CN114966508A - Automatic calibration method for ultra-fast space-time coding nuclear magnetic resonance spectrum distortion - Google Patents
Automatic calibration method for ultra-fast space-time coding nuclear magnetic resonance spectrum distortion Download PDFInfo
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Abstract
The invention provides an automatic calibration method for ultra-fast time-space coding nuclear magnetic resonance spectrum distortion, and mainly relates to the calibration of spectrum distortion through an optimization algorithm. Firstly, calibrating distortion caused by non-ideal factors of asymmetric effective strength of a positive gradient field and a negative gradient field during sampling; secondly, calibrating distortion generated by non-ideality factors of inconsistent opening time of a gradient field and sampling starting time in a sampling period; then, the distortion caused by the non-ideal factor that the initial phase of the parity data is inconsistent during sampling is calibrated, so that a distortion-free ultra-fast space-time coding nuclear magnetic resonance spectrum is obtained. The main effects of the invention are: the distortion calibration in the ultra-fast space-time coded nuclear magnetic resonance spectrum can be realized only by sampling the signal itself.
Description
Technical Field
The invention belongs to a Nuclear Magnetic Resonance (NMR) spectroscopy signal processing method, and particularly relates to an automatic calibration method for ultra-fast space-time coding Nuclear Magnetic Resonance spectrum distortion.
Background
Multidimensional nuclear magnetic resonance spectroscopy can provide more abundant important information such as molecular structure, material composition and the like than the traditional one-dimensional spectroscopy, but also requires very long experimental time. The space-time coding technology proposed in recent years improves the problem, and by carrying out space-level coding and decoding on samples, the multidimensional nuclear magnetic resonance spectrum can be obtained only by single sampling, so that the experimental time required by multidimensional spectrum acquisition is greatly shortened. However, some non-ideal factors on experimental hardware can cause the obtained space-time coding spectrogram to generate certain distortion, and the application of the space-time coding method is hindered.
Disclosure of Invention
The invention aims to provide an automatic calibration method for distortion in an ultra-fast space-time coding nuclear magnetic resonance spectrum, which can be applied to a plurality of different types of magnetic resonance spectrums adopting space-time coding technology, effectively solves the distortion of the space-time coding magnetic resonance spectrum caused by hardware non-ideality factors, and enlarges the application range of the ultra-fast space-time coding spectrum technology.
In order to solve the technical problem of ultra-fast space-time coding nuclear magnetic resonance spectrogram distortion, the invention adopts the following technical scheme:
an automatic calibration method for ultrafast space-time coding nuclear magnetic resonance spectrum distortion comprises the following steps:
1) dividing ultra-fast space-time coding data acquired by an experiment into two groups of subdata of odd lines and even lines;
2) aiming at the non-ideality factor of the effective intensity asymmetry of the positive and negative gradient fields during sampling, an optimization model for calibrating the distortion caused by the non-ideality factor is constructed for the odd-numbered line sampling data:
in the above formula, the first and second carbon atoms are,
for correction parameters to be solved, FT * And IFT * Representing data progression along specified dimensions, respectivelyA line fourier transform or an inverse fourier transform,
for odd row data in the space-time coding data acquired by experiment, l and m are coordinate values of corresponding dimensions respectively,
an L1 norm representing the matrix;
after solving the optimal solution of the formula (1), performing first-step correction on the original odd-numbered line data by using the optimal solution;
3) carrying out distortion calibration operation on even-numbered line sampling data as in 2) aiming at non-ideality factors of effective strength asymmetry of positive and negative gradient fields in the sampling period;
4) for an undesirable factor that the gradient field on time during sampling is inconsistent with the sampling start time, an optimized model for calibrating the distortion caused by the undesirable factor is constructed for the sampled data:
in the above formula, C x For the correction parameters to be solved for,
and
odd-numbered line data and even-numbered line data respectively representing the original dimensions after the correction steps (1) to (3).
After solving the optimal solution of the formula (2), performing second-step correction on the original odd-numbered line data and the original even-numbered line data by using the optimal solution;
5) for non-ideality factors that are inconsistent in the initial phase of the parity data during sampling, an optimal model is constructed for the sampled data that corrects for the distortion caused by the non-ideality factors:
in the above formula, C 0 For the correction parameter to be solved, IntFT * Representing an interleaved fourier transform of the data along a specified dimension,
and
respectively representing odd lines and even lines of data of the original dimension after the correction steps from (1) to (4);
after solving the optimal solution of the formula (3), performing third-step correction on the original even-numbered line data by using the optimal solution;
6) and outputting the ultrafast space-time coding spectrum after the distortion is corrected.
Compared with the prior art, the invention has the following beneficial effects:
the method provided by the invention can calibrate the spectrogram distortion caused by non-ideal factors of hardware facilities based on the self properties of the space-time coding nuclear magnetic resonance spectrum, thereby obtaining the ultra-fast space-time coding nuclear magnetic resonance spectrum without distortion and greatly improving the analyzability of the space-time coding spectrum. Meanwhile, compared with the original spectrogram which can only be obtained by adopting odd or even row data, the spectrogram calibrated by the method is greatly improved in signal-to-noise ratio and direct dimensional spectral width. In addition, the method has wide applicability to various nuclear magnetic resonance spectrums based on the space-time coding technology and has good robustness.
Drawings
FIG. 1 is a diagram of an odd line space-time coded signal and spectrogram with distortion due to non-ideality.
FIG. 2 is a diagram of an even line space-time coded signal and spectrogram with distortion due to non-ideality.
Fig. 3 shows the odd-numbered line space-time coded signal and the spectrogram obtained after the first distortion correction.
Fig. 4 is a diagram of an even-numbered line space-time coded signal and a spectrogram obtained after the first distortion correction.
Fig. 5 shows the odd-numbered line space-time coded signal and the spectrogram obtained after the second distortion correction.
Fig. 6 shows the even-numbered lines space-time coded signal and the spectrogram obtained after the second distortion correction.
Fig. 7 is a final space-time coding spectrum obtained after the third distortion correction.
Detailed Description
The specific implementation process of the invention comprises the following steps:
dividing ultra-fast space-time coding data acquired by an experiment into two groups of subdata of odd lines and even lines.
aiming at the non-ideality factor of the effective intensity asymmetry of the positive and negative gradient fields during sampling, an optimization model for calibrating the distortion caused by the non-ideality factor is constructed for the odd-numbered line sampling data:
in the above formula, the first and second carbon atoms are,
for correction parameters to be solved, FT * And IFT * Respectively representing fourier or inverse fourier transforming data along a specified dimension,
for odd row data in the space-time coding data acquired by experiment, l and m are coordinate values of corresponding dimensions respectively,
representing the L1 norm of the matrix.
After solving the optimal solution of equation (1), the original odd line data is corrected in a first step by using the optimal solution.
Step 3, correcting the distortion of even line data caused by the non-ideality factor of the effective intensity of the positive and negative gradient fields during sampling
And (3) carrying out the same distortion calibration operation as the step 2 on the even-numbered line sampling data aiming at the non-ideality factor of the asymmetry of the effective strength of the positive and negative gradient fields during the sampling.
Step 4, calibrating distortion caused by non-ideality factors of the gradient opening time and the sampling start time in the sampling period
For non-ideality factors where the gradient open time during sampling does not coincide with the sampling start time, an optimized model is constructed for the sampled data that corrects for the distortion caused by the non-ideality factors:
in the above formula, C x For the correction parameters to be solved for,
and
odd-numbered line data and even-numbered line data respectively representing the original dimensions after the correction steps (1) to (3).
After solving the optimal solution of equation (2), the original odd and even line data are corrected in a second step using the optimal solution.
Step 5, correcting the distortion caused by the non-ideality factor of the initial phase inconsistency of the parity data during sampling
For non-ideality factors that are inconsistent in the initial phase of the parity data during sampling, an optimal model is constructed for the sampled data that corrects for the distortion caused by the non-ideality factors:
in the above formula, C 0 For correction parameters to be solved, IntFT * Representing an interleaved fourier transform of the data along a specified dimension,
and
odd-numbered line data and even-numbered line data respectively representing the original dimensions after the correction steps (1) to (4).
After solving the optimal solution of equation (3), the original even line data is corrected in a third step by using the optimal solution.
And 6, outputting the ultrafast space-time coding spectrum after the distortion is calibrated.
The following is a specific example:
referring to fig. 1-7, firstly, dividing ultrafast space-time coded data of water acquired by an experiment, respectively taking out odd lines and even lines of the data to form new two groups of data, and performing fourier transform on the new two groups of data to obtain corresponding space-time coded spectrograms, as shown in fig. 1 and 2; secondly, respectively carrying out optimization algorithm solving on the odd-numbered line data and the even-numbered line data according to a model shown in the formula (1), and carrying out first-step distortion calibration on the optimal solution after solving the optimal solution; then, carrying out optimization algorithm solving on the odd-numbered line data and the even-numbered line data according to a model shown in the formula (2), and carrying out distortion calibration of a second step after solving the optimal solution; and finally, carrying out optimization algorithm solving on the odd-numbered line data and the even-numbered line data according to a model shown in the formula (3), and carrying out distortion calibration in the third step after solving out the optimal solution of the odd-numbered line data and the even-numbered line data to finally obtain a distortion-free ultrafast space-time coding nuclear magnetic resonance spectrum.
The above embodiments are only used to further illustrate the method for automatically calibrating the distortion of the ultrafast space-time coded nuclear magnetic resonance spectrum according to the present invention, but the present invention is not limited to the embodiments, and any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical spirit of the present invention fall within the scope of the technical solution of the present invention.
Claims (4)
1. An automatic calibration method for ultrafast space-time coding nuclear magnetic resonance spectrum distortion is characterized by comprising the following steps:
1) dividing ultra-fast space-time coding data acquired by an experiment into two groups of subdata of odd lines and even lines;
2) aiming at the non-ideal factors of the effective intensity of the positive and negative gradient fields during sampling, constructing an optimization model for calibrating the distortion caused by the non-ideal factors on the odd-line sampling data, solving the optimal solution of the optimization model, and then using the optimal solution to carry out first-step correction on the original odd-line data;
3) aiming at the non-ideal factors that the effective intensity of the positive and negative gradient fields is not symmetrical during sampling, carrying out the same distortion calibration operation as the step 2 on the even-numbered line sampling data;
4) aiming at an undesirable factor that the opening time of a gradient field is inconsistent with the sampling starting time in the sampling period, constructing an optimization model for calibrating distortion caused by the undesirable factor on sampling data, solving the optimal solution of the optimization model, and then performing second-step correction on original odd-numbered row data and even-numbered row data by using the optimal solution;
5) aiming at the non-ideal factors of initial phase inconsistency of the parity data in the sampling period, constructing an optimization model for calibrating distortion caused by the non-ideal factors on the sampling data, solving the optimal solution of the optimization model, and then performing third-step correction on the original even-numbered row data by using the optimal solution;
6) and outputting the ultrafast space-time coding spectrum after the distortion is corrected.
2. The method for automatically calibrating the distortion of the ultrafast space-time coded nuclear magnetic resonance spectrum according to claim 1, wherein: the optimization model in the step 2 is as follows:
in the above formula, the first and second carbon atoms are,
for the correction parameter to be solved, FT * And IFT * Respectively representing fourier or inverse fourier transforming data along a specified dimension,
for odd row data in the space-time coding data acquired by experiment, l and m are coordinate values of corresponding dimensions respectively,
representing the L1 norm of the matrix.
3. The method for automatically calibrating the distortion of the ultrafast space-time coded nuclear magnetic resonance spectrum according to claim 1, wherein: the optimization model in the step 4 is as follows:
in the above formula, C x For the correction parameters to be solved for,
and
odd and even line data representing the original dimensions after the step 1-step 3 correction steps, respectively.
4. The method for automatically calibrating the distortion of the ultrafast space-time coded nuclear magnetic resonance spectrum according to claim 1, wherein: the optimization model in step 5 is:
in the above formula, C 0 For correction parameters to be solved, IntFT * Representing an interleaved fourier transform of the data along a specified dimension,
and
odd and even line data representing the original dimensions after the step 1-step 4 correction steps, respectively.
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