Noise robust ASR

A composite stent device comprises a shape memory alloy stent sleeve which is treated so that it can exert an outward force on a lumen in which the stent device is to be deployed, and a restraint element which restricts the maximum transverse dimension to which the stent sleeve can expand outwardly. The restraint sleeve can minimize damage to a lumen by a stent located within it. It can be arranged to allow the stent device to be deformed in a bending mode, for example when the lumen in which the device is located is subjected to a transverse flattening deformation, relying on the enhanced elastic properties of the shape memory alloy stent sleeve to recover to the open, generally rounded configuration.