An ultrasonic imaging system includes an ultrasonic transducer having an image data array and a tracking array at each end of the image data array. The tracking arrays are oriented transversely to the image data array. Images from the image data array are used to reconstruct a three-dimensional representation...http://www.google.co.uk/patents/US6014473?utm_source=gb-gplus-sharePatent US6014473 - Multiple ultrasound image registration system, method and transducer
