Magnetic and contrast properties of labeled platelets for magnetomotive optical coherence tomography

This article introduces a new functional imaging paradigm that uses optical coherence tomography (OCT) to detect rehydrated, lyophilized platelets (RL platelets) that are in the preclinical trial stage and contain superparamagnetic iron oxides (SPIOs) approved by the U.S. Food and Drug Administration. Platelets are highly functional blood cells that detect and adhere to sites of vascular endothelial damage by forming primary hemostatic plugs. By applying magnetic gradient forces, induced nanoscale displacements (magnetomotion) of the SPIO-RL platelets are detected as optical phase shifts in OCT. In this article, we characterize the iron content and magnetic properties of SPIO-RL platelets, construct a model to predict their magnetomotion in a tissue medium, and demonstrate OCT imaging in tissue phantoms and ex vivo pig arteries. Tissue phantoms containing SPIO-RL platelets exhibited >3 dB contrast/noise ratio at ≥1.5 × 10⁹ platelets/cm³. OCT imaging was performed on ex vivo porcine arteries after infusion of SPIO-RL platelets, and specific contrast was obtained on an artery that was surface-damaged (P < 10⁻⁶). This may enable new technologies for in vivo monitoring of the adherence of SPIO-RL platelets to sites of bleeding and vascular damage, which is broadly applicable for assessing trauma and cardiovascular diseases.