Magnetomotive dynamics of magnetic particles for optical imaging contrast and elastography

Magnetic particles offer several distinct advantages compared to other types of contrast agents. Their controllable size, high magnetic susceptibility and the ability of non contact manipulation through external magnetic fields allow their use in a wide variety of applications in biology and medicine. In this thesis, the controlled movement of magnetic particles termed as magnetomotion is exploited for enhancing optical imaging contrast and elastography using optical coherence tomography (OCT). A combination of simulations and experiments were performed to study the spatial and temporal characteristics of the magnetomotive (MM) response under dynamic excitation. Magnetomotive contrast in optical imaging was shown using functionalized protein shell microspheres in a rabbit atherosclerosis model and further improvement in MM OCT imaging speed was demonstrated allowing the rapid acquisition of 3 D MM OCT datasets over a larger depth range. The temporal dynamics of the magnetomotive response were investigated for probing the mechanical properties of both homogeneous and heterogeneous samples. The feasibility of generating elastograms showing relative mechanical contrast based on the frequency response of the MM-signal was investigated. In addition, quantitative estimates of the complex shear modulus were obtained by measuring the propagating mechanical waves generated by an excitation of an inclusion containing magnetic nanoparticles (MNPs)