title: Making renal stones change size-impact of CT image post processing and reader variability.
abstract: OBJECTIVE
  The objectives of this study were to quantify the impact of image post-processing parameters on the apparent renal stone size, and to quantify the intra- and inter-reader variability in renal stone size estimation.
  
  
  METHODS
  Fifty CT datasets including a renal or ureteral stone were included retrospectively during a prospective inclusion period. Each of the CT datasets was post-processed in different ways regarding slice thickness, slice increment and window setting. In the first part of the study a single reader repeated size estimations for the renal stones using different post-processing parameters. In the intra-reader variability experiment one reader reported size estimations for the same images with a one-week interval. The inter-reader variability data were obtained from 11 readers reporting size estimations for the same renal stones.
  
  
  RESULTS
  The apparent stone size differed according to image post-processing parameters with the largest mean differences seen with regard to the window settings experiment (1.5 mm, p < 0.001) and slice thickness (0.8 mm, p < 0.001). Changes in parameters introduced a bias and a pseudo-random variability. The inter-reader variability was considerably larger than the intra-reader variability.
  
  
  CONCLUSIONS
  Our results indicate a need for the standardisation of making measurements on CT images.
authors.affiliation: School of Health and Medical Sciences, Örebro University, 701 82, Örebro, Sweden. matsliden@yahoo.com
authors.forename: Mats
authors.initials: M
authors.lastname: Lidén
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Andersson
authors.forename: Håkan
authors.initials: H
authors.lastname: Geijer
mesh_terms: D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007669:Kidney Calculi / Q000000981:diagnostic imaging / Q000473:pathology*; D008297:Male; D015588:Observer Variation; D011871:Radiology / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014514:Ureteral Calculi / Q000000981:diagnostic imaging / Q000473:pathology*