Derivation for relating calcification and size in small pulmonary nodules

Pulmonary nodules less than 10 mm in length are often detected on computed tomography (CT) scans after the examination is completed. No further imaging may be possible and it would be useful to determine whether the nodule is sufficiently calcified to be considered benign. We wanted to use the relationship between the true and apparent nodule density on 10-mm CT sections to determine the true density of the nodule. An understanding of the partial volume effect on 10-mm CT images of small pulmonary nodules allowed us to identify accurately those which were diffusely calcified without having to resort to obtaining additional 1-mm CT sections.