Mo-99/Tc-99m Generator Elution Yield Estimator

Enter Day 1 Activity

MBq

Day 1–7 (Week 1)

Day	Week 1

Day 8–14 (Week 2)

Day	Week 2

Note: The estimated yield may be overestimated in Week 2 as Moly breakthrough was not considered in the calculation.

Mo-99 / Tc-99m Generator Elution Yield Estimator

This calculator estimates the expected activity of a Mo-99/Tc-99m generator over time based on the initial activity on Day 1. It is intended for use in nuclear medicine departments to help plan generator utilization and estimate the available activity during the first two weeks after generator calibration.

In most nuclear medicine procedures, radiopharmaceuticals used for SPECT imaging are labeled with technetium-99m. This radionuclide is obtained from a generator system in which molybdenum-99 decays to technetium-99m. Because Mo-99 has a finite half-life, the generator activity decreases continuously with time. Estimating this decay helps clinicians and radiopharmacists plan daily elutions and patient studies.

The activity of molybdenum-99 is modeled using the standard radioactive decay equation:

\[ A(t) = A_0 e^{-\lambda t} \]

where:

\(A(t)\) — activity at time \(t\)
\(A_0\) — initial activity on Day 1
\(\lambda\) — decay constant
\(t\) — time elapsed since calibration

The decay constant is determined from the half-life:

\[ \lambda = \frac{\ln(2)}{T_{1/2}} \]

For molybdenum-99 the half-life used in the calculation is:

\[ T_{1/2} = 66 \text{ hours} \]

Time is converted to hours according to the day number:

\[ t = (day - 1) \times 24 \]

The calculator evaluates the remaining generator activity for each day from Day 1 to Day 14 and displays the results grouped into Week 1 and Week 2.

Note that this tool estimates generator activity based solely on the radioactive decay of Mo-99. It does not account for generator efficiency, elution losses, or molybdenum breakthrough, therefore the actual activity obtained during elution may differ from the calculated values.