Quality control in PET systems employing 2-D modular detectors

The authors have developed and put into operation three automated quality control procedures for PET (positron emission tomography) with 2-D modular detectors that are designed to detect problems quickly with a minimum effort on the part of the user. These procedures check the following: (1) the stability of the system in terms of the efficiencies of the detectors in a module or block; (2) resolution and its uniformity throughout the field of view; and (3) the stability of the whole system in terms of the data reproducibility. The stability of the detector modules is checked in terms of the uniformity of detector efficiencies by conducting a chi-square type test on the count rates of each detector in a block. In order to check the resolution and its uniformity and also the placement of the data in the PET scans, a cylindrical lucite phantom was fabricated which has a set of axial holes placed at 2-cm intervals. A computer program has been developed to analyze the images produced by this phantom and determine deviations from the normal resolution and correct placement of the data. A third procedure examines the reproducibility of the system by scanning a cylinder filled with a solution of Ge-68 several times and comparing the count rates in a small region of interest