title: The Effect of Radiographic Beam Angle on Acromiohumeral Interval: 3D-CT Analytic Study.
abstract: BACKGROUND
  An acromiohumeral interval (AHI) narrower than 7 mm measured on AP shoulder radiographs has been considered pathology and strongly indicative for rotator cuff tears. No study to date has investigated the effect ofradiographic beam position on acromiohumeral interval (AHI) measurement.
  
  
  OBJECTIVE
  To study the AHI measurement on conventional radiographs compared with 3D computed tomography (3D-CT) scans and the effectiveness of tilted CT images in physician-performed AHI measurement.
  
  
  METHODS
  Twenty-eight patients were measured the AHI on conventional radiographs. The same measurement was performed on 3D-CT image tilted in coronal plane--15 degree, 0 degree (Baseline), +15-degree, +30-degree and +45- degree views. For baseline 3D-CT scan, the image position was set as 30 degrees medial and 10-degree downward tilts.
  
  
  RESULTS
  The mean AHI on conventional radiographs (8.8 ± 2.4.mm) is significantly more than the AHI on 3D-CT image (7.10 ± 1.5 mm, p = 0.002). The AHI on conventional radiographs and baseline 3D-CT image showed significant moderate to high correlation (r = 0.647, p < 0.001). The upward 3D-CT angle affected the AHI significantly (p = 0.002).
  
  
  CONCLUSIONS
  The AHI measurement on conventional radiographs is significantly higher than 3D-CTscan, with moderate to high correlation. The different position ofthe CT image tilts affected the AHI measurements.
authors.forename: Worawit
authors.initials: W
authors.lastname: Ongbumrungphan
authors.forename: Waraporn
authors.initials: W
authors.lastname: Srikhum
authors.forename: Bancha
authors.initials: B
authors.lastname: Chernchujit
mesh_terms: D000173:Acromioclavicular Joint / Q000000981:diagnostic imaging*; D000704:Analysis of Variance; D001837:Body Weights and Measures / Q000379:methods*; D005260:Female; D006801:Humans; D058430:Humeral Head / Q000000981:diagnostic imaging*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007592:Joint Diseases; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011857:Radiographic Image Interpretation, Computer-Assisted; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*