Quantitative radial imaging of porous particles beds with varying water contents

Radial imaging protocols suitable for monitoring water transport in biopolymer and food materials during processes such as drying and rehydration are developed and tested on a well-characterized model sample. This model consisted of a randomly packed bed of Sephadex beads with varying water content. The results are interpreted with theoretical models for the dependence of the initial water magnetization, transverse relaxation, and diffusive attenuation on water content for two slice-selective radial imaging pulse sequences. It is shown that volume shrinkage and changes in packing density complicate the dependence of the initial magnetization on water content, so that the transverse relaxation rate provides the most reliable monitor of water content. Radial imaging is shown to offer many advantages over conventional two-dimensional imaging whenever the sample can be made with cylindrical symmetry.