Optimized receive filters and phase-coded pulse sequences for contrast agent and nonlinear imaging

Phase- or amplitude-coded pulse sequences are commonly used to discriminate linear form nonlinear scatterers or to enhance image quality by imaging spectral components that are due to nonlinear sound propagation. The transmit pulse sequences are designed so that a coherent, weighted summation of the resultant echoes followed by a demodulation enhances the image contrast between nonlinear and linear scatters or the separation of higher harmonics from the fundamental. Because of limitations in the signal generation in ultrasound scanners and unknown effects of the sound propagation, experimental results do not agree with those of simulations. Separate receive filters for each of the echoes can compensate for the above-mentioned shortcomings and unknown factors. In this paper, an algorithm for the design of FIR filters based on training data is presented and experimental results are discussed.