Chemical analysis by ultrahigh-resolution nuclear magnetic resonance in the earth's magnetic field

High-resolution NMR spectroscopy is a powerful tool for non-destructive structural investigations of matter(1). EM Typically, expensive and immobile superconducting magnets are required for chemical analysis by high-resolution NMR spectroscopy. Here we present the feasibility of liquid-state proton (H-1), lithium (Li-7) and fluorine (F-19) ultrahigh-resolution NMR spectroscopy' in the Earth's magnetic field. We show that in the Earth's field the transverse relaxation time T, of the Li-7 nucleus is very sensitive to its mobility in solution. The J-coupling constants(3) of silicon-containing (Si-29) and fluorine-containing molecules are measured with just a single scan. The accuracy of the measured H-1-Si-29 and H-1-F-19 J-coupling constants is between a few millihertz up to 20 mHz. This is at least one order of magnitude better than the precision obtained with superconducting magnets. The high precision allows the discrimination of similar chemical structures of small molecules as well as of macromolecules

Magnetic resonance temporal diffusion tensor spectroscopy of disordered anisotropic tissue

Molecular diffusion measured with diffusion weighted MRI (DWI) offers a probe for tissue microstructure. However, inferring microstructural properties from conventional DWI data is a complex inverse problem and has to account for heterogeneity in sizes, shapes and orientations of the tissue compartments contained within an imaging voxel. Alternative experimental means for disentangling the signal signatures of such features could provide a stronger link between the data and its interpretation. Double diffusion encoding (DDE) offers the possibility to factor out variation in compartment shapes from orientational dispersion of anisotropic domains by measuring the correlation between diffusivity in multiple directions. Time dependence of the diffusion is another effect reflecting the dimensions and distributions of barriers. In this paper we extend on DDE with a modified version of the oscillating gradient spin echo (OGSE) experiment, giving a basic contrast mechanism closely linked to both the temporal diffusion spectrum and the compartment anisotropy. We demonstrate our new method on post mortem brain tissue and show that we retrieve the correct temporal diffusion tensor spectrum in synthetic data from Monte Carlo simulations of random walks in a range of disordered geometries of different sizes and shapes