We have reported in our previous studies on the methodology, and feasibility of 4D-PET (Gated PET) acquisition, to reduce respiratory motion artifact in PETimaging of the thorax. In this study, we expand our investigation to address the problem of respiration motion in PET/CT imaging. The respiratory motion of four lungcancer patients were monitored by tracking external markers placed on the thorax. A 4D-CT acquisition was performed using a “step-and-shoot” technique, in which computed tomography(CT) projection data were acquired over a complete respiratory cycle at each couch position. The period of each CT acquisition segment was time stamped with an “x-ray ON” signal, which was recorded by the tracking system. 4D-CT data were then sorted into 10 groups, according to their corresponding phase of the breathing cycle. 4D-PET data were acquired in the gated mode, where each breathing cycle was divided into ten 0.5 s bins. For both CT and PET acquisitions, patients received audio prompting to regularize breathing. The 4D-CT and 4D-PET data were then correlated according to respiratory phase. The effect of 4D acquisition on improving the co-registration of PET and CTimages, reducing motion smearing, and consequently increase the quantitation of the SUV, were investigated. Also, quantitation of the tumor motions in PET, and CT, were studied and compared. 4D-PET with matching phase 4D-CTAC showed an improved accuracy in PET-CT image co-registration of up to 41%, compared to measurements from 4D-PET with clinical-CTAC. Gating PET data in correlation with respiratory motion reduced motion-induced smearing, thereby decreasing the observed tumor volume, by as much as 43%. 4D-PET lesions volumes showed a maximum deviation of 19% between clinical CT and phase- matched 4D-CT attenuation corrected PETimages. In CT, 4D acquisition resulted in increasing the tumor volume in two patients by up to 79%, and decreasing it in the other two by up to 35%. Consequently, these corrections have yielded an increase in the measured SUV by up to 16% over the clinical measured SUV, and 36% over SUV’s measured in 4D-PET with clinical-CT Attenuation Correction (CTAC) SUV’s. Quantitation of the maximum tumor motion amplitude, using 4D-PET and 4D-CT, showed up to 30% discrepancy between the two modalities. We have shown that 4D PET/CT is clinically a feasible method, to correct for respiratory motion artifacts in PET/CT imaging of the thorax. 4D PET/CT acquisition can reduce smearing, improve the accuracy in PET-CT co-registration, and increase the measured SUV. This should result in an improved tumor assessment for patients with lungmalignancies.
The authors appreciate all the support from General Electric Medical Systems, and Varian Medical Systems. The authors would also like to thank Katherine Kolbert for all her support in using the MIAU software package. The authors would like to thank Dr. Micheal Lovelock for making his software package for CT contouring and centroid measurement available. This study was supported in part by National Institutes of Health Grant No. [P01-CA-59017].
II. MATERIALS AND METHODS
II.A. Patient data and preparation
II.B. Respiratory motion tracking
II.C. PET/CT scanner
II.D. CT data acquisition
II.E. PET data acquisition
II.F. 4D PET/CT data processing
II.G. Data analysis
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