title: Source-to-detector distance and beam center do not affect radiographic measurements of acetabular morphology.
abstract: OBJECTIVE
  Multiple radiographic acquisition techniques have been evaluated for their effect on measurements of acetabular morphology. This cadaveric study examined the effect of two acquisition parameters not previously evaluated: beam center position and source-to-detector distance. This study also evaluated the effect of reader differences on measurements.
  
  
  METHODS
  Following calibration of measurements between two readers using five clinical radiographs (training), radiographs were obtained from two cadavers using four different source-to-detector distances and three different radiographic centers for a total of 12 radiographic techniques (experimental). Two physician readers acquired four types of measurements from each cadaver radiograph: lateral center edge angle, peak-to-edge distance, Sharp's angle, and the Tonnis angle. All measurements were evaluated for intra-class correlation coefficient (ICC), kappa statistics for hip dysplasia, and factors that resulted in measurement differences using a mixed statistical model.
  
  
  RESULTS
  After training of the two physician readers, there was strong agreement in their hip morphology measurements (ICC 0.84-0.93), agreement in the presence of hip dysplasia (κ = 0.58-1.0), and no measurement difference between physician readers (p = 0.12-1.0). Experimental cadaver measurements showed moderate-to-strong agreement of the readers (ICC 0.74-0.93) and complete agreement on dysplasia (κ = 1). After accounting for reader and radiographic technique, there was no difference in hip morphology measurements (p = 0.83-0.99).
  
  
  CONCLUSIONS
  In this cadaveric study, measurements of hip morphology were not affected by varying source-to-detector distance or beam center. We conclude that these acquisition parameters are not likely to affect the diagnosis of hip dysplasia in a clinical setting.
authors.affiliation: Department of Orthopaedic Surgery, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Ashton H
authors.initials: AH
authors.lastname: Goldman
authors.affiliation: Department of Radiology, Virginia Commonwealth University, 1250 E Marshall St. 3rd Floor, PO Box 980615, Richmond, VA, 23298, USA. kevin.hoover@vcuhealth.org.
authors.forename: Kevin B
authors.initials: KB
authors.lastname: Hoover
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D002102:Cadaver; D005260:Female; D006617:Hip Dislocation / Q000000981:diagnostic imaging*; D006801:Humans; D015588:Observer Variation; D011859:Radiography / Q000379:methods*; D015203:Reproducibility of Results
keywords: Acetabular morphology; Hip dysplasia; Parallax; Radiographic center; Source-to-film distance