Improved Configurations for 3D Acoustoelectric Tomography With a Minimal Number of Electrodes.

OBJECTIVE: Acoustoelectric tomography (AET) is a hybrid imaging technique combining ultrasound and electrical impedance tomography (EIT). It exploits the acoustoelectric effect (AAE): an US wave propagating through the medium induces a local change in conductivity, depending on the acoustoelectric properties of the medium. Typically, AET image reconstruction is limited to 2D and most cases employ a large number of surface electrodes. METHODS: This article investigates the detectability of contrasts in AET. We characterize the AEE signal as a function of the medium conductivity and electrode placement, using a novel 3D analytical model of the AET forward problem. The proposed model is compared to a finite element method simulation. RESULTS: In a cylindrical geometry with an inclusion contrast of 5 times the background and two pairs of electrodes, the maximum, minimum, and mean suppression of the AEE signal are 68.5%, 3.12%, and 49.0%, respectively, over a random scan of electrode positions. The proposed model is compared to a finite element method simulation and the minimum mesh sizes required successfully model the signal is estimated. CONCLUSION: We show that the coupling of AAE and EIT leads to a suppressed signal and the magnitude of the reduction is a function of geometry of the medium, contrast and electrode locations. SIGNIFICANCE: This model can aid in the reconstruction of AET images involving a minimum number of electrodes to determine the optimal electrode placement.

Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses.

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500 mL, in 5-7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2 minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT:spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [-15% (-46-32)] and expiratory [10% (-32-20)] flows and inspiratory [-6% (-25-18)] and expiratory [5% (-9-20)] times. Agreement for nadir flows was poor [-22% (-87-369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horses.