Electrical Impedance Tomography Parameters Research Articles

Electrical impedance tomography meets reduced order modelling: a framework for faster and more reliable electrical conductivity estimations

Objective.Inclusion of individualised electrical conductivities of head tissues is crucial for the accuracy of electrical source imaging techniques based on electro/magnetoencephalography and the efficacy of transcranial electrical stimulation. Parametric electrical impedance tomography (pEIT) is a method to cheaply and non-invasively estimate them using electrode arrays on the scalp to apply currents and measure the resulting potential distribution. Conductivities are then estimated by iteratively fitting a forward model to the measurements, incurring a prohibitive computational cost that is generally lowered at the expense of accuracy. Reducing the computational cost associated with the forward solutions would improve the accessibility of this method and unlock new capabilities.Approach.We introduce reduced order modelling (ROM) to massively speed up the calculations of these solutions for arbitrary conductivity values.Main results.We demonstrate this new ROM-pEIT framework using a realistic head model with six tissue compartments, with minimal errors in both the approximated numerical solutions and conductivity estimations. We show that the computational complexity required to reach a multi-parameter estimation with a negligible relative error is reduced by more than an order of magnitude when using this framework. Furthermore, we illustrate the benefits of this new framework in a number of practical cases, including its application to real pEIT data from three subjects.Significance.Results suggest that this framework can transform the use of pEIT for seeking personalised head conductivities, making it a valuable tool for researchers and clinicians.

A novel method for detecting intracranial pressure changes by monitoring cerebral perfusion via electrical impedance tomography

BackgroundAcute and critical neurological diseases are often accompanied with elevated intracranial pressure (ICP), leading to insufficient cerebral perfusion, which may cause severe secondary lesion. Existing ICP monitoring techniques often fail to effectively meet the demand for real-time noninvasive ICP monitoring and warning. This study aimed to explore the use of electrical impedance tomography (EIT) to provide real-time early warning of elevated ICP by observing cerebral perfusion.MethodsAn intracranial hypertension model was prepared by injecting autologous un-anticoagulated blood into the brain parenchyma of twelve Landrace swine. Invasive ICP monitoring was used as a control method, and a high-precision EIT system was used to acquire and analyze the changing patterns of cerebral perfusion EIT image parameters with respect to ICP. Four EIT parameters related to cerebral perfusion were extracted from the images, and their potential application in detecting ICP elevation was analyzed.ResultsWhen ICP increased, all EIT perfusion parameters decreased significantly (P < 0.05). When the subjects were in a state of intracranial hypertension (ICP > 22 mmHg), the correlation between EIT perfusion parameters and ICP was more significant (P < 0.01), with correlation coefficients ranging from −0.72 to −0.83. We tested the objects when they were in baseline ICP and in ICP of 15–40 mmHg. Under both circumstances, ROC curve analysis showed that the comprehensive model of perfusion parameters based on the random forest algorithm had a sensitivity and specificity of more than 90% and an area under the curve (AUC) of more than 0.9 for detecting ICP increments of both 5 and 10 mmHg.ConclusionThis study demonstrates the feasibility of using perfusion EIT to detect ICP increases in real time, which may provide a new method for real-time non-invasive monitoring of patients with increased ICP.

Electrical impedance tomography provides information of brain injury during total aortic arch replacement through its correlation with relative difference of neurological biomarkers

Postoperative neurological dysfunction (PND) is one of the most common complications after a total aortic arch replacement (TAAR). Electrical impedance tomography (EIT) monitoring of cerebral hypoxia injury during TAAR is a promising technique for preventing the occurrence of PND. This study aimed to explore the feasibility of electrical impedance tomography (EIT) for warning of potential brain injury during total aortic arch replacement (TAAR) through building the correlation between EIT extracted parameters and variation of neurological biomarkers in serum. Patients with Stanford type A aortic dissection and requiring TAAR who were admitted between December 2021 to March 2022 were included. A 16-electrode EIT system was adopted to monitor each patient’s cerebral impedance intraoperatively. Five parameters of EIT signals regarding to the hypothermic circulatory arrest (HCA) period were extracted. Meanwhile, concentration of four neurological biomarkers in serum were measured regarding to time before and right after surgery, 12 h, 24 h and 48 h after surgery. The correlation between EIT parameters and variation of serum biomarkers were analyzed. A total of 57 TAAR patients were recruited. The correlation between EIT parameters and variation of biomarkers were stronger for patients with postoperative neurological dysfunction (PND(+)) than those without postoperative neurological dysfunction (PND(−)) in general. Particularly, variation of S100B after surgery had significantly moderate correlation with two parameters regarding to the difference of impedance between left and right brain which were MRAIabs and TRAIabs (0.500 and 0.485 with p < 0.05, respectively). In addition, significantly strong correlations were seen between variation of S100B at 24 h and the difference of average resistivity value before and after HCA phase (ΔARVHCA), the slope of electrical impedance during HCA (kHCA) and MRAIabs (0.758, 0.758 and 0.743 with p < 0.05, respectively) for patients with abnormal S100B level before surgery. Strong correlations were seen between variation of TAU after surgery and ΔARVHCA, kHCA and the time integral of electrical impedance for half flow of perfusion (TARVHP) (0.770, 0.794 and 0.818 with p < 0.01, respectively) for patients with abnormal TAU level before surgery. Another two significantly moderate correlations were found between TRAIabs and variation of GFAP at 12 h and 24 h (0.521 and 0.521 with p < 0.05, respectively) for patients with a normal GFAP serum level before surgery. The correlations between EIT parameters and serum level of neurological biomarkers were significant in patients with PND, especially for MRAIabs and TRAIabs, indicating that EIT may become a powerful assistant for providing a real-time warning of brain injury during TAAR from physiological perspective and useful guidance for intensive care units.

Determination of optimal positive end-expiratory pressure using electrical impedance tomography in infants under general anesthesia: Comparison between supine and prone positions.

This study determined the optimal positive end-expiratory pressure levels in infants in supine and prone positions under general anesthesia using electrical impedance tomography (EIT). This prospective observational single-centre study included infants scheduled for surgery in the prone position. An electrical impedance tomography sensor was applied after inducing general anesthesia. The optimal positive end-expiratory pressure in the supine position was determined in a decremental trial based on EIT and compliance. Subsequently, the patient's position was changed to prone. Electrical impedance tomography parameters, including global inhomogeneity index, regional ventilation delay, opening pressure, the centre of ventilation, and pendelluft volume, were continuously obtained up to 1 h after prone positioning. The optimal positive end-expiratory pressure in the prone position was similarly determined. Data from 30 infants were analyzed. The mean value of electrical impedance tomography-based optimal positive end-expiratory pressure in the prone position was significantly higher than that in the supine position [10.9 (1.6) cmH2O and 6.1 (0.9) cmH2O, respectively (p < .001)]. Significant differences were observed between electrical impedance tomography- and compliance-based optimal positive end-expiratory pressure. Peak and mean airway, plateau, and driving pressures increased 1 h after prone positioning compared with those in the supine position. In addition, the centre of ventilation for balance in ventilation between the ventral and dorsal regions improved. The prone position required higher positive end-expiratory pressure than the supine position in mechanically ventilated infants under general anesthesia. EIT is a promising tool to find the optimal positive end-expiratory pressure, which needs to be individualized.

Electrical Impedance Tomography as a monitoring tool during weaning from mechanical ventilation: an observational study during the spontaneous breathing trial

BackgroundProlonged weaning from mechanical ventilation is associated with poor clinical outcome. Therefore, choosing the right moment for weaning and extubation is essential. Electrical Impedance Tomography (EIT) is a promising innovative lung monitoring technique, but its role in supporting weaning decisions is yet uncertain. We aimed to evaluate physiological trends during a T-piece spontaneous breathing trail (SBT) as measured with EIT and the relation between EIT parameters and SBT success or failure.MethodsThis is an observational study in which twenty-four adult patients receiving mechanical ventilation performed an SBT. EIT monitoring was performed around the SBT. Multiple EIT parameters including the end-expiratory lung impedance (EELI), delta Tidal Impedance (ΔZ), Global Inhomogeneity index (GI), Rapid Shallow Breathing Index (RSBIEIT), Respiratory Rate (RREIT) and Minute Ventilation (MVEIT) were computed on a breath-by-breath basis from stable tidal breathing periods.ResultsEELI values dropped after the start of the SBT (p < 0.001) and did not recover to baseline after restarting mechanical ventilation. The ΔZ dropped (p < 0.001) but restored to baseline within seconds after restarting mechanical ventilation. Five patients failed the SBT, the GI (p = 0.01) and transcutaneous CO2 (p < 0.001) values significantly increased during the SBT in patients who failed the SBT compared to patients with a successful SBT.ConclusionEIT has the potential to assess changes in ventilation distribution and quantify the inhomogeneity of the lungs during the SBT. High lung inhomogeneity was found during SBT failure. Insight into physiological trends for the individual patient can be obtained with EIT during weaning from mechanical ventilation, but its role in predicting weaning failure requires further study.

Effect of routine suction on lung aeration in critically ill neonates and young infants measured with electrical impedance tomography

Endotracheal suctioning is a widely used procedure to remove secretions from the airways of ventilated patients. Despite its prevalence, regional effects of this maneuver have seldom been studied. In this study, we explore its effects on regional lung aeration in neonates and young infants using electrical impedance tomography (EIT) as part of the large EU-funded multicenter observational study CRADL. 200 neonates and young infants in intensive care units were monitored with EIT for up to 72 h. EIT parameters were calculated to detect changes in ventilation distribution, ventilation inhomogeneity and ventilation quantity on a breath-by-breath level 5–10 min before and after suctioning. The intratidal change in aeration over time was investigated by means of regional expiratory time constants calculated from all respiratory cycles using an innovative procedure and visualized by 2D maps of the thoracic cross-section. 344 tracheal suctioning events from 51 patients could be analyzed. They showed no or very small changes of EIT parameters, with a dorsal shift of the center of ventilation by 0.5% of the chest diameter and a 7% decrease of tidal impedance variation after suctioning. Regional time constants did not change significantly. Routine suctioning led to EIT-detectable but merely small changes of the ventilation distribution in this study population. While still a measure requiring further study, the time constant maps may help clinicians interpret ventilation mechanics in specific cases.

Optimal positive end-expiratory pressure titration of intraoperative mechanical ventilation in different operative positions of female patients under general anesthesia

ObjectiveThis study aimed to compare the effectiveness and safety of different titrated methods used to determine individual positive end-expiratory pressure (PEEP) for intraoperative mechanical ventilation in female patients undergoing general anesthesia in different operative positions, and provide reference ranges of optimal PEEP values based on the titration. MethodsA total of 123 female patients who underwent elective open abdominal surgery under general anesthesia were included in this study. After endotracheal intubation, patients' body position was adjusted to the supine position, Trendelenburg positions at 10° and 20° respectively. PEEP was titrated from 20 cmH2O to 4 cmH2O, decreasing by 2 cmH2O every 1 min. Electrical impedance tomography (EIT), hemodynamic and respiratory mechanics parameters were continuously monitored and recorded. Optimal PEEP values and reference ranges were respectively calculated based on optimal EIT parameters, mean arterial pressure (MAP), and lung dynamic compliance (Cdyn). ResultsEIT-guided optimal PEEP was found to have higher values than those of the MAP-guided and Cdyn-guided methods for all three body positions (P < 0.001), and it was observed to more significantly inhibit hemodynamics (P < 0.05). The variable coefficients of EIT-guided optimal PEEP values were smaller than those of the other two methods, and this technique could provide better ventilation uniformity for dorsal/ventral lung fields and better balance for pulmonary atelectasis/collapse. The 95% reference ranges of EIT-guided optimal PEEP values were 4.6–13.8 cmH2O, 7.0–15.0 cmH2O and 8.6–17.0 cmH2O for the supine position, Trendelenburg 10°, and Trendelenburg 20° positions, respectively. ConclusionEIT-guided optimal PEEP titration was found to be a superior method for lung protective ventilation in different operative positions under general anesthesia. The calculated reference ranges of PEEP values based on the EIT-guided method can be used as a reference for intraoperative mechanical ventilation.

Early prediction of pulmonary outcomes in preterm infants using electrical impedance tomography.

Electrical impedance tomography (EIT) allows assessment of ventilation and aeration homogeneity which may be associated with respiratory outcomes in preterm infants. This was a secondary analysis to a recent randomized controlled trial in very preterm infants in the delivery room (DR). The predictive value of various EIT parameters assessed 30 min after birth on important respiratory outcomes (early intubation <24 h after birth, oxygen dependency at 28 days after birth, and moderate/severe bronchopulmonary dysplasia; BPD) was assessed. Thirty-two infants were analyzed. A lower percentage of aerated lung volume [OR (95% CI) = 0.8 (0.66-0.98), p = 0.027] as well as a higher aeration homogeneity ratio (i.e., more aeration in the non-gravity-dependent lung) predicted the need for supplemental oxygen at 28 days after birth [9.58 (5.16-17.78), p = 0.0028]. Both variables together had a similar predictive value to a model using known clinical contributors. There was no association with intubation or BPD, where numbers were small. In very preterm infants, EIT markers of aeration at 30 min after birth accurately predicted the need for supplemental oxygen at 28 days after birth but not BPD. EIT-guided individualized optimization of respiratory support in the DR may be possible.

Relationship between lung ultrasound and electrical impedance tomography as regional assessment tools during PEEP titration in acute respiratory distress syndrome caused by multi-lobar pneumonia: a pilot study.

Acute respiratory distress syndrome (ARDS) caused by multilobar pneumonia (MLP) is markedly different from typical ARDS in pathology, imaging characteristics, and lung mechanics. Regional lung assessment is required. We aimed to analyze the relationship between two regional assessment tools, lung ultrasound (LUS) and electrical impedance tomography (EIT) during positive end-expiratory pressure (PEEP) titration, and determine an appropriate PEEP level. We conducted a prospective study of patients with ARDS caused by MLP with PaO2/FiO2 < 150mmHg. All subjects were equipped with two EIT belts connected with a single EIT machine to measure upper and lower hemithorax impedance change alternatingly at each PEEP level. LUS score was simultaneously determined in chest wall regions corresponding to the EIT regions during PEEP titration. We acquired EIT and LUS data in eight regions of interest at seven PEEP levels in 12 subjects. Therefore, 672 pairs of data were obtained for analysis. There were significant relationships between LUS score and tidal impedance variation and pixel compliance (Cpix). The Spearman's rho between LUS score vs. tidal impedance variation and LUS score vs. the Cpix were -0.142, P < 0.001, and -0.195, P < 0.001, respectively. The relationship between the LUS score and Cpix remained the same at every PEEP level but did not reach statistical significance. The individual's mean expected PEEP by LUS was similar to the EIT [10.33(± 1.67) vs. 10.33(± 1.44) cm H2O, P = 0.15]. Regarding the MLP, the LUS scores were associated with EIT parameters, and LUS scores might proof helpful for finding individual PEEP settings in MLP.

The influence of reference electrode in electrical impedance tomography

BackgroundSome electrical impedance tomography (EIT) devices equip reference electrodes. In practice, it is not uncommon to observe high contact impedance for the reference electrode. The influence of bad contact reference electrode on data quality is unknown. The study aimed to investigate the influence of reference electrode on EIT image reconstruction. MethodsThirty lung healthy volunteers were prospectively examined with EIT. The subjects were spontaneously breathing in supine position. Three scenarios were constructed: 1. Normal measurement; 2. Reference electrode disconnected without recalibration; 3. Reference electrode disconnected, and the measurement restarted after recalibration of the system. EIT-based parameters measuring spatial and temporal ventilation distributions were calculated and compared. A so-call deviation score was calculated to assess the differences in EIT parameters between scenarios 2 and 1, between 3 and 1. ResultsThe absolute differences for all parameters were significantly higher than zero (p < 0.01 for all parameters and scenarios). Deviation score for scenario 2 was 4.5 ± 3.5. Four subjects had a deviation score of 0 in scenario 2 and five subjects had a score of 1. The deviation in scenario 3 was higher (6.1 ± 3.1). No subjects had a score of 0 and only two subjects had a score of 1. ConclusionsFor EIT systems that equips with reference electrode, it is important to ensure the proper contact and functionality of the reference electrode. The EIT data quality would remain unchanged in only a small portion of subjects.

Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure.

Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet. Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure. Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of EIT measurements was 53 ± 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks. Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort. Clinical trial registered with www.clinicaltrials.gov (NCT02962505).

Performance Prediction, Sensitivity Analysis and Parametric Optimization of Electrical Impedance Tomography Using A Bioelectrical Tissue Simulation Platform.

There is an urgent need to bring forth portable, low-cost, point-of-care diagnostic instruments to monitor patient health and wellbeing. This is elevated by the COVID-19 global pandemic in which the availability of proper lung imaging equipment has proven to be pivotal in the timely treatment of patients. Electrical impedance tomography (EIT) has long been studied and utilized as such a critical imaging device in hospitals especially for lung ventilation. Despite decades of research and development, many challenges remain with EIT in terms of 1) optimal image reconstruction algorithms, 2) simulation and measurement protocols, 3) hardware imperfections, and 4) uncompensated tissue bioelectrical physiology. Due to the inter-connectivity of these challenges, singular solutions to improve EIT performance continue to fall short of the desired sensitivity and accuracy. Motivated to gain a better understanding and optimization of the EIT system, we report the development of a bioelectric facsimile simulator demonstrating the dynamic operations, sensitivity analysis, and reconstruction outcome prediction of the EIT sensor with stepwise visualization. By building a sandbox platform to incorporate full anatomical and bioelectrical properties of the tissue under study into the simulation, we created a tissue-mimicking phantom with adjustable EIT parameters to interpret bioelectrical interactions and to optimize image reconstruction accuracy through improved hardware setup and sensing protocol selections.

Clinical value of electrical impedance tomography (EIT) in the management of patients with acute respiratory failure: a single centre experience

Objective. We will describe our clinical experience using electrical impedance tomography (EIT) in the management of mechanical ventilation in patients with acute respiratory failure and to determine to which extent EIT-guided positive end-expiratory pressure (PEEP) setting differed from clinically set values. Approach. We conducted a retrospective, observational cohort study performed in a hub centre for the treatment of acute respiratory failure and veno-venous extracorporeal membrane oxygenation (ECMO). Main results. Between January 2017 and December 2019, EIT was performed 54 times in 41 patients, not feasible only in one case because of signal instability. More than 50% was on veno-venous ECMO support. In 16 cases (30%), EIT was used for monitoring mechanical ventilation, i.e. to evaluate recruitability or sigh setting. In 37 cases (70%), EIT was used to set PEEP both with incremental (11 cases in nine patients) and decremental (26 cases, 18 patients) PEEP trial. Clinical PEEP before the decremental PEEP trial (PEEPPRE) was 14.1 ± 3.4 cmH2O and clinical PEEP set by clinicians after the PEEP trial (PEEPPOST) was 13.6 ± 3.1 (p = ns). EIT analyses demonstrated that more hypoxic patients were higher derecruited when compared to less hypoxic patients that were, on the contrary, more overdistended (p < 0.05). No acute effects of PEEP adjustment based on EIT on respiratory mechanics or regional EIT parameters modification were observed. Significance. The variability of EIT findings in our population confirmed the need to provide ventilation settings individually tailored and EIT was confirmed to be an optimal useful clinical bedside noninvasive tool to provide real-time monitoring of the PEEP effect and ventilation distribution.

Diagnosing and monitoring pleural effusion using parametric electrical impedance tomography - a computational 3D model and preliminary experimental results

PurposeDiagnosing and monitoring pleural effusion (PE) is challenging due unsuitability of existing modalities. In the present study, a novel parametric electrical impedance tomography (pEIT) technique, tailored to a clinically feasible system to diagnose PE is presented. MethodsAn electrical impedance tomography (EIT) numeric solver was applied to a 3D realistic normal model and five PE models to simulate sets of surface measurements. Simulations were triggered by a series of eight independent projections using five electrodes positioned around the thorax. The relative changes in the potential between the PE models and the normal model were assessed and the error in the estimated PE volume was examined at varying signal to noise ratio (SNR) levels. For experimental feasibility, measurements were performed in four healthy subjects and were correlated with the potentials that were calculated from the normal model. ResultsRelative potential changes were notable (reached until ~55%) and increased with the increasing PE volumes. Maximal error of ± 20 [mL] was obtained for SNR levels >50 [dB]. The feasibility real measurements in healthy subjects showed a strong linear correlation (R2 > 0.85) and a successful diagnosis for all subjects. ConclusionThe proposed technique can estimate PE volumes from a redundant set of measurements in a realistic 3D human model and may be utilized for monitoring PE patients.

Regional ventilation distribution in healthy lungs: can reference values be established for electrical impedance tomography parameters?

BackgroundAlthough electrical impedance tomography (EIT) is widely used for monitoring regional ventilation distribution, reference values have yet to be established for clinical use. The present study aimed to evaluate the feasibility of creating reference values for standard EIT parameters for potential clinical application.MethodsA total of 75 participants with healthy lungs were included in this prospective study (male:female, 48:27; age, 34±14 years; height, 172±7 cm; weight, 73±12 kg). The subjects were examined during spontaneous breathing in the supine position. EIT measurements were performed at the level of the 4th intercostal space. Commonly used EIT-based parameters, including the center of ventilation (CoV), dorsal and most dorsal fractions of ventilation distribution (TVD and TVROI4 respectively), global inhomogeneity (GI) index, and standard deviation of regional ventilation delay index (RVDSD) were calculated.ResultsFollowing outlier detection, EIT data from 71 subjects were finally evaluated. The values of the evaluated parameters were: CoV, 48.7%±1.7%; TVD, 48.1%±5.4%; TVROI4, 7.1%±1.8%; GI, 0.49±0.04; and RVDSD, 7.0±2.0. The coefficients of variation for CoV and GI were low (0.03 and 0.07, respectively), but those for TVROI4 and RVDSD were comparatively high (0.26 and 0.28, respectively). None of the evaluated parameters showed a significant correlation with age. The GI index showed a weak but significant correlation with body mass index (R=0.29, P=0.01). The RVDSD was slightly higher in males than in females.ConclusionsOur study indicated that CoV and GI were stable parameters with small coefficients of variation in participants with healthy lungs. The creation of EIT parameter reference values for setting treatment targets may be feasible.

Model Selection Based Algorithm in Neonatal Chest EIT.

This paper presents a new method for selecting a patient specific forward model to compensate for anatomical variations in electrical impedance tomography (EIT) monitoring of neonates. The method uses a combination of shape sensors and absolute reconstruction. It takes advantage of a probabilistic approach which automatically selects the best estimated forward model fit from pre-stored library models. Absolute/static image reconstruction is performed as the core of the posterior probability calculations. The validity and reliability of the algorithm in detecting a suitable model in the presence of measurement noise is studied with simulated and measured data from 11 patients. The paper also demonstrates the potential improvements on the clinical parameters extracted from EIT images by considering a unique case study with a neonate patient undergoing computed tomography imaging as clinical indication prior to EIT monitoring. Two well-known image reconstruction techniques, namely GREIT and tSVD, are implemented to create the final tidal images. The impacts of appropriate model selection on the clinical extracted parameters such as center of ventilation and silent spaces are investigated. The results show significant improvements to the final reconstructed images and more importantly to the clinical EIT parameters extracted from the images that are crucial for decision-making and further interventions.

SUN-397 The Osteosee System Measurements, Based on Parametric Electrical Impedance Tomography, Correlate with Dual X-Ray Absorptiometry Results for the Diagnosis of Osteoporosis

Introduction: Dual X-Ray Absorptiometry (DXA) is the gold standard for the diagnosis of osteoporosis, but it has its pitfalls. The OsteoSee @Clinic is a novel portable and user-friendly system, which uses parametric Electrical Impedance Tomography (pEIT), being developed to allow screening and diagnosis of osteoporosis at the primary care clinic Aim: To test the new system and compare its results to those of the DXA system. Methods and Subjects: This prospective study was conducted between 01/01/2019 and 01/06/2019. Subjects who presented for a routine DXA scan (lumbar spine and proximal femur with Lunar Prodigy GE healthcare system) were enrolled. After signing an informed consent form, they were scanned with the OsteoSee @Clinic system (OsteoSee Ltd., Israel) using 5 electrodes placed around the left distal forearm and around the pelvis. Results: OsteoSee @Clinic data were compared to DXA total hip bone mineral density (BMD). Correlations were examined between pEIT-index of the pelvis versus DXA total hip BMD. Sensitivity and specificity were calculated according to the diagnosis obtained by DXA based on the total hip T-score. An analysis based on 182 subjects (35 healthy, 115 osteopenia, 32 osteoporosis) scanned on the wrist showed an R-value of 0.795 (p-value < 0.001) representing the correlation between the pEIT-wrist index and DXA results. From the ROC plot, we obtained a sensitivity of 84% and specificity of 71% to diagnose osteoporotic vs osteopenic & normal subjects, and a sensitivity of 82% and specificity of 86% for identifying osteopenic & osteoporotic vs normal subjects. An analysis of 98 subjects (17 healthy, 66 osteopenic, 15 osteoporosis) scanned on the pelvis showed an R-value of 0.740 (p-value < 0.001), representing the correlation between the pEIT-pelvis index and DXA BMD. From the ROC plot, we obtained a sensitivity of 80% and specificity of 81% to diagnose osteoporotic vs osteopenic & normal subjects, and a sensitivity of 70% and specificity of 76% for identifying osteopenic & osteoporotic Vs normal subjects. Conclusions: The OsteoSee @Clinic system results correlate well with DXA measurements, especially when taking into account clinical interpolations. Sensitivity and specificity values indicate that the OsteoSee @Clinic system can provide screening and diagnosis of osteoporosis. With the DXA system being costly to operate and inaccessible to many patients, the OsteoSee @Clinic system may address the unmet need for diagnosing and treating osteoporosis, and offer an alternative for a broader screening of the population at risk of fractures.Disclosure: The study was funded by OsteoSee Ltd., Israel

Effect of sternal electrode gap and belt rotation on the robustness of pulmonary electrical impedance tomography parameters

Objective:Non-adhesive textile electrode belts offer several advantages over adhesive electrodes and are increasingly used in neonatal patients during continuous electrical impedance tomography (EIT) lung monitoring. However, non-adhesive belts may rotate in unsedated patients and discrepancies between chest circumference and belt sizes may result in a gap between electrodes near the sternum. This project aimed to determine the effects of belt rotation and sternal electrode gap on commonly used lung EIT parameters.Approach:We developed a simulation framework based on a 3D finite-element model and introduced lung regions with little or no ventilation that could be changed according to a decremental positive end-expiratory pressure (PEEP) trial. Four degrees of sternal gap and belt rotation were simulated and their effect on the EIT parameters silent spaces, centre of ventilation, global inhomogeneity index and overdistension/collapsed lung (OD/CL) analysed. Additionally, seven premature infants were examined to assess the influence of leftward and rightward belt rotations in a clinical setting.Main results:Small violations of the electrode equidistance criterion and rotations of the belts less than one electrode space exert only minor effects on the EIT parameters and do not impede the interpretation. Rotations of two and three electrode spaces induce non-negligible effects that might lead to flawed interpretations. The ‘best PEEP’ determined with the OD/CL approach was robust and identifiable with all studied sternal gaps and belt rotations.Significance:We revealed an important challenge for neonatal EIT applications related to a wide electrode gap at the sternum and belt rotation, which should be avoided in clinical application.

Comparison of two experimental ARDS models in pigs using electrical impedance tomography.

BackgroundAnimal trials contribute to major achievements in medical science. The so-called lavage model is frequently used to evaluate ventilation strategies in acute respiratory distress syndrome (ARDS) using electrical impedance tomography (EIT). But, the lavage model itself might have systematic impacts on EIT parameters. Therefore, we established an additional experimental model, in which ARDS is caused by intravenously administered lipopolysaccharide (LPS). In this study, we want to examine if EIT measurements provide consistent results in both experimental models or whether the pathophysiology of the model influences the findings. Overall, we want to compare both experimental models regarding clinical parameters and EIT-derived indices, namely the global inhomogeneity (GI) index and the regional ventilation delay (RVD) index.MethodsNineteen pigs were included in this study, allocated to the control group (CO; n = 5), lavage group (LAV; n = 7) and LPS group (LPS; n = 7). After baseline measurements and the establishment of ARDS, assessment of respiratory mechanics, hemodynamics, gas exchange and EIT recordings were performed hourly over eight hours.ResultsIn both experimental ARDS models, EIT measurements provided reliable results. But, the GI and the RVD index did not show consistent results as compared to the CO group. Initially, GI and RVD index were higher in the LAV group but not in the LPS group as compared to the CO group. This effect disappeared during the study. Furthermore, the GI index and the RVD index were higher in the LAV group compared to the LPS group in the beginning as well. This, once again, disappeared. Clinical lung injury parameters remained more stable when using LPS.ConclusionThe two models showed quite different influences on the GI and RVD index. This implies, that the underlying pathophysiology affects EIT parameters and thus the findings. Hence, translation to EIT-guided clinical therapy in humans suffering from ARDS might be limited.

Simulation of impedance changes with a FEM model of a myelinated nerve fibre

Objective. Fast neural electrical impedance tomography (EIT) is a method which permits imaging of neuronal activity in nerves by measuring the associated impedance changes (dZ). Due to the small magnitudes of dZ signals, EIT parameters require optimization, which can be done using in silico modelling: apart from predicting the best parameters for imaging, it can also help to validate experimental data and explain the nature of the observed dZ. This has previously been completed for unmyelinated fibres, but an extension to myelinated fibres is required for the development of a full nerve model which could aid imaging neuronal traffic at the fascicular level and optimise neuromodulation of the supplied internal organs to treat various diseases. Approach. An active finite element method (FEM) model of a myelinated fibre coupled with external space was developed. A spatial dimension was added to the experimentally validated space-clamped model of a human sensory fibre using the double cable paradigm. Electrical parameters of the model were changed so that nodal and internodal membrane potential as well as propagation velocity agreed with experimental values. Impedance changes were simulated during activity under various conditions and the optimal parameters for imaging were determined. Main results. When using AC, dZ could be recorded only at frequencies above 4 kHz, which is supported by experimental data. Optimal bandwidths for dZ measurement were found to increase with AC frequency. Significance. The novel fully bi-directionally coupled FEM model of a myelinated fibre was able to optimize EIT for myelinated fibres and explain the biophysical basis of the measured signals.