Generation of mutually orthogonal polyphase complementary sequences for use in ultrasound imaging

A pair of complementary sequences, such as Golay codes, is ideal for improving the SNR of ultrasound imaging, since a high amplitude impulse-like pulse can be obtained quite easily. However, pulse compression with a pair of complementary sequences suffers from low frame rate because it requires two transmit-and-receive (T/R) events for each scan line. In this paper, we present a new method for generating a set of complementary sequences that can be simultaneously transmitted and yet compressed into a short pulse on receive. In the present work, a pair of new complementary sequences is generated using the Jonston´s QMF bank design method. The sum of these complementary sequences has spread spectrum whose bandwidth is much wider than those of typical ultrasound transducers, which need to be modified to match with the transducer response. To this end, we also propose a modulation method that could maximize the transmit power efficiency (TPE) of the new orthogonal complementary codes. The new complementary sequences can be used to improve the SNR of ultrasound imaging without sacrificing the spatial resolution and frame rate, compared to conventional pulse-echo imaging. Computer simulations are performed to verify the proposed method.