What might echography learn from image science?

We review the current state of knowledge of the processes by which the information content of ultrasonic pulse-echo images is transferred to an observer, to the point of contributing to diagnostic judgments. As systematic knowledge in this specific field is rather sparse, we present relevant information and techniques derived from other areas of image science, both medical and otherwise. Quantitative measures both of the information content of ultrasonic and other images and of their characteristic noise content are first considered. An account is then given of the relevant aspects of human visual psychophysics, with particular reference to perception of contrast and detail, image texture, movement and colour, again with emphasis on documenting quantitative aspects of such behaviour. Against this background, we consider the efficiency, in current practice, of image information transfer to a human observer, how and to what extent this could be improved by changes in practice and, in particular, in what situations substantial innovations in machine processing of image data would be expected to improve human performance. It is suggested that several problems in the field may provide a worthwhile and challenging scope for future research.