title: Quantification of trapped gas with CT and 3 He MR imaging in a porcine model of isolated airway obstruction.
abstract: OBJECTIVE
  To quantify regional gas trapping in the lung by using computed tomographic (CT)-determined specific gas volume and hyperpolarized helium 3 ((3)He) magnetic resonance (MR) imaging in a porcine model of airway obstruction.
  
  
  METHODS
  Four porcine lungs were removed after sacrifice for unrelated cardiac experiments, for which animal studies approval was obtained. Dynamic expiratory thin-section CT and (3)He MR imaging were performed during passive deflation from total lung capacity after obstructions were created with inverted one-way endobronchial exit valves in segmental or lobar bronchi to produce identifiable regions of trapped gas. Changes in specific gas volume were assessed from CT data for defined regions of interest within and outside of obstructed segments and for entire lobes. Helium 3 data were analyzed according to the corresponding regional signal reduction during expiration, compared with the total magnetic moment at each time point.
  
  
  RESULTS
  In 4.5 seconds of free collapse, volume decreased by 6% +/- 2 (standard error) and 53% +/- 3, respectively, in trapped-gas lobes and in unobstructed regions (P < .0001). Specific gas volume changed by 6% +/- 2 in areas of trapped gas and decreased by 56% +/- 3 in unobstructed regions, from 3.4 mL/g +/- 0.2 to 1.5 mL/g +/- 0.1 (P < .0001). The (3)He signal intensity decreased by 25% +/- 6 and 71% +/- 3, respectively, in trapped-gas and normal regions (P = .0008). In unobstructed regions, the percentage decreases in specific gas volume and (3)He signal intensity were not statistically different from one another (P = .89).
  
  
  CONCLUSIONS
  The results obtained from the model of gas trapping demonstrate that CT-determined specific gas volume and (3)He MR imaging can help identify and quantify the extent of regional trapped gas in explanted porcine lungs.
authors.affiliation: Department of Bioengineering, Politecnico di Milano, Milan, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Salito
authors.forename: Andrea
authors.initials: A
authors.lastname: Aliverti
authors.forename: David S
authors.initials: DS
authors.lastname: Gierada
authors.forename: Gaetan
authors.initials: G
authors.lastname: Deslée
authors.forename: Richard A
authors.initials: RA
authors.lastname: Pierce
authors.forename: Peter T
authors.initials: PT
authors.lastname: Macklem
authors.forename: Jason C
authors.initials: JC
authors.lastname: Woods
mesh_terms: D000402:Airway Obstruction / Q000000981:diagnostic imaging* / Q000473:pathology*; D000818:Animals; D005740:Gases; D006371:Helium; D066298:In Vitro Techniques; D007554:Isotopes; D008168:Lung / Q000000981:diagnostic imaging* / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D013552:Swine; D014057:Tomography, X-Ray Computed
chemical_list: D005740:Gases; D007554:Isotopes; D006371:Helium
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