Conventional pulse-echo imaging systems used in ultrasonics can become limited in average transmit power by transmitter, transducer, and medium peak-power limitations. In addition, imaging systems which use multi-element arrays are limited in speed by the necessity to transmit sequentially when scanning in more than one direction in order to avoid interfering echoes. A new system is studied which can overcome both the speed and power limitations by using correlation receivers and pseudo-random transmit codes. First, the performance of several single-mode correlation systems are compared to conventional pulse-echo systems in the presence of clutter and moving targets. The system which uses special pseudo-random codes called Golay codes is shown to provide the best overall performance. A multi-mode correlation system is then studied which images in many different modes (e.g. scan directions) simultaneously. This multi-mode system is studied under the effects of moving targets, clutter and background receiver noise. A comparison with the operation of Conventional sequentially-scanned phased array systems is made under a variety of signal-to-noise ratio (SNR) conditions and operating speeds to determine the optimal type of imaging system. Results indicate that under many conditions, a simultaneous multi-mode system can provide improved SNR and/or speed over conventional sequential multi-mode systems. The multi-mode system which uses Golay codes is shown to provide the best overall performance

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