Sci-Sat AM(1): Imaging-04: Respiratory errors in cardiac PET/CT with manual alignment of the CT image

Respiratory motion can produce misregistration errors between CT and PET images in cardiac PET/CT imaging. The objective of this study was to determine if manual registration of a single-phase end-expiration CT scan to the PET image would eliminate respiratory-induced artifacts. Listmode data from 71 cardiac PET patient scans were rebinned into a 8-frame respiratory-gated image series based on a respiratory trigger signal obtained with an optical tracking system. CT-based attenuation correction (AC) was performed after registering the CT image with the mean position of the PET images. The 8 phases of the gated PET study were coregistered and the breathing motion was measured. Images from end-inspiration and end-expiration were compared to assess the effect of motion. Studies in which the motion was >8mm were reconstructed again, with the CT scan aligned to end-expiration or end-inspiration, to determine if phase-specific registration could reduce the residual errors. The motion was found to be greatest in the axial direction (mean 4.1mm +\- 1.8mm) and 4 Rb stress studies (17%) had motion >8mm. The maximum displacement during breathing was greater for Rb-stress imaging (<15mm) than for resting (<7.5mm) or NH3-stress (<5.4mm) imaging. No significant differences were noted between the respiratory phases of the rest studies. Errors in myocardial radiotracer uptake of up to 35% were noted between end-inspiration and end-expiration for studies with >8mm of motion. Phase-specific registration of the CT reduced the extent of the errors but did not fully resolve them, suggesting that more sophisticated AC is required.