Figure 3. Fluorine-19 relaxometry of metalated PFPE emulsions.

a, R₁ and ¹⁹F NMR spectra of FETRIS nanoemulsion (4.5 g/L ¹⁹F, 3.5 mM diketone) in the presence of 0.5 mM metal ions, 15 mM HEPES, and at pH 7.4. The peaks from different ¹⁹F spectra are scaled to the same absolute intensity. b, Relaxometric analysis of Fe³⁺ and Gd³⁺ binding capacity. Shown are measurements of R₁ for both PFPE (fluorous phase) and trifluoroacetate reference (TFA) added to the aqueous phase. c, Magnetic field dependence at T = 295 K and d, temperature (B₀ = 9.4 T) dependence of observed relaxation rates R₁ (●) and R₂ (x) in FETRIS nanoemulsion (22.5 g/L ¹⁹F, 17.5 mM diketone, 2.8 mM Fe³⁺) and predicted R₁ (—) values using Eqs. S1–S4. Predicted R₁ values represent best fit to SBM equations, with r = 1.19 nm, τ_F (295 K) = 0.80 ns, τ_v (295 K) = 3.59 ps, the Arrhenius temperature dependence with activation energies of 3.6 kcal/mol for τ_F and 4.5 kcal/mol for τ_v. The diamagnetic contributions to R₁ are presumed to be negligible and Δ fixed at 0.2 cm⁻¹. R₁ values increase, while R₂ values decrease, at lower magnetic field strengths, suggesting that there will be no degradation of SNR at clinical fields due to line broadening.