Abstract
Molecularly-specific contrast can greatly enhance the biomedical utility of optical coherence tomography (OCT). We describe a contrast mechanism, magnetomotive OCT (MMOCT), where a modulated magnetic field induces motion of magnetic nanoparticles. The motion of the nanoparticles modifies the amplitude of the OCT interferogram. High specificity is achieved by subtracting the background fluctuations of the specimen, and sensitivity to 220 microg/g magnetite nanoparticles is demonstrated. Optically and mechanically correct tissue phantoms elucidate the relationships between imaging contrast and nanoparticle concentration, imaging depth, tissue optical scattering, and magnetic field strength. MMOCT is demonstrated in a living Xenopus laevis tadpole where the results were consistent with corresponding histology.
Highlights
Optical coherence tomography (OCT) is a non-invasive, micron resolution, biomedical imaging modality [1] with clinical application in several areas including ophthalmology, gastroenterology, and cardiology
For the nanoparticles used in this study, we find no significant difference in the magnetomotive OCT (MMOCT) signal when premagnetizing ferromagnetic nanoparticle-embedded samples at different angles with respect to B
Due to hardware positioning limitations the lateral sampling size was larger than the axial. (It should be noted that, due to the pancake-shaped resolution volume of the OCT system, MMOCT is w0√(4ln2)/lc ~ 4× less sensitive to lateral movement via Eq (8))
Summary
Optical coherence tomography (OCT) is a non-invasive, micron resolution, biomedical imaging modality [1] with clinical application in several areas including ophthalmology, gastroenterology, and cardiology. We have employed optically and mechanically equivalent tissue phantoms to study the sensitivity, depth dependence, and dynamic range of MMOCT, as well as to investigate the underlying mechanics of how the MMOCT signal scales with the magnetic field, average tissue scattering amplitude, and magnetic particle concentration. Quantifying these parameters in a homogenous sample is a crucial first step toward producing calibrated concentration maps of targeted nanoparticles within structured tissues. We show that MMOCT is practical for in vivo imaging by identifying regions of higher (but non-toxic) magnetic particle concentrations within a living Xenopus laevis tadpole and matching these results with corresponding histology
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