Tissue harmonic compounded imaging with dual-frequency chirp excitation

Dual-frequency (DF) transmit waveform comprises of signals at both fundamental frequency (f₀) and second harmonic frequency (2f₀). With the DF transmit waveform, tissue harmonic imaging can be simultaneously performed not only using the conventional 2f₀ second harmonic signal but also the f₀ frequencydifference harmonic signal. Nonetheless, when chirp excitation is incorporated into the DF transmit waveform for improvement of harmonic SNR, particular waveform design is required to maintain the bandwidth of the f₀ harmonic signal. In this study, two different chirp waveforms (i.e., UD11 and UU13) are proposed to provide the desired signal bandwidth. Experimental results indicate that the UU13 tends to suffer from high range side lobe level due to severe 3f₀ interference. Consequently, the 2f₀ harmonic envelope of the UD11 is consistently superior to that of the UU13 while the quality of the f₀ harmonic envelope remains similar between the two DF transmit waveforms. B-mode harmonic images also show that the UD11 is less susceptible to range side lobe artifacts than the UU13. Therefore, it is concluded that the UD11 waveform is a better solution for chirp-encoded DF harmonic imaging.