; gamma raySAnd gammaIThe magnetic rotation ratios of electrons and atomic nuclei, respectively.
Preferably, the microwave pulse is a continuous wave or a pulse.
Preferably, the echo time te is 2 ms.
Preferably, the initial value of d1 in step d) is greater than 1 ms.
Preferably, in the data of the M1 longitudinal magnetization vectors changing with the microwave pulse time d1, the intensity of the longitudinal magnetization vector increases with the increase of the microwave time d1 under the constant microwave power, and the following relationship is formed:
Figure BDA0003330506890000032
preferably, the relationship between the transverse magnetization vector in the M2 echo signals and the echo time te and M2 is:
Figure BDA0003330506890000033
preferably, M2 ═ 2y≥256。
Further, M1 ═ 64.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention is based on the method for establishing time for dynamic nuclear polarization atomic nuclear polarization, and the time is 5 times T1The experiment waiting time d2 is shortened to zero, so that the time of a single experiment is greatly reduced;
2. the signal-to-noise ratio of the two-dimensional relaxation experiment is improved by utilizing the dynamic nuclear polarization technology, and compared with the traditional two-dimensional experiment, the method does not need to accumulate, so that the experiment time is reduced to a great extent.
Drawings
FIG. 1 is a diagram of the overlapping of peaks of one-dimensional relaxation spectra;
FIG. 2 is a two-dimensional T1-T2A spectrum;
FIG. 3 is a two-dimensional T of the present invention1-T2A sequence timing diagram;
FIG. 4 shows a fast T of the present invention1-T2Method, relaxation distribution in two systems;
fig. 5 is a diagram of an inversion-recovery pulse sequence.
Detailed Description
The present invention will be described in further detail with reference to examples for the purpose of facilitating understanding and practice of the invention by those of ordinary skill in the art, and it is to be understood that the present invention has been described in the illustrative embodiments and is not to be construed as limited thereto.
The terms to which the invention relates are first explained as follows:
"polarization": when the atomic nuclei with magnetic moments are placed in a constant magnetic field in a certain direction, the nuclear magnetic moments are aligned to the direction of the constant magnetic field, and finally, the nuclear magnetic moments are in the same direction or opposite direction to the constant magnetic field, and the process that the magnetic moments of the atomic nuclei are completely randomly distributed from a natural state to be aligned to be parallel to the external magnetic field is called the polarization of the atomic nuclei.
"pulsing of the radio frequency channel": the process of effective perturbation of a nucleus with a magnetic moment by a Radio Frequency (RF) signal of a particular frequency is similar to the process of energy level transition, and the nucleus will "select" the RF of a particular frequency to extract energy from it, which is equal to the energy difference between the two energy states. After the RF interference is removed, the atomic nucleus can gradually return to a stable low energy state in a thermal equilibrium state and release an RF signal, which is a signal detected by a nuclear magnetic resonance device.
"magnetic": refers to the strong external magnetic field applied when NMR phenomenon occurs
Figure BDA0003330506890000041
The magnetic atomic nuclei will be oriented individually
Figure BDA0003330506890000042
And (4) aligning.
When the '90 DEG pulse' and '180 DEG pulse' magnetic cores are placed in the main magnetic field, the total magnetic moment direction and the Z axis (Z axis and Z axis)
Figure BDA0003330506890000043
Are aligned with the X, Y axis around
Figure BDA0003330506890000044
At an angular velocity ωLarmorRotating) in the same direction. With RF field perpendicular to the main magnetic field (typically using
Figure BDA0003330506890000045
Represented) of magnetic core, with a magnetic field
Figure BDA0003330506890000046
Larmor precession with the axis of rotation producing a continuous change in the magnetic moment of the nucleus from the Z-axis angle, the application time required to change the overall magnetic moment direction to the opposite (180) direction to the Z-axis is called 180 pulse time (or 180 pulse width, P2); the application time required to first flip this angle from 0 to 90 is called the 90 pulse time (or 90 pulse width, P1).
"longitudinal relaxation and transverse relaxation": when in static magnetic field
Figure BDA0003330506890000047
When the proton in (1) reaches a stable equilibrium state, the overall magnetic moment of the sample is shown as being equal to
Figure BDA0003330506890000048
In the same direction
Figure BDA0003330506890000049
After 90-degree pulse satisfying resonance condition is applied, two effects are generatedAnd (4) fruit: one is that a longitudinal component is caused
Figure BDA00033305068900000410
The second one of which results in a lateral component
Figure BDA0003330506890000051
Is present, and
Figure BDA0003330506890000052
is equal to
Figure BDA0003330506890000053
This state, which is reached by means of external disturbances, is not stable and the system will gradually return to the equilibrium state after the excitation has ended. During this gradual recovery two relaxations occur: on one hand, the proton in high energy state moves from anti-parallel to positive-parallel, and the longitudinal magnetism
Figure BDA0003330506890000054
Gradually return to
Figure BDA0003330506890000055
(longitudinal relaxation); on the other hand, spin-induced phase dispersion and transverse magnetization
Figure BDA0003330506890000056
From
Figure BDA0003330506890000057
Decays rapidly to 0 (transverse relaxation).
“T1And T2": the time required from the moment of the 90 ° RF pulse withdrawal to the time of restoration to the full longitudinal magnetization state is defined by the longitudinal relaxation time T1(spin-lattice relaxation time) and this phenomenon is known as T1Relaxation, in general, T of liquids1T is more solid than1T of long, slower moving macromolecules1Shorter than small molecules that move faster; after the 90 ° RF pulse disappears, the phases of the magnetic nuclei begin to gradually disperse until the magnetic moments of the nuclei are at XOYThe in-plane (transverse) components are completely randomly distributed, macroscopically appearing as a zero transverse magnetization vector. The time from the in-phase motion recovery of all magnetic moments to the completely random distribution of the phases is represented by the transverse relaxation time T2(spin-spin relaxation) determination, this process is called T2Relaxation, T of liquids relative to solids2It is longer.
The "CPMG" consists of a sequence of one 90 pulse followed by a plurality of 180 pulses, the CPMG sequence first applying a 90 RF pulse to completely flip the longitudinal magnetization vector to the XOY plane. When the 90 DEG RF pulse is removed, all protons are in the same phase precession state, the longitudinal magnetization vector is 0, and the transverse magnetization vector M isXYTo a value of M0And is also the maximum value. The proton population then begins to show a dephasing phase before complete dephasing (the phases of all protons are completely randomly distributed, resulting in MXYA zero state), a 180 ° RF pulse is followed to shift the phase of the proton by 180 °, the proton with the originally lagging phase change amount and the slower change rate is located at the position with the larger phase after 180 ° inversion, the proton moves continuously in the previous direction after the 180 ° RF pulse is cancelled, the phase-loose process originally supposed to occur becomes a phase-gathering process, and the reappeared peak value is an "echo" (echo). This 180 RF pulse may be followed by a further application of a plurality of 180 RF pulses, with subsequent RF pulses having the effect of forming echoes. The time interval between two adjacent 180 ° RF pulses is generally referred to as the echo time te (time echo), and the time interval between the 90 ° RF pulse and the 180 ° RF pulse is defined as the half echo time te/2. CPMG sequence makes up for hardware and environment pair T2The effect of the attenuation, so that T can be measured2Rather than T2*. Due to static magnetic field B0It is impossible to achieve absolute uniformity and external electromagnetic interference cannot be completely shielded, which results in different larmor frequencies of protons at different positions, thereby accelerating dephasing of protons and accelerating T2The attenuation of (2). Less than T2Is called T2*。
"gradient" the basic method for determining the spatial position of the MR signal source is to use an additional linear gradient, i.e. an imaging gradient. ToIn an external magnetic field B0The hydrogen protons in (B) generate the same nuclear magnetic resonance frequency regardless of their spatial positions if they are in the external magnetic field B0A linear gradient magnetic field is superposed on the magnetic field along a certain direction, resulting in a total magnetic field (external magnetic field B)0And the vector sum of the gradient magnetic fields) is higher at one end and lower at the other end along the direction of the gradient magnetic fields, and the magnetic field intensity between the two ends is in gradient distribution. A predictable change in the resonant frequency is produced in the direction of the magnetic field gradient. The magnetic field gradient is often generated by an external magnetic field B in a magnetic resonance imager0Generated by gradient coils within the main magnet bore. Three perpendicular magnetic field gradients are used for carrying out spatial three-dimensional positioning on the nuclear magnetic resonance signal source in different time.
The frequency for "dynamic nuclear polarisation" is equal to or close to the electronic Larmor frequency ωeThe microwave irradiates the sample and reaches a saturation state, so the population number on the related electron energy level reaches equal, namely the electron saturation, the distribution of the population number on the initial thermal equilibrium state on the nuclear spin energy level is damaged due to the electron-nuclear interaction Hen, the difference of the population number is increased, the absolute value of the nuclear polarization is greatly increased, and the dynamic nuclear polarization is realized.
Example 1
Step 1, adding free radicals for enhancing NMR signals of an aqueous phase or an oil phase into a mixed sample of a solid and a liquid: a sample of 1000-mesh glass sand to which an excess of 20mM TEMPO (tetramethylpiperidine oxide) aqueous solution was added was treated, the system comprising two components of free water (TEMPO aqueous solution) and restricted water (TEMPO aqueous solution in glass sand); TEMPO is paramagnetic and is used in biochemistry as an electron spin label.
Step 2, the nuclear magnetic resonance equipment is a nuclear magnetic resonance imaging system generated by a certain company, the magnet is a permanent magnet, the field intensity is 0.06T, the field intensity is a static magnetic field, and the two-dimensional T is adopted1-T2The sequence timing diagram is shown in FIG. 3, and includes a radio frequency channel, a gradient channel, and a microwave channel, and T is acquired through the radio frequency channel2Echo data of the dimension;
step 3, executing two-dimensional T1-T2Scanning a sample in a target area, and performing two-dimensional inverse Laplace transform on the change data of the longitudinal magnetization vector of the sample along with the microwave pulse time d1 and the spin echo signal data to obtain T1-T2Relaxation of S (T)1,T2) Are distributed to obtain two-dimensional T1-T2Spectrum, performing two-dimensional T1-T2The sequence of steps includes:
a) applying a non-zero small-angle pulse to the sample at the radio frequency channel, in this embodiment, applying a 90 ° pulse to the sample at the radio frequency channel with a pulse width of 7 us; a non-zero degree small angle pulse, i.e. (0 °,180 °).
b) Applying a damage gradient to the sample in a gradient channel, wherein the direction and climbing amplitude of the gradient are not particularly required, and the rising edge time of the gradient in the embodiment is 0.2ms, and the platform time is 0.4 ms;
c) repeat step a) → b) or b) → a), stop repeating the cycle after the application of the wavefront detection macroscopic magnetization vector 0, the number of repeating the cycle N being 10 times in the present embodiment; ensuring the magnetization vector before microwave to be 0;
d) applying a microwave pulse with variable time length to the microwave channel to irradiate the sample, wherein the time length of the microwave pulse is recorded as d1, and d1 in the embodiment is changed from 1ms to 1.5s relative to the sample; the microwave pulse may be in a continuous wave mode or a pulsed mode; the frequency omega of the microwave pulses being equal to or close to the electronic lamor frequency omegae(ii) a The microwave power is 8W;
at a fixed microwave power, the longitudinal magnetization vector intensity increases with increasing microwave time, with T1The relationship of exponential increase, the formula is as follows:
Figure BDA0003330506890000071
wherein f is a leakage factor, xi is a coupling factor, s is a saturation factor, and the parameters are related to the dynamic nuclear polarization process and are constants under the condition of determining the microwave power and the same sample system; gamma raySAnd gammaIThe magnetic rotation ratios of electrons and atomic nuclei respectively;
e) not waiting, applying a 90-degree hard pulse with a pulse width of 7us to the sample in a radio frequency channel immediately after the microwave pulse, and waiting for te/2 time, wherein the echo time te is 2 ms;
f) applying M2 times 180 DEG hard pulse to the sample in the radio frequency channel, wherein the pulse width is 14us, the echo time te is used as the time interval between two adjacent 180 DEG pulses, the te/2 time after the 180 DEG pulse is the central maximum time of the echo, obtaining M2 echo signals, forming a CPMG sequence, obtaining spin echo signal data, and obtaining the transverse magnetization vector along with T during the period2The exponential decay of (c):
Figure BDA0003330506890000072
then wait time d2 is set to 0; m2 ═ 2y≥256；
g) Increasing the length of the microwave pulse time d1, repeating the steps a) to f) M1 times, and enabling d1 to be d1nN is the number of repetitions, 3T1≤d1M1≤5T1M1 is more than or equal to 16, the change data of M1 longitudinal magnetization vectors along with the microwave pulse time d1 is obtained, and the initial value of d1 in the step d) is more than 1 ms;
for different samples before the experiment, T1The value is known, about a few hundred milliseconds.
The magnetization vectors evolve over time in steps a) to g) as follows:
Figure BDA0003330506890000073
in this embodiment, the echo time te is 2ms, T1Dimension code M1 ═ 64 times, T2Dimension code M2 is 256 times, the larger the M1 and M2 are, the larger the two-dimensional T1-T2The higher the resolution of the spectrum;
repeating steps a) to g) to obtain all the raw data, i.e. T1Dimensional raw data and T2Sum of dimensional raw data: performing two-dimensional Laplace inverse transformation on the M2 matrix data and M1 matrix data to obtain T1-T2Relaxation of S (T)1,T2) Are distributed to obtain two-dimensional T1-T2A spectrum;
the above steps can rapidly complete a two-dimensional experiment within 90s, and a two-dimensional T is obtained through two-dimensional inverse Laplace transform1-T2Spectra, see fig. 4. A two-dimensional Laplace inverse transformation method is disclosed in the literature "SONG Y-Q, VENKATARAMANAN L, HuRLIMANN M, et al.T 1-T2 correction specific induced using a fast two-dimensional Laplace inversion [ J].J Magn Reson,2002,154(2):261-8”。
Comparative example
Longitudinal relaxation time T1The most widely used method of determination is the "inversion-recovery" method, in which the magnetization Mz is first inverted to the direction of the-z axis by a 180 pulse, and then a waiting period τ is used1The magnetization will be restored to a certain extent in the longitudinal direction, this waiting period is called the restoration period, then a 90 ° pulse is sent out, the obtained free induction decay signal (FID) is recorded and fourier transformed, and the obtained frequency domain signal intensity is the longitudinal magnetization Mz. The longer the recovery period is, the smaller the amplitude of the obtained longitudinal magnetization is, the length of the recovery period tau is gradually changed to obtain a series of longitudinal magnetizations Mz, and the least square fitting is performed on all values according to the formula (D-1) to obtain the longitudinal relaxation time T to be measured1The value is obtained. The inversion-recovery pulse sequence is shown in fig. 5.
Figure BDA0003330506890000081
Longitudinal relaxation being applied magnetic field B0The time required for the magnetic moment in the z-axis direction to return from zero to a maximum, which is very long and even infinite to return to the exact same state before excitation, is therefore 63% of the time required to return to the original equilibrium state, called the longitudinal relaxation time, the magnitude of the longitudinal magnetization vector, i.e. the applied static magnetic field B0The magnitude mz (t) of the magnetization vector when aligned with the z-axis direction, M0 is the maximum magnitude of the magnetization vector under the action of the external magnetic field.
Detection of an Mz value generally requires accumulation, whereas determination of Mz as a function of the duration τ of the alternating magnetic field requires a series of different τ values, sinceThis measure longitudinal relaxation time T1A double cycle is required. Other assays T1The method also comprises a saturation recovery method and a zero point method, and all pulse sequences for measuring the longitudinal relaxation time have the common characteristics that: a recovery period is essential.
Transverse relaxation time T2The measurement of (2) is generally carried out by a CPMG pulse sequence, i.e. after a 90 DEG pulse, a series of 180 DEG pulses are applied consecutively with intervals of tau, so as to obtain a series of spin echo signals, the amplitude of which, i.e. the amplitude Mx (t) of the transverse magnetization vector, is expressed in relation to time as:
Figure BDA0003330506890000091
M0xis the maximum value of the transverse magnetization vector, i.e. the transverse magnetization vector magnitude at time t equal to 0 after the end of the 90 ° pulse.
The experiment was therefore carried out at a static magnetic field strength of 0.06T. Sample 1 (hydrogel dissolved in 1.5mM TEMPO aqueous solution at a hydrogel concentration of 20mg/200uL) was subjected to conventional two-dimensional relaxation experiments based on the inversion recovery method to obtain a conventional two-dimensional T1-T2 spectrum as a comparative example, te 2ms, N1 32 times, N2 512 times, 8 times in total, which took 16min, and T was obtained after inverse two-dimensional laplace transformation1-T2Spectrum, accumulating 16 times, consuming 32min, obtaining T after two-dimensional Laplace inverse transformation1-T2Spectra.
It should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims (8)

1. Method for rapid measurement of two-dimensional relaxation by dynamic nuclear polarization enhancement build-up time by letting the radio frequency channel, gradient channel and microwave channel perform a two-dimensional T1-T2Sequence ofScanning a sample in the target region, and performing two-dimensional inverse Laplace transform on the data of the change of the longitudinal magnetization vector of the sample with the microwave pulse time d1 and the spin echo signal data to obtain T1-T2Relaxation of S (T)1,T2) Are distributed to obtain two-dimensional T1-T2Spectrum, characterized by the fact that a two-dimensional T is performed1-T2The sequence of steps includes:
a) applying a non-zero small-angle pulse, namely (0 DEG and 180 DEG), to the sample at the radio frequency channel;
b) then applying a destructive gradient to the sample in the gradient channel;
c) repeating steps a) → b) or b) → a), stopping the repeating cycle after the application of the wavefront detection macroscopic magnetization vector 0;
d) applying a microwave pulse with variable time length and constant power to the microwave channel to irradiate the sample, wherein the time length of the microwave pulse is recorded as d 1; the frequency omega of the microwave pulses being equal to or close to the electronic lamor frequency omegae；
e) Applying a 90-degree hard pulse to the sample in a radio frequency channel after the microwave pulse, and waiting for te/2 time;
f) applying M2 times of 180-degree hard pulses to a sample in a radio frequency channel, taking echo time te as a time interval between two adjacent 180-degree pulses, and taking te/2 time after the 180-degree pulses as the central maximum time of an echo to obtain M2 echo signals, so as to form a CPMG sequence and obtain spin echo signal data; latency d2 is set to 0;
g) increasing the length of the microwave pulse time d1, repeating the steps a) to f) M1 times, and enabling d1 to be d1nN is the number of repetitions, 3T1≤d1M1≤5T1M1 is more than or equal to 16, and data of M1 longitudinal magnetization vectors changing along with the microwave pulse time d1 are obtained;
the magnetization vectors evolve over time in steps a) to g) as follows:
Figure FDA0003330506880000011
wherein f is a leakage factor, xi is a coupling factor, s is a saturation factor, and the parameters are related to the dynamic nuclear polarization process and are constants under the condition of determining power and the same sample system; gamma raySAnd gammaIThe magnetic rotation ratios of electrons and atomic nuclei, respectively.
2. The method for rapid measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time as claimed in claim 1, characterized in that said microwave pulse is a continuous wave or a pulse.
3. The method for rapid measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time as claimed in claim 2, characterized in that the echo time te is 2 ms.
4. Method for the rapid measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time according to claim 3 characterized in that the initial value of d1 in step d) is larger than 1 ms.
5. The method for rapid measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time as claimed in claim 4, wherein the longitudinal magnetization vector intensity increases with increasing microwave time d1 at constant microwave power in the data of M1 longitudinal magnetization vectors with changing microwave pulse time d1, in the following relationship:
Figure FDA0003330506880000021
6. the method for fast measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time as claimed in claim 5, wherein the relationship of the transverse magnetization vector in M2 echo signals with echo time te and M2 is:
Figure FDA0003330506880000022
7. the method for rapid measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time as claimed in claim 6, wherein M2-2y≥256。
8. The method for rapid measurement of two-dimensional relaxation with dynamic nuclear polarization enhancement build-up time as claimed in claim 7, wherein M1-64.
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