Retrospective Transmit Correction of Blocked Arrays Applied to Cardiac Ultrasound Imaging.

The acoustic window used for transthoracic echocardiography (TTE) is limited by the space between the ribs. Therefore, a common source of artifacts in TTE is aperture blockage. In this article, we demonstrate that aperture blockages reduce the image quality and lead to depth-varying geometrical distortions that tilt structures and increase the sidelobe levels. We also propose a method to compensate for the blocked array in the retrospective transmit beamforming (RTB) by changing the beam weighting. The array blockage for individual transmit directions is detected from the received power in each channel. The estimated array blockage is used to modify the RTB weights to compensate for the rib blockage by correcting the masking of the region insonified by a single transmit beam. In addition, a correction using the retrospective encoding for conventional ultrasound sequences (REFoCUS) algorithm is presented and produces a similar result to the proposed RTB correction. The method is validated both in simulations using Field II and experimentally using in vivo TTE data with rib blockage recorded using a GE Vivid E95 system and a 4Vc-D matrix array.