03 Nuclear
Mo-99 breakthrough
USP / NRC limit: ≤ 0.15 μCi Mo-99 per mCi Tc-99m (0.15 kBq/MBq) at administration.
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Simulation
Mo-99 breakthrough — Change the numbers; the scene follows.
Where it works
Hot lab
Generator
At the Mo-99/Tc-99m generator — elution yield, secular equilibrium, Mo breakthrough.
Open this machineFormula
Variables
Results
R_now
Ratio at assay
0.002µCi/mCi
R_inj
Ratio at administration
0.0037µCi/mCi
limit
Limit
0.15µCi/mCi
Explanation
What it means
A ⁹⁹Mo/⁹⁹ᵐTc generator can leak parent into the eluate. Mo-99 emits 740 keV γ that degrade image quality and add patient dose, so every elution is assayed in a lead pig that shields Tc-99m (140 keV) but not Mo-99. The limit is 0.15 μCi Mo per mCi Tc at the time of administration — note that the ratio grows with time because Tc decays faster (6 h vs 66 h). This is a working relation in Nuclear medicine.
Where it is used
Clinically it sits on the Hot lab — Generator. At the Mo-99/Tc-99m generator — elution yield, secular equilibrium, Mo breakthrough. Nuclear-medicine relations sit in the hot lab, on the camera, and in the voxel: decay, SUV, TOF, and counting statistics. They decide whether an uptake is real or a clock error.
Hot lab · Open this machineHow to use it
Enter measured Mo-99 and Tc-99m at assay, plus the hours until injection. Read the ratio now and at injection, and a pass/fail against 0.15. Units: μCi Mo and mCi Tc (or any consistent pair). Change one input and watch the curve and the simulation follow.
Symbols
- A_MoMo-99 activity0.5 µCi
- A_TcTc-99m activity250 mCi
- tHours until administration6 h
Worked example
A typical case from the default values: A_Mo = 0.5 µCi (Mo-99 activity); A_Tc = 250 mCi (Tc-99m activity); t = 6 h (Hours until administration). Substituting into the relation gives R_now = 0.002 µCi/mCi; R_inj = 0.0037 µCi/mCi; limit = 0.15 µCi/mCi. These are teaching numbers — align them with your machine.
Typical values give
- R_now = 0.002µCi/mCi
- R_inj = 0.0037µCi/mCi
- limit = 0.15µCi/mCi
Where it comes from
The displayed formula is the working relation. USP / NRC limit: ≤ 0.15 μCi Mo-99 per mCi Tc-99m (0.15 kBq/MBq) at administration. Usual reference: USP <821> / 10 CFR 35.204. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: USP <821> / 10 CFR 35.204
Assumptions & limits
Does not replace the dose calibrator + pig SOP. Activity units must match the 0.15 μCi/mCi convention (numerically equal to 0.15 kBq/MBq). Other parents (Sn-113, Ge-68) have their own breakthrough limits.
Pitfalls
Activity is not counts. SUV needs the true injected activity, the residual, and the correct decay time — a clock off by 10 min on ¹⁸F is a several-percent error. Do not compare SUVs across reconstructions. Does not replace the dose calibrator + pig SOP. Activity units must match the 0.15 μCi/mCi convention (numerically equal to 0.15 kBq/MBq). Other parents (Sn-113, Ge-68) have their own breakthrough limits.
Keep this
Write the assay time next to every activity. Decay does the rest. Does not replace the dose calibrator + pig SOP. Activity units must match the 0.15 μCi/mCi convention (numerically equal to 0.15 kBq/MBq). Other parents (Sn-113, Ge-68) have their own breakthrough limits.
In this specialty