Multiple window spatial registration error of a gamma camera: 133Ba point source as a replacement of the NEMA procedure

A long-lived 133Ba point source with gamma energies close to 67Ga and a single bore lead collimator were used to measure the multiple window spatial registration error. Calculation of the positions of the point source in the images used the NEMA algorithm. The results were validated against the values obtained by the standard NEMA procedure which uses a liquid 67Ga source with collimation.Of the source-collimator configurations under investigation an optimum collimator geometry, consisting of a 5 mm thick lead disk with a diameter of 46 mm and a 5 mm central bore, was selected. The multiple window spatial registration errors obtained by the 133Ba method showed excellent reproducibility (standard deviation < 0.07 mm). The values were compared with the results from the NEMA procedure obtained at the same locations and showed small differences with a correlation coefficient of 0.51 (p < 0.05). In addition, the 133Ba point source method proved to be much easier to use. A Bland-Altman analysis showed that the 133Ba and the 67Ga Method can be used interchangeably.The 133Ba point source method measures the multiple window spatial registration error with essentially the same accuracy as the NEMA-recommended procedure, but is easier and safer to use and has the potential to replace the current standard procedure.The ability of a gamma camera to perform quantitative dual isotope imaging depends critically on its ability to accurately position photons of different energies when imaged through different photo peak energy windows. This is particularly true when localizing small organs by subtraction scintigraphy, such as the parathyroid glands[1,2] or lung perfusion-ventilation imaging [3,4]. Poor multiple window spatial resolution (MWSR) also deteriorates spatial resolution when imaging a single radionuclide that has multiple photo peaks (e.g. 67Ga, 201Tl, 111In). Both the NEMA [5] and the IEC [6] standards use the same procedure to assess the accuracy of MWSR. It consists in p