Weak-Diffusion Theory of NMR Signal in Magnetically Heterogeneous Media

✍ Scribed by J.H. Jensen; R. Chandra

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 176 KB
• Volume: 126
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.1997.1178

✦ Synopsis

A general theory is developed for the effect of molecular diffufor the effects of diffusion to first order in D. A general sion on the NMR signal obtained from magnetically heterogeneous formulation is utilized that allows an arbitrary sequence of media in the limit of weak diffusion. The theory is based on a gradients and 180Њ spin-flip pulses to be considered, permitrigorous expansion in the diffusion constant D, with the correction ting a direct application to many of the complex sequences to first order in D being given explicitly for unrestricted, isotropic now employed for MR imaging.

diffusion. The expansion allows for an arbitrary sequence of field

The O(D) correction is shown to depend on two funcgradients and 180Њ spin-flip pulses, making it applicable to a wide tions, F 0 and F 1 , that are determined by the details of the variety of NMR protocols. The theory may be useful for estimating random magnetic field. As examples, explicit expressions the magnitude of diffusion effects and in determining some of a are obtained for F 0 and F 1 for a Gaussian random field and medium's microscopic magnetic properties. ᭧ 1997 Academic Press a field due to randomly distributed impurities. We also discuss in detail the effect of diffusion for the standard cases of free-induction decay and spin echo. Finally, we demon-193