title: A lung area estimation method for analysis of ventilation inhomogeneity based on electrical impedance tomography.
abstract: OBJECTIVE
  To evaluate a novel method for lung area estimation (LAE method) in electrical impedance tomography (EIT) images as a prerequisite of quantitative analysis of ventilation inhomogeneity.
  
  
  METHODS
  The LAE method mirrors the lung regions in the functional EIT (fEIT) image and subsequently subtracts the cardiac related areas. In this preliminary study, 51 mechanically ventilated patients were investigated, including 39~patients scheduled for thoracic surgery (test group); 10 patients scheduled for orthopedic surgery without pulmonary disease (control group) and 2 ICU patients undergoing chest computed tomography (CT) examination. EIT data was recorded in all groups. The results of the LAE method were compared to those obtained with the fEIT method and to CT images.
  
  
  RESULTS
  The lung area size determined with fEIT in control group is S(C,fEIT) = 361 +/- 35 (mean +/- SD) and in test group S(T,fEIT) = 299 +/- 61 (p< 0.01). The sizes estimated with the LAE method in control group S(C,LAE) = 353 +/- 27 and in test group S(T,LAE) = 353 +/- 61 (p=0.41). The result demonstrates that the novel LAE method improves the identification of lung region in EIT images, from which the analysis of ventilation distribution will benefit. The preliminary comparison with CT images exemplary indicates a closer match of the lung area shapes after the LAE than after the fEIT-based analysis.
  
  
  CONCLUSIONS
  The LAE method is a robust lung area determination method, suitable for patients with healthy or seriously injured lungs.
authors.affiliation: Department of Biomedical Engineering, Furtwangen University, Villingen-Schwenningen, Germany. zhanqi.zhao@hs-furtwangen.de
authors.forename: Zhanqi
authors.initials: Z
authors.lastname: Zhao
authors.forename: Daniel
authors.initials: D
authors.lastname: Steinmann
authors.forename: Danijela
authors.initials: D
authors.lastname: Müller-Zivkovic
authors.forename: Jörg
authors.initials: J
authors.lastname: Martin
authors.forename: Inéz
authors.initials: I
authors.lastname: Frerichs
authors.forename: Josef
authors.initials: J
authors.lastname: Guttmann
authors.forename: Knut
authors.initials: K
authors.lastname: Möller
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D016014:Linear Models; D008168:Lung / Q000033:anatomy & histology*; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D013909:Thorax / Q000033:anatomy & histology; D014054:Tomography / Q000379:methods*