title: Impact of CT attenuation correction method on quantitative respiratory-correlated (4D) PET/CT imaging.
abstract: OBJECTIVE
  Respiratory-correlated positron emission tomography (PET/CT) 4D PET/CT is used to mitigate errors from respiratory motion; however, the optimal CT attenuation correction (CTAC) method for 4D PET/CT is unknown. The authors performed a phantom study to evaluate the quantitative performance of CTAC methods for 4D PET/CT in the ground truth setting.
  
  
  METHODS
  A programmable respiratory motion phantom with a custom movable insert designed to emulate a lung lesion and lung tissue was used for this study. The insert was driven by one of five waveforms: two sinusoidal waveforms or three patient-specific respiratory waveforms. 3DPET and 4DPET images of the phantom under motion were acquired and reconstructed with six CTAC methods: helical breath-hold (3DHEL), helical free-breathing (3DMOT), 4D phase-averaged (4DAVG), 4D maximum intensity projection (4DMIP), 4D phase-matched (4DMATCH), and 4D end-exhale (4DEXH) CTAC. Recovery of SUV(max), SUV(mean), SUV(peak), and segmented tumor volume was evaluated as RC(max), RC(mean), RC(peak), and RC(vol), representing percent difference relative to the static ground truth case. Paired Wilcoxon tests and Kruskal-Wallis ANOVA were used to test for significant differences.
  
  
  RESULTS
  For 4DPET imaging, the maximum intensity projection CTAC produced significantly more accurate recovery coefficients than all other CTAC methods (p < 0.0001 over all metrics). Over all motion waveforms, ratios of 4DMIP CTAC recovery were 0.2 ± 5.4, -1.8 ± 6.5, -3.2 ± 5.0, and 3.0 ± 5.9 for RC(max), RC(peak), RC(mean), and RC(vol). In comparison, recovery coefficients for phase-matched CTAC were -8.4 ± 5.3, -10.5 ± 6.2, -7.6 ± 5.0, and -13.0 ± 7.7 for RC(max), RC(peak), RC(mean), and RC(vol). When testing differences between phases over all CTAC methods and waveforms, end-exhale phases were significantly more accurate (p = 0.005). However, these differences were driven by the patient-specific respiratory waveforms; when testing patient and sinusoidal waveforms separately, patient waveforms were significantly different between phases (p < 0.0001) while the sinusoidal waveforms were not significantly different (p = 0.98). When considering only the subset of 4DMATCH images that corresponded to the end-exhale image phase, 4DEXH, mean and interquartile range were similar to 4DMATCH but variability was considerably reduced.
  
  
  CONCLUSIONS
  Comparative advantages in accuracy and precision of SUV metrics and segmented volumes were demonstrated with the use of the maximum intensity projection and end-exhale CT attenuation correction. While respiratory phase-matched CTAC should in theory provide optimal corrections, image artifacts and differences in implementation of 4DCT and 4DPET sorting can degrade the benefit of this approach. These results may be useful to guide the implementation, analysis, and development of respiratory-correlated thoracic PET/CT in the radiation oncology and diagnostic settings.
authors.affiliation: Department of Radiation Oncology, University of Washington, Seattle, Washington 98195-6043.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Nyflot
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Washington 98195-6043.
authors.forename: Tzu-Cheng
authors.initials: TC
authors.lastname: Lee
authors.affiliation: Department of Radiology, University of Washington, Seattle, Washington 98195-6043.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Alessio
authors.affiliation: GE Healthcare, Waukesha, Wisconsin 53188.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Wollenweber
authors.affiliation: GE Healthcare, Waukesha, Wisconsin 53188.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Stearns
authors.affiliation: Department of Radiation Oncology, University of Washington, Seattle, Washington 98195-6043 and Department of Radiology, University of Washington, Seattle, Washington 98195-6043.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Bowen
authors.affiliation: Department of Radiology, University of Washington, Seattle, Washington 98195-6043.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Kinahan
mesh_terms: D016477:Artifacts; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008171:Lung Diseases / Q000000981:diagnostic imaging / Q000503:physiopathology; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D012119:Respiration