Time sidelobe reduction of pulse-compressed parametric ultrasound with maximum-length sequence excitation

In this study, maximum-length sequence (M-sequence) excitation was applied to parametric ultrasound with pulse compression to reduce artifacts caused by time sidelobes in low-frequency ultrasound imaging. A modulated primary ultrasound at a carrier frequency of 2.8 MHz was used to generate a 400-kHz parametric ultrasound coded by an M-sequence with a chip length equal to one cycle of a 400-kHz signal for experiments in water. Increasing the order of the M-sequence reduced the time sidelobes of the compressed parametric ultrasound signal and clearly separated the front and rear surfaces of an acrylic plate in the A-mode image. Moreover, the waveform of parametric ultrasound method was less affected by the ringing of a transmitter, and the attenuation in a medium was smaller than that obtained by the high-frequency ultrasound method at 2.8 MHz. These results suggest that the M-sequence excitation is well-suited for low-frequency parametric ultrasound imaging with reduced time sidelobes. (C) 2018 The Japan Society of Applied Physics