Preparation And Application Of Nuclear Spin Singlet-state In Magnetic Resonance Technique

As a special quantum state,the long-lived nuclear spin singlet state does not evolve with the gradient field in a magnetic field and has a decay lifetime much longer than the T1 relaxation time,which has broad application prospects.This article discusses the preparation of nuclear spin singlets in multiple spin systems,and applies nuclear spin singlets to two-dimensional nuclear magnetic resonance spectroscopy,magnetic resonance imaging and diffusion measurement.(1)Takes NAA molecule as an example,discusses the preparation of nuclear spin singlet in two coupling modes,and analyzes the effect of spin coupling on the preparation efficiency during singlet state preparation.The preparation and detection of singlet states are applied to two-dimensional spectroscopy to achieve targeted observation of specific groups in complex environments.This method can provide an effective means for analyzing the NMR spectra of complex macromolecules.(2)Aims at the special four-spin system in the lactic acid molecule.The nuclear spin singlet sequence was prepared by designing hard pulses and optimized pulses,and combining this method with imaging technology to achieve selective filtering of lactic acid molecules Imaging.(3)Apply the singlet's long-lived characteristic to the measurement of diffusion coefficient,and analyzes the advantages of this method and the source of error.At the same time,singlet molecules are used as probes to realize the measurement of the diffusion coefficient of the solution in the porous material under the condition of non-uniform field.In summary,this article discusses the influence of the coupling of the spin system on the efficiency of the singlet preparation.And realize the singlet-state 2-D spectrum and magnetic resonance imaging of target molecules.At the same time,it has also been verified that the long-life characteristics of the single state make it have a unique advantage in diffusion measurement.