Applications of controlled-flow laser-polarized xenon gas to porous and granular media study

Biomedical imaging with hyperpolarized noble gases

Hyperpolarized noble gases (HNGs), polarized to approximately 50% or higher, have led to major advances in magnetic resonance (MR) imaging of porous structures and air-filled cavities in human subjects, particularly the lung. By boosting the available signal to a level about 100 000 times higher than that at thermal equilibrium, air spaces that would otherwise appear as signal voids in an MR image can be revealed for structural and functional assessments. This review discusses how HNG MR imaging differs from conventional proton MR imaging, how MR pulse sequence design is affected and how the properties of gas imaging can be exploited to obtain hitherto inaccessible information in humans and animals. Current and possible future imaging techniques, and their application in the assessment of normal lung function as well as certain lung diseases, are described.

Studying porous materials with krypton-83 NMR spectroscopy

This report is the first review of (83)Kr nuclear magnetic resonance as a new and promising technique for exploring the surfaces of solid materials. In contrast to the spin I = 1/2 nucleus of (129)Xe, (83)Kr has a nuclear spin of I = 9/2 and therefore possesses a nuclear electric quadrupole moment. Interactions of the quadrupole moment with the electronic environment are modulated by surface adsorption processes and therefore affect the (83)Kr relaxation rate and spectral lineshape. These effects are much more sensitive probes for surfaces than the (129)Xe chemical shielding and provide unique insights into macroporous materials in which the (129)Xe chemical shift is typically of little diagnostic value. The first part of this report reviews the effect of quadrupolar interactions on the (83)Kr linewidth in zeolites and also the (83)Kr chemical shift behavior that is distinct from that of its (129)Xe cousin in some of these materials. The second part reviews hyperpolarized (hp) (83)Kr NMR spectroscopy of macroporous materials in which the longitudinal relaxation is typically too slow to allow sufficient averaging of thermally polarized (83)Kr NMR signals. The quadrupolar-driven T(1) relaxation times of hp (83)Kr in these materials are sensitive to surface chemistry, surface-to-volume ratios, coadsorption of other species on surfaces, and surface temperature. Thus, (83)Kr T(1) relaxation can provide information about surfaces and chemical processes in macroscopic pores and can generate surface-sensitive contrast in hp (83)Kr MRI.

Time-of-flight flow imaging using NMR remote detection

A time-of-flight imaging technique is introduced to visualize fluid flow and dispersion through porous media using NMR. As the fluid flows through a sample, the nuclear spin magnetization is modulated by rf pulses and magnetic field gradients to encode the spatial coordinates of the fluid. When the fluid leaves the sample, its magnetization is recorded by a second rf coil. This scheme not only facilitates a time-dependent imaging of fluid flow, it also allows a separate optimization of encoding and detection subsystems to enhance overall sensitivity. The technique is demonstrated by imaging gas flow through a porous rock.