Purpose: 4D positron emission tomography and computed tomography (PET∕CT) can be used to reduce motion artifacts by correlating the raw PET data with the respiratory cycle. The accuracy of each PET phase is dependent on the reproducibility and consistency of the breathing cycle during acquisition. The objective of this study is to evaluate the impact of breathing amplitude and phase irregularities on the quantitative accuracy of 4D PET standardized uptake value (SUV) measurements. In addition, the magnitude of quantitative errors due to respiratory motion and partial volume error are compared.
Methods: Phantom studies were performed using spheres filled with (18)F ranging from 9 to 47 mm in diameter with background activity. Motion was simulated using patient breathing data. The authors compared the accuracy of SUVs derived from gated PET (4 bins and 8 bins, phase-based) for ideal, average, and highly irregular breathing patterns.
Results: Under ideal conditions, gated PET produced SUVs that were within (-5.4 ± 5.3)% of the static phantom measurements averaged across all sphere sizes. With breathing irregularities, the quantitative accuracy of gated PET decreased. Gated PET SUVs (best of 4 bins) were (-9.6 ± 13.0)% of the actual value for an average breather and decreased to (-17.1 ± 10.8)% for a highly irregular breather. Without gating, the differences in the SUV from actual value were (-28.5 ± 18.2)%, (-25.9 ± 14.4)%, and (-27.9 ± 18.2)% for the ideal, average, and highly irregular breather, respectively.
Conclusions: Breathing irregularities reduce the quantitative accuracy of gated PET∕CT. Current gated PET techniques may underestimate the actual lesion SUV due to phase assignment errors. Evaluation of respiratory trace is necessary to assess accuracy of data binning and its effect on 4D PET SUVs.