Automated fetal breathing movement detection from internal small displacement measurement

We have previously proposed a method to measure small displacements of internal tissue which is based on an ultrasonic pulsed Doppler technique. The Doppler frequency shift of the ultrasonic waves due to the tissue movement is detected using a modified quadrature detector, and the displacement of the internal tissue is estimated by using an arctangent method. Based on the algorithm, we have constructed a quantitative monitoring system for fetal breathing movement. The fetal breathing movement is a rhythmic movement of the fetal diaphragm and it is recorded as a nearly sinusoidal displacement with a repetition frequency from 0.5 Hz to 2 Hz. In this paper, an automated fetal breathing movement detection algorithm for the displacement data observed by using the small displacement measurement system is proposed. This method uses a modified autocorrelation technique for detecting the displacement due to the fetal breathing movement. The method is applied to five fetuses of late pregnancy and the result is compared with the manual detection.