Porous Silicon-Superparamagnetic Iron Oxide Complexes and Impact on Negative Contrast Enhancement in MRI

Purpose: Encapsulation of contrast agent within a nanoporous matrix has been shown to enhance contrast performance. Previous investigators have shown an up to 40-fold increase in T1 image contrast enhancement of gadolinium with encapsulation in carbon nanotubes. In this study we examined silicon encapsulation as a means of contrast enhancement in superparamagnetic iron oxide nanoparticles (SPIONs) using a particle-agarose phantom. Methods: 1μm discoidal pSi particles were loaded with 30 nm SPIONs through capillary action. Loaded particle preparations along with free SPION controls were homogeneously distributed within an agarose substrate and imaged using a 7-tesla small-bore MRI. ICP-AES was used to determine the concentration of free elemental iron in sample preparations. Results: Silicon encapsulation of 30nm SPIONs did not result in a clinically significant enhancement of negative contrast (T2 and T2*) in MRI. However, it is unclear the extent to which limited diffusion of water protons, both through silicon encapsulation and the use of an agarose substrate, counteracts the theoretical increase in relaxivity due to aggregation.