Efficiency normalization techniques for 3D PET data

Determination of the individual geometrical and efficiency normalization factors is a more involved procedure in 3D than in 2D because of the incorporation of oblique lines-of-response which results in an order of magnitude increase in the number of correction factors required. Techniques using rotating rod source scans in both 2D and 3D, and a uniform cylinder scan in 3D, have been developed for estimating normalization factors. However, a uniform plane source is generally considered the best combination of a low scatter environment and a centrally-located isotope distribution. Plane sources are difficult and expensive to construct with the required uniformity and long half-life. The authors have investigated the use of a scanning germanium line source which simulates a plane source distribution by slowly traversing across the field-of-view. They compare 3D reconstructions using estimates of the geometrical and efficiency correction factors for normalization obtained from rotating rod, plane (scanning line) and cylinder source distributions. No significant difference is found to distinguish the 3D reconstructions of the uniform cylinder.