Purpose: Detection of change between CT images is crucial in lung cancer screening. We analysed whether subtraction images can detect change in nodular size between successive low-dose CT images. Methods and Materials: Given two successive CT scans lung segmentation and non-rigid registration between the two scans is performed and a subtraction image is obtained by subtracting the deformed prior scan from the current scan. Subtraction images of a total of 111 participants of a lung cancer screening trial that were referred to a pulmonologist on the basis of the last CTwere studied. An experienced radiologist annotated all relevant nodular changes by inspecting the subtraction images. The two original images were available side-by-side for confirmation. In addition, the quality of the subtraction images, was scored on a 1-5 scale. Results: The quality of the subtraction images was rated high: only six subtraction images (4\%) had a rating lower than 4, meaning that the images were significantly degraded by artefacts. In the referred cases 58 new nodules > 5 mm were found. Furthermore 45 nodules with significant growth were noted. A significant nodule was missed in 8 cases, of which 2 were stable and hence not visible on the subtraction image, 1 was missed because of its pleural location and 5 showed a mean increase in the diameter of 21\%. Conclusion: Temporal subtraction of CT images is a promising tool for the visual detection of change, especially significant growth of nodules, between successive CT scans.
Temporal subtraction of chest CT in lung cancer screening
E. Scholten, C. Jacobs, C. Schaefer-Prokop, J. Rühaak, H. de Koning, M. Oudkerk, P. de Jong, M. Prokop and B. van Ginneken
European Congress of Radiology 2016.