Figure 1.

Schematic plot to illustrate quasi-steady-state (secular equilibrium) phase of radioligand binding. In this phase, the radioligand is washing out from both regions rich in amyloid (target) and devoid of amyloid (reference). The ratio of regional radioactivity between target and reference is near horizontal or slowly increasing. The quasi-steady-state phase in principle is open ended, in practice bracketed by complete radioactive decay and radioligand elimination from the body many hours after injection. SUVR, standardized uptake value ratio.