MRI edge enhancement as a diffusive discord of spin phase structure

The enhancement of magnetic resonance image intensity near impermeable boun daries can be nicely described by a new approach where the diffusional spin echo attenuation is linked to the correlation function of molecular motion . In this method the spin phase structure created by the applied gradient i s considered to be a composition of plane waves with the wave vectors repre senting feasible momentum states of a particle in confinement, The enhancem ent of edges on the magnetic resonance images (MRI) comes out as a discord of plane waves due to particle motion, It results from the average of the w ave phase by using the cumulant expansion in the Gaussian approximation. Th e acquired analytical expression describes the MRI signal space distributio n where the enhancement of edges depends on the intensity and the duration of gradient sequence as well as on the length of the mean squared particle displacement in restricted geometry. This new method works well with gradie nts of general waveform and is, therefore, suitable for imaging sequences w here finite or even modulated gradients are usually used. (C) 1999 Academic Press.