All of the following units express radiopharmaceutical specific activity except?

Specific activity in the context of radiopharmaceuticals refers to the radioactivity of a particular quantity of a substance, often expressed in terms that relate the amount of radioactivity to the mass of the substance. It is important for determining how much active substance is present relative to an inactive carrier.

The correct answer, which indicates a unit that does not express specific activity, is based on the understanding of how specific activity is defined. Specific activity is commonly expressed in units that relate radioactivity to mass, such as microcuries per milligram (uCi/mg), curies per gram (Ci/g), or megabecquerels per mole (MBq/mol). These units effectively communicate how much radioactivity is associated with a specific amount of the radiopharmaceutical, thus enabling efficacy evaluation in various applications.

The unit kBq/mL, however, denotes the activity of a radiopharmaceutical in terms of a volume (milliliters) rather than relating radioactivity specifically to a mass of the substance. Consequently, it does not represent specific activity because it does not provide a ratio of radioactivity to an equivalent mass measurement; instead, it describes overall activity in a given volume, lacking the necessary context to be classified as specific activity.