tained in a solution, is then adsorbed onto an alumina (Al2O3) column that is contained in cylinders that are about the diameter of a large pencil. The columns are shipped to radiopharmacies and hospitals in radiation-shielded cartridges known as technetium generators (Figure 2.1).

The Mo-99 in the generators decays with about a 66-hour half-life to Tc-99m. The Tc-99m is typically recovered by passing a saline solution through the alumina column in the generator, a process known as eluting the generator. The saline removes the Tc-99m but leaves the Mo-99 in place. A technetium generator can be eluted several times a day for about a week before it needs to be replaced4 with a fresh generator (Figure 2.2).

There are numerous Tc-99m kits5 for producing radiopharmaceuticals to examine the brain, kidney, heart, bone, liver, and lung. Table 2.1 provides a selected list of Tc-99m labeled radiopharmaceuticals in use today. The list is not intended to be exhaustive but to illustrate the range of diseases and conditions where Tc-99m based diagnostic imaging is useful. Figure 2.3 provides examples of images that can be obtained from diagnostic imaging procedures.

Because of its relatively short half-life (66 hours), Mo-99 cannot be stockpiled for use. It must be made on a weekly or more frequent basis to ensure continuous availability. The processes for producing Mo-99 and technetium generators and delivering them to customers are tightly scheduled and highly time dependent. An interruption at any point in the production, transport, or delivery of Mo-99 or technetium generators can have substantial impacts on patient care, as discussed in Chapter 4.


There are two primary approaches for producing the medical isotope Mo-99, as described in Appendix D: fission of U-235, which produces Mo-99 and other medically important isotopes such as I-131 and Xe-133, and neutron capture by Mo-98 to produce Mo-99. For the reasons described in Appendix D, the committee dismissed neutron capture as a viable process for producing Mo-99 in the quantities needed to meet U.S. or global demand for Mo-99. None of the four global producers of Mo-99 (Chapter 1) use the neutron capture method to produce Mo-99 because of its inefficiencies. However, this process can be used to make smaller


The technetium generator is replaced after about a week because it loses its elution efficiency and also because the Tc-99m can become contaminated with Mo-99 from the column. The latter process is referred to as Mo-99 breakthrough. After it is replaced, the old generator may continue to be used for research that does not involve human subjects.


Kits are composed of all of the required chemicals (e.g., the pharmaceutical agent, chelating compound, and saline solution) for formulating the radiopharmaceutical to which Tc-99m is added.

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