Figure 2.

Tracer administration techniques used in metabolic research. A: Constant infusion of the tracer, where the tracer-to-tracee ratio (TTR) increases with time until isotopic equilibrium (plateau) is reached. B: Bolus injection of the tracer, where the TTR decreases with time. C: Primed constant infusion of the tracer, where a large tracer dose is given as a single bolus before the constant infusion, and isotopic plateau is reached immediately (an ideal tracer prime is shown; the dashed lines represent the theoretical increase and decrease in TTR from constant infusion and bolus injection, respectively).