Geometrical confinement of gadolinium-based contrast agents in nanoporous particles enhances T(1) contrast

Magnetic resonance imaging contrast agents are currently designed by modifying their structural and physiochemical properties in order to improve relaxivity and to enhance image contrast. Here we show a general method for increasing relaxivity by confining contrast agents inside the nanoporous structure of silicon particles. Magnevist, gadofullerenes and gadonanotubes were loaded inside the pores of quasi-hemispherical and discoidal particles. For all combinations of nanoconstructs, a boost in longitudinal proton relaxivity r(1) was observed: for Magnevist, r(1)~14 mM(-1)s(-1)/Gd(3+)ion (~8.15×10(+7) mM(-1)s(-1)/construct); for gadofullerenes, r(1)~200 mM(-1)s(-1)/Gd(3+)ion (~7×10(+9) mM(-1)s(-1)/construct); for gadonanotubes, r(1)~150 mM(-1)s(-1)/Gd(3+)ion (~2×10(+9) mM(-1)s(-1)/construct). These relaxivity values are about 4 to 50 times larger than that of clinically-available gadolinium-based agents (~4 mM(-1)s(-1) /Gd(3+)ion). The enhancement in contrast is attributed to the geometrical confinement of the agents, which influences the paramagnetic behavior of the Gd3+ions. Thus, nanoscale confinement offers a new and general strategy for enhancing the contrast of gadolinium-based contrast agents.