New Methods For Resolution Enhancement Of Nuclear Magnetic Resonance Spectroscopy

Nuclear magnetic resonance(NMR)exhibits the features of being non-destructive and non-invasive,and provides sufficiently high resolutions to analysis chemical component,resolve molecular-level information and test in medicine production.The simplest and widely-used 1D NMR spectrum is able to provide the information about molecular constructions and amounts of interested nuclear inside molecules.The multi-dimensional(nD)NMR spectrum is also a powerful tool for at least two reasons.First,presenting the information in more than one dimension improves the readability by reducing the overlapping of resonance peaks.Second,the nD NMR spectrum can provide more information,such as the information of coherences between carbons and protons,which can hardly be obtained by the 1D NMR spectrum.However,conventional NMR 2D NMR spectra require multiple scans that is very time-consuming.Another requirement for obtaining high-resolution NMR spectra is the homogeneity of static magnetic field.However,in some cases,the homogeneous magnetic field is hard to ensure.For example,in tissues with susceptibility incontinuity or at interfaces among different tissues,signifying the importance and necessity of developing high-resolution NMR spectroscopy under inhomogeneous magnetic fields.Therefore,reducing the experiment time while maintaining the high resolution,and acquiring high-resolution spectra under inhomogeneous field is necessary and important.Our works are based on these two issues.First,a method for improving resolution is introduced;then,a new technology for using the above-mentioned method to improve resolutions of spectra taken within an extremely short time is proposed;finally,our latest work about acquiring high resolution spectra under inhomogeneous field is introduced.The related contents can be summarized as follows:1.Introduction of the 2D covariance NMR spectroscopy.The covariance NMR spectrum is acquired by the covariance method,which bases on the statistic theory for acquiring coherence information between nuclear inside molecules.Therefore,even under the situation of the resolution in F1 dimension decreasing due to reducing the experiment time,as long as the amount of data is large enough for statistical analysis,high-resolution NMR spectra with coherence information can be acquired.There are many different kinds of covariance method,not only methods for homonuclear spectra,but also methods designed for heteronuclear spectra.These methods can be applied to improving resolution without extend the experiment time.2.Method to improve resolutions of spatial-encode spectra by the covariance method is introduced.Spatial-encode spectroscopy enables short-time acquisition within a single scan by replacing the time encode with the spatially encode.However,this method suffers low resolution in the F1 dimension,especially when high resolution acquired in the F2 dimension.In this work,the covariance method is applied to the spatial-encode method to improve its resolution.Since artifacts arise in this process,a filter mask to remove artifacts is developed based on the pattern recognition.Finally,the goal of acquiring a high-resolution spectrum with an extremely short time is achieved.3.A method based on partial homogeneity to provide high-resolution spectra under inhomogeneous field.Resonances in different position under inhomogeneous field have different frequencies shifts,which results in overlapping of peaks.In a small voxel,the magnetic field almost remains unchanged,which enables acquisitions of high-resolution spectra inside a small range.ZL.Wei proposed a new method using gradient magnetic field to acquire 1D spectra of small voxels,and adds the data from all voxels by an algorism to acquire high-resolution 1D spectra.In this work,we developed a new method base on a similar theory to acquire high-resolution 2D NMR spectra under inhomogeneous field.