Ironclad fluoroemulsion boosts MRI sensitivity

Magnetic resonance imaging has become a critical technology in medical diagnostics, and chemists continue to devise new types of MRI contrast agents. In one of the latest examples, a team led by Eric T. Ahrens, Roger Y. Tsien, and Alexander A. Kislukhin of the University of California, San Diego, has created a paramagnetic fluorinated nanoemulsion with embedded metal ions that provides up to a fivefold boost in sensitivity over previously reported ¹⁹F MRI cellular detection systems (Nat. Mater. 2016, DOI: 10.1038/nmat4585). The researchers first crafted a metal-binding fluorinated compound by introducing β-diketone groups to the ends of a perfluoropolyether precursor. They then emulsified this fluorinated oil (yellow) in an aqueous solution containing a commercial surfactant. The researchers next added various transition and lanthanide metals, which were bound by the diketonate groups. In a surprise finding, the team observed that iron(III) provided the best MRI sensitivity, surpassing that of gadolinium(III), which typically provides the best image contrast for conventional ¹H MRI. Kislukhin says the intended use of the new nanoemulsion is for labeling therapeutic stem cells and immune cells to track their movement via ¹⁹F MRI once the cells are implanted in a patient, which the team demonstrated in mice.