Method for matching small pulmonary nodules that is robust to temporal changes on follow-up thoracic CT images

This report presents a novel method for matching small pulmonary nodules (SPNs) that is robust to the temporal changes in the nodules on follow-up thoracic CT images. The observation of SPNs on follow-up CT images is very important in the diagnosis of lung cancer, but such observation places a heavy burden on the physician. This is because the differences in the position of the patient on the CT table and the effects of cardiac and respiratory motion usually lead to deformation on follow-up CT images. In addition, due to the development of metastases or the effects of chemotherapy, nodules may appear or disappear or may fuse or separate. In order to reduce the burden on the physician, we have developed a method for assisting him or her during the observation of SPNs on follow-up CT scans. The proposed method employs both rigid and non-rigid registration methods to co-register follow-up CT scans in order to compensate for lung deformation. Taking into consideration the temporal changes in the SPNs, we calculate three matching patterns to identify the corresponding nodules based on various features such as the location of the center of gravity, the diameter, and the average intensity. We applied the proposed method to 3 patients (14 thoracic CT scans) and correctly matched 94.6% of the segmented SPNs. The results also showed that our method is robust to changes in SPNs such as the appearance/disappearance or the fusion/separation of nodules. (author)