High ${\rm T}_{1}$- and ${\rm T}_{2}$-Contrast Ability of Ultra-Fine PEGylated Iron Oxide Nanoparticles in Ultra-Low Field MRI Measured By a High- ${\rm T}_{\rm c}$ DC-SQUID

The effect of ultra-fine superparamagneticPEGylated iron oxide nanoparticles (SPIONs) on the
¹
H nuclei spin relaxation time T
₁
and T
₂
were systematically investigated for the performance as T
₁
or T
₂
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) r
₁
and r
₂
were fitted and compared with high field (3 T) NMR results. An impressive improvement of more than an order in r
₁
was found for all SPIONs of different sizes, which leads to a much lowered relaxivity ratio r
₂
/r
₁
. For all SPIONs measured, r
₂
/r
₁
was around 1, which implies that SPIONs are high performance T1 contrast agent in ULF NMR&MRI. The highest r
₁
and r
₂
values were found in the sample containing 16.7 nm nanoparticles, both of them being around 200 mMol
^-1
s
^-1
. Furthermore, we also demonstrated T
₁
-weighted contrast imaging using 16.7 nm nanoparticles. Clear intensity gradient were shown in the images, indicating a good contrast enhancement capability.