Fig. 5. Relation of typical values of blood–brain equilibration time t1/2ke0( A ) and Ce50( B ) versus age, modeled using nonlinear mixed effects modeling. As age increases, t1/2ke0increases and Ce50decreases. •= Approximate entropy (ApEn); ○= 95% spectral edge frequency (SEF95); □= canonical univariate parameter (CUP).