Contrast artifact in CPS plane wave imaging using array subapertures

Contrast plane wave (PW) imaging has been recently proposed as an improvement in contrast imaging mode. The capability of acquiring contrast images with a high frame rate and with limited bubble destruction [1] led to novel investigation approaches such as the tracking of single bubbles in motion [2][3]. Some of these studies are based on classical contrast sequences using Pulse Inversion (PI) [2] or Contrast Pulse Sequence (CPS) mode [1]. The use of subaperture transmit is used to create half the amplitude in CPS sequence with clinical scanners due to technological limitations. However, subaperture transmit induces differences in the radiation pattern of the acoustic beam. Hence, when only half of the elements of the ultrasonic probe are used in transmit (subaperture), the form of the beam is no longer a plane wave and the assumptions for plane wave imaging are no longer really valid and acoustic artifacts occur. We investigate here the origin and the mechanisms behind these artifacts.