Objective: Our study evaluated the accuracy and reliability of 3 radiochemical purity (RCP) measurement methods of 99mTc-sestamibi. A regular-sized (1.0 cm x 9.0 cm) Whatman 31 ET Chr paper strip (regular 31 ET) also was included in our evaluation because of its ease in handling.
Methods: The miniaturized and regular 31 ET methods were compared with the standard RCP testing method (aluminum oxide-coated plastic thin-layer chromatography [TLC] plate, with > or = 95% ethanol as the developing solvent). A total of 30 experimental runs were performed in triplicate (n = 90) over an RCP range of 82%-98%. The 99mTc-sestamibi preparations were reconstituted purposely to ensure that 50% of the tested samples had RCP values below the 90% limit.
Results: The evaluated RCP ranges were 89.9% +/- 6.3%, 91.0% +/- 3.8%, and 91.4% +/- 4.3% for the TLC, miniature 31 ET, and regular 31 ET methods, respectively (n = 30 each). A strong correlation was found between the TLC and miniature 31 ET methods (r = 0.92), as well as between the TLC and regular 31 ET methods (r = 0.94). Both alternative methods tended to overestimate RCP value as determined by the TLC method, especially in an RCP range below 95%. This resulted in a false-positive rate of 27% for the miniature 31 ET method and 33% for the regular 31 ET method. The test/retest reliability was 99% for both the TLC and regular 31 ET methods, and 91% for the TLC and miniature 31 ET methods.
Conclusion: The miniature and regular 31 ET methods produced a high false-positive rate, which makes them unacceptable for the determination of RCP value of 99mTc-sestamibi.