1. An E-mode imaging apparatus comprising: a compressor adapted to apply a varying deformation to a material to be imaged; an image acquisition system collecting a series of images of the material to be imaged during different stages of deformation by the compressor; an electronic computer receiving the series of images to calculate E-mode images indicating a stiffness of the material with a quality value indicating a quality of E-mode data obtainable from a currently acquired subset of the series of images; and an output of the quality value for adjusting the varying deformation to improve the quality of E-mode data; wherein the compressor is manipulable by an operator and the output is an operator interface providing a real-time representation of the quality value selected from the group consisting of: a displayed number, a displayed visual gauge, a displayed indicator light, an audio signal; and wherein the quality value is a combination of at least two different types of measurements of information obtainable from the subset including: (1) a comparison that compares a correlation of the images corrected for relative compression of the images; and (2) a comparison that compares at least one of: (a) similarity among derived E-mode images; and (b) information content of at least one derived E-mode image.