title: Two- and three-dimensional CT measurements of urinary calculi length and width: a comparative study.
abstract: BACKGROUND
  The standard imaging procedure for a patient presenting with renal colic is unenhanced computed tomography (CT). The CT measured size has a close correlation to the estimated prognosis for spontaneous passage of a ureteral calculus. Size estimations of urinary calculi in CT images are still based on two-dimensional (2D) reformats.
  
  
  OBJECTIVE
  To develop and validate a calculus oriented three-dimensional (3D) method for measuring the length and width of urinary calculi and to compare the calculus oriented measurements of the length and width with corresponding 2D measurements obtained in axial and coronal reformats.
  
  
  METHODS
  Fifty unenhanced CT examinations demonstrating urinary calculi were included. A 3D symmetric segmentation algorithm was validated against reader size estimations. The calculus oriented size from the segmentation was then compared to the estimated size in axial and coronal 2D reformats.
  
  
  RESULTS
  The validation showed 0.1 ± 0.7 mm agreement against reference measure. There was a 0.4 mm median bias for 3D estimated calculus length compared to 2D (P < 0.001), but no significant bias for 3D width compared to 2D.
  
  
  CONCLUSIONS
  The length of a calculus in axial and coronal reformats becomes underestimated compared to 3D if its orientation is not aligned to the image planes. Future studies aiming to correlate calculus size with patient outcome should use a calculus oriented size estimation.
authors.affiliation: School of Health and Medical Sciences, Örebro University, Örebro, Sweden Department of Radiology, Örebro University Hospital, Örebro, Sweden Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden matsliden@yahoo.com.
authors.forename: Mats
authors.initials: M
authors.lastname: Lidén
authors.affiliation: School of Health and Medical Sciences, Örebro University, Örebro, Sweden Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Thunberg
authors.affiliation: Modeling and Simulation Research Center, Örebro University, Örebro, Sweden.
authors.forename: Mathias
authors.initials: M
authors.lastname: Broxvall
authors.affiliation: School of Health and Medical Sciences, Örebro University, Örebro, Sweden Department of Radiology, Örebro University Hospital, Örebro, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Geijer
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014545:Urinary Calculi / Q000000981:diagnostic imaging*
keywords: CT; Urinary; computer applications – 3D; kidney; segmentation; ureter