Range side-lobe inversion for dual-frequency harmonic imaging with chirp excitation

Compared to conventional single-frequency harmonic imaging, dual-frequency harmonic imaging has been proposed by transmitting and receiving at both fundamental frequency (f₀) and second harmonic frequency (2f₀) to achieve spectral compounding for improved image quality. In our previous work, particular chirp excitation is developed to boost the harmonic generation for dual-frequency harmonic imaging while maintaining the harmonic signal bandwidths. However, spectral overlap between the harmonic imaging bands may lead to marked range side lobes and corresponding image artifacts. In this study, a range side lobe inversion (RSI) method has been developed to change the polarity of the range side lobes by firing an auxiliary chirp. When the original and auxiliary chirps are combined, the range side lobes can be eliminated. The RSI method has been verified using hydrophone measurement and B-mode imaging. When the signal bandwidth is 60 %, the compression quality improves by 16 % which corresponds to a 7-dB decrease of side-lobe-magnitude (SLM) in harmonic imaging. Therefore, the RSI method can effectively eliminate the range side lobes and suppress the image artifacts in DF harmonic imaging.