a target having a characteristic ultrasonic signature for implantation beneath the skin is described . the target , when placed within an implanted injection port enables ultrasonic echographic discrimination of the target from surrounding tissue . in particular , the target enables one to locate its position beneath the skin non - invasively by means of ultrasonic echograpy . in practice , the signature comprises reflections of ultrasonic waves from a target comprising varying thicknesses of a material having sound transmission characteristics different from human tissue . ultrasonic sound waves reflected from different surfaces of the target arrive at a detector with a characteristic time delay thereby providing a signature . biocompatible plastics , such as methacrylate , polysulfone , polytetrafluoroethylene or polyethylene , or elastomers such as silicone may be used for the target .