1. Obstetric uses of the ultrasonic motion sensor;Bishop;Am J Obst Gynec,1966
2. Ultrasonic Doppler observation of the fetal heart;Callagan;Obst Gynec,1964
3. Ultrasonic blood rheograph Proc 3rd ICME;Satomura,1960
4. Doppler ultrasound in obstetrics;Brown;JAMA,1971
5. Studies on fetal heart signal and fetal bloodflow signal obtained by an ultrasound Doppler method;Maeda;Med Ultrason,1970