title: Fast level-set based image segmentation using coherent propagation.
abstract: OBJECTIVE
  The level-set method is known to require long computation time for 3D image segmentation, which limits its usage in clinical workflow. The goal of this study was to develop a fast level-set algorithm based on the coherent propagation method and explore its character using clinical datasets.
  
  
  METHODS
  The coherent propagation algorithm allows level set functions to converge faster by forcing the contour to move monotonically according to a predicted developing trend. Repeated temporary backwards propagation, caused by noise or numerical errors, is then avoided. It also makes it possible to detect local convergence, so that the parts of the boundary that have reached their final position can be excluded in subsequent iterations, thus reducing computation time. To compensate for the overshoot error, forward and backward coherent propagation is repeated periodically. This can result in fluctuations of great magnitude in parts of the contour. In this paper, a new gradual convergence scheme using a damping factor is proposed to address this problem. The new algorithm is also generalized to non-narrow band cases. Finally, the coherent propagation approach is combined with a new distance-regularized level set, which eliminates the needs of reinitialization of the distance.
  
  
  RESULTS
  Compared with the sparse field method implemented in the widely available ITKSnap software, the proposed algorithm is about 10 times faster when used for brain segmentation and about 100 times faster for aorta segmentation. Using a multiresolution approach, the new method achieved 50 times speed-up in liver segmentation. The Dice coefficient between the proposed method and the sparse field method is above 99% in most cases.
  
  
  CONCLUSIONS
  A generalized coherent propagation algorithm for level set evolution yielded substantial improvement in processing time with both synthetic datasets and medical images.
authors.affiliation: Center for Medical Image Science and Visualization (CMIV), Linköping University, SE-58185 Linköping, Sweden and Division of Radiological Sciences (IMH), Linköping University, SE-58185 Linköping, Sweden.
authors.forename: Chunliang
authors.initials: C
authors.lastname: Wang
authors.affiliation: Division of Scientific Computing, Uppsala University, Uppsala SE-75105, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Frimmel
authors.affiliation: Center for Medical Image Science and Visualization (CMIV), Linköping University, SE-58185 Linköping, Sweden and Division of Radiological Sciences (IMH), Linköping University, SE-58185 Linköping, Sweden.
authors.forename: Örjan
authors.initials: Ö
authors.lastname: Smedby
mesh_terms: D000465:Algorithms; D000792:Angiography / Q000379:methods; D001011:Aorta / Q000033:anatomy & histology; D001921:Brain / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D011860:Radiography, Abdominal / Q000379:methods; D012984:Software; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods