title: Haustral loop extraction for CT colonography using geodesics.
abstract: OBJECTIVE
  The human colon has complex geometric structures because of its haustral folds, which are thin flat protrusions on the colon wall. The haustral loop is the curve (approximately triangular in shape) that encircles the highly convex region of the haustral fold, and is regarded as the natural landmark of the colon, intersecting the longitude of the colon in the middle. Haustral loop extraction can assist in reducing the structural complexity of the colon, and the loops can also serve as anatomic markers for computed tomographic colonography (CTC). Moreover, haustral loop sectioning of the colon can help with the performance of precise prone-supine registration.
  
  
  METHODS
  We propose an accurate approach of extracting haustral loops for CT virtual colonoscopy based on geodesics. First, the longitudinal geodesic (LG) connecting the start and end points is tracked by the geodesic method and the colon is cut along the LG. Second, key points are extracted from the LG, after which paired points that are used for seeking the potential haustral loops are calculated according to the key points. Next, for each paired point, the shortest distance (geodesic line) between the paired points twice is calculated, namely one on the original surface and the other on the cut surface. Then, the two geodesics are combined to form a potential haustral loop. Finally, erroneous and nonstandard potential loops are removed.
  
  
  RESULTS
  To evaluate the haustral loop extraction algorithm, we first utilized the algorithm to extract the haustral loops. Then, we let the clinicians determine whether the haustral loops were correct and then identify the missing haustral loops. The extraction algorithm successfully detected 91.87% of all of the haustral loops with a very low false positive rate.
  
  
  CONCLUSIONS
  We believe that haustral loop extraction may benefit many post-procedures in CTC, such as supine-prone registration, computer-aided diagnosis, and taenia coli extraction.
authors.affiliation: Department of Biomedical Engineering, Tsinghua University, Beijing, 10084, China.
authors.forename: Yongkai
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Biomedical Engineering, Tsinghua University, Beijing, 10084, China. dcj_thu@126.com.|Research Center for Biomedical Engineering of Graduate School at Shenzhen, Tsinghua University, Shenzhen, 518055, China. dcj_thu@126.com.
authors.forename: Chaijie
authors.initials: C
authors.lastname: Duan
authors.affiliation: Department of Radiology and Computer Science, State University of New York at Stony Brook, Stony Brook, NY, 11794, USA.
authors.forename: Jerome
authors.initials: J
authors.lastname: Liang
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Hu
authors.affiliation: Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, 710032, Shanxi, China.
authors.forename: Hongbing
authors.initials: H
authors.lastname: Lu
authors.affiliation: Department of Radiology, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510630, China.
authors.forename: Mingyue
authors.initials: M
authors.lastname: Luo
mesh_terms: D000465:Algorithms; D003106:Colon / Q000000981:diagnostic imaging*; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging*; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic / Q000379:methods*; D006801:Humans; D016684:Prone Position; D015203:Reproducibility of Results
keywords: CTC; Geodesics; Haustral loop; Virtual colonoscopy