title: Two-dimensional versus three-dimensional CT scan for aortic measurement.
abstract: OBJECTIVE
  To examine if 3-dimensional (3D) reconstructions of computed tomographic (CT) data, by imaging perpendicular to blood flow, can improve aortic diameter measurement accuracy over axial (2D) CT.
  
  
  METHODS
  Two independent, blinded observers used electronic calipers to measure the minor axis and the line perpendicular to it on 40 2.5-mm 2D CT scans from 31 patients. A circular electronic tool was used to estimate diameters on 3D reconstructions from the same 40 scans. Measurements of the aortic neck were obtained 5 mm below the renal arteries and the widest slice of the aneurysm was used to measure sac diameter. Only the minor axis was measured at the iliac arteries immediately above the left (LI) and right (RI) iliac bifurcations. Datasets were compared with an intraclass correlation coefficient (ICC), Bland and Altman variation assessments, and absolute differences.
  
  
  RESULTS
  ICC between 2D and 3D scans demonstrated high correlation with 2D minor axis measurements (neck=0.9282, sac=0.8956, RI=0.8755, LI=0.7381). 3D to 2D major axis correlation was lower (neck=0.6388, sac=0.8995). Variation between 3D and 2D minor axis measurements was low (0.51-mm average variation from the mean for the minor axis and 1.30-mm variation for the major axis). Average absolute difference between 3D and 2D diameters was 1.01 mm (minor axis) versus 2.61 mm (major axis). Interobserver correlation was highest for sac measurements both in 2D minor axis (ICC=0.8990) and 3D (ICC=0.9518).
  
  
  CONCLUSIONS
  Minor axis measurements on axial CT scan can substitute for diameters obtained from 3D reconstructions in most clinical situations.
authors.affiliation: Divisions of Vascular Surgery, University of Pittsburgh Medical Center, Pittsburgh Pennsylvania 15213, USA.
authors.forename: Ellen D
authors.initials: ED
authors.lastname: Dillavou
authors.forename: David G
authors.initials: DG
authors.lastname: Buck
authors.forename: Satish C
authors.initials: SC
authors.lastname: Muluk
authors.forename: Michel S
authors.initials: MS
authors.lastname: Makaroun
mesh_terms: D017544:Aortic Aneurysm, Abdominal / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D021621:Imaging, Three-Dimensional; D014057:Tomography, X-Ray Computed / Q000379:methods*