Quantification of blood volume by electrical impedance tomography using a tissue-equivalent phantom

Rosalind Sadleir, Richard Fox

Research output: Contribution to journalArticle

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Abstract

An in vivo electrical impedance tomography (EIT) system was designed to accurately estimate quantities of intra-peritoneal blood in the abdominal cavity. For this it is essential that the response is relatively independent of the position of the high conductivity anomaly (blood) in the body. The sensitivity of the system to the introduction of blood-equivalent resistivity anomalies was assessed by using a cylindrical tissue-equivalent phantom. It was found that a satisfactorily uniform response of the system in both radial (transverse) and axial (longitudinal) directions in the phantom could be achieved by filtering resistivity profile images obtained by EIT measurement, and by using extended electrodes to collect data. Post-processing of single impedance images gave rise to a quantity denoted the resistivity index. A filter was then used to remove the remaining radial variation of the resistivity index. It was calculated by evaluating the resistivity index of a number of theoretically calculated images, and constructing a correction filter similar to those used to remove lens imperfections, such as coma, in optical components. The 30% increase in the resistivity index observed when an anomaly was moved to the maximum extent allowed by the filter calculation (0.75 of the phantom radius) was reduced by the filter tO 6%. A study of the axial dependence observed in the resistivity index using electrodes extended in the axial direction by ±5 cm found that the variation in resistivity index with axial position was about half of that observed using small circular electrodes similar to those used in the Sheffield mark I system.

Original languageEnglish (US)
Pages (from-to)501-516
Number of pages16
JournalPhysiological Measurement
Volume19
Issue number4
DOIs
StatePublished - Dec 11 1998
Externally publishedYes

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Keywords

  • Electrical impedance tomography
  • Intra-peritoneal bleeding
  • Linearized backprojection
  • Volume estimation

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Biomedical Engineering
  • Physiology (medical)

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