A study of SPECT/CT camera stability for quantitative imaging
Wendy A McDougald1, Robert S Miyaoka2, Adam M Alessio2
1Imaging Research Laboratory, Department of Radiology, University of Washington, 222 Portage Bay Building, Box 357987, Seattle, WA, 98195-7987, USA. wam2@uw.edu.
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.
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