UCLA

Sensitive imaging of superparamagnetic nanoparticles or aggregates is of great importance in magnetic resonance molecular imaging and medical diagnosis. For this purpose, a conceptually new approach, termed "active feedback magnetic resonance", was developed. In the presence of the Zeeman field, a dipolar field is induced by the superparamagnetic nanoparticles or aggregates. Such dipolar field creates a spatial and temporal (due to water diffusion) variations to the precession frequency of the near-by water 1H magnetization. Sensitive imaging of magnetic nanoparticles or aggregates can be achieved by manipulating the intrinsic spin dynamics by "selective self-excitation" and "fixed-point dynamics" under active feedback fields. Phantom experiments of superparamagnetic nanoparticles, in vitro experiments of brain tissue with blood clots, and in vivo mouse images of colon cancers labeled by magnetic nanoparticles suggest this new approach provide enhanced, robust, and positive contrast in imaging magnetic nanoparticles or aggregates for early lesion detection.