Figure 1.

Picture (a) and illustration (b) of the phantom used to investigate the precision of a PET imaging system, specifically the quantitative errors associated with the relative position of an object. (a) The phantom consisted of spheres of radioactivity submerged in a water bath. This phantom was repeatedly imaged with identical acquisition and reconstruction parameters. Between each acquisition, three spheres were repositioned at 1 mm increments along either the radial direction (Δr) or the axial direction (Δz). These three spheres were arranged as shown in the illustrations (b), where their centres lay along a single plane and perpendicular to the direction of motion. Vertical lines in the illustration depict axial slice separation as defined by the orientation of the detector rings. Two additional spheres were also present in the phantom; however, these were fixed to a stationary base and their position kept constant for all images.