The device has a display for representing ultrasonic data. A user or operator interface (120) e.g. keyboard, defines a proximal level and a distal level within the ultrasonic data. The proximal and the distal levels define a region of interest. A signal processor (116) extracts two layers within the region of interest based on the ultrasonic data, where the two layers are parallel to each other and are represented on the display. An independent claim is also included for a method for representing parallel layers.