Ultrasonic Multipath and Beamforming Clutter Reduction: A Chirp Model Approach

In vivo ultrasonic imaging with transducer arrays suffers from image degradation resulting from beamforming limitations, including diffraction-limited beamforming and beamforming degradation caused by tissue inhomogeneity. Additionally, based on recent studies, multipath scattering also causes significant image degradation. To reduce degradation from both sources, we propose a model-based signal decomposition scheme. The proposed algorithm identifies spatial frequency signatures to decompose received wavefronts into their most significant scattering sources. Scattering sources originating from a region of interest are used to reconstruct decluttered wavefronts, which are beamformed into decluttered RF scan lines or A-lines. To test the algorithm, ultrasound system channel data were acquired during liver scans from 8 patients. Multiple data sets were acquired from each patient, with 55 total data sets, 43 of which had identifiable hypoechoic regions on normal B-mode images. The data sets with identifiable hypoechoic regions were analyzed. The results show the decluttered B-mode images have an average improvement in contrast over normal images of 7.3 +/- 4.6 dB. The contrast-to-noise ratio (CNR) changed little on average between normal and decluttered B-mode, -0.4 +/- 5.9 dB. The in vivo speckle SNR decreased; the change was -0.65 +/- 0.28. Phantom speckle SNR also decreased, but only by -0.40 +/- 0.03.