T2 relaxation induced by clusters of superparamagnetic nanoparticles:: Monte Carlo simulations

Clustering strongly affects the transverse (7,) relaxation induced by superparamagnetic nanopartictes in magnetic resonance experiments. In this study, we used Monte Carlo simulations to investigate systematically the relationship between T-2 values and the geometric parameters of nanoparticle clusters. We computed relaxation as a function of particle size, number of particles per cluster, interparticle distance, and cluster shape (compact vs. linear). We found that compact clusters induced relaxation equivalent to similarly sized single particles. For small particles, the shape and density of clusters had a significant effect on T-2. In contrast, for larger particles, T-2 relaxation was relatively independent of cluster geometry until interparticle distances within a cluster exceeded ten times the particle diameter. Results from our simulations suggest principles for the desgin of nanoparticle aggregation-based sensors for MRI. (c) 2008 Elsevier Inc. All rights reserved.