Dosimetry measurement of HIFU field using a fiber-optical probe hydrophone

Abstract

Characterization of the acoustic field of high-intensity focused ultrasound (HIFU) transducers by conventional PVDF membrane and needle hydrophones is problematic due to limited bandwidth, spatial averaging, and damage to the hydrophone. Here, we report the use of a self-calibrated fiber-optical probe hydrophone (FOPH-500) for HIFU dosimetry measure- ment. The hydrophone (0.1-mm sensing element) was scanned in the focal volume of a 1.1-MHz HIFU transducer (F=63 mm, f number=0.9) at 0.2-mm steps using a computer-controlled 3D positioning system. When the input voltage Vp−p applied to the transducer was increased from 28 to 225 volts, the peak compressive and tensile pressure values at the transducer focus were found to be P+=1.7–18.9 MPa and P−=−1.33–−8.14 MPa, respectively. The corresponding spatial peak intensities were calculated to be ISP=69–3968 W/cm2. Nonlinear propagation with harmonics generation was dominant at high intensity levels, leading to a reduced −6-dB beamwidth of the compressive wave from 1.8 to 1.3 mm and an increased −6-dB beamwidth of the tensile wave from 1.6 to 1.8 mm. Overall, FOPH-500 was found to be a reliable tool for characterizing the acoustic field of HIFU transducers.