Comparing respiratory and patient movement during dynamic PET

Movement degrades image quality in PET/CT. Two types of motion can be described: respiratory and global body motion, also called patient motion. In this study, an analysis of both types of movement is carried out in the context of dynamic PET acquisition for oncology research, using [18F]FL T and [18F]FDG data from patients with various types of tumours. To investigate the influence of the two types of motion during the acquisition, the PET data were partitioned in time frames and phases of the respiratory cycle ("gating"). Assuming the tumour does not deform during acquisition, we have used locally rigid registration to estimate its motion. Registrations were validated visually, using profiles and by checking alignment of the centre-of-mass of the segmented tumour. Dynamic patient motion of up to 1.5cm and respiratory motion of up to 1cm were observed, indicating that both types of motion in PET images cannot be neglected for certain applications. In addition, we show that patient movement changes the relation between tumour position and RPM position. This needs to be taken into account when using displacement gating for respiratory motion correction.