A method for simultaneous multi-zone focusing along multiple scan lines using orthogonal codes and its application to multi-dimensional array imaging

A method for achieving simultaneous transmit multizone (STMZ) focusing along multiple scan lines using orthogonal codes is presented. To demonstrate the performance of the proposed method, we performed experiments using a 192-element linear array transducer with the center frequency of 7.5MHz, 6dB bandwidth of 60% and element pitch of 0.2mm. We used Golay codes of length 8 (M=2, N=8) and two chirp signals with frequency bands 3.5 MHz 8.2MHz and 11.5 MHz 6.8 MHz, with different focusing delays for two transmit foci at 2cm and 5cm. The experimental results showed that the proposed method can produce simultaneously four beam vectors along two scan lines. We also observed that the proposed method provides almost the same lateral resolution compared to the conventional multi-zone pulse echo imaging, with higher frame rate and SNR. Computer simulation study also showed that multi-zone focusing in the elevation direction on transmission can be achieved without sacrificing frame rate, which contributes greatly to improving the efficacy of multi-dimensional arrays.