Phase-resolved magnetomotive OCT for imaging nanomolar concentrations of magnetic nanoparticles in tissues

Magnetic nanoparticles (MNPs) are increasingly important in magnetic resonance and biomedical optical imaging. We describe a method for imaging MNPs by detecting nanoscale displacements using a phase-resolved spectral-domain optical coherence tomography (OCT) system. Biological tissues and phantoms are exposed to similar to 800 G magnetic fields modulated at 56 and 100 Hz to mechanically actuate embedded iron oxide MNPs(similar to 20 nm diameter). Sensitivity to 27 mu g/g (similar to 2 nM) MNPs within tissue phantoms is achieved by filtering paramagnetic from diamagnetic vibrations. We demonstrate biological feasibility by imaging topically applied MNPs during their diffusion into an excised rat tumor over a 2 hour time period. (c) 2008 Optical Society of America.