Automatic Quantification of Completeness of Pulmonary Fissures on a Large Database

PURPOSE To investigate the variation in incomplete pulmonary fissures on volumetric high-resolution CT scans using a completely automatic method. METHOD AND MATERIALS A set of 1000 volumetric CT scans was randomly selected from the NELSON study, a lung cancer screening trial with low-dose CT (16x 0.75 mm collimation, 30 mAs). The lungs were automatically segmented and the pulmonary fissures were enhanced using a k-nearest neighbor classifier employing Hessian eigenvalues and gray value information. Based on the lung and fissure information, a linear discriminant classifier was trained to assign each voxel to a pulmonary lobe based on its relative position in the lung and its distance from and position relative to the fissures. To determine the completeness of the pulmonary fissures, each point on the enhanced fissures that was above a certain threshold was assigned to the closest point on the lobe border. Voxels on the lobe border not assigned to a fissure voxel were considered to be non-fissure and therefore incomplete. The percentage of incomplete border voxels quantifies the incompleteness of the fissures. Results were calculated for the major fissure in the left lung and the major and minor fissures in the right lung. Based on experimentation four categories were defined for quantification: (almost) complete (0-20% missing), slightly incomplete (20-35%), incomplete (35-90%) and absent (90%-100%). The method was validated by manual assessments of fissural completeness in a subset of 50 cases. RESULTS Visual and automatic categorization of fissural completeness were consistent in 87% of cases for the left and right major fissures and in 82% of cases for the right minor fissure. The left major fissure was complete in 53% of subjects, 23% was slightly incomplete, 23% was incomplete and in 1% was absent. For the right major fissure those numbers were 42%, 34%, 24% and 0% respectively. The right minor fissure was most often incomplete; 8%, 12%, 66% and 14% for the respective categories. CONCLUSION A quantitative measure for fissural completeness can be determined fully automatically. There is substantial variation in fissural completeness with fissures often being incomplete. CLINICAL RELEVANCE/APPLICATION Fissural completeness may be an indicator of collateral ventilation and have significance in endobronchial valve treatment planning for emphysema patients.