Adaptive transthoracic focusing using dual‐mode ultrasound arrays.

Abstract

Dual‐mode ultrasound array (DMUA) systems have been recently shown to be capable of refocusing high‐intensity focused ultrasound beams in the presence of strongly scattering objects, e.g., the ribs. A refocusing approach based on a modified forward/inverse propagation operator accounting for the ribs was experimentally demonstrated. The propagation operator is obtained from DMUA‐based images of the target region, including the ribs. This image‐based approach to refocusing implicitly accounts for the heterogeneity by defining a propagation operator to the proximal rib surface using DMUA directivity vectors assuming a homogeneous medium. In this paper, we address the consequences of this simplification on the quality of the refocused beam. We also present an adaptive refocusing approach that identifies the inhomogeneous directivity vectors to the target location(s) in the presence of the ribs. Example experimental results will be presented using a true real time DMUA system where the adaptive refocusing is achieved within milliseconds. Implications on real time adaptive refocusing in the context of scanning multiple target points and motion compensation will also be discussed with illustrative experimental data.