Optimal selection of threshold in EIT reconstructed images for estimating size of objects

Abstract

It is useful to convert reconstructed images to binary form for quantitatively establishing shapes and sizes of objects. In this work, we present guidelines for selecting appropriate threshold values based on systematic numerical investigations assuming prior knowledge of conductivity contrast. Various configurations of objects immersed in a background were considered. Open source software electrical impedance diffused optical reconstruction software (EIDORS) was used for reconstructing differential EIT images for these configurations. Diametric conductivity profiles were used to identify appropriate values of threshold to obtain accurate object size over a wide range of contrast. The calculated values of threshold and the resulting effect on estimated object size were compared with the usually preferred thresholds of 1/2 (FWHM) and 1/4 (FWQM) of maximum amplitude on the basis of size accuracy. It was found that the proposed threshold offers better size accuracy with respect to change in position and size of the object over a wide range of contrasts. The proposed threshold values were found to work satisfactorily for 15 dB signal to noise ratio and 10% error in conductivity contrast.