Magnetomotive imaging of iron oxide nanoparticles as cellular contrast agents for optical coherence tomography

Recent studies in animal models provided proof-of-principle evidence for cell transplantation as a potential future therapeutic approach for retinal pathologies in humans such as Retinitis pigmentosa or age-related macular degeneration. In this case, donor cells are injected into the eye in order to protect or replace degenerating photoreceptors or retinal pigment epithelium. However, currently there is no three-dimensional imaging technique available that allows tracking of cell migration and integration into the host tissue under in vivo conditions. Therefore, we investigate about magnetomotive optical coherence tomography (OCT) of substances labeled with iron oxide nanoparticles as a potential method for noninvasive, three-dimensional cell tracking in the retina. We use a self-developed spectral domain OCT system for high-resolution imaging in the 800 nm-wavelength region. A suitable AC magnetic field for magnetomotive imaging was generated using two different setups, which consist of an electrically driven solenoid in combination with a permanent magnet, and a mechanically driven all-permanent magnet configuration. In the sample region the maximum magnetic flux density was 100 mT for both setups, with a field gradient of 9 T/m and 13 T/m for the solenoid and the all-permanent magnet setup, respectively. Magnetomotive OCT imaging was performed in elastic tissue phantoms and single cells labeled with iron oxide nanoparticles. Particle-induced sub-resolution movement of the elastic samples and the single cells could successfully be detected and visualized by means of phase-resolved Doppler OCT analysis. Therefore, this method is a potential technique to enhance image contrast of specific cells in OCT.