Simultaneous Electrical Impedance Tomography Research Articles

Evaluation of Different Contrast Agents for Regional Lung Perfusion Measurement Using Electrical Impedance Tomography: An Experimental Pilot Study.

Monitoring regional blood flow distribution in the lungs appears to be useful for individually optimizing ventilation therapy. Electrical impedance tomography (EIT) can be used at the bedside for indicator-based regional lung perfusion measurement. Hypertonic saline is widely used as a contrast agent but could be problematic for clinical use due to potential side effects. In five ventilated healthy pigs, we investigated the suitability of five different injectable and clinically approved solutions as contrast agents for EIT-based lung perfusion measurement. Signal extraction success rate, signal strength, and image quality were analyzed after repeated 10 mL bolus injections during temporary apnea. The best results were obtained using NaCl 5.85% and sodium-bicarbonate 8.4% with optimal success rates (100%, each), the highest signal strengths (100 ± 25% and 64 ± 17%), and image qualities (r = 0.98 ± 0.02 and 0.95 ± 0.07). Iomeprol 400 mg/mL (non-ionic iodinated X-ray contrast medium) and Glucose 5% (non-ionic glucose solution) resulted in mostly well usable signals with above average success rates (87% and 89%), acceptable signal strength (32 ± 8% and 16 + 3%), and sufficient image qualities (r = 0.80 ± 0.19 and 0.72 ± 0.21). Isotonic balanced crystalloid solution failed due to a poor success rate (42%), low signal strength (10 ± 4%), and image quality (r = 0.43 ± 0.28). While Iomeprol might enable simultaneous EIT and X-ray measurements, glucose might help to avoid sodium and chloride overload. Further research should address optimal doses to balance reliability and potential side effects.

Standalone electrical impedance tomography predicts spirometry indicators and enables regional lung assessment.

Electrical impedance tomography (EIT) is a bio-medical imaging modality that has several clinical applications namely for human lungs. Yet, its relationship with gold standard lung diagnostic tools including spirometry is not available. In this study, simultaneous EIT and spirometry measurements were collected for 14 healthy subjects who performed forced breathing paradigms of different efforts simulating a wide range of spirometry indicators. It is demonstrated that EIT can predict standard spirometry indicators over a wide dynamic range, with a potential sensitivity and specificity of 98% and 100%, respectively, in detecting obstructive patterns. It is also shown that EIT can provide a regional mapping of the spirometry indicator which are shown to be consistent with their corresponding global indicators. Overall, EIT can predict spirometry indicators and can assess regional lung health through parametric mapping. Clinical Relevance- This study shows that EIT can infer standard spirometry indicators and potentially assess regional lung health. Therefore, EIT can be used for screening, diagnosis, and monitoring of obstructive and resistive lung diseases.

On the Implementation of Simultaneous Multi-Frequency Excitations and Measurements for Electrical Impedance Tomography

The investigation of quickly-evolving flow patterns in high-pressure and high-temperature flow rigs requires the use of a high-speed and non-intrusive imaging technique. Electrical Impedance Tomography (EIT) allows reconstructing the admittivity distribution characterizing a flow from the knowledge of currents and voltages on its periphery. The need for images at high frame rates leads to the strategy of simultaneous multi-frequency voltage excitations and simultaneous current measurements, which are discriminated using fast Fourier transforms. The present study introduces the theory for a 16-electrode simultaneous EIT system, which is then built based on a field programmable gate array data acquisition system. An analysis of the propagation of uncertainties through the measurement process is investigated, and experimental results with fifteen simultaneous signals are presented. It is shown that the signals are successfully retrieved experimentally at a rate of 1953 frames per second. The associated signal-to-noise ratio varies from 59.6–69.1 dB, depending on the generated frequency. These preliminary results confirm the relevance and the feasibility of simultaneous multi-frequency excitations and measurements in EIT as a means to significantly increase the imaging rate.

Real-Time Identification of Upper Airway Occlusion Using Electrical Impedance Tomography.

Real-time monitoring of upper airway collapse during sleep could be instrumental for studies in biomechanics of obstructive sleep apnea (OSA) and selecting individualized treatment modalities. Although some imaging techniques are used under sedated sleep, none are available during the entire natural sleep process. We hypothesized that electrical impedance tomography (EIT) can be used for noninvasive continuous imaging of the upper airway during natural sleep and quantifying upper airway collapse in terms of its size. After determining surface landmarks to attach the electrodes for monitoring the retroglossal airway, EIT was conducted in 10 healthy participants. As a feasibility test of EIT in detecting upper airway collapse, transient airway closure was induced by the swallowing maneuver. These EIT images were confirmed by simultaneous magnetic resonance imaging (MRI) scans. Subsequently, EIT scans were conducted in 7 healthy participants and 10 patients with OSA under nonsedated sleep to determine whether it could identify upper airway narrowing or collapse. Respiratory events were identified by concurrent polysomnography (PSG). Swallowing-induced airway closure was identified successfully in all 10 participants on simultaneous EIT and MRI scans. Sizes and positions of the upper airway closures in reconstructed EIT images were well correlated with those in magnetic resonance images. Obstructive hypopnea and apnea were detected successfully by EIT in 10 patients with OSA, and no significant changes in EIT data were observed in 7 healthy participants during concurrent EIT and PSG tests. Additionally, conductivity changes in the airway were greater during obstructive apnea than during hypopnea (64.3% versus 26.3%, respectively; P < .001) compared with those during baseline respiration. EIT could be a useful real-time monitoring device for detecting upper airway narrowing or collapse during natural sleep in patients with OSA. Currently, changes in the upper airway size can be estimated with good accuracy, but shape estimation needs future improvements in the EIT image quality.

Global and regional lung function in cystic fibrosis measured by electrical impedance tomography.

Electrical impedance tomography (EIT) delivers information about global and regional ventilation. Linearity of EIT during tidal breathing is known. We investigated the feasibility of EIT during lung function tests in pediatric patients with cystic fibrosis (CF) and healthy controls. Eleven CF patients and 11 age-matched controls underwent spirometry and simultaneous EIT. Global EIT results were scaled to spirometric forced vital capacity (FVC). Subsequently, global and regional "EIT-spirometry" was calculated and correlated with clinical findings, radiology, and lung function results before and after bronchospasmolysis (BSL). Spirometry and global EIT results correlated essentially (r2 = 0.71-1.0, P < 0.001). While lung function results were comparable for both groups, EIT demonstrated inhomogeneous ventilation and individual changes after BSL. EIT changes during forced expiration correlate with lung function parameters, clinical findings, and radiology. Regional analysis of EIT illustrates regional lung function and visualizes individual therapeutic effects. Pediatr Pulmonol. 2016;51:1191-1199. © 2016 Wiley Periodicals, Inc.

Epoprostenol-induced pulmonary vasodilatation in patients with pulmonary hypertension measured by electrical impedance tomography

Electrical impedance tomography (EIT) has been proposed as a method to monitor dynamic changes in the pulmonary vascular bed. In this study we examined the validity of EIT in the measurement of pulmonary vasodilatation in eight patients with primary and secondary pulmonary hypertension when given the vasodilating agent epoprostenol (Flolan®). Therefore, catheterization of the pulmonary artery was performed in the ICU and the cardiac output was measured by means of the Fick method. The pulmonary vascular resistance (PVR) and mean pulmonary arterial pressure (mPAP) were determined. Epoprostenol was given in increasing doses to test reversibility of pulmonary hypertension. The maximum test dose was 12 ng kg−1 min−1. During each step simultaneous EIT (DAS-01 P Portable Data Acquisition System, Sheffield, England) measurements were performed with the 16 electrodes equidistantly positioned in the third intercostal space. The maximal systolic impedance change, relative to end-diastole, ΔZperf, was chosen as a measure of pulmonary perfusion. The impedance change between baseline and highest tolerable epoprostenol concentration was compared with the change in PVR.The mean PVR (dyn s/cm5) decreased from 636 (±399) to 366 (±242): p < 0.01. ΔZperf (in arbitrary units) for the whole patient group increased from 901 (±295) × 10−3 to 1082 (±472) × 10−3 (p < 0.05). Only one patient showed a reduction in pulmonary artery pressure >20%, which is defined as significant vasodilatation. A strong relationship was found between the impedance changes and the change in PVR and mPAP in the patient with a significant vasodilatation on epoprostenol. From these results we conclude that EIT is a reliable method to measure blood volume changes due to pharmacologically induced vasodilatation in the pulmonary bed.

Simultaneous electrical impedance tomography and videofluoroscopy in the assessment of swallowing

Simultaneous videofluoroscopy and electrical impedance tomography (EIT) were performed in 13 patients. Subjects swallowed a low-conductivity and a higher-conductivity bolus of between 5 and 20 ml. EIT images from the two swallows were then subtracted to cancel out movement related changes. The peak in the conductivity change was most closely associated in time with a point at which the pharynx is filled with bolus: this suggests that the subtraction process does produce data and images which are related to the bolus rather than to movement of involved structures. The full width at 50% and 75% of the maximum of the time conductivity plot was correlated with the time taken for the bolus to be cleared from the mouth (r = 0.63 and 0.68 respectively, p < 0.05 for both). Despite the sampling frequency of only 9 frames , compared to 50 frames for videofluoroscopy, EIT recordings from the neck are able to detect the presence of a conductive bolus in the pharynx and for the first time the relationship between parameters of an EIT time - conductivity plot and a measure of bolus transit using an accepted technique has been established. Keywords: electrical impedance tomography, videofluoroscopy, dysphagia, swallowing

Detection of gastroesophageal reflux by electrical impedance tomography.

In children with vomiting, dyspepsia, and feeding problems, gastroesophageal reflux (GOR) and altered gastric emptying are common. We have used electrical impedance tomography (EIT) to study children with suspected gastric emptying disorders. Abnormalities of the gastric emptying curve suggestive of GOR were seen in some, with marked negative or positive shifts related to sharp increases or decreases in intragastric resistance. These findings could represent fluid leaving or entering the stomach, as might occur in GOR. To confirm the origin of the abnormal EIT curves, we devised and in vitro tank test system, and we performed simultaneous 2-h EIT and intraoesophageal pH monitoring after a glucose meal on six patients. In vitro, reflux of > or = 25 ml produced clearly detectable changes on the emptying curves. In vivo, the overall correlation between the times of 42 GOR episodes lasting > or = 1 min detected by pH study and the times of 38 negative peaks due to > or = 15% changes of the maximum intragastric resistivity detected by simultaneous EIT was significant; the correlation was highly significant in four of six patients. When the peaks were used to define GOR episodes on EIT gastric emptying curves, the two methods still showed good agreement. Retrospective examination of 50 patients who had undergone both EIT and 24-h intraoesophageal pH study during their diagnostic workup showed that EIT had a sensitivity of 94.6% and a specificity of 76.9% (with positive and negative predictive values of 0.92 and 0.83, respectively) for the detection of pathological GOR.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of Gastroesophageal Reflux by Electrical Impedance Tomography

SummaryIn children with vomiting, dyspepsia, and feeding problems, gastroesophageal reflux (GOR) and altered gastric emptying are common. We have used electrical impedance tomography (EIT) to study children with suspected gastric emplying disorders. Abnormalities of the gastric emptying curve suggestive of GOR were seen in some, with marked negative or positive shifts related to sharp increases or decreases in intragastric resistance. These findings could represent fluid leaving or entering the stomach, as might occur in GOR. To confirm the origin of the abnormal EIT curves, we devised and in vitro tank test system, and we performed simultaneous 2‐h EIT and intraoesophageal pH monitoring after a glucose meal on six patients. In vitro, reflux of ±25 ml produced clearly detectable changes on the emptying curves. In vivo, the overall correlation between the times of 42 GOR episodes lasting ±1 min detected by pH study and the times of 38 negative peaks due to ±15% changes of the maximum intragastric resistivity detected by simultaneous EIT was significant; the correlation was highly significant in four of six patients. When the peaks were used to define GOR episodes on EIT gastric emptying curves, the two methods still showed good agreement. Retrospective examination of 50 patients who had undergone both EIT and 24‐h intraoesophageal pH study during their diagnostic workup showed that EIT had a sensitivity of 94.6% and a specificity of 76.9% (with positive and negative predictive values of 0.92 and 0.83, respectively) for the detection of pathological GOR. We have shown, for the first time that EIT not only allows gastric emptying to be measured but can also detect GOR. Therefore, EIT can be used as a noninvasive screening test in patients with vomiting, dyspepsia, and feeding problems.