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Generators are units that contain a radioactive “parent” nuclide with a relatively long half‐life that decays to a short‐lived “daughter” nuclide. The most commonly used generator is the technetium‐99m (^99mTc) generator (Figure 3.1), which consists of a heavily shielded column with molybdenum‐99 (⁹⁹Mo; parent) bound to the alumina of the column. The ^99mTc (daughter) is “milked” (eluted) by drawing sterile saline through the column into the vacuum vial. The parent ⁹Mo (small gray circles) remains on the column, but the daughter ^99mTc (white circles) is washed away in the saline.

A generator like the one just described is frequently called a cow, the elution of the daughter nuclide is referred to as milking, and the surrounding lead is called a pig, a term used for any crude cast‐metal container. Another generator that is used extensively for cardiac imaging is the ⁸²Sr–⁸²Rb generator. Its design and construction is very similar to the ⁹⁹Mo–^99mTc generator but due to the 75 second half‐life of ⁸²Rb, the generator must be located on site—usually right next to the PET scanner where the generator is eluted and the solution is infused into the patient in one automated step.

Table 3.1 describes the features of three common generators.