1.    If intended for clinical use, output of the generator must be sterile and pyrogen-free. There is no compromise on either of these requirements.

2.    The chemical properties of the daughter must be different than those of the parent to permit separation of daughter from parent. Separations are usually performed by affinity or ion exchange chromatography.

3.    Generator should be eluted with 0.9% saline solution and should involve no violent chemical reactions. Human intervention should be minimal to minimize radiation dose. Eluents other than 0.9% NaCl may require tedious pH adjustment, associated with a significant radiation dose, and are therefore undesirable.

4.    Daughter isotope for diagnostic studies should be short-lived gamma-emitting nuclide (t_phys =  hrs-days). Beta particles are undesirable as they confer a high radiation dose and are not imageable.

5.    Physical half-life of parent should be short enough so daughter in-growth after elution is rapid, but long enough for practicality. The Mo/Tc generator is a perfect example- in-growth of Tc-99m is very rapid, but the shelf-life of the generator is two weeks.

6.    Daughter chemistry should be amenable to the preparation of a wide variety of compounds, especially those in kit form. In the case of the Mo/Tc generator, there are cold kits for imaging essentially any organ or system in the human body.

7.    Very long-lived or stable granddaughter so no radiation dose is conferred to patient by decay of subsequent generations. In the case of Tc-99 ground state, the granddaughter of Mo-99, the half-life of 220,000 yr guarantees a minimal radiation dose to the patient, regardless of the effective half-life.

8.    Inexpensive, effective shielding of generator, minimizing radiation dose to those using it. This is easy to accomplish since lead is very dense and therefore a good attenuator of radiation. In addition, it is a very inexpensive metal and can be easily molded into almost any shape desired.

9.    Generator is easily recharged (we do NOT recharge Mo/Tc generators- radiation dose associated with this procedure would be excessive). After their useful life is over, we store them in a decay area until a background reading is obtained at the surface of the generator.