Device for measurement of fetal breathing movements—I The TD-recorder. A new system for recording the distance between two echogenerating structures as a function of time

Abstract A new device (time-distance recorder; TD-recorder) is presented for the measurement of the relative movements of two echoes visualized by a two-dimensional real-time scanner. One of the real-time image lines is selected and the instant distance between two echoes, indicated by markers, is assessed on-line. The output analog signal passes through a slew-rate filter which is activated by disturbing signals. During the measurement the ultrasonic energy output of the scanner can be considerably reduced by a low intensity mode facility. The system was originally developed for recording human fetal breathing movements.