d-PFG experiment (symbols) and simulations (solid line) of the corresponding echo attenuations vs. ϕ for q = 29.7, 39.6, 49.5, 59.4, 69.3, 79.2, and 89 mm−1 for ROIs within the phantom: a.– b.) 5 μm, c.–d.) 10 μm, e.–f.) 25 μm, and g.) free diffusing D5