COMPUTERIZED DELINEATION AND ANALYSIS OF COSTOPHRENIC ANGLES IN DIGITAL CHEST RADIOGRAPHS

Rationale and Objectives. The authors developed a computerized method for delineating the costophrenic angles in digital posteroanterior che st radiographs to derive quantitative information that allows for dete ction of abnormal blunting of the costophrenic angle. Materials and Me thods. An automated lung-segmentation scheme was used, and small regio ns of interest were placed in the approximate position of the costophr enic angles in 600 clinical posteroanterior chest radiographs to defin e a subimage for further analysis. The diaphragmatic aspect of the cos tophrenic angle was delineated based on column-wise contrast informati on, and the costal aspect was delineated based on row-wise gray-level maxima. The angle formed by the convergence of these two aspects provi ded the basis for assessing abnormality. Curve fitting was then perfor med on these segments to form a continuous costophrenic angle delineat ion. Results. The computer-determined angles for 1,166 hemithoraces we re compared with independent diagnostic assessments by a radiologist. An encouraging level of agreement was found between these two measurem ents, with the area under the receiver operating characteristic curve attaining a value of 0.83. Conclusion. This delineation method enhance s the automated lung-segmentation scheme. Quantitative information obt ained from the costophrenic angles can be used for automatic evaluatio n of the presence of costophrenic angle blunting, which may indicate t he presence of pleural effusion.