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Optimization of contrast sensitivity and specificity of quadratic ultrasonic imaging

We present a new algorithm of post-beamforming second order Volterra filter (SOVF) for deriving the quadratic kernel based on the convolution of the singular modes quadratic kernels which give the highest contrast-to-tissue ratio (CTRs) to extract quadratic components from ultrasound contrast agent (UCA) nonlinear echoes with single transmission. The new algorithm leads to reduction of tissue component and increase the specificity while optimizing the sensitivity to the UCA. The algorithm is demonstrated experimentally using images from in vivo kidney after bolus injection with UCA. Illustrative images of the kidney of a juvenile pig were obtained before and after infusion of contrast agent (SonoVue, Bracco, Geneva, Switzerland) at various concentrations. The imaging results given in this paper indicate that a signal processing approach to this clinical challenge is feasible.