title: Comparing approaches to correct for respiratory motion in NH3 PET-CT cardiac perfusion imaging.
abstract: OBJECTIVE
  Respiratory motion affects cardiac PET-computed tomography (CT) imaging by reducing attenuation correction (AC) accuracy and by introducing blur. The aim of this study was to compare three approaches for reducing motion-induced AC errors and evaluate the inclusion of respiratory motion correction.
  
  
  METHODS
  AC with a helical CT was compared with averaged cine and gated cine CT, as well as with a pseudo-gated CT, which was produced by applying PET-derived motion fields to the helical CT. Data-driven gating was used to produce respiratory-gated PET and CT images, and 60 NH3 PET scans were attenuation corrected with each of the CTs. Respiratory motion correction was applied to the gated and pseudo-gated attenuation-corrected PET images.
  
  
  RESULTS
  Anterior and lateral wall intensity measured in attenuation-corrected PET images generally increased when PET-CT alignment improved and decreased when alignment degraded. On average, all methods improved PET-CT liver and cardiac alignment, and increased anterior wall intensity by more than 10% in 36, 33 and 25 cases for the averaged, gated and pseudo-gated CTAC PET images, respectively. However, cases were found where alignment worsened and severe artefacts resulted. This occurred in more cases and to a greater extent for the averaged and gated CT, where the anterior wall intensity reduced by more than 10% in 21 and 24 cases, respectively, compared with six cases for the pseudo-gated CT. Application of respiratory motion correction increased the average anterior and inferior wall intensity, but only 13% of cases increased by more than 10%.
  
  
  CONCLUSIONS
  All methods improved average respiratory-induced AC errors; however, some severe artefacts were produced. The pseudo-gated CT was found to be the most robust method.
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas' Hospital, London, UK.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Schleyer
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Doherty
authors.forename: Sally F
authors.initials: SF
authors.lastname: Barrington
authors.forename: Geraint
authors.initials: G
authors.lastname: Morton
authors.forename: Paul K
authors.initials: PK
authors.lastname: Marsden
mesh_terms: D000641:Ammonia; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009068:Movement; D064847:Multimodal Imaging; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D000641:Ammonia