A new method for multidirectional motion detection and display in a re
al-time ultrasonic scanner is presented. The image is generated by a s
uperposition of a grey scale image representing static structures and
a colour-coded pattern representing the displacement amplitude of the
moving interfaces. This is a truly duplex system where the image is ev
aluated for both interface motion and static structures. The displacem
ent detection, based on image subtraction. features high accuracy and
high signal to noise ratio, since the technique displays in colour onl
y the regions where the changes occur, and all other echoes representi
ng static structures are cancelled. The technique is able to detect an
y slow interface motion within the image area with a resolution of 0.0
1 mm. The flexibility of the design allows the module to be used as a
stand alone unit or to be incorporated in existing ultrasonic equipmen
t.