FIG. 2.

a: Transverse relaxivity (s^–1 mM^–1) versus bound water lifetime τ_B (s) for Eu³⁺ at 0.54 T and 37°C as predicted by the Swift–Connick equation (Eq. 5) showing a maximum r_2exch of 0.055 s^–1 mM^–1 at 163 μs. b: The same data but now at 9.4 T. The maximum r_2exch is now 17.4 times larger and occurs at a faster exchange rate (0.962 s^–1 mM^–1 at 9.36 μs). Markers for the measured Eu³⁺ data are in good agreement with both theoretical Swift–Connick plots. A Δω of 42.5 ppm was used in both plots, with each Eu³⁺ compound being within ±2 ppm of this value.