title: Accuracy and feasibility of three different methods for software-based image fusion in whole-body PET and CT.
abstract: BACKGROUND
  Even as PET/CT provides valuable diagnostic information in a great number of clinical indications, availability of hybrid PET/CT scanners is mainly limited to clinical centers. A software-based image fusion would facilitate combined image reading of CT and PET data sets if hardware image fusion is not available. To analyze the relevance of retrospective image fusion of separately acquired PET and CT data sets, we studied the accuracy, practicability and reproducibility of three different image registration techniques.
  
  
  METHODS
  We evaluated whole-body 18F-FDG-PET and CT data sets of 71 oncologic patients. Images were fused retrospectively using Stealth Station System, Treon (Medtronic Inc., Louisville, CO, USA) equipped with Cranial4 Software. External markers fixed to a vacuum mattress were used as reference for exact repositioning. Registration was repeated using internal anatomic landmarks and Automerge software, assessing accuracy for all three methods, measuring distances of liver representation in CT and PET with reference to a common coordinate system.
  
  
  RESULTS
  On first measurement of image fusions with external markers, 53 were successful, 16 feasible and 2 not successful. Using anatomic landmarks, 42 were successful, 26 feasible and 3 not successful. Using Automerge Software only 13 were successful. The mean distance between center points in PET and CT was 7.69±4.96 mm on first, and 7.65±4.2 mm on second measurement. Results with external markers correlate very well and inaccuracies are significantly lower (P<0.001) than results using anatomical landmarks (10.38±6.13 mm and 10.83±6.23 mm). Analysis revealed a significantly faster alignment using external markers (P<0.001).
  
  
  CONCLUSIONS
  External fiducials in combination with immobilization devices and breathing protocols allow for highly accurate image fusion cost-effectively and significantly less time, posing an attractive alternative for PET/CT interpretation when a hybrid scanner is not available.
authors.affiliation: Department of Radiology, Innsbruck Medical University, Innsbruck, Austria - daniel.putzer@i-med.ac.at.
authors.forename: Daniel
authors.initials: D
authors.lastname: Putzer
authors.forename: Benjamin
authors.initials: B
authors.lastname: Henninger
authors.forename: Peter
authors.initials: P
authors.lastname: Kovacs
authors.forename: Christian
authors.initials: C
authors.lastname: Uprimny
authors.forename: Dorota
authors.initials: D
authors.lastname: Kendler
authors.forename: Werner
authors.initials: W
authors.lastname: Jaschke
authors.forename: Reto J
authors.initials: RJ
authors.lastname: Bale
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012984:Software; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging; D055815:Young Adult