Abstract: The invention relates to apparatus which co-operate with an ultrasonic scanner. The apparatus includes a line dataprocessor which takes control of the activation of the ultrasonic crystals in the scanner head such that between each ultrasonic crystal activation for a viewing line on the image screen of the ultrasonic scanner a sequential activation takes place of two or three crystals or crystal groups each representing a respective measuring line. A marker is placed for each measuring line in a selected part-structure, such as a vessel, presented on the image screen, Echo-tracking dataprocessors seek the boundaries for the vessel along the measuring lines and lock onto these boundaries. A result dataprocessor computes continuously the changes in the vessel boundaries and calculates pulsewave diagrams for the vessel at the selected measuring lines and presents these diagrams on a presentation unit.