Multibeam Simultaneous Transmit Multizone (MB-STMZ) focusing method using modulated orthogonal codes for ultrasound imaging

In this paper, a novel method for simultaneous transmit multi-zone (STMZ) focusing along multiple scan lines using modulated orthogonal codes is presented. In this method, M mutually orthogonal Golay codes are transmitted along M respective directions to obtain M scan lines simultaneously, where each Golay code consists of M complementary sequences. This implies that along each scan direction M complementary sequences comprising one of the Golay code are to be fired sequentially. Therefore, total M transmit and receive (T/R) events are required to obtain M scan lines. In the proposed method, however, each complementary code is convolved with the sum of L orthogonal chirps that are focused at L different depths. Consequently, the proposed method requires M T/R events to obtain M scan lines with L transmit foci each, whereas ML T/R events are required in conventional pulse echo imaging. After M firings, first the M orthogonal Golay codes are separately compressed, secondly each compressed Golay signal is correlated with L respective orthogonal chirps, and finally the L compressed chirp signals are independently focused and combined to provide the dynamically focused beams along M scan lines, each with multi-zone transmit foci. Experimental results with a 7.5MHz linear array, for M=L=2, showed that the proposed method can provide ultrasound images with higher frame rates and significantly improved SNR compared to conventional multi-zone focusing methods using short pulses.