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Objective selection of hyperparameter for EIT

B M Graham and A Adler

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An algorithm for objectively calculating the hyperparameter for linearized one-step electrical impedance tomography (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 trade-off 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, we evaluate and compare 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.


PACS

87.63.Pn Electrical impedance tomography (EIT)

06.20.fb Standards and calibration

87.19.R- Mechanical and electrical properties of tissues and organs

87.57.C- Image quality

87.57.N- Image analysis

Subjects

Instrumentation and measurement

Biological physics

Medical physics

Dates

Issue 5 (May 2006)

Received 1 November 2005, accepted for publication 27 February 2006

Published 18 April 2006



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