title: Air trapping in children: evaluation with dynamic lung densitometry with spiral CT.
abstract: OBJECTIVE
  To evaluate the feasibility of the use of a simple method of dynamic lung densitometry with spiral computed tomography (CT) to differentiate air trapping from compensatory hyperinflation in children.
  
  
  METHODS
  Eight children (mean age, 4 years 2 months) who had focal areas of radiolucency on chest radiographs underwent spiral CT (5-second acquisition time, fixed table position) during quiet breathing. Data were reconstructed with 0.7-second temporally overlapping scans. Lung attenuation in selected regions of interest was plotted against time.
  
  
  RESULTS
  In children with air trapping (n = 5), mean lung attenuation (+/- 1 standard deviation) in hyperlucent regions was -815 HU +/- 52, and mean respiratory excursion was 28 HU +/- 7. In patients with compensatory hyperinflation (n = 4), mean lung attenuation was -664 HU +/- 31, and respiratory excursion was 84 HU +/- 15. The differences were statistically significant (P = .001 for mean attenuation; P < .0005 for respiratory excursion).
  
  
  CONCLUSIONS
  Dynamic spiral CT lung densitometry is a quick, simple method for quantitative confirmation of the presence of air trapping and differentiation from compensatory hyperinflation.
authors.affiliation: Department of Radiology, Children's Hospital of Philadelphia, PA 19104, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Johnson
authors.forename: S S
authors.initials: SS
authors.lastname: Kramer
authors.forename: S
authors.initials: S
authors.lastname: Mahboubi
mesh_terms: D015502:Absorptiometry, Photon; D002675:Child, Preschool; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008171:Lung Diseases / Q000000981:diagnostic imaging; D019568:Lung, Hyperlucent / Q000000981:diagnostic imaging*; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*