title: How much will linked deformable registrations decrease the quality of multi-atlas segmentation fusions?
abstract: OBJECTIVE
  Multi-atlas segmentation can yield better results than single atlas segmentation, but practical applications are limited by long calculation times for deformable registration. To shorten the calculation time pre-calculated registrations of atlases could be linked via a single atlas registered in runtime to the current patient. The primary purpose of this work is to investigate and quantify segmentation quality changes introduced by such linked registrations. We also determine the optimal parameters for fusing linked multi-atlas labels using probabilistic weighted fusion.
  
  
  METHODS
  Computed tomography images of 10 head and neck cancer patients were used as atlases, with parotid glands, submandibular glands, the mandible and lymph node levels II-IV segmented by an experienced radiation oncologist following published consensus guidelines. The change in segmentation quality scored by Dice similarity coefficient (DSC) for linking free-form deformable registrations, modeled by B-splines, was investigated for both single- and multi-atlas label fusion by using a leave-one-out approach.
  
  
  RESULTS
  The median decrease of the DSC was in the range 2.8% to 8.4% compared to direct registrations for all structures while reducing the computer calculation time to that of a single deformable registration. Linking several registrations showed a DSC decrease almost linear to the number of links, suggesting that extrapolation to zero links provides an observer independent measure of the inherent precision with which the segmentation guidelines can be applied.
  
  
  CONCLUSIONS
  Linking pre-made registrations of multiple atlases via a runtime registration of a single atlas provides a feasible method for reducing computation time in multi-atlas registration.
authors.affiliation: Section for Medical Radiation Physics, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Akademiska Sjukhuset, Sjukhusfysik Ing. 82, SE-751 85, Uppsala, Sweden. carl.sjoberg@onkologi.uu.se.|Elekta Instrument AB, Box 1704, S-75147, Uppsala, Sweden. carl.sjoberg@onkologi.uu.se.
authors.forename: Carl
authors.initials: C
authors.lastname: Sjöberg
authors.affiliation: Section for Oncology, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Akademiska Sjukhuset, Sjukhusfysik Ing. 82, SE-751 85, Uppsala, Sweden. silvia.johansson@onkologi.uu.se.
authors.forename: Silvia
authors.initials: S
authors.lastname: Johansson
authors.affiliation: Section for Medical Radiation Physics, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Akademiska Sjukhuset, Sjukhusfysik Ing. 82, SE-751 85, Uppsala, Sweden. anders.ahnesjo@onkologi.uu.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Ahnesjö
mesh_terms: D000465:Algorithms; D001271:Atlases as Topic; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*