Synthesis and characterization of SPIO-loaded PEG-b-PS micelles as contrast agent for long-term nanoparticle-based MRI phantom

Nanoparticle-based magnetic resonance imaging (MRI) phantom was developed from the suspension of magnetic nanoparticles composing methoxy poly(ethylene glycol)-block-poly(styrene) (PEG-b-PS) micelles and superparamagnetic iron oxide (SPIO) nanoparticles in the core of micelles. The size of SPIO-loaded micelles was determined by dynamic light scattering (DLS) and transmission electron microscopy. Larger-size micelles were found when SPIO loading was increased. The effect of the hydrophobic section of block copolymer on the size of micelles was studied by DLS. Transverse relaxivity was evaluated on both 1.5 and 3 T clinical MRI scanner. Higher SPIO-loading provided higher relaxivity, where the relaxivity of 10% SPIO-loaded PEG(5 kDa)-b-PS(5 kDa) were 144.0 and 174.0 mM^-1 s^-1 for 1.5 and 3 TMRI, respectively. This formulation showed stability over a 10-week period, and the standard deviations of the relaxivities were 3.0 and 8.0% for 1.5 and 3 T MRI, respectively. Thus, SPIO-loaded PEG-b-PS micelles have a potential to be applied as a contrast agent for nanoparticle-based MRI phantom.