High - and -Contrast Ability of Ultra-Fine PEGylated Iron Oxide Nanoparticles in

The effect of ultra-fine superparamagneticPEGylated iron oxide nanoparticles (SPIONs) on the ¹H nuclei spin relaxation time T₁ and T₂ were systematically investigated for the performance as T₁ or T₂ contrast agents in ultra-low field (ULF) nuclear magnetic resonance and resonance imaging (NMR&MRI). A high-T_c dc-SQUID sensor was used to detect the resonance signal from water samples containing SPIONs of different sizes and concentrations. The relaxation rates (T_1,2^-1) was shown to depend linearly on the iron concentration (C, in mMol of Fe). The relaxivities (defined as d(T_1,2^-1)/dC) r₁ and r₂ were fitted and compared with high field (3 T) NMR results. An impressive improvement of more than an order in r₁ was found for all SPIONs of different sizes, which leads to a much lowered relaxivity ratio r₂/r₁. For all SPIONs measured, r₂/r₁ was around 1, which implies that SPIONs are high performance T1 contrast agent in ULF NMR&MRI. The highest r₁ and r₂ values were found in the sample containing 16.7 nm nanoparticles, both of them being around 200 mMol^-1s^-1. Furthermore, we also demonstrated T₁-weighted contrast imaging using 16.7 nm nanoparticles. Clear intensity gradient were shown in the images, indicating a good contrast enhancement capability.