Spatial inhomogeneities in the acoustic velocity of tissues degrade the contrast and resolution of diagnostic ultrasonic images. A system which iteratively adjusts the phase of signals transmitted and received from individual elements in a phased array scanner in order to restore image quality when imaging through inhomogeneous layers is described. The adjustments are selected to maximize a quality factor in an operator-selectable region-of-interest. The use of several quality factors in improving image quality, including the average local and the peak echo magnitude of diffuse and point-like targets and integral powers of these magnitudes were investigated. Theory and experimental results related to these investigations is presented.