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...http://www.google.se/patents/US5201715?utm_source=gb-gplus-sharePatent US5201715 - Implantable devices having ultrasonic echographic signature
