Fig. 9.

A–D: Four coronal slices of NEXI parametric maps calculated using NLLS from a multi-shell multi-$\mathit{t}$ dataset. The maps enable a good differentiation between GM & WM as well as between different cortical layers (white arrows) or hippocampal subfields (black arrow). E: Median & IQR of model parameters in the cortex and hippocampus ROIs across the four datasets. The exchange time estimate is also compared with ${\mathit{t}}_{\mathit{e}\mathit{x}}^{\mathit{K}(\mathit{t})}$, Eq. (7). Experimental trends agree with the simulations. Regarding ${\mathit{t}}_{\mathit{e}\mathit{x}}^{\mathit{K}(\mathit{t})}$, the estimation agrees with ${\mathit{t}}_{\mathit{e}\mathit{x}}$ very well for Dataset #4, which had the highest SNR (larger voxels), and is otherwise shorter.