A sum-of-harmonics time-domain method to distinguish harmonic and broadband signals during passive acoustic mapping of ultrasound therapies

Passive Acoustic Mapping (PAM), a novel technique for real-time monitoring of ultrasound-based therapies, performs passive beamforming of nonlinear acoustic emissions simultaneously received on an array of transducers. These emissions can be classified according to their frequency content into harmonic, indicative of nonlinear scattering, stable cavitation or tissue boiling, and broadband, indicative of inertial cavitation. However, the magnitude of coherent reflections often greatly exceeds that of incoherent broadband emissions arising from inertial cavitation and the ability to distinguish these two components is, thus, key to successful detection and mapping of inertial cavitation. We propose a novel time-domain-based filter that uses a parametric model in order to estimate a time-varying amplitude harmonic component in the presence of a lower-amplitude broadband signal. Performance evaluation on simulated and experimental data has shown that the model is able to accurately detect a time-varying ampli...