Interactive registration between supine and prone scans in computed tomography colonography using band-height images

In computed tomographic colonography (CTC), a patient is commonly scanned twice including supine and prone scans to improve the sensitivity of polyp detection. Typically, a radiologist must manually match the corresponding areas in the supine and prone CT scans, which is a difficult and time-consuming task, even for experienced scan readers. In this paper, we propose a method of supine-prone registration utilizing band-height images, which are directly constructed from the CT scans using a ray-casting algorithm containing neighboring shape information. In our method, we first identify anatomical feature points and establish initial correspondences using local extreme points on centerlines. We then correct correspondences using band-height images that contain neighboring shape information. We use geometrical and image-based information to match positions between the supine and prone centerlines. Finally, our algorithm searches the correspondence of user input points using the matched anatomical feature point pairs as key points and band-height images. The proposed method achieved accurate matching and relatively faster processing time than other previously proposed methods. The mean error of the matching between the supine and prone points for uniformly sampled positions was 18.41±22.07mm in 20 CTC datasets. The average pre-processing time was 62.9±8.6s, and the interactive matching was performed in nearly real-time. Our supine-prone registration method is expected to be helpful for the accurate and fast diagnosis of polyps.