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In vitro evaluation of an oscillating dual-mode ultrasound probe for sector imaging and directive therapy

Interstitial probes have been shown as effective devices to deliver high-intensity ultrasound therapy. Here, cylindrically-focused dual-mode transducers with either one or 5-elements were characterized, and a monoelement probe was evaluated in vitro. In therapy mode, the transducers were maximally efficient (≥70%) at 5.6 MHz with surface intensities up to 20 W/cm2. In imaging mode, fractional bandwidths were 46% and 50±4% (ave±std) for the monoelement and 5-element transducers respectively. Axial and lateral resolutions were 0.5 mm and 1.0 mm, respectively, for both transducers as measured with a point scatterer in the focal plane. After characterization, the oscillating probe was used to image and apply therapy to porcine liver. B-mode images over a 140° sector were formed before and after therapy, which was applied for 90 s at each of 5 angles separated by 20° (e.g. −40°, −20°, 0°, 20°, 40°) to form a composite lesion. Transducer surface intensity was 18 W/cm2. Therapy was interrupted at 125 ms intervals to collect pulse/echo data along the therapy axes. Data were displayed in real-time as an M-mode image to monitor therapy. B-mode images adequately represented the liver tissue. M-mode image data agreed well with the formation of lesions in the liver.