Normalization in 3D PET: comparison of detector efficiencies obtained from uniform planar and cylindrical sources

The authors have performed a comparison between 3D PET Normalization Factors (NFs) obtained from a uniform planar source and a uniform cylindrical phantom. The NFs have geometric and detector efficiency components. Detector efficiency data were measured using both phantoms. Both efficiency data sets were corrected using geometric factors obtained from a low-scattering planar distribution. NFs derived from 3D planar and 3D cylindrical efficiency data were applied to the sinogram data, yielding axial uniformity indices of 0.78% (2D), 1.71% (3D planar), and 3.40% (3D cylinder), and respective radial uniformity indices of 2.00%, 4.81%, and 4.07%. Correcting the cylinder for scatter prior to calculating the detector efficiencies was found to slightly improve axial uniformity and to slightly degrade radial uniformity. The uniformity obtained from cylinder-derived detector efficiencies is nearly identical to that obtained from plane-source derived efficiencies; the predominant influence on the accuracy of the normalization is the geometric factors used to correct the detector efficiency data