ABSTRACT

Acoustic inhomogeneity of soft tissue induces wavefront distortion which in turn causes image degradation. Wavefront distortion includes amplitude and phase distortion. Many adaptive compensation algorithms have been developed in the literature; they correct phase distortions and leave co-existing amplitude distortion intact. Amplitude distortion produces a significantly high background level in the image which causes low contrast lesions to appear “speckled”. A toward inverse filtering (TIF) technique has been developed in the frequency domain which compensates frequency dependent amplitude distortion in combination with phase deaberration. The well-known inverse filtering (IF) technique is optimal for imaging fidelity but it is unstable. TIF approaches the IF performance while demonstrating adequate stability. One-way experiments with a 2-D aperture and breast specimens have demonstrated that TIF represents a substantially improvement in contrast resolution. The sidelobe level of the system point-spread function has been restored to -30 dB level. Two-way experiments with 1-D array and a standard testing phantom have shown that low contrast lesions have been resolved with better contrast by TIF compared with phase deaberration alone. In this paper, we briefly review phase deaberration algorithms developed by other groups, and we introduce the TIF technique.