Cobalt nanoparticles as a novel magnetic resonance contrast agent-relaxivities at 1.5 and 3 Tesla

Two samples of polymer-coated cobalt nanoparticles were synthesized and dispersed in agarose gel and water. The relaxivities r(1) and r(2) of the two samples were obtained at different temperatures (25, 37 and 40 degrees C) and magnetic field strengths (1.5 and 3 T). The average cobalt core diameters of the two samples were 3.3 and 3.9 nm (measured by transmission electron microscopy); the corresponding average total diameters (cobalt core + polymer coating) were 13 and 28 nm (measured by dynamic light scattering). The larger particles had the higher r(1) relaxivity, whilst r(2) was similar for the two samples. There was no significant change in r(1) or r(2) relaxivities with temperature but r(1) at 1.5 T was approximately double the value at 3 T. The highest relaxivities were obtained at 1.5 T with values for r(1) and r(2) of 7.4 and 88 mM(-1) s(-1), respectively. These values are similar to those reported for iron oxide with larger core size, suggesting the potential of the cobalt nanoparticles for development and future use as a negative contrast agent. Copyright (C) 2008 John Wiley & Sons, Ltd.