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Conductivity image enhancement in MREIT using adaptively weighted spatial averaging filter

Authors
  • Oh, Tong In1
  • Kim, Hyung Joong1
  • Jeong, Woo Chul1
  • Wi, Hun1
  • Kwon, Oh In2
  • Woo, Eung Je1
  • 1 Kyung Hee University, Department of Biomedical Engineering and Impedance Imaging Research Center, Yongin, 446-701, Korea , Yongin (South Korea)
  • 2 Konkuk University, Department of Mathematics, Seoul, 143-701, Korea , Seoul (South Korea)
Type
Published Article
Journal
BioMedical Engineering OnLine
Publisher
Springer (Biomed Central Ltd.)
Publication Date
Jun 26, 2014
Volume
13
Issue
1
Identifiers
DOI: 10.1186/1475-925X-13-87
Source
Springer Nature
Keywords
License
Yellow

Abstract

BackgroundIn magnetic resonance electrical impedance tomography (MREIT), we reconstruct conductivity images using magnetic flux density data induced by externally injected currents. Since we extract magnetic flux density data from acquired MR phase images, the amount of measurement noise increases in regions of weak MR signals. Especially for local regions of MR signal void, there may occur excessive amounts of noise to deteriorate the quality of reconstructed conductivity images. In this paper, we propose a new conductivity image enhancement method as a postprocessing technique to improve the image quality.MethodsWithin a magnetic flux density image, the amount of noise varies depending on the position-dependent MR signal intensity. Using the MR magnitude image which is always available in MREIT, we estimate noise levels of measured magnetic flux density data in local regions. Based on the noise estimates, we adjust the window size and weights of a spatial averaging filter, which is applied to reconstructed conductivity images. Without relying on a partial differential equation, the new method is fast and can be easily implemented.ResultsApplying the novel conductivity image enhancement method to experimental data, we could improve the image quality to better distinguish local regions with different conductivity contrasts. From phantom experiments, the estimated conductivity values had 80% less variations inside regions of homogeneous objects. Reconstructed conductivity images from upper and lower abdominal regions of animals showed much less artifacts in local regions of weak MR signals.ConclusionWe developed the fast and simple method to enhance the conductivity image quality by adaptively adjusting the weights and window size of the spatial averaging filter using MR magnitude images. Since the new method is implemented as a postprocessing step, we suggest adopting it without or with other preprocessing methods for application studies where conductivity contrast is of primary concern.

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