Clutter suppression for harmonic Doppler detection in swept-scan high-frequency system

In high-frequency swept-scan Doppler system, the spectral broadening of tissue clutter limits the detectability of low-velocity flow signal. Conventionally, the scanning speed of transducer has to be reduced to alleviate the clutter interference but at the cost of imaging frame rate. With third harmonic (3f₀) transmit phasing, the tissue harmonic clutter is suppressed and the cut-off frequency of wall filtering can be reduced to preserve low-velocity flow without compromising the frame rate. Our results indicate that the 3f₀ transmit phasing effectively reduces the harmonic clutter magnitude and thus improves the flow signal-to-clutter ratio. Compared to the conventional counterpart, the clutter-suppressed color flow and power Doppler images show fewer clutter artifacts and is capable of detecting more low-velocity flow of microbubbles. The resultant color-pixel-density also improves with clutter suppression. For the swept-scan high-frequency system, 3f₀ transmit phasing is capable of providing effective clutter suppression. With the same achievable scanning speed, the resultant Doppler image has higher sensitivity for low-velocity flow and is less susceptible to clutter artifacts.