Suppression of Static Magnetic Field in Diffusion Measurements of Heterogeneous Materials

The paper describes a magnetic resonance (MR) method for establishing the diffusion coefficients in heterogeneous materials. The pulsed field gradient stimulated-echo methods have a reduced coupling between the applied magnetic field gradient and a constant internal magnetic field gradient caused by different susceptibilities throughout the sample. When studying systems where it is necessary to keep the duration of the pulse sequence at a minimum or to study diffusion as a function of observation time, the spin-echo method should be chosen. The basic idea is to acquire the spin echo amplitude with pulsed field gradient of opposite signs and to subtract in a suitable way the NMR signals measured. The measuring method and the digital signal processing enable eliminating the effect of static magnetic field on the accuracy of measuring. The method proposed can be used to measure diffusion-weighted images of liquids found in porous materials, and in the development of new MR tomography measuring methods in the Institute of Scientific Instruments of the Academy of Sciences of the Czech Republic, v.v.i.