Table 1 Size, magnetization, and contrast power of different CAs at 6.5 mT.

Data for 25-nm carboxylated iron oxide nanoparticles (HS-COOH), 25-nm PEGylated iron oxide nanoparticles (HS-PEG), Feraheme SPIONs (ferumoxytol, FDA-approved for iron-deficiency anemia treatments), and Magnevist (Gd-DTPA) are shown. Core sizes and hydrodynamic diameter (HD) are reproduced from (26, 41) or taken from manufacturer datasheets. Magnetic moment (M) values at 6.5 mT were calculated per kilogram of Fe/Gd from ULF susceptibility imaging and are consistent with data available elsewhere (see Materials and Methods and note S1 for measurement details) (22, 26, 32).

CACore (nm)HD (nm)M (A·m2/kg Fe/Gd)r1 (mM−1 s−1)r2 (mM−1 s−1)r2/r1
HS-COOH24.243.438.5 ± 1.5320 ± 15365 ± 431.14 ± 0.13
HS-PEG24.292.933.3 ± 1.9261 ± 20329 ± 451.26 ± 0.17
Ferumoxytol3.3304 ± 0.631 ± 131 ± 41.00 ± 0.13
Gd-DTPAGd3+1.80.010 ± 0.0023.4 ± 0.111 ± 13.24 ± 0.29