Recovery coefficient in PET as a function of object size and respiratory motion trajectory

We have measured recovery coefficients (RCs) for spherical objects imaged under prescribed breathing motion conditions using a GE Discovery LS PET/CT scanner equipped with a Varian RPM gating system. Eight spheres, with inside diameters 4.0, 6.2, 7.9, 9.9, 12.4, 15.4, 19.8 and 31.3 mm, were placed on a moving platform driven by a computer-controlled stepper motor. The spheres were filled with activity relative to the background of approximately 8.3:1. The motion of the platform followed respiratory motion trajectories adapted from a model used in radiation therapy. RC was estimated as the maximum pixel value within a region of interest that included the sphere relative to the activity at the center of the static image of the largest sphere. The experiment was repeated with spheres in a low-density background. The RC decreases with increased motion amplitude, as expected. The RC is less affected by motion with a greater post expiratory pause. Respiratory gating greatly improves signal recovery deteriorated by respiratory motion. The presence of low-density background, which would cause misalignment of the attenuation correction map in PET image reconstruction, did not affect the signal recovery significantly.