title: Computerized delineation and analysis of costophrenic angles in digital chest radiographs.
abstract: OBJECTIVE
  The authors developed a computerized method for delineating the costophrenic angles in digital posteroanterior chest radiographs to derive quantitative information that allows for detection of abnormal blunting of the costophrenic angle.
  
  
  METHODS
  An automated lung-segmentation scheme was used, and small regions of interest were placed in the approximate position of the costophrenic angles in 600 clinical posteroanterior chest radiographs to define a subimage for further analysis. The diaphragmatic aspect of the costophrenic angle was delineated based on column-wise contrast information, and the costal aspect was delineated based on row-wise gray-level maxima. The angle formed by the convergence of these two aspects provided the basis for assessing abnormality. Curve fitting was then performed on these segments to form a continuous costophrenic angle delineation.
  
  
  RESULTS
  The computer-determined angles for 1,166 hemithoraces were compared with independent diagnostic assessments by a radiologist. An encouraging level of agreement was found between these two measurements, with the area under the receiver operating characteristic curve attaining a value of 0.83.
  
  
  CONCLUSIONS
  This delineation method enhances the automated lung-segmentation scheme. Quantitative information obtained from the costophrenic angles can be used for automatic evaluation of the presence of costophrenic angle blunting, which may indicate the presence of pleural effusion.
authors.affiliation: Kurt Rossmann Laboratories for Radiologic Image Research, Department of Radiology, University of Chicago, IL 60637, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Armato
authors.forename: M L
authors.initials: ML
authors.lastname: Giger
authors.forename: H
authors.initials: H
authors.lastname: MacMahon
mesh_terms: D019540:Area Under Curve; D019992:Databases as Topic; D003936:Diagnosis, Computer-Assisted; D003964:Diaphragm / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000000981:diagnostic imaging*; D010996:Pleural Effusion / Q000000981:diagnostic imaging; D012372:ROC Curve; D011856:Radiographic Image Enhancement; D013902:Radiography, Thoracic; D011871:Radiology; D012272:Ribs / Q000000981:diagnostic imaging*