title: Iterative reconstruction for quantitative computed tomography analysis of emphysema: consistent results using different tube currents.
abstract: OBJECTIVE
  To assess the advantages of iterative reconstruction for quantitative computed tomography (CT) analysis of pulmonary emphysema.
  
  
  METHODS
  Twenty-two patients with pulmonary emphysema underwent chest CT imaging using identical scanners with three different tube currents: 240, 120, and 60 mA. Scan data were converted to CT images using Adaptive Iterative Dose Reduction using Three Dimensional Processing (AIDR3D) and a conventional filtered-back projection mode. Thus, six scans with and without AIDR3D were generated per patient. All other scanning and reconstruction settings were fixed. The percent low attenuation area (LAA%; < -950 Hounsfield units) and the lung density 15th percentile were automatically measured using a commercial workstation. Comparisons of LAA% and 15th percentile results between scans with and without using AIDR3D were made by Wilcoxon signed-rank tests. Associations between body weight and measurement errors among these scans were evaluated by Spearman rank correlation analysis.
  
  
  RESULTS
  Overall, scan series without AIDR3D had higher LAA% and lower 15th percentile values than those with AIDR3D at each tube current (P<0.0001). For scan series without AIDR3D, lower tube currents resulted in higher LAA% values and lower 15th percentiles. The extent of emphysema was significantly different between each pair among scans when not using AIDR3D (LAA%, P<0.0001; 15th percentile, P<0.01), but was not significantly different between each pair among scans when using AIDR3D. On scans without using AIDR3D, measurement errors between different tube current settings were significantly correlated with patients' body weights (P<0.05), whereas these errors between scans when using AIDR3D were insignificantly or minimally correlated with body weight.
  
  
  CONCLUSIONS
  The extent of emphysema was more consistent across different tube currents when CT scans were converted to CT images using AIDR3D than using a conventional filtered-back projection method.
authors.affiliation: Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Nishihara, Okinawa, Japan.
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Yamashiro
authors.affiliation: Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Nishihara, Okinawa, Japan.
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Miyara
authors.affiliation: Department of Radiology, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Honda
authors.affiliation: Department of Radiology, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Tomiyama
authors.affiliation: Department of Radiology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Ohno
authors.affiliation: Department of Radiology, Tenri Hospital, Tenri, Nara, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Noma
authors.affiliation: Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Nishihara, Okinawa, Japan.
authors.forename: Sadayuki
authors.initials: S
authors.lastname: Murayama
mesh_terms: D000368:Aged; D001835:Body Weight; D004867:Equipment Design; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007564:Japan; D008168:Lung / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography / Q000295:instrumentation / Q000379:methods*; D011237:Predictive Value of Tests; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging*; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D015898:Tomography Scanners, X-Ray Computed
keywords: Adaptive Iterative Dose Reduction using Three Dimensional Processing; computed tomography; emphysema; iterative reconstruction