Shadowing and enhancement in ultrasonic echograms by reflection and refraction.

The action of reflection and refraction in producing shadows and enhancement in ultrasonic echograms behind cystic structures is well known, but the physical explanations usually used are incomplete. In this paper the emergent beam patterns for a number of cases are plotted and this data used to explain the shadows and enhancement observed. Cases are also illustrated of echoes displayed incorrectly within the shadow region and of reflectors within the shadow region displayed elsewhere. The use of the echographic appearances to assess the velocity of propagation in cystic structures is described.