title: Evaluation of similarity measures for reconstruction-based registration in image-guided radiotherapy and surgery.
abstract: OBJECTIVE
  A promising patient positioning technique is based on registering computed tomographic (CT) or magnetic resonance (MR) images to cone-beam CT images (CBCT). The extra radiation dose delivered to the patient can be substantially reduced by using fewer projections. This approach results in lower quality CBCT images. The purpose of this study is to evaluate a number of similarity measures (SMs) suitable for registration of CT or MR images to low-quality CBCTs.
  
  
  METHODS
  Using the recently proposed evaluation protocol, we evaluated nine SMs with respect to pretreatment imaging modalities, number of two-dimensional (2D) images used for reconstruction, and number of reconstruction iterations. The image database consisted of 100 X-ray and corresponding CT and MR images of two vertebral columns.
  
  
  RESULTS
  Using a higher number of 2D projections or reconstruction iterations results in higher accuracy and slightly lower robustness. The similarity measures that behaved the best also yielded the best registration results. The most appropriate similarity measure was the asymmetric multi-feature mutual information (AMMI).
  
  
  CONCLUSIONS
  The evaluation protocol proved to be a valuable tool for selecting the best similarity measure for the reconstruction-based registration. The results indicate that accurate and robust CT/CBCT or even MR/CBCT registrations are possible if the AMMI similarity measure is used.
authors.affiliation: Department of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Darko
authors.initials: D
authors.lastname: Skerl
authors.forename: Dejan
authors.initials: D
authors.lastname: Tomazevic
authors.forename: Bostjan
authors.initials: B
authors.lastname: Likar
authors.forename: Franjo
authors.initials: F
authors.lastname: Pernus
mesh_terms: D000465:Algorithms; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D013514:Surgical Procedures, Operative / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*