Abstract 3429: Molecular Imaging of Vulnerable Plaque with Optical Coherence Tomography
Background: The risk of plaque rupture is increased by the infiltration of macrophages. Developing a technique to image macrophages in situ would enhance our ability to diagnose vulnerable plaque. Optical Coherence Tomography (OCT) is an emerging technology that has the resolution to detect cellular components of the plaque, but is currently unable to distinguish macrophages from other cells.
Hypothesis: Iron oxide nanoparticles taken up by plaque-based macrophages can be placed in motion by an oscillating magnetic field and detected with OCT.
Methods: ApoE knockout mice (n=12) and hyperlipidemic Watanabe rabbits (n=4) were IV injected with 0.2 mmol/kg of supermagnetic iron oxide particles or saline. After 3 days, the animals were sacrificed and the aorta was removed and cut into mm sized squares (n=60). The iron oxide particles taken up by macrophages were placed in motion by an oscillating magnetic field (2T) and this movement was detected by OCT. Histological analysis with Prussian blue for iron oxide and RAM-11 for macrophage identification was performed.
Results: OCT was able to identify the presence of iron labeled macrophages in the aortic plaques of animals injected with the iron oxide nanoparticles. Since the magnetic force applied to the iron nanoparticles is proportional to the square of the magnetic field gradient, the frequency response of the tissue is twice that of the stimulus frequency. For instance, in figure 1⇓, the tissue motion is 4 Hz which is twice the magnetic field input frequency of 2 Hz.
Conclusion: Molecular imaging of tissue based macrophages is feasible with OCT when engulfed iron oxide particles are placed in motion by an oscillating magnetic field.