title: Nonrigid versus rigid registration of thoracic 18F-FDG PET and CT in patients with lung cancer: an intraindividual comparison of different breathing maneuvers.
abstract: In lung cancer, (18)F-FDG PET, CT, and (18)F-FDG PET/CT are used for noninvasive staging and therapy planning. Even with improved image registration techniques-especially in the modern hybrid PET/CT scanners-inaccuracies in the fusion process may occur, leading to errors in image interpretation. The aim of this study was to investigate by an intraindividual analysis whether, in comparison with a rigid algorithm, a nonrigid registration algorithm improves the quality of fusion between (18)F-FDG PET and CT.
  
  
  METHODS
  Sixteen patients with histologically proven non-small cell lung cancer underwent a thoracic (18)F-FDG PET acquisition in radiotherapy treatment position and 3 CT acquisitions (expiration, inspiration, and mid breath-hold) on the same day. All scans were registered with rigid and nonrigid procedures, resulting in 6 fused datasets: rigid inspiration, rigid expiration, rigid mid breath-hold, nonrigid inspiration, nonrigid expiration, and nonrigid mid breath-hold. The quality of alignment was assessed by 3 experienced readers at 8 anatomic landmarks: lung apices, aortic arch, heart, spine, sternum, carina, diaphragm, and tumor using an alignment score ranging from 1 (no alignment) to 5 (exact alignment).
  
  
  RESULTS
  Nonrigid PET/CT showed better alignment than rigid PET/CT (3.5 +/- 0.7 vs. 3.3 +/- 0.7, P < 0.001). Regarding the breathing maneuver, no difference between nonrigid mid breath-hold and rigid mid breath-hold was observed. In contrast, the alignment quality significantly improved from rigid expiration to nonrigid expiration (3.4 +/- 0.7 vs. 3.6 +/- 0.7, P < 0.001) and from rigid inspiration to nonrigid inspiration (3.1 +/- 0.7 vs. 3.3 +/- 0.7, P < 0.001). With regard to individual landmarks, an improvement in fusion quality through the use of nonrigid registration was obvious at the lung apices, carina, and aortic arch.
  
  
  CONCLUSIONS
  The alignment quality of thoracic (18)F-FDG PET/CT exhibits a marked dependence on the breathing maneuver performed during the CT acquisition, as demonstrated in an intraindividual comparison. Nonrigid registration is a significant improvement over rigid registration if the CT is performed during full inspiration or full expiration. The best fusion results are obtained with the CT performed at mid breath-hold using rigid registration, without an improvement using nonrigid algorithms.
authors.affiliation: Department of Nuclear Medicine, Saarland University Medical Center, Homburg/Saar, Germany. aleksandar.grgic@uks.eu
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Grgic
authors.forename: Ursula
authors.initials: U
authors.lastname: Nestle
authors.forename: Andrea
authors.initials: A
authors.lastname: Schaefer-Schuler
authors.forename: Stephanie
authors.initials: S
authors.lastname: Kremp
authors.forename: Elena
authors.initials: E
authors.lastname: Ballek
authors.forename: Jochen
authors.initials: J
authors.lastname: Fleckenstein
authors.forename: Christian
authors.initials: C
authors.lastname: Rübe
authors.forename: Carl-Martin
authors.initials: CM
authors.lastname: Kirsch
authors.forename: Dirk
authors.initials: D
authors.lastname: Hellwig
mesh_terms: D000368:Aged; D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008175:Lung Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D049268:Positron-Emission Tomography; D013902:Radiography, Thoracic; D012119:Respiration; D012189:Retrospective Studies; D013909:Thorax / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
chemical_list: D019788:Fluorodeoxyglucose F18