Production of positron-emitting radionuclides

Specific activity of a sample is defined as the radioactivity per unit mass of a radionuclide or a labeled compound. If a 50-mg sample contains 100 mCi (370MBq), then the specific activity of the sample is given as 100/50 = 2 mCi/mg or 74 MBq/mg. One should not confuse the specific activity with the concentration, which is given in mCi/ml or MBq/ml. The specific activity is at times expressed in units of mCi/mole (MBq/mole) or mCi/pmole (MBq/qmole). 

The specific activity of a carrier-free radionuclide can be calculated by 

The specific activity is an important parameter to consider in radiolabehng and in vivo biodistribution of tracers. Cold molecules in low-specific-activity radiopharmaceuticals compete with radioactive molecules and lower the uptake of the tracer in tissues. Similarly, low-specific-activity radionuclides yield poor radiolabeling. 

Since only a limited number of short-lived radionuclides are useful for PET imaging, production of those in routine clinical use and a few with potential for future clinical use are described here. A few essential long-lived positron emitters are also included. The different characteristics of these radionuclides are summarized in Table 7.2. 

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