Post-beamforming Volterra filter for contrast agent imaging

We present a new algorithm for deriving a 2nd order Volterra filter (SVF) capable of separating linear and quadratic components from echo signals resulting from a single transmission covering the full (fundamental) bandwidth of the transducer. A robust algorithm for deriving the filter has been developed and tested on real-time imaging data from contrast and tissue-mimicking media. Comparisons with pulse inversion technique demonstrate that the SVF-based signal separation achieves comparable or higher levels of contrast enhancements without loss in spatial resolution. An important feature of images produced based on the quadratic component of the SVF is a significant increase in the image dynamic range compared to standard echo and pulse-inversion images. This is due to the fact that the quadratic component of the SVF filter combines a broad band of frequency components from low frequency and second harmonic components thus significantly reducing beam-forming artifacts. Furthermore, the quadratic Volterra kernel inherently rejects additive Gaussian noise. These properties were experimentally verified using a commercial scanner imaging with contrast agents in quality assurance flow phantoms.