Figure 2. Schematic overview of the fate of labeled substrates and substrate analogs.

Radiolabeled ¹¹C-substrate is taken up into the cell and undergoes complete oxidation, eventually leading to the release of ¹¹CO2. After their uptake into the cell, substrate analogs labeled with ¹⁸F or ¹²³I are partially metabolized and then retained. The majority of perfusion tracers require preserved cellular metabolism to be taken up by the cell. Substrate oxidation rates can also be monitored using ¹⁵O and measuring the release of H2¹⁵O.