Thoracic EIT in 3D: experiences and recommendations

OBJECTIVE In EIT applications to the thorax,a single electrode plane has typically been used to reconstruct a transverse 2D "slice".However, such images can be misleading as EITis sensitive to contrasts above and below the electrodeplane, and ventilation and aeration inhomogeneitiescan be distributed in complex ways.Using two (or more) electrode planes, 3D EITimages may be reconstructed, but 3Dreconstructions are currently little used in thoracic EIT.In this paper, we investigate an incrementalpathway towards 3D EIT reconstructions,using two electrode planes to calculate improvedtransverse slices as an intermediate step.We recommend a specific placement ofelectrode planes, and further demonstrate the feasibilityof multi-slice reconstruction in two species. Approach: Simulations of the forward and reconstructedsensitivities were analysed for two electrodeplanes using a "square" pattern of electrodeplacement as a function of two variables:the stimulation and measurement "skip",and the electrode plane separation. Next, single- vs. two-plane measurements werecompared in a horse and in human volunteers.We further show the feasibility of 3D reconstructionsby reconstructing multiple transverse and, unusually, frontal slices during ventilation. Main results: Using two electrode planes leads to a reducedposition error and improvement in off-plane contrast rejection. 2D reconstructions from two-plane measurements showed better separation of lungs, as compared to thesingle plane measurements which tend to push contrastsin the center of the image.3D reconstructions of the same data show anatomically plausibleimages, inside as well as outside the volume between the two electrode planes. Significance: Based on the results, we recommend EIT electrodeplanes separated by less than half of the minimum thoracicdimension with a "skip 4" pattern and "square" placementto produce images with good slice selectivity.