Abstract. An algorithm for objectively calculating the hyperparameter for the class of linearized one step EIT image reconstruction algorithms is proposed and compared to existing strategies. EIT is an ill-conditioned problem in which regularization is used to calculate a stable and accurate solution by incorporating some form of prior knowledge into the solution. A hyperparameter is used to control the balance between conformance to data and conformance to the prior. A remaining challenge is to develop and validate methods of objectively selecting the hyperparameter. In this paper evaluate an compare and evaluate five different strategies for hyperparameter selection. We propose a calibration based method of objective hyperparameter selection, called BestRes, that leads to repeatable and stable image reconstructions that are indistinguishable from heuristic selections. Results indicate: 1) heuristic selections of hyperparameter are inconsistent among experts, 2) Generalized Cross-Validation approaches produce under-regularized solutions, 3) L-Curve approaches are unreliable for EIT, and 4) BestRes produces good solutions comparable to expert selections. Additionally, we show that it is possible to reliably detect an inverse crime based on analysis of these parameters.
This paper investigates several configurations for placing electrodes on a 3D cylindrical medium to reconstruct 3D images using 16 electrode EIT equipment intended for use with a 2D adjacent drive protocol. Seven different electrode placement configurations are compared in terms of the following figures of merit: resolution, radial and vertical position error, image magnitude, immunity to noise, immunity to electrode placement errors, and qualitative evaluation of image artefacts. Results show that for ideal conditions, none of the configurations considered performed significantly better than the others. However, when noise and electrode placement errors were considered the planar electrode placement configuration (two rings of vertically aligned electrodes with electrodes placed sequentially in each ring) had the overall best performance. Based on these results, we recommend planar electrode placement configuration for 3D EIT lung imaging of the thorax.
We test strategies for placing EIT electrodes on a 3D medium for the purpose of calculating 3D reconstructions using clinical equipment intended for use with a 2D adjacent drive protocol. The goal of this work was to compare seven such strategies in order to determine if any were clearly superior to the others for clinical applications. For the limited set of strategies investigated, none were significantly better than the others in terms of performance under ideal conditions. However, when noise and electrode placement errors were considered the Planar Electrode Placement Strategy emerged as a recommended strategy for clinical use.
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