Improved FPGA controlled artificial vascular system for plethysmographic measurements

Abstract

Abstract:The fetal oxygen saturation is an important parameter to determine the health status of a fetus, which is until now mostly acquired invasively. The transabdominal, fetal pulse oximetry is a promising approach to measure this non-invasively and continuously. The fetal pulse curve has to be extracted from the mixed signal of mother and fetus to determine its oxygen saturation. For this purpose efficient algorithms are necessary, which have to be evaluated under constant and reproducable test conditions. This paper presents the improved version of a phantom which can generate artificial pulse waves in a synthetic tissue phantom. The tissue phantom consists of several layers that mimic the different optical properties of the fetal and maternal tissue layers. Additionally an artificial vascular system and a dome, which mimics the bending of the belly of a pregnant woman, are incorporated. To obtain data on the pulse waves, several measurement methods are included, to help understand the behavior of the signals gained from the pulse waves. Besides pressure sensors and a transmissive method we integrated a capacitive approach, that makes use of the so called "Pin Oscillator" method. Apart from the enhancements in the tissue phantom and the measurements, we also improved the used blood substitute, which reproduces the different absorption characteristics of fetal and maternal blood. The results show that the phantom can generate pulse waves similar to the natural ones. Furthermore, the phantom represents a reference that can be used to evaluate the algorithms for transabdominal, fetal pulse oximetry.

Review of optical methods for fetal monitoring in utero

“…Additionally, different materials were investigated to mimic optical properties of the mother and fetus [32]. The phantom models were improved by including a dome to better mimic the geometry of a pregnant mother, adding a sensor to measure the mechanical dilation of the artificial vessel, and improving the synthetic blood substitutes [33]. Using the modified phantom, they took measurements and implemented a comb filter to suppress the maternal heart beat and obtain just the fetal one.…”

Estimating the Shape of the Fetal Pulse Curve for Transabdominal Pulse Oximetry using Synchronous Averaging

“…The generation of this signal is based on resampling and assembling of single pulse curves, following the explanation in our former work [7]. Three more datasets are measured at the phantom presented by Laqua et al in [11]. The measurement setups are shown in Fig 3. The configuration of the LED and photosensors is a complex system that is discussed in our previous work [9].…”

Effect of the presence of amniotic fluid for optical transabdominal fetal monitoring using Monte Carlo simulations

“…There are several approaches taken to determine feasibility of fetal pulse oximetry. Computational modeling in the literature [5][6][7][8][9][10][11][12][13][14] was used to determine design parameters and efficacy of detection and phantom studies [7,8,11,[15][16][17][18][19] were used to test prototypes. Pre-clinical [20][21][22][23] and clinical studies [7,[24][25][26][27][28] were performed to determine overall feasibility with the realistic conditions that transabdominal fetal pulse oximetry might encounter.…”