Fast and Intuitive Interactive Lung Lobe Segmentation in Thoracic Computed Tomography Scans

PURPOSE Segmentation of the pulmonary lobes in CT data is useful for diagnosis, monitoring, and quantification of pulmonary diseases. In patients with severe disease, automated lobe segmentation is infeasible and interactive methods are needed. METHOD AND MATERIALS An automated lobar segmentation method was developed that performs a watershed transformation with a cost image based on the information from fissures, bronchi, and pulmonary vessels. Lobar markers required by the watershed transformation are calculated by an analysis of the automatically labeled bronchial tree. This segmentation fails on cases with severe disease or largely incomplete fissures. Therefore an interactive method was developed where an observer adjusts the automatic result by drawing parts of the correct lobar boundaries on any plane. Each curve is converted to a set of sampling points and the software immediately adapts the segmentation on the current plane but also extrapolates intelligently to adjacent slices. The immediate feedback allows the user to refine the segmentation iteratively, typically on multiple orthogonal planes. The procedure can also be performed from scratch. A set of 55 publically available chest CT scans with submillimeter resolution from a lung and lung lobe segmentation challenge (LOLA11) was used for evaluation. This data set contains many difficult cases with gross abnormalities. An observer applied the interactive correction using the automatic result as starting point and performed the full lobar segmentation from scratch for each scan. RESULTS The overall score based on the average overlap with a LOLA11 reference standard for the 5 lobes was 0.881 for the automatic method. The interactive corrections improved this to 0.918. The observer needed on average 7 interactions in 1.5 minutes per scan. The segmentation from scratch reached an overall score of 0.923 and required on average 4 minutes of processing time per scan. CONCLUSION Fast interactive lobar segmentation in thoracic CT is feasible. CLINICAL RELEVANCE/APPLICATION Lobar segmentation is a prerequisite for regional quantitative analysis of chest CT and other applications such as surgery planning and automated diagnosis.