Scanning techniques in grey-scale ultrasonography

In the past two years the technological basis of ultrasonic diagnosis has developed rapidly in the direction of grey-scale imaging. Hitherto ultrasonic imaging has been directed primarily at twodimensional display of the relatively large ultrasonic echoes that are returned by major organ interfaces: the new development aims at displaying, in addition, the relatively weak echoes that arise from the fine structure of tissues themselves. Such a technique results in the visualization of the consistency of the organ rather than its mere outline. This permits differential diagnosis of diffuse pathologies which are recognized by the specific pattern produced by each pathological process. Thus, in liver for example, the appearances of fatty infiltration, cirrhosis, diffuse lymphocytic infiltration, malignant infiltration, chronic inflammatory changes and viral hepatitis may be separately differentiated. There is an important practical implication of this new approach, which arises from the process by which the echoes are caused. Echoes from major organ interfaces, such as the fetal skull, appear to result from a process akin to specular reflection of light and are thus seen most efficiently where the ultrasonic beam strikes the interface at normal incidence, and it is this concept that has given rise to the technique of “compound scanning”, in which an attempt is made to angle the transducer so as to find the maximum echo (Donald, McVicar and Brown, 1958).