title: Functional validation and comparison framework for EIT lung imaging.
abstract: BACKGROUND
  Electrical impedance tomography (EIT) is an emerging clinical tool for monitoring ventilation distribution in mechanically ventilated patients, for which many image reconstruction algorithms have been suggested. We propose an experimental framework to assess such algorithms with respect to their ability to correctly represent well-defined physiological changes. We defined a set of clinically relevant ventilation conditions and induced them experimentally in 8 pigs by controlling three ventilator settings (tidal volume, positive end-expiratory pressure and the fraction of inspired oxygen). In this way, large and discrete shifts in global and regional lung air content were elicited.
  
  
  METHODS
  We use the framework to compare twelve 2D EIT reconstruction algorithms, including backprojection (the original and still most frequently used algorithm), GREIT (a more recent consensus algorithm for lung imaging), truncated singular value decomposition (TSVD), several variants of the one-step Gauss-Newton approach and two iterative algorithms. We consider the effects of using a 3D finite element model, assuming non-uniform background conductivity, noise modeling, reconstructing for electrode movement, total variation (TV) reconstruction, robust error norms, smoothing priors, and using difference vs. normalized difference data.
  
  
  CONCLUSIONS
  Our results indicate that, while variation in appearance of images reconstructed from the same data is not negligible, clinically relevant parameters do not vary considerably among the advanced algorithms. Among the analysed algorithms, several advanced algorithms perform well, while some others are significantly worse. Given its vintage and ad-hoc formulation backprojection works surprisingly well, supporting the validity of previous studies in lung EIT.
authors.affiliation: Department of Medical Physics in Radiology, German Cancer Research Centre (DKFZ), Heidelberg, Germany; Fraunhofer Project Group for Automation in Medicine and Biotechnology, Mannheim, Germany.
authors.forename: Bartłomiej
authors.initials: B
authors.lastname: Grychtol
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center of Schleswig-Holstein, Kiel, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Elke
authors.affiliation: Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital Frankfurt, Frankfurt am Main, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Meybohm
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center of Schleswig-Holstein, Kiel, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Weiler
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center of Schleswig-Holstein, Kiel, Germany.
authors.forename: Inéz
authors.initials: I
authors.lastname: Frerichs
authors.affiliation: Systems and Computer Engineering, Carleton University, Ottawa, Ontario, Canada.
authors.forename: Andy
authors.initials: A
authors.lastname: Adler
mesh_terms: D000465:Algorithms; D017097:Electric Impedance; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000502:physiology*; D012121:Respiration, Artificial; D012129:Respiratory Function Tests; D012984:Software; D014054:Tomography / Q000379:methods*
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