Subharmonic threshold quantification of ultrasound contrast agents

Abstract

The measurement and prediction of the subharmonic threshold of ultrasound contrast agents is of significant interest, particularly for high frequency applications. Theoretical analytical predictions typically follow from a weakly nonlinear analysis assuming continuous, single frequency forcing. Furthermore, numerical simulation and experimental definitions are often based on the quantification of spectral response of the nonlinear harmonics. Limitations of these approaches are investigated with respect to pulsed forcing and associated non-stationary (chirp) excitations. Novel quantification and definitions are proposed with respect to instantaneous frequency and relative energy content of an empirical mode decomposition of the scattered pressure. Teager-Kasiser energy operator allows for additional quantification. The methodology is examined with respect to experimental polymer contrast agent data.