Binary apodization schemes for plane wave transmits

Traditionally, diagnostic ultrasound uses focused beams on transmit and receive. In contrast, modern systems (both research and clinical) are transitioning towards high frame rate sequences that insonify the entire field of view and sample the backscattered energy on all system channels in parallel. Full-field transmit beams (e.g. plane waves or wide spherical waves) are known to have a trailing wave that lags behind the main wavefront, adding clutter to the image. The trailing wave can be suppressed using Tukey apodization on transmit. However, most hardware cannot transmit continuous apodization profiles. Binary (on/off) apodization schemes present a possible alternative. Several binary apodization schemes were evaluated using Field II simulations. The simulations were compared using several metrics, including relative trailing wave amplitude and CNR in anechoic cyst phantoms. Results indicate that, as expected, plane wave image degradation is largely due to high side lobe levels. However, the results also demonstrate that there are additional impacts from the trailing wave, which can be suppressed in some cases. The trailing wave suppression by binary apodization is highly depth dependent, and the most efficient way to improve image quality metrics is to reduce the lateral extent of the plane wave.