Diffusion spin echo suppression in the presence of inhomogeneous gradients

A spin echo is usually expected to exhibit a maximum at a time 2τ, where τ is the pulse spacing; for high diffusivities in presence of linear gradients, however, a maximum is observed at times 2 τ . Here we show that in the presence of non-linear gradients a strong departure from the linear case is obtained. For long echo times a plateau for the maximum signal time is reached, thus a diffusion correlation time dependent both on the diffusion coefficient and the gradients strengths can be defined. Results for laser polarized 3He and 129Xe are compared with Monte Carlo simulations.