In Situ Measurement of Acoustic Attenuation for Focused Ultrasound Ablation Surgery Using a Boiling Bubble at the Focus

Objective: Acoustic attenuation in the propagation path of focused ultrasound ablation surgery determines the energy loss toward the focal region and is critical to the consequent treatment outcomes. In situ non-invasive, reli-able, and accurate measurement is challenging for multi-layered heterogeneous tissues within the focusing angle.Methods: A novel measurement approach is proposed and its performance is evaluated using ex vivo porcine ten-derloin and bovine heart. A big boiling bubble (i.e., larger than a few millimeters in size) was produced at the focus as a strong reflector inside the tissue, and the echo amplitudes were used to determine the acoustic attenua-tion. Two models, acoustic ray and energy loss, were developed to derive the equivalent acoustic attenuation coef-ficient for a focused beam.Results: The measured acoustic attenuation coefficients of ex vivo porcine tenderloin and bovine heart at 0.97 MHz and a thickness of 3 cm are 0.159 +/- 0.002 and 0.250 +/- 0.005 Np/cm, respectively, which are all within the scope of measured values in the literature. In addition, the echo amplitude is sensitive to the conditions of the propaga-tion path, and the inverse acoustic attenuation coefficient of the silicone gel pad placed in front of the tissue sam-ple was 0.807 +/- 0.002 Np/cm, which is comparable to the measurement using the insertion substitution method, 0.766 +/- 0.003 Np/cm.Conclusion: Our proposed approach could determine the tissue acoustic attenuation for focused ultrasound abla-tion surgery reliably and accurately in situ. The easy operating protocol may allow clinical translation and adop-tion for improved safety and efficacy.