title: Reconstruction algorithms influence the follow-up variability in the longitudinal CT emphysema index measurements.
abstract: OBJECTIVE
  We wanted to compare the variability in the longitudinal emphysema index (EI) measurements that were computed with standard and high resolution (HR) reconstruction algorithms (RAs).
  
  
  METHODS
  We performed a retrospective review of 475 patients who underwent CT for surveillance of lung nodules. From this cohort, 50 patients (28 male) were included in the study. For these patients, the baseline and follow-up scans were acquired on the same multidetector CT scanner and using the same acquisition protocol. The CT scans were reconstructed with HR and standard RAs. We determined the difference in the EI between CT1 and CT2 for the HR and standard RAs, and we compared the variance of these differences.
  
  
  RESULTS
  The mean of the variation of the total lung volume was 0.14 L (standard deviation [SD] = 0.13 L) for the standard RA and 0.16 L (SD = 0.15 L) for the HR RA. These differences were not significant. For the standard RA, the mean variation was 0.13% (SD = 0.44%) for EI -970 and 0.4% (SD = 0.88%) for EI -950; for the HR RA, the mean variation was 1.9% (SD = 2.2%) for EI -970 and 3.6% (SD = 3.7%) for EI -950. These differences were significant.
  
  
  CONCLUSIONS
  Using an HR RA appears to increase the variability of the CT measurements of the EI.
authors: Universidade Federal do Rio de Janeiro, Radiology Department, Av. Pedro Calmon, n° 550 - Cidade Universitária, 21941-901, Rio de Janeiro, RJ, Brazil. brunohochhegger@gmail.com
authors: Bruno
authors: B
authors: Hochhegger
authors: Klaus Loureiro
authors: KL
authors: Irion
authors: Edson
authors: E
authors: Marchiori
authors: Jose Silva
authors: JS
authors: Moreira
mesh_terms: D000368:Aged; D000465:Algorithms; D016477:Artifacts; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed