Session: P1C

the superiority of the quadratic images to second harmonic (SH) images in phantoms, both in terms of spatial and contrast resolutions. Furthermore, we have shown that the quadratic images produce contrast-to-tissue ratios (CTRs) at the same level of those produced by pulse inversion (PI) without the need for multiple transmission. The imaging results have also shown that quadratic imaging also allows for using transmission pulses utilizing the full bandwidth of the transducer (thus preserving the spatial resolution). In addition, quadratic filtering is effective in reducing additive Gaussian noise compared to linear filtering leading to quadratic images with increased dynamic range. An algorithm for extracting the coefficients of the quadratic kernel from the beamformed data was developed and shown to be robust and sensitive to the presence of nonlinear echoes at levels of -20 dB or more below linear tissue components. In this paper, we present the first verification of the contrast enhancement achieved in vivo. Images of the kidney of a juvenile pig were obtained before and after infusion of contrast agent (SonoVue, Bracco, Geneva, Switzerland) at various concentrations. For example, at a concentration of 0.01 ml/Kg, B-mode images (3 cycles at 1.56 MHz transmit frequency) show no quantifiable change due to the presence of the contrast agent. PI images without SH filtering showed 10 dB enhancement and evidence of residual tissue components due to motion. SH imaging on PI data produced 14 enhancement with some loss in resolution. On the other hand, quadratic filtering produced 23 dB enhancement at twice the frame rate. This performance was achieved with quadratic filters derived using a new algorithm leading to a computationally efficient separable implementation of the quadratic kernel. This implementation should allow for real-time implementation of quadratic filtering on commercial ultrasound scanners. Funded by grant from Esaote, S.p.A., Genoa, Italy.