A study of SPECT/CT camera stability for quantitative imaging

BACKGROUND The purpose of this study was twofold: to evaluate the quantitative stability of a SPECT/CT gamma camera over time and to determine if daily flood acquisitions can reliably serve as calibration factors for quantitative SPECT. Using a cylindrical water phantom filled with measured amounts of (99m)Tc, factors were calculated to convert counts/cc to activity/cps. Measurements were made over an 18-month period. System sensitivity data calculated from (57)Co daily quality assurance (DQA) flood acquisitions were then compared to the (99m)Tc calibration factors to determine the relationship of the factors. RESULTS The coefficient of variation is 2.7 % for the (99m)Tc cylinder conversion factors and 2.6 % for the (57)Co DQA flood data. The greatest difference between the cylinder conversion factors and the flood data is less than 3 %. CONCLUSIONS Based on the results, the camera was stable within 3 % over an 18-month time period. The daily flood source acquisitions can be a reliable source for tracking camera stability and may provide information on updating the calibration factor for quantitative imaging.