title: Simultaneous assessment of airway instability and respiratory dynamics with low-dose 4D-CT in chronic obstructive pulmonary disease: a technical note.
abstract: BACKGROUND
  Advanced-stage chronic obstructive pulmonary disease (COPD) is associated with severely altered respiratory dynamics. Dynamic airway instability is usually diagnosed by invasive bronchoscopy. Cine-computed tomography (CT) may be used alternatively, but is limited to predefined anatomical positions. Also, a paradoxical diaphragmatic motion has been described in patients with emphysema.
  
  
  OBJECTIVE
  As the airways and chest wall show inherently high contrast to airway lumen and lung tissue, low-dose CT acquisitions potentially suffice for depicting tracheobronchial and chest wall motion. Therefore, we propose low-dose dynamic respiratory-gated multidetector CT (4D-CT) of the whole chest as a new method to assess respiratory dynamics.
  
  
  METHODS
  4D-CT was performed in 3 patients (52, 62 and 76 years old) with suspected tracheal instability due to COPD or tracheal stenosis at minimal pitch (0.09) and radiation exposure (1.4-1.9 mSv) during regular tidal breathing registered by a belt system. Image reconstruction involved a raw data-based iterative algorithm (1.5-mm slice thickness, 1.0-mm z-axis increment, 5% respiratory increment), resulting in a stack of 6,700 images, which were evaluated with a 4D-viewing tool.
  
  
  RESULTS
  An excessive dynamic collapse of the trachea in combination with tracheobronchomalacia (TBM) of the main-stem and segmental bronchi, and a paradoxical diaphragmatic motion were demonstrated in 1 case. Moreover, we detected a saber-sheath trachea and main-stem TBM in another case. The third case showed a fixed tracheal stenosis.
  
  
  CONCLUSIONS
  4D-CT provides unprecedented z-axis coverage and time-resolved volumetric datasets of the whole chest. Airway instability, stenosis and paradoxical diaphragmatic motion may be assessed simultaneously, preceding interventions such as airway stabilization or lung volume reduction.
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital of Heidelberg, Heidelberg, Germany.
authors.forename: Mark O
authors.initials: MO
authors.lastname: Wielpütz
authors.forename: Ralf
authors.initials: R
authors.lastname: Eberhardt
authors.forename: Michael
authors.initials: M
authors.lastname: Puderbach
authors.forename: Oliver
authors.initials: O
authors.lastname: Weinheimer
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Kauczor
authors.forename: Claus P
authors.initials: CP
authors.lastname: Heussel
mesh_terms: D000368:Aged; D003964:Diaphragm / Q000000981:diagnostic imaging / Q000503:physiopathology; D005240:Feasibility Studies; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology; D015656:Respiratory Mechanics; D035441:Thoracic Wall / Q000000981:diagnostic imaging / Q000503:physiopathology; D014132:Trachea / Q000000981:diagnostic imaging* / Q000503:physiopathology