{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,19]],"date-time":"2026-01-19T01:47:17Z","timestamp":1768787237267,"version":"3.49.0"},"reference-count":38,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2019,3,8]],"date-time":"2019-03-08T00:00:00Z","timestamp":1552003200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Fetal heart rate (fHR) monitoring using Doppler Ultrasound (US) is a standard method to assess fetal health before and during labor. Typically, an US transducer is positioned on the maternal abdomen and directed towards the fetal heart. Due to fetal movement or displacement of the transducer, the relative fetal heart location (fHL) with respect to the US transducer can change, leading to frequent periods of signal loss. Consequently, frequent repositioning of the US transducer is required, which is a cumbersome task affecting clinical workflow. In this research, a new flexible US transducer array is proposed which allows for measuring the fHR independently of the fHL. In addition, a method for dynamic adaptation of the transmission power of this array is introduced with the aim of reducing the total acoustic dose transmitted to the fetus and the associated power consumption, which is an important requirement for application in an ambulatory setting. The method is evaluated using an in-vitro setup of a beating chicken heart. We demonstrate that the signal quality of the Doppler signal acquired with the proposed method is comparable to that of a standard, clinical US transducer. At the same time, our transducer array is able to measure the fHR for varying fHL while only using 50% of the total transmission power of standard, clinical US transducers.<\/jats:p>","DOI":"10.3390\/s19051195","type":"journal-article","created":{"date-parts":[[2019,3,8]],"date-time":"2019-03-08T11:21:59Z","timestamp":1552044119000},"page":"1195","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":29,"title":["Fetal Heart Rate Monitoring Implemented by Dynamic Adaptation of Transmission Power of a Flexible Ultrasound Transducer Array"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7023-9322","authenticated-orcid":false,"given":"Paul","family":"Hamelmann","sequence":"first","affiliation":[{"name":"Department of Electrical Engineering, Eindhoven University of Technology, 5612 AP Eindhoven, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Massimo","family":"Mischi","sequence":"additional","affiliation":[{"name":"Department of Electrical Engineering, Eindhoven University of Technology, 5612 AP Eindhoven, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexander F.","family":"Kolen","sequence":"additional","affiliation":[{"name":"Philips Research, 565 AE Eindhoven, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Judith O. E. H.","family":"van Laar","sequence":"additional","affiliation":[{"name":"M\u00e1xima Medical Center, 5504 DB Veldhoven, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2392-6098","authenticated-orcid":false,"given":"Rik","family":"Vullings","sequence":"additional","affiliation":[{"name":"Department of Electrical Engineering, Eindhoven University of Technology, 5612 AP Eindhoven, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jan W. M.","family":"Bergmans","sequence":"additional","affiliation":[{"name":"Department of Electrical Engineering, Eindhoven University of Technology, 5612 AP Eindhoven, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,3,8]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"545","DOI":"10.1016\/j.ajog.2018.03.011","article-title":"Electronic fetal monitoring or cardiotocography, 50 years later: What\u2019s in a name?","volume":"218","year":"2018","journal-title":"Am. J. Obstet. Gynecol."},{"key":"ref_2","first-page":"e132","article-title":"The future of fetal monitoring","volume":"5","author":"Wolfberg","year":"2012","journal-title":"Rev. Obstet. Gynecol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1016\/j.ijgo.2015.06.020","article-title":"FIGO consensus guidelines on intrapartum fetal monitoring: Cardiotocography","volume":"131","author":"Spong","year":"2015","journal-title":"Int. J. Gynecol. Obstet."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"2021","DOI":"10.1016\/j.ajog.2004.04.026","article-title":"Umbilical cord pH and base excess values in relation to adverse outcome events for infants delivering at term","volume":"191","author":"Victory","year":"2004","journal-title":"Am. J. Obstet. Gynecol."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Alfirevic, Z., Devane, D., Gyte, G.M.L., and Cuthbert, A. (2017). Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst. Rev., 2.","DOI":"10.1002\/14651858.CD006066.pub3"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"169","DOI":"10.1159\/000327133","article-title":"Intra-and interobserver variability of intrapartum cardiotocography: A multicenter study comparing the figo classification with computer analysis software","volume":"72","author":"Schiermeier","year":"2011","journal-title":"Gynecol. Obstet. Invest."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Warrick, P.A., Hamilton, E.F., Kearney, R.E., and Precup, D. (2012). A Machine Learning Approach to the Detection of Fetal Hypoxia during Labor and Delivery. AI Mag., 1865\u20131870.","DOI":"10.1609\/aaai.v24i2.18826"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Chudacek, V., Spilka, J., Lhotska, L., Janku, P., Koucky, M., Huptych, M., and Bursa, M. (September, January 30). Assessment of features for automatic CTG analysis based on expert annotation. Proceedings of the 2011 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Boston, MA, USA.","DOI":"10.1109\/IEMBS.2011.6091495"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"93","DOI":"10.1111\/aogs.12286","article-title":"Fetal heart rate variability during pregnancy, obtained from non-invasive electrocardiogram recordings","volume":"93","author":"Warmerdam","year":"2014","journal-title":"Acta Obstet. Gynecol. Scand."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Signorini, M.G., Fanelli, A., and Magenes, G. (2014). Monitoring fetal heart rate during pregnancy: Contributions from advanced signal processing and wearable technology. Comput. Math. Methods Med., 2014.","DOI":"10.1155\/2014\/707581"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Doret, M., Spilka, J., Chud\u00e1\u010dek, V., Gon\u00e7alves, P., and Abry, P. (2015). Fractal analysis and Hurst parameter for intrapartum fetal heart rate variability analysis: A versatile alternative to frequency bands and LF\/HF ratio. PLoS ONE, 10.","DOI":"10.1371\/journal.pone.0136661"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"387","DOI":"10.1088\/0967-3334\/37\/3\/387","article-title":"Using uterine activity to improve fetal heart rate variability analysis for detection of asphyxia during labor","volume":"37","author":"Warmerdam","year":"2016","journal-title":"Physiol. Meas."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"259","DOI":"10.1016\/j.earlhumdev.2011.01.028","article-title":"Normalized spectral power of fetal heart rate variability is associated with fetal scalp blood pH","volume":"87","author":"Peters","year":"2011","journal-title":"Early Hum. Dev."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"585","DOI":"10.1088\/0967-3334\/25\/2\/015","article-title":"Beat-to-beat detection of fetal heart rate: Doppler ultrasound cardiotocography compared to direct ECG cardiotocography in time and frequency domain","volume":"25","author":"Peters","year":"2004","journal-title":"Physiol. Meas."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"691","DOI":"10.1016\/j.phpro.2010.01.087","article-title":"Robust estimation of fetal heart rate from US Doppler signals","volume":"Volume 3","author":"Voicu","year":"2010","journal-title":"Physics Procedia"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Sameni, R., and Clifford, G.D. (2010). A review of fetal ECG signal Procesing; Issues and Promising Directions. Open Pacing Electrophysiol. Ther. J.","DOI":"10.2174\/1876536X01003010004"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1521","DOI":"10.1088\/0967-3334\/35\/8\/1521","article-title":"Non-invasive fetal ECG analysis","volume":"35","author":"Clifford","year":"2014","journal-title":"Physiol. Meas."},{"key":"ref_18","unstructured":"Vullings, R. (2010). Non-Invasive Fetal Electrocardiogram: Analysis and Interpretation, Technische Universiteit Eindhoven."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"590","DOI":"10.1111\/aogs.12387","article-title":"Influence of maternal body mass index on accuracy and reliability of external fetal monitoring techniques","volume":"93","author":"Cohen","year":"2014","journal-title":"Acta Obstet. Gynecol. Scand."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1821","DOI":"10.1088\/1361-6579\/aa8a1a","article-title":"Improved ultrasound transducer positioning by fetal heart location estimation during Doppler based heart rate measurements","volume":"38","author":"Hamelmann","year":"2017","journal-title":"Physiol. Meas."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1103","DOI":"10.1007\/s00404-012-2413-4","article-title":"Intrapartum signal quality with external fetal heart rate monitoring: A two way trial of external Doppler CTG ultrasound and the abdominal fetal electrocardiogram","volume":"286","author":"Reinhard","year":"2012","journal-title":"Arch. Gynecol. Obstet."},{"key":"ref_22","first-page":"35","article-title":"The influence of signal loss episodes on fetal heart rate variability","volume":"23","author":"Wrobel","year":"2014","journal-title":"J. Med. Inform. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.ijgo.2010.03.011","article-title":"Twenty-five years after the FIGO guidelines for the use of fetal monitoring: Time for a simplified approach?","volume":"110","author":"Bernardes","year":"2010","journal-title":"Int. J. Gynecol. Obstet."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"156","DOI":"10.1053\/j.sult.2007.12.003","article-title":"Safety Assurance in Obstetrical Ultrasound","volume":"29","author":"Miller","year":"2008","journal-title":"Semin. Ultrasound CT MRI"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"368","DOI":"10.1016\/j.actbio.2016.11.049","article-title":"Tuning acoustic and mechanical properties of materials for ultrasound phantoms and smart substrates for cell cultures","volume":"49","author":"Cafarelli","year":"2017","journal-title":"Acta Biomater."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1341","DOI":"10.1109\/JMEMS.2010.2076786","article-title":"Encapsulation of Capacitive Micromachined Ultrasonic Transducers Using Viscoelastic Polymer","volume":"19","author":"Lin","year":"2010","journal-title":"J. Microelectromech. Syst."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Cobbold, R.S.C. (2007). Foundations of Biomedical Ultrasound, Oxford University Press.","DOI":"10.1093\/oso\/9780195168310.001.0001"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Hamelmann, P., Kolen, A., Schmitt, L., Vullings, R., Van Assen, H., Mischi, M., Demi, L., Van Laar, J., Bergmans, J., and Van Assen, H. (2016, January 16\u201320). Ultrasound Transducer Positioning Aid for Fetal Heart Rate Monitoring. Proceedings of the 2016 38th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Orlando, FL, USA.","DOI":"10.1109\/EMBC.2016.7591629"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1575","DOI":"10.1109\/TUFFC.2014.3071","article-title":"Apodization and Windowing Functions","volume":"61","author":"Parker","year":"2013","journal-title":"IEEE Trans. Ultrason. Ferroelectr. Freq. Control"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"417","DOI":"10.1109\/58.585126","article-title":"Clutter rejection filters in color flow imaging: A theoretical approach","volume":"44","author":"Torp","year":"1997","journal-title":"IEEE Trans. Ultrason. Ferroelectr. Freq. Control"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"92","DOI":"10.1186\/1475-925X-10-92","article-title":"A novel technique for fetal heart rate estimation from Doppler ultrasound signal","volume":"10","author":"Jezewski","year":"2011","journal-title":"Biomed. Eng. Online"},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Piontelli, A. (2010). Development of Normal Fetal Movements, Springer.","DOI":"10.1007\/978-88-470-1402-2"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"572","DOI":"10.1016\/S1701-2163(16)30716-2","article-title":"Obstetric ultrasound biological effects and safety","volume":"27","author":"Bly","year":"2005","journal-title":"J. Obstet. Gynaecol. Canada JOGC"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1117","DOI":"10.1016\/S0301-5629(00)00253-2","article-title":"The DopFet system: A new ultrasonic Doppler system for monitoring and characterization of fetal movement","volume":"26","author":"Karlsson","year":"2000","journal-title":"Ultrasound Med. Biol."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"430","DOI":"10.1016\/j.ultrasmedbio.2006.09.014","article-title":"The Actifetus system: A multidoppler sensor system for monitoring fetal movements","volume":"33","author":"Tranquart","year":"2007","journal-title":"Ultrasound Med. Biol."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"950","DOI":"10.1109\/TBME.2003.814528","article-title":"Robust Estimation of Fetal Heart Rate Variability Using Doppler Ultrasound","volume":"50","author":"Fernando","year":"2003","journal-title":"IEEE Trans. Biomed. Eng."},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Hamelmann, P., Vullings, R., Mischi, M., Kolen, A.F., Schmitt, L., and Bergmans, J.W.M. (2018). An Extended Kalman Filter for Fetal Heart Location Estimation During Doppler-Based Heart Rate Monitoring. IEEE Trans. Instrum. Meas., 1\u201311.","DOI":"10.1109\/TIM.2018.2876779"},{"key":"ref_38","first-page":"251","article-title":"Detection of fetal movement using Doppler ultrasound","volume":"70","author":"Wheeler","year":"1987","journal-title":"Obstet. Gynecol."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/5\/1195\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:37:26Z","timestamp":1760186246000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/5\/1195"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,3,8]]},"references-count":38,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2019,3]]}},"alternative-id":["s19051195"],"URL":"https:\/\/doi.org\/10.3390\/s19051195","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,3,8]]}}}