Delay-encoded harmonic imaging (DE-HI) in multiplane-wave compounding

Ultrafast ultrasound imaging offers great opportunities to new imaging technologies such as shear wave elastography and ultrafast Doppler. Multiplane wave (MW) imaging is a new technique in which multiple positively or negatively encoded plane waves are emitted successively with short interleaved time during one transmission event (i.e. pulse-echo event), aiming at increasing the signal-to-noise ratio (SNR) of ultrafast imaging. However, the long transmit pulses of MW imaging also increase the reverberation artifacts. Here we propose a delay-encoded harmonic imaging (DE-HI) technique to enable HI for MW imaging to reduce reverberation. DE-HI encodes the 2^nd harmonic signals with transmit delays rather than reversing the pulse polarities, thus addressing the MW encoding challenge that the 2^nd harmonic polarity is independent of transmit pulse. DE-HI improves the ultrafast imaging by reducing the reverberation with HI and increasing SNR by emitting multiplane waves.