The relationship of problems in biomedical MRI to the study of porous media

The NMR methods that are used to characterize inanimate porous media measur e relaxation times and related phenomena and material transport, fluid disp lacement and flow. Biological tissues are comprised of multiple small, flui d-filled compartments, such as cells, that restrict the movement of the bul k solvent water and whose constituents influence water proton relaxation ti mes via numerous interactions with macromolecular surfaces. Several of the methods and concepts that have been developed in one field of application a re also of great value in the Ether, and it may be expected that technical developments that have been spurred by biomedical applications of MR imagin g will be used in the continuing study of porous media. Some recent specifi c studies from our laboratory include the development of multiple quantum c oherence methods for studies of ordered water in anisotropic macromolecular assemblies, studies of the degree of restriction of water diffusion in cel lular systems, multiple selective inversion imaging to depict the ratios of proton pool sizes and rates of magnetization transfer between proton popul ations, and diffusion tensor imaging to depict tissue anisotropies. These i llustrate how approaches to obtain structural information from biological m edia are also relevant to porous media. For example, the recent development of oscillating gradient spin echo techniques (OGSE), an approach that exte nds our ability to resolve apparent diffusion changes over different time s cales in tissues, has also been used to compute surface to volume measureme nts in assemblies of pores. Each of the new methods can be adapted to provi de spatially resolved quantitative measurements of properties of interest, and these can be efficiently acquired with good accuracy using fast imaging methods such as echo planar imaging. The community of NMR scientists focus ed on applications to porous media should remain in close communication wit h those who use MRI to study problems in biomedicine, to their mutual benef its. (C) 2001 Elsevier Science Inc. All rights reserved.