A Custom-Built Piezo-Optical System for Visualization and Characterization of High Intensity Focused Ultrasound

Abstract High intensity focused ultrasound (HIFU) is a noninvasive treatment technique to induce thermal or mechanical bioeffects. Characterising the wave field is essential for reliable and reproducible transducer operation in clinical use. This paper presents a schlieren technique to visualise and quantify transducer wave fields. The technique is based on the piezo-optical effect of water, i.e. the refractive index variation caused by sound pressure. Our custom-built system equipped with a Raspberry Pi HQ camera can capture schlieren photographs of acoustic fields generated by a clinical HIFU system. Alternatively, a high-speed camera allows analysis of short burst pulses. We investigated the focal zone shape of continuously generated HIFU fields at acoustic powers of 10- 250 W. Images of the focal area at 100 W indicated dimensions comparable to the reported literature values. Notably, as power increases, we observe waveform distortion in the focal zone due to nonlinear propagation of ultrasound. Our findings demonstrate the efficacy of our system in visualizing and characterizing the acoustic fields generated by a clinical HIFU device.