Attenuation of MR spin-echo signal by restricted diffusion confined to a laminar system and a large rectangular box

We investigate magnetic resonance (MR) signal attenuation caused by confined by restricted diffusion confined to a laminar system and a large rectangular box using the pulsed gradient spin-echo MR method. Applying asymptotic expansions, we derive corrections up to order 1/L², where L is the characteristic system size, and show that in the limit of large L, the attenuation converges to the free diffusion expression. In the fast diffusion regime, where γ²G²δ²D∆≫1, interference effects become significant, limiting the applicability of the asymptotic expansion. Our findings refine diffusion-weighted MRI models and provide insights into confined molecular transport.