INTERNAL TISSUE DISPLACEMENT MEASUREMENT BASED ON ULTRASONIC WAVE DOPPLER SIGNAL DIGITAL DETECTION AND ITS APPLICATION TO FETAL MOVEMENT MONITORING

We have developed a fetal movement monitoring system based on small di splacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by us ing an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency o f four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the are-tangent method. The basic algorithm of the det ection method has already been used in the area of blood flow sensing however, we apply the algorithm to the displacement measurement of int ernal tissues. The comparison between the proposed method and the conv entional method is presented. The fetal movement quantitative monitori ng system based on the method which has been constructed is shown.