Acoustic holography methods for characterizing transducers, fields, and materials in therapeutic ultrasound

Medical ultrasound applications typically involve megahertz frequencies and millimeter wavelengths in conjunction with centimeter length scales for sources and propagation distances. In this regime, holography techniques for source characterization based on a planar hydrophone scan and linear projection of the corresponding field are well known. However, topics of interest remain regarding practical implementation, e.g., acceleration of hydrophone scans, alignment of field reconstructions, and estimation of relevant uncertainties for inclusion in international standards. In addition, as modern tools facilitate the routine acquisition and processing of large holograms that fully capture an arbitrary beam and its angular spectrum, applications emerge beyond the characterization of therapeutic and diagnostic transducers. Such applications include (1) calculation of radiation force on a spherical particle that represents a kidney stone; (2) high-precision measurement of absorption and sound speed in layered materials without diffraction artifacts; (3) calculation of radiation force on a wide, absorbing target to enable more accurate calibration of hydrophone sensitivity with a radiation force balance; and (4) calibration of hydrophone directional responses by consideration of reference holograms measured with a small hydrophone. Here we describe implementations of holography across this range of applications with sample results. [Work supported by NIH, Grant R01EB025187.]