Molybdenum Breakthrough

Molybdenum breakthrough refers to contamination of ^99mtechnetium obtained by elution of a molybdenum-99 column. The ^99mTc generated must be tested for molybdenum before administration to patients. The US Nuclear Regulatory Commission (NRC) allow no more than 0.15 μCi of ⁹⁹Mo per 1 mCi of ^99mTc at the time of administration. The last part is important. Because the half life of ⁹⁹Mo is longer than that of ^99mTc (66 hours vs 6 hours), if you let the eluate sit around, the relative concentration of ⁹⁹Mo will rise, making it unusable.

Testing for molybdenum breakthrough is usually done by placing the eluate in a lead shield and using a commercial dose calibrator whose energy is set to that of ⁹⁹Mo photons(740 keV and 780 keV).

References

Mettler FA and Guiberteau MJ. Chapter 3: Quality Control. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. p 44.