Development Of Digital Ultrasonic Doppler Fetal Heart Rate Measurement System

Fetal monitoring can help to identify the pathological conditions such as fetal hypoxia,so as to take timely medical intervention before irreversible changes take place.The detection of fetal heart rate(FHR)is the main technique of fetal monitoring.Using continuous monitoring of FHR,we can observe dynamic changes of fetal heart motion,especially those subtle changes,which has important significance for evaluating health of baby in the womb.Ultrasonic Doppler technique is the most important technique in the detection of FHR.It has the advantages of noninvasive,real-time,cheap,and has been widely used in clinical practice.At present,most of the commercial products of ultrasonic Doppler fetal heart monitoring use analog multiplication demodulation to obtain the Doppler shift signal,and they are easily influenced by noise and disturbances.In view of this situation,a digital ultrasonic Doppler FHR measurement system was developed.The system has two key features:(1)the anti-interference ability is improved by using direct sampling of the ultrasonic echo and digital demodulation instead of analog multiplier;(2)the wireless communication mode between the ultrasonic detection system and the host system is more convenient for clinical use.In this paper,the software and hardware development of the system is completed.The system is composed of two parts: wireless probe and host system.Wireless probe consists of MCU+CPLD architecture,and is mainly responsible for the excitation and receiving ultrasonic signals,ultrasonic echo sampling,digital quadrature demodulation,FHR calculation.It communicates with the hos system through the wireless Bluetooth module to transfer the FHR value and the fetal heart sound in real time.The host system use MCU as the core,and it is responsible for the human-computer interaction control,real-time display of the FHR value and the FHR trend line,and real-time broadcasting of fetal heart sounds.The system software mainly includes the system control program and the FHR detection algorithm.The FHR detection algorithm was first developed in the MATLAB environment,and then transplanted to the hardware system.In this paper,the prototype system was tested and the performance of the system was evaluated.Firstly,the performance of the system was tested based on the fetal heart simulator,and the 25 typical clinical fetal heart signals were tested to evaluate the accuracy and stability of the system.Then the prototype system was applied to the hospital,and more than 30 cases were tested.The test results show that the system has good accuracy and stability,and good sensitivity,and has reached the clinical requirement of fetal monitor.