A study of SPECT/CT camera stability for quantitative imaging

Abstract

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 99mTc, factors were calculated to convert counts/cc to activity/cps. Measurements were made over an 18-month period. System sensitivity data calculated from 57Co daily quality assurance (DQA) flood acquisitions were then compared to the 99mTc calibration factors to determine the relationship of the factors. Results: The coefficient of variation is 2.7 % for the 99mTc cylinder conversion factors and 2.6 % for the 57Co 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.