ESTIMATION OF THE EFFECTIVE SELF-DIFFUSION TENSOR FROM THE NMR SPIN-ECHO

The diagonal and off-diagonal elements of the effective self-diffusion tensor, D(eff), are related to the echo intensity in an NMR spin-echo experiment. This relationship is used to design experiments from whic h D(eff) is estimated. This estimate is validated using isotropic and anisotropic media, i.e., water and skeletal muscle. It is shown that s ignificant errors are made in diffusion NMR spectroscopy and imaging o f anisotropic skeletal muscle when off-diagonal elements of D(eff) are ignored, most notably the loss of information needed to determine fib er orientation. Estimation of D(eff) provides the theoretical basis fo r a new MRI modality, diffusion tensor imaging, which provides informa tion about tissue microstructure and its physiologic state not contain ed in scalar quantities such as T1, T2, proton density, or the scalar apparent diffusion constant. (C) 1994 Academic Press, Inc.