Analysis of MRI images of a silicone elastomer under different axial loading conditions

Silicone elastomers have been used as implants in orthopaedics for replacements of small joints such as the metacarpophalangeal joint. A series of experiments was conducted an axially tensioned silicone elastomer tendon spacer samples to determine whether there is a relationship between stress in the material and image intensity. With increasing load, reduced image intensites were observed using spin echo (SE), gradient echo (GE) and magnetic resonance imaging (MRI) snapshot techniques. MR attenuation was accentuated in the GE experiment. The T1 and T2 snapshot images were dim and showed a low signal-to-noise ratio, so analysis was limited. Changes in magnetic susceptibility are suggested as the mechanism causing reduced image intensity, due to the more pronounced attenuation in the GE image. An alternative mechanism is the alteration of crystallinity during loading, whereby molecular realignment modifies nuclear relaxation. The changes in spin-lattice (T1) and spin-spin (T2) relaxation times, which would support this, were not, however, satisfactorily demonstrated.