title: Functional Regions of Interest in Electrical Impedance Tomography: A Secondary Analysis of Two Clinical Studies.
abstract: BACKGROUND
  Patients with acute respiratory distress syndrome (ARDS) typically show a high degree of ventilation inhomogeneity, which is associated with morbidity and unfavorable outcomes. Electrical impedance tomography (EIT) is able to detect ventilation inhomogeneity, but it is unclear which method for defining the region of interest (ROI) should be used for this purpose. The aim of our study was to compare the functional region of interest (fROI) method to both the lung area estimation method (LAEM) and no ROI when analysing global parameters of ventilation inhomogeneity. We assumed that a good method for ROI determination would lead to a high discriminatory power for ventilation inhomogeneity, as defined by the area under the receiver operating characteristics curve (AUC), comparing patients suffering from ARDS and control patients without pulmonary pathologies.
  
  
  METHODS
  We retrospectively analysed EIT data from 24 ARDS patients and 12 control patients without pulmonary pathology. In all patients, a standardized low-flow-pressure volume maneuver had been performed and was used for EIT image generation. We compared the AUC for global inhomogeneity (GI) index and coefficient of variation (CV) between ARDS and control patients using all EIT image pixels, the fROI method and the LAEM for ROI determination.
  
  
  RESULTS
  When analysing all EIT image pixels, we found an acceptable AUC both for the GI index (AUC = 0.76; 95% confidence interval (CI) 0.58-0.94) and the CV (AUC = 0.74; 95% CI 0.55-0.92). With the fROI method, we found a deteriorating AUC with increasing threshold criteria. With the LAEM, we found the best AUC both for the GI index (AUC = 0.89; 95% CI 0.78-1.0) and the CV (AUC = 0.89; 95% CI 0.78-1.0) using a threshold criterion of 50% of the maximum tidal impedance change.
  
  
  CONCLUSIONS
  In the assessment of ventilation inhomogeneity with EIT, functional regions of interest obscure the difference between patients with ARDS and control patients without pulmonary pathologies. The LAEM is preferable to the fROI method when assessing ventilation inhomogeneity.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Str. 3, Haus 12, 24105, Kiel, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Becher
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Str. 3, Haus 12, 24105, Kiel, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Vogt
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Str. 3, Haus 12, 24105, Kiel, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kott
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Str. 3, Haus 12, 24105, Kiel, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schädler
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Str. 3, Haus 12, 24105, Kiel, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Weiler
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Arnold-Heller-Str. 3, Haus 12, 24105, Kiel, Germany.
authors.forename: Inéz
authors.initials: I
authors.lastname: Frerichs
mesh_terms: D016022:Case-Control Studies; D017097:Electric Impedance; D006801:Humans; D012372:ROC Curve; D012189:Retrospective Studies; D014054:Tomography / Q000379:methods*