Ultrasonic Nonlinear Contrast-Enhanced Imaging Using Chirp-Coded Excitation and Volterra Filtering

Contrast-enhanced ultrasound imaging relies on nonlinear microbubble signatures for improved visualization of perfused regions. This study aims to enhance the detection of ultrasound contrast agent perfused regions by integrating chirp-coded excitation with nonlinear signal processing. In vitro experiments were conducted in a flow phantom and ex ovo in a chicken embryo using the commercial contrast agent SonoVue. Data were acquired across a range of agent concentrations, excitation pressures, and imaging depths. Radio frequency data were processed using fundamental and subharmonic matched filtering, followed by beamforming, singular value decomposition (SVD)-based clutter suppression, and cubic Volterra filtering. Imaging performance was quantified using contrast-to-tissue ratio (CTR) and axial width measurements. The combined approach of subharmonic matched filtering, SVD, and cubic Volterra filtering resulted in substantial improvements in CTR, with gains of up to 50 dB compared to SVD-enhanced subharmonic imaging across experimental conditions. Improvements were maintained at increased imaging depths, demonstrating robustness to attenuation. Experiments in the chicken embryo model showed an enhanced visualization of perfused structures. The integration of chirp-coded subharmonic excitation with SVD and Volterra filtering improves ultrasound contrast agent imaging performance. Significance: The proposed framework offers potential for advancing contrast-enhanced ultrasound imaging, including for deep targets and low signal-to-noise conditions.