Measuring water distribution in extrudates using magnetic resonance imaging (MRI)

Magnetic resonance imaging (MRI) has been applied to the evaluation of the distribution of water in extrudates produced by extruding pastes. Two model drugs similar in chemical structure were mixed with microcrystalline cellulose (MCC) and with two different amounts of water and extruded at two different extrusion speeds using a ram extruder. Extrudates were collected during the steady-state stage of the extrusion profile and were analysed for the water distribution using MRI. The percolation threshold for each sample was calculated to evaluate the degree of water structure within the sample. The water distribution inside the extrudates was surprisingly uniform. The extrudates produced using the faster extrusion speed had a significant lower percolation threshold, which suggests the existence of a greater water structure in the extrudates. A significant correlation was found between the percolation threshold and the extrusion force, which had been used to provide the extrudates. (C) 1999 Elsevier Science B.V. All rights reserved.