A method of detecting collisions between elements in a medical procedure
such as between a magnet and another element in the procedure mounting on
the medical device a flexible body within which is mounted one or more
parallel side by side optical fibers arranged such that the impact causes
bending of one or more of the optical fibers and detecting changes in
light transmission through the optical fiber to detect the bending and
thus the collision. The single fiber or fibers are located in a junction
between a lower body of resilient foam and a surface layer of a stiffer
flexible material.