The Pharmaceutics and Compounding Laboratory
Radiopharmaceuticals:
TC-99M Sulfur Colloid

Dispensing TC-99M Sulfur Colloid Doses

Radiopharmaceuticals are labeled to contain a certain radioconcentration, e.g., µCi/ml, at a given time stated on the label. This is the calibration time. The radiopharmacist must use this information and the half-life of the particular radionuclide to obtain doses for all other times when doses are requested. The physical decay chart can also be used to determine the fraction of activity left in the product at various times after calibration.

Example: The calibration activity and time of your product was found to be 3.3 µCi/ml at 3:00 p.m. You want to inject 6 µCi of activity into a patient at 6:00 p.m.  What volume of your product must be used to have 6 µCi at 6:00 p.m.?

  1. Calculate the activity your product will have at 6:00 p.m. (use physical decay chart).
      3.3 µCi/ml × 0.708 = 2.34 µCi/ml


  2. Calculate the number of ml of your product needed to contain 6 µCi.
      6 µCi/2.34 µCi/ml = 2.56 ml

So, you would dispense 2.56 ml of your product in a syringe labeled with the "stringed tag" found in the sulfur colloid kit.