title: Computed tomography dose and variability of airway dimension measurements: how low can we go?
abstract: BACKGROUND
  Quantitative CT shows promise as an outcome measure for cystic fibrosis (CF) lung disease in infancy, but must be accomplished at a dose as low as reasonably achievable.
  
  
  OBJECTIVE
  To determine the feasibility of ultra-low-dose CT for quantitative measurements of airway dimensions.
  
  
  METHODS
  Two juvenile pigs were anesthetized and their lungs scanned at 25 cm H(2)O face-mask pressure in apnoea using beam currents of 5, 10, 20, 40 and 100 mAs. The lumen diameters and wall thicknesses of matched airways (n=22) at each dose were measured by two observers using validated software. Measurement variability at each dose was compared to that at 100 mAs (reference dose) for large and small airways (lumen diameter <2.5 mm).
  
  
  RESULTS
  Lowering CT dose (mAs) affected measurement variability for lumen diameter of small and large airways (P<0.001) and for wall thickness of small (P<0.001), but not large (P=0.63), airways. To obtain the same measurement variability at 5 mAs as at 100 mAs, four to six small airways or one to three large airways have to be measured and averaged.
  
  
  CONCLUSIONS
  Quantitative airway measurements are feasible on images obtained at as low as 5 mAs, but more airways need to be measured to compensate for greater measurement variability.
authors.affiliation: Department of Radiology, Meander Medical Centre, Amersfoort, The Netherlands.
authors.forename: Pim A
authors.initials: PA
authors.lastname: de Jong
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Long
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Nakano
mesh_terms: D000818:Animals; D003550:Cystic Fibrosis / Q000000981:diagnostic imaging / Q000473:pathology; D004195:Disease Models, Animal; D011829:Radiation Dosage; D012137:Respiratory System / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*