Passive acoustic mapping in aberrating media with the angular spectrum approach

Abstract

The ability to localize and characterize ultrasound-induced microbubble oscillations through the intact skull with high spatial and temporal resolution holds significant promise for the diagnosis and treatment of brain diseases and disorders. In this study, we investigated the ability of angular spectrum (AS) method, a fast planar projection method, to perform passive acoustic mapping of microbubbles through an intact skull. Finite-difference time-domain numerical simulations were used to model microbubble emissions’ propagation through homogeneous, stratified, and 2D inhomogeneous (skull) environments approximately 80 mm by 160 mm. Reconstructions with the AS approach were performed with constant and effective sound speeds, as well as with multi-step propagation, to evaluate their ability to correct for induced aberrations and localize the microbubbles. We also investigated the impact of the receiver position on the localization accuracy. Results for skull simulations indicated that the multi-step AS method reduced the error in axial localization of the microbubbles by on the order of 50% compared with the effective sound speed method, while incurring approximately a 25% increase in computation time for each doubling of the number of propagation steps. Both AS methods were several orders of magnitude faster than time-domain reconstruction. Further investigation of the potential of this approach to correct skull aberrations is warranted.