title: Comparison of end-expiratory respiratory gating methods for PET/CT.
abstract: BACKGROUND
  Respiratory motion in positron emission tomography/computed tomography (PET/CT) causes underestimation of standardized uptake value (SUV) and variation of lesion volume, while PET and CT attenuation correction (CTAC) mismatch may introduce artefacts. The aim was to compare end-expiratory gating methods of PET and CTAC.
  
  
  METHODS
  Three methods named the minimum-constant, slope-based and amplitude-median were developed and evaluated on gating efficiency. Method evaluation and optimization was performed on 23 simulated and 23 recorded signals from a mixed patient group. The optimized methods were applied in PET/CT imaging of seven patients, consisting of non-gated CTAC, whole-body PET and four-dimensional (4D) PET/CT. Gating efficiency was evaluated by preservation of the respiratory signal, PET-CTAC alignment, image noise and measurement of lesion SUV maximum (SUVmax), SUV mean (SUVmean) and volume. The methods were evaluated with non-gated PET and end-expiratory phase of five-bin phase-gated PET. End-expiratory gated 4D-CTAC and averaged CTAC were compared for attenuation correction of end-expiratory gated PET.
  
  
  RESULTS
  Mean fraction of data preserved was larger (23-34%) with end-expiratory gating compared to phase-gated PET. End-expiratory gating showed increased SUVmax (8.2-8.4 g/ml), SUVmean (5.7-5.8 g/ml) and decreased lesion volume (-11.3-16.8%) compared to non-gated PET (SUVmax 6.2 g/ml, SUVmean 4.7 g/ml) and phase-gated PET (SUVmax 8.0 g/ml, SUVmean 5.6 g/ml). Using averaged CTAC and end-expiratory 4D-CTAC produced similar results concerning SUVmax, with less than 5% difference. Additionally, CTAC-PET-mismatch was minimal when end-expiratory 4D-CTAC was used.
  
  
  CONCLUSIONS
  End-expiratory gating in PET/CT results in SUVmax and SUVmean increase and reduced lesion volume compared to non-gated PET and phase-gated PET. End-expiratory 4D-CTAC or averaged CTAC will offer similar accuracy for attenuation correction of end-expiratory gated PET.
authors: Department of Mathematics and Statistics, University of Turku , Turku , Finland.
authors: Markus
authors: M
authors: Harteela
authors: Heidi
authors: H
authors: Hirvi
authors: Anna
authors: A
authors: Mäkipää
authors: Jarmo
authors: J
authors: Teuho
authors: Tuomas
authors: T
authors: Koivumäki
authors: Marko M
authors: MM
authors: Mäkelä
authors: Mika
authors: M
authors: Teräs
mesh_terms: D016477:Artifacts; D045853:Exhalation; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D009068:Movement; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography / Q000379:methods*