The method is model-independent because it does not depend on any specific compartmental model configuration for the tracer, and the minimal assumption is that the behavior of the tracer can be approximated by two compartments – a "central" (or reversible) compartment that is in rapid equilibrium with plasma, and a "peripheral" (or irreversible) compartment, where tracer enters without ever leaving during the time of the measurements.
The method is model-independent as it does not rely on specific configurations for the tracer's behavior, and the minimal assumption involves two compartments – a "central" (or reversible) compartment in rapid equilibrium with plasma and a "peripheral" (or irreversible) compartment where tracer remains without leaving during measurements.