TY - JOUR T1 - Impact of Recent Change in the National Institute of Standards and Technology Standard for <sup>18</sup>F on the Relative Response of <sup>68</sup>Ge-Based Mock Syringe Dose Calibrator Standards JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1453 LP - 1457 DO - 10.2967/jnumed.115.159384 VL - 56 IS - 9 AU - Brian E. Zimmerman AU - Denis E. Bergeron AU - Jeffrey T. Cessna Y1 - 2015/09/01 UR - http://jnm.snmjournals.org/content/56/9/1453.abstract N2 - As a result of a recent change in the National Institute of Standards and Technology (NIST) activity standard for 18F, we have determined new relative response ratios for a 68Ge solid epoxy mock syringe source used in activity calibrators as a long-lived substitute for 18F. New standardized solutions of each radionuclide were used to determine the response ratios while maintaining traceability to national standards. This work updates our previously published data from 2010. Methods: Following our previously published methodology, solution-filled mock syringe sources, identical in geometry to the solid 68Ge epoxy calibration source currently on the market, were prepared using NIST-calibrated solutions of 68GeCl4 and 18F-FDG and directly compared in several models of activity calibrators to determine empirically the relative response ratios for these 2 radionuclides. Results: The new relative response ratios measured in this study reflect the change in 18F activity measurements that arise from the recent −4% change in the NIST activity standard. The results allow the 68Ge activity of the mock syringe source to be expressed in terms of equivalent 18F activity, with a relative combined standard uncertainty of about 0.8% for the activity calibrators used in this study. Conclusion: This work revises our previously derived relative response ratios for 18F and 68Ge by −3.7%, allowing users of the commercial mock syringe surrogate source to calibrate their activity calibrators in a way that is consistent with the recent change in the NIST 18F standard. ER -