Low-Loss Ultrasound Transmission Through Waveguide From Double Parabolic Reflectors (DPLUS) for Thermal Ablation

In this paper, to advance acoustic waveguide transducers towards practical thermal ablation applications, we studied DPLUS (double parabolic reflectors wave-guided ultrasonic transducer) with a 1-m long (0.6-mm radius) and low-loss fused quartz thin waveguide working at the optimal frequency of 2.2 MHz, and the thermal effects to the tissue under different ultrasound exposure time. The measured vibration attenuation coefficient of the fused quartz thin waveguide is $\sim 0.0123$ dB/MHz/cm, and such low-loss characteristic is one of the keys of the studied DPLUS for realizing thermal ablation. Under the transmitted axial vibration velocity amplitude $v_{\mathrm {max}}$ at the thin waveguide tip of 1 m/s and the ultrasound exposure time of 1 s, 5 s, 10 s, 20 s, the measured temperature rises in the chicken breast tissue showed good agreements with the simulation results. Lesions were observed in the tissue under the exposure of 10 s, 20 s, and 30 s. The lesion size increases with the exposure time but the measured axial and lateral widths of the lesions were smaller than 2 mm. The presented results in this paper showed that thermal ablation was achieved by a m-range long thin-waveguide DPLUS which becomes an important progress of DPLUS towards practical MIT applications.