Refocusing dual-mode ultrasound arrays in the presence of strongly scattering obstacles

This paper provides a first experimental verification of the use of image-based feedback for refocusing the therapeutic beam in the presence of strongly scattering objects. This capability may be critical in the use of dual mode ultrasound array (DMUA) systems for noninvasive targeting of liver tumors and noninvasive cardiac ablation. In both cases, the target is partially obstructed by the rib cage, which limits the access and distorts the geometrically-focused high-intensity focused ultrasound (HIFU) therapeutic beam. The optimization procedure is based on the use of single-transmit focus (STF) imaging, in which a single transmit imaging beam employing delays derived from phasing for the therapeutic beam is used. We present experimental results of a DMUA refocusing algorithm that selects the control points from the target(s) and the ribs visible in the STF image. In addition, STF images before and after refocusing provide similar feedback by consistently showing increased echogenicity of the target region while the echogenicity of the ribs is not increased (often reduced).