Dual-mode 5-element transducer for image-guided interstitial ultrasound therapy: In vitro evaluation

Interstitial probes With dual-mode transducers are effective devices to guide and monitor With Ultrasound imaging the application of ultrasound therapy. Here, a dual-mode 5-element transducer, with oscillatory motion for sector imaging and directive therapy, Was characterized and evaluated in vitro with porcine liver. The transducer had 3.8x3.0-mm(2) elements, a 20x3.0-mm(2) aperture, and was cylindrically focused to 14-mm. In therapy mode, elements were maximally efficient, 72 +/- 4% (ave +/- std), at 5.6-MHz. In imaging mode, the pulse-echo impulse response for cacti electrically-matched element was 160 +/- 16 ns long at -6 dB, and insertion loss Was minimally 9.8 +/- 0.5 dB at 5.2-MHz. Electrical crosstalk was less than -57 dB at 5.6-MHz. Lateral resolution, measured by scanning a wire of 0.1-mm diameter wire though file focal plane, was 1.0-mm at -6 dB. During experiment, an initial B-mode image was formed over a 140 degrees sector. Then, therapy Was applied for 90 s, with 18-W/cm(2) transducer surface intensity, at each of 5 angles (Delta theta=20 degrees) to form volumes of composite protein denaturization. Pulse-echo data were collected periodically to monitor therapy with real-time M-mode imaging. After therapy, another B-mode image was formed, and the depth of protein denaturization was measured by gross histology. B-mode images adequately represented the liver structure. Analysis of M-mode images was consistent with gross histology.