P93: Electrical Impedance for Accurate detection of degree of Ileus

Abstract

Background: Postoperative ileus is a frequent complication of visceral surgery. It puts an additional financial burden on the U.S. health-care amounting to 1.5 billion dollars per year. A reliable way of assessing ileus is lacking. A highly sensitive electrical impedance-based measurement tool is presented. Methods: The system uses two coupled high Q-resonators (transmit resonator under the patient, receive resonator held by hand over the abdomen) as shown in Fig. 1(a). The normal mode resonant frequencies shift as the transmit receive distance changes. Over some range of separation distances, a constant, maximum efficiency can be achieved if the ideal operating frequency is selected (13.56MHz). This constant efficiency region corresponds to the V-shaped plateau as shown in Fig. 1(b-d). As the distance between the transmitting and receiving resonators changes, the frequency at which maximum efficiency occurs also changes. This allows for accurate distance measurement with 97% accuracy. Based on the dielectric properties of air, water, blood, and tissue at 13.56MHz we designed a phantom that simulates an abdominal cavity. The optimized coil geometries found in ANSYS Electronic Desktop 2021 R2 were implemented to fabricate the coils from copper via abrasive water jet cutting technology with the Flow NanoJet. Results: Reflection coefficients (S11 and S22) vs. distance vs. resonant frequency for the back and abdominal are shown in Fig. 2(b) and (c). The transmission coefficient (S21) between the resonators is shown in Fig. 2(d). The results indicate that as the distance between resonators changes, the resonant frequency changes as well. Abdominal girth was detected using an exponential regression model. Conclusion: An accurate predictive change of abdominal girth can be detected by electrical impedance in resonantly coupled regimen. This may aid in early detection and help in prognostication in cases of postoperative ileus.