Development of patient-specific fetal head phantom for experimental evaluation of vacuum assisted delivery

Sammanfattning: Vacuum assisted delivery (VAD) is a common procedure used in the final stage of labor in the situation of a difficult natural delivery. Since the only biomechanical studies concerning the clinical safe traction force were conducted during 70s using simplified models to mimic the fetal head, concerns remain regarding the side effects of this medical intervention when applying high levels of traction forces. For experimental evaluation of VAD, a tissue-mimicking accurate fetal head phantom, having the same skull and brain dimension as a newborn, as well as, proper mechanical and acoustic properties of materials, can be used as a useful resource in terms of establishing safe levels of traction forces. The goal of this project is to develop a realistic patient-specific fetal head phantom that will be used to investigate the relation between applied traction force and imposed brain deformation in VAD in an experimental setting. A realistic fetal head phantom was developed using geometry accurate segmented meshes of pediatric skull and brain from a CT fetal head dataset. The fetal skull was 3D printed while the segmented mesh of the brain was used to create a fetal brain mold. The fetal brain phantom was developed using a PVA and graphite solution (10% and 3% mass concentration), whereas the sutures and fontanels, the scalp and the cerebrospinal fluid were mimicked using silicone, surgical latex and water, respectively. All the tissue-mimicking materials used corresponded with the biomechanical properties of the fetal head tissues. After the construction of the fetal head phantom, grey-scale long- and short- axis ultrasound images as well as the fetal brain phantom elasticity map were obtained. Furthermore, using sonomicrometry crystals, the reference strain values during manual hand pressure and VAD experimental procedures were acquired. The results showed negative strain values (compression) reaching 15% in the manual pressure experimental procedure, and higher positive strain values (stretching) reaching over 40% in the VAD experimental procedure. However, due to experimental limitations only one measurement using clinically realistic levels for both vacuum pressure (65 kPa) and traction force (70 N) was achieved. The developed fetal head phantom has potential to provide trustful biomechanical evidence to guide safe vacuum assisted delivery as well as to provide useful resource in terms of defining the clinical effective force of the vacuum extractor (VE).