title: Improving the Spatial Alignment in PET/CT Using Amplitude-Based Respiration-Gated PET and Respiration-Triggered CT.
abstract: Respiratory motion during PET can cause inaccuracies in the quantification of radiotracer uptake, which negatively affects PET-guided radiotherapy planning. Quantitative accuracy can be improved by respiratory gating. However, additional miscalculation of standardized uptake value (SUV) in PET images can be caused by inappropriate attenuation correction due to a spatial mismatch between gated PET and CT. In this study, the effect of respiration-triggered CT on the spatial match between CT and amplitude-based respiration-gated PET images is investigated.
  
  
  METHODS
  (18)F-FDG PET/CT was performed in 38 patients. Images were acquired on 2 PET/CT scanners, one without and one with continuous bed motion during PET acquisition. The amplitude limits of the amplitude-based respiration-gated PET were used for the respiration-triggered sequential low-dose CT. Both standard (spiral) and triggered CT scans were used to reconstruct the PET data. Spatial mismatch was quantified using the position difference between the lung-liver boundary in PET and CT images, the distance between PET and CT lung lesions' centroids, and the amount of overlap of lesions indicated by the Jaccard similarity coefficient. Furthermore, the effect of attenuation correction was quantified by measuring SUVs in lung lesions.
  
  
  RESULTS
  For triggered CT, the average distance between the lung-liver boundary in PET and CT was significantly reduced (4.5 ± 6.7 mm) when compared with standard CT (9.2 ± 8.1 mm) (P < 0.001). The mean distance between the lesions' centroids in PET and CT images was 6.3 ± 4.0 and 5.6 ± 4.2 mm (P = 0.424), for the standard and triggered CT, respectively. Similarly, the Jaccard similarity coefficient was 0.30 ± 0.21 and 0.32 ± 0.20 (P = 0.609) for standard and triggered CT, respectively. For 6 lesions, there was no overlap of PET and CT when the standard CT was used; compared with the triggered CT, these lesions showed (partial) overlap. The maximum and mean SUV increase of the PET/CT compared with the PET/triggered CT was 5.7% ± 11.2% (P < 0.001) and 6.1% ± 10.2% (P = 0.001), respectively.
  
  
  CONCLUSIONS
  Amplitude-based respiration-gated PET in combination with respiration-triggered CT resulted in a significantly improved match in the area of the liver dome and a significantly higher SUV for lung lesions. However, lesions in the lungs did not show a consistent improvement in spatial match.
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud university medical center, Nijmegen, The Netherlands MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands charlotte.vandervos@radboudumc.nl.
authors.forename: Charlotte S
authors.initials: CS
authors.lastname: van der Vos
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud university medical center, Nijmegen, The Netherlands.
authors.forename: Willem
authors.initials: W
authors.lastname: Grootjans
authors.affiliation: Department of Radiology, University of Tennessee Graduate School of Medicine, Knoxville, Tennessee.
authors.forename: Dustin R
authors.initials: DR
authors.lastname: Osborne
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud university medical center, Nijmegen, The Netherlands.
authors.forename: Antoi P W
authors.initials: AP
authors.lastname: Meeuwis
authors.affiliation: Siemens Healthcare, Knoxville, Tennessee; and.
authors.forename: James J
authors.initials: JJ
authors.lastname: Hamill
authors.affiliation: Department of Radiology, University of Tennessee Graduate School of Medicine, Knoxville, Tennessee.
authors.forename: Shelley
authors.initials: S
authors.lastname: Acuff
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud university medical center, Nijmegen, The Netherlands MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Lioe-Fee
authors.initials: LF
authors.lastname: de Geus-Oei
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud university medical center, Nijmegen, The Netherlands.
authors.forename: Eric P
authors.initials: EP
authors.lastname: Visser
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008099:Liver / Q000000981:diagnostic imaging; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D009038:Motion; D064847:Multimodal Imaging / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods* / Q000706:statistics & numerical data; D019275:Radiopharmaceuticals; D015656:Respiratory Mechanics; D014055:Tomography, Emission-Computed / Q000379:methods* / Q000706:statistics & numerical data; D036542:Tomography, Spiral Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: amplitude-based optimal respiratory gating; image quantification in PET; lung tumors; respiration-triggered CT; spatial alignment