title: Optimal imaging protocol for measuring dynamic expiratory collapse of the central airways.
abstract: OBJECTIVE
  To compare measurements of expiratory collapse obtained using multidetector computed tomography (MDCT) of the central airways on routine axial and multiplanar reformatted (MPR) images.
  
  
  METHODS
  Fifty volunteers with normal pulmonary function and no smoking history were imaged using a 64 MDCT system (40 mAs, 120 kVp, 0.625 mm collimation) with spirometric monitoring at end-inspiration and during forced expiration. Measurements of the trachea, right main (RMB) and left main bronchus (LMB) were obtained on axial and MPR images. Inspiratory and dynamic-expiratory cross-sectional area (CSA) measurements were used to calculate the mean percentage expiratory collapse (%Collapse). A paired t-test was used to assess within-subject differences and a Bland-Altman plot was used to assess agreement between the methods.
  
  
  RESULTS
  Among 24 men and 26 women (mean age±standard deviation 50±15 years), CSA values were significantly greater on axial than MPR images (all p<0.001); however, the mean difference in %Collapse values for axial versus MPR were small: trachea ≈1% (55 ±19 versus 56±18, p=0.338); LMB identical (60±20 versus 60±17 p=0.856); and, RMB 4% (62 ±19 versus 66±19 p<0.001). On average, creation of MPR required 12 minutes of additional time per case (range=10-15 min).
  
  
  CONCLUSIONS
  Differences in mean %Collapse for axial versus MPR images were small and unlikely to influence clinical management. This finding suggests that MPR may not be indicated for routine assessment of central airway collapse.
authors.affiliation: Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, USA; Department of Pediatric Pulmonology, Sophia Children's Hospital, Erasmus Medical Center, Rotterdam, The Netherlands; Department of Radiology, Sophia Children's Hospital, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Ciet
authors.affiliation: Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Boiselle
authors.affiliation: Yale School of Medicine, LCI 100C, 20 York Street, New Haven, CT 06510, USA.
authors.forename: G
authors.initials: G
authors.lastname: Michaud
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, USA.
authors.forename: C
authors.initials: C
authors.lastname: O'Donnell
authors.affiliation: Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, USA. Electronic address: dlitmano@bidmc.harvard.edu.
authors.forename: D E
authors.initials: DE
authors.lastname: Litmanovich
mesh_terms: D000328:Adult; D000368:Aged; D045853:Exhalation; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D013147:Spirometry; D055089:Tracheobronchomalacia / Q000000981:diagnostic imaging*