ANALYSIS OF MRI IMAGES OF A SILICONE ELASTOMER UNDER DIFFERENT AXIAL LOADING CONDITIONS

Silicone elastomers have been used as implants in orthopaedics for rep lacements of small joints such as the metacarpophalangeal joint. A ser ies of experiments was conducted an axially tensioned silicone elastom er tendon spacer samples to determine whether there is a relationship between stress in the material and image intensity. With increasing lo ad, reduced image intensites were observed using spin echo (SE), gradi ent echo (GE) and magnetic resonance imaging (MRI) snapshot techniques . MR attenuation was accentuated in the GE experiment. The T-1 and T-2 snapshot images were dim and showed a low signal-to-noise ratio, so a nalysis was limited. Changes in magnetic susceptibility are suggested as the mechanism causing reduced image intensity, due to the more pron ounced attenuation in the GE image. An alternative mechanism is the al teration of crystallinity during loading, whereby molecular realignmen t modifies nuclear relaxation. The changes in spin-lattice (T-1) and s pin-spin (T-2) relaxation times, which would support this, were not, h owever, satisfactorily demonstrated. (C) 1998 Published by Elsevier Sc ience Ltd. All rights reserved.