The effect on radiochemical purity of modifications to the method of preparation and dilution of 99mTc-sestamibi.

Background: 99mTc-sestamibi is a useful radiopharmaceutical for myocardial perfusion imaging, parathyroid imaging and breast tumour imaging. However, the preparation is time consuming and the limit of 3 ml on the volume of liquid that can be added to the Cardiolite kit vial means that it is often difficult to draw up small doses for patient studies.

Aim: To modify the method of preparation of 99mTc-sestamibi in order to reduce the preparation time and to give a preparation which is more convenient for withdrawing patient doses.

Method: A modified kit was prepared by reconstituting a Cardiolite kit vial with 3 ml Sodium Chloride Injection (0.9%) BP, sub-dividing it into two separate nitrogen-filled vials before adding sodium pertechnetate and boiling for radiolabelling. 99mTc-sestamibi was also prepared according to the manufacturer's recommended method and diluted with sodium chloride injection after preparation. Radiochemical purity was assessed by thin-layer chromatography and high-performance liquid chromatography.

Results: 99mTc-sestamibi prepared according to the manufacturer's recommended method had high radiochemical purity (96.9%+/-1.1%) and retained >90% radiochemical purity over 8 h following dilution. However, 99mTc-sestamibi prepared by the modified method gave variable and inconsistent results.

Conclusion: The modified method of preparation was not robust enough to give reproducibly high radiochemical purity. However, dilution of 99mTc-sestamibi prepared according to the manufacturer's recommended method was satisfactory. This study highlights problems with the analysis of 99mTc-sestamibi and the limitations of modifying the method of preparation.