Abstract

High-Contrast Pulse-Echo Ultrasonic Imaging with Post-Beamforming Nonlinear Filters

E.S.Ebbini, P.Phukpattarnont, H.Yao (Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, USA)

e-mail: emad@ece.umn.edu

We introduce a system-identification post-beamfroming nonlinear filter approach to pulse-echo ultrasonic imaging. Based on an assumed polynomial dynamic model for the pulse-echo beamformed data, optimal filter coefficients can be obtained by solving a minimum-norm least-squares problem. The model has been validated using simulations based on both the KdVB and KZK equations as well as experimental data with contrast agents in tissue and tissue-mimicking phantoms. Echoes with quadratic and higher order dependence can be separated to form high-contrast images of nonlinear medium without loss of spatial resolution. Furthermore, this signal separation is achieved without the need for multiple transmissions thus preserving the frame rate of the imaging system. It is shown that the system identification approach to nonlinear ultrasonic imaging is robust and can be applied to form nonlinear echo images throughout the imaging field, i.e., not confined to the ROI where the filter coefficients were computed. Image reconstructions from a variety of tissue media and using different array transducers demonstrate the superior contrast enhancement achieved using the post-beamforming nonlinear filter. Comparisons with other recently proposed methods for imaging nonlinear media (e.g., second harmonic and pulse inversion) will be used to illustrate the relative merits of our system identification approach.

Section : 5