Cartilage estimation in noncontrast thoracic CT

Pectus excavatum (PE) is the most common major congenital deformity that involves the lower sternum and cartilages. Noncontrast CT is useful to assess the deformity of the bones and guide minimally invasive surgery. However, it has very poor visibility of cartilages even for the experienced clinicians who need to assess the 3D geometry of cartilages. In this study, we propose a novel method to estimate cartilages in noncontrast CT scans. The ribs and sternum are first segmented using region growing. The skeleton of the ribs is extracted and modeled by cosine series expansion. Then a statistical shape model is built with the cosine coefficients to estimate the cartilages as curves that connect the ribs and sternum. The results are refined by the cartilage surface that is approximated by contracting the skin surface to the bones. Leave-one-out validation was performed on 12 CT scans from healthy and PE subjects. The average distance between the estimated cartilages and ground truth is 1.53 mm. The promising results indicate that our method could estimate the costal cartilages in noncontrast CT effectively and assist to develop an image-based surgical planning system for PE correction.