Abstract 1923: Positive Contrast Magnetic Resonance Imaging Enables Temporal Tracking of Iron-Labeled Mesenchymal Stem Cells in a Rabbit Hindlimb Ischemia Model
Background: Mesenchymal stem cells (MSCs) have been shown to produce angiogenic factors that may be useful for therapy. Cell labeling with iron oxide nanoparticles is useful for serial monitoring of cell therapy by magnetic resonance imaging (MRI). Positive contrast MRI methods have been proposed for more specific visualization of labeled cells. We investigate the feasibility of using positive contrast MRI to monitor the delivery and persistence of labeled MSCs in a hindlimb ischemia model.
Methods: Hindlimb ischemia was induced in 12 New Zealand White rabbits by endovascular placement of platinum coils in the left superficial femoral artery. At 24h post-coiling, six intramuscular injections (2x106 MSCs/injection) of allogeneic ferumoxide-labeled MSCs were placed in the ischemic adductor compartment of the left hindlimb of 6 rabbits. Control rabbits received 45 μL ferumoxide in 1.5 mL PBS. Inversion recovery with on-resonant water suppression MRI was performed immediately after injections (d0), and 1 (w1) and 2 (w2) weeks post-injection. Labeled cell distribution and persistence in positive contrast images were evaluated using full width, half maximum criteria to determine the total volume of signal enhancement.
Results: Ferumoxide-labeled cells appear as hyperintense regions in positive contrast MR images. Volume of enhancement immediately following injections was greater in rabbits receiving ferumoxides only. Total volume of enhancement decreased to a greater extent and monotonically over time in control (d0: 2.16 ± 2.69 mL; w1: 0.72 ± 1.25 mL; w2: 0.46 ± 0.58 mL) compared to treated animals which stabilized at 1 week (d0: 1.39 ± 1.36 mL; w1: 0.47 ± 0.59 mL; 0.43 ± 0.43 mL).
Conclusions: Positive contrast MRI can be used to effectively monitor the delivery and persistence of MSCs and may be useful in future studies involving cellular therapies.