Comparison of four alternative radiochemical purity testing methods for⁹⁹Tc^m-sestamibi

Four different methods for determining the radiochemical purity (RCP) of⁹⁹Tc^m-sestamibi have been proposed to replace the recommended thin-layer chromatography (TLC) method, as the recommended method is inconvenient and time-consuming. The purpose of this study was to compare the recommended TLC method with the four proposed rapid QC methods for⁹⁹Tc^m-sestamibi: (1) chloroform extraction (CE), (2) mini-paper chromatography with chloroform/tetrahydrofuran (1:1, v/v) (MPC), (3) Waters™ Sep-Pak®alumina N cartridge with 100% ethanol (SPE), and (4) Waters™ Sep- Pak®C18 cartridge with normal saline (SPNS). For RCP values ranging from 21.8 to 98.7% (n = 20), both the CE and SPNS methods produced falsely high RCP values (RCP difference: 14.1 ± 23.5% for CE and 15.0 ± 24.9% for SPNS). The MPC and SPE methods were in good agreement (r = 0.98 for MPC and 0.88 for SPE) with the recommended TLC method over the critical RCP range (i.e. 77.0-98.7%, n = 52) (RCP difference:-0.9 ± 1.2% for MPC and-4.3 ± 3.2% for SPE). None of the⁹⁹Tc^m-sestamibi preparations that had been rejected (i.e. RCP <90%) by the TLC method were accepted by either the MPC or SPE method. However, 4 of the 52⁹⁹Tc^m-sestamibi preparations with acceptable RCP by the TLC method had unacceptable RCP by the MPC method, whereas 8 of the same 52 preparations were unacceptable by the SPE method. The SPE method requires the loading of 0.05-0.1 ml⁹⁹Tc^m-sestamibi to the cartridge, which may consist of up to 1.2 GBq (33.3 mCi)⁹⁹Tc^mactivity per application (based upon the 37 GBq or 1000 mCi/3 ml per kit preparation). The MPC method takes only a 5 µl sample (9.3 MBq or 250 µCi) and 3-4 min for each RCP analysis. In conclusion, the MPC method is the best alternative method for the RCP determination of⁹⁹Tc^m-sestamibi, especially in emergency situations.