A new extended range ultrasonic synthetic aperture tissue harmonic imaging system

Tissue harmonic imaging(THI) has been widely used in the diagnostic ultrasonic imaging system thanks to its benefits such as lowered artifacts and improved contrast resolution. Recently we reported that the THI can be successfully combined with synthetic aperture imaging(SAI) to improve the signal-to-noise ratio(SNR) of the THI. Nevertheless, conversion of the propagating ultrasound in the tissue to the harmonic component is concentrated mainly around the transmission(Tx) focal point. This limits the effective imaging range of the THI. In order to mitigate this issue, we propose new SAI methods which utilize distributed virtual sources to spread out the conversion of harmonic components of the propagating wave. As an example, two new SAI methods are proposed, where one method maximizes SNR with cost of frame rate, while the other method compromises SNR and frame rate. The usefulness of these methods is verified through computer simulations using both PZFlex and Field II, and the results show that the proposed methods can extend the effective range successfully.