Acoustic holography for calibration of ultrasound sources and in situ fields in therapeutic ultrasound

Abstract

Therapeutic ultrasound sources, which are typically piezoelectric transducers, are intended to deliver known acoustic pressures to targeted tissue sites. Each transducer vibrates in a unique way and radiates a corresponding 3D ultrasound field. Accordingly, transducer vibrations should be known accurately in order to characterize the pressures delivered to the patient. Acoustic holography is a technique that relies on hydrophone measurements to reconstruct a source hologram that characterizes transducer vibrations [Sapozhnikov et al., JASA, 138(3), 1515–1532 (2015)]. In this way, a hologram is a signature of each transducer that can be monitored over time for quality assurance. Using holography-defined source boundary conditions, numerical forward projection of the ultrasound field based on the nonlinear wave equation can be used to accurately predict in situ temperatures and pressures in heterogeneous media for treatment planning. As such, acoustic holography goes beyond simple hydrophone scans and is uniquely suited to meet clinical needs for quantifying therapeutic ultrasound fields. In this paper, several examples of acoustic holography implementation are presented, including the characterization of single-element and multi-element flat and spherically curved sources working in linear and nonlinear regimes and in continuous and pulsed modes. [Work supported by NIH 1R01EB025187, R01EB007643, and R21CA219793; RFBR 17-02-00261 and 17-54-33034.]