Cross Population Motion Modeling Applied to Attenuation Correction of Respiratory Gated F18-FDG PET

Accurate attenuation correction in PET/CT relies upon anatomically matched PET and CT scans, however, attenuation mismatch artifacts are often present due to continuous respiration during both the PET and CT scans. Acquiring respiratory gated CT and PET scans in which each frame of the 4DCT is matched with a frame in a respiratory gated PET scan is one strategy for obtaining temporally correlated PET and CT images. In this paper we propose a cross population model as an alternative to 4DCT for estimating the deformation of attenuating objects within the thorax. Principal components analysis was used to extract components of motion from the 4DCT scans of a cohort of 10 patients and the components were then fitted to the frames from a respiratory gated PET scan. The cross population model produced an artificial, yet realistic patient specific deformation field for each frame even though no 4DCT was acquired in conjunction with the gated PET scan. The deformation field was then applied to the static spiral CT image to produce CT frames matching each PET frame. The first 5 components of motion accounted for 95% of the movement in regions where there was sufficient PET camera sensitivity to detect motion. We propose this approach as the basis for a robust method of transforming a static spiral CT into spatially matched attenuation maps. We investigate improvements in image contrast as a result of using our method for attenuation correction.