1. A motion tracking method for determining the location and orientation of at least one object being imaged by a medical imaging device and moving in space relative to a motion tracking device, comprising the steps of: affixing a target on the object; projecting a structured light pattern onto the target; receiving return light from the target through an optical receiver on the motion tracking device; converting the return light into a first digital image and a second digital image; and comparing the first digital image and the second digital image to obtain object motion information.