Objective To label rabbit bone marrow-derived mesenchymal stem cells (MSCs) with superparamagnetic iron oxide particles (SPIO) and study the effects of magnetic labeling on the proliferation and differentiation of MSCs.  Methods Rabbit M

SCs were isolated

purified

expanded

then incubated with various doses of SPIO complexed to protamine sulfate (Pro) transfection agents for 12 h. Prussian blue staining and transmission electron microscopy were performed to show intracellular iron. Cell viability and differentiation were evaluated. Vials containing cells underwent 1.5T MR imaging (MRI) with GRE T

2

*WI weighted and SE T

2

WI sequence

and the signal intensity were measured and statistically analyzed.  Results Intracytoplasmic nanoparticles were confirmed by Prussian blue staining and transmission electron microscopy. As compared with the unlabeled cells

no significant difference was found in cell viability

growth rate and differentiation of the labeled MSCs. GRE T

2

*WI and T

2

*WI demonstrated significant decrease of signal intensity (SI) in vials containing 1×10

6

and 5×10

5

labeled cells

in comparison with unlabeled cells (P0.05). The percentage change of SI (△SI) was significantly higher in 1×10

6

labeled cells than that in 5×10

5

labeled cells

particularly on GRE T

2

*WI (P0.05). Among pulse sequences

GRE T

2

demonstrated the highest △SI ut significant (P0.05).  Conclusion MSCs can be labeled with Fe-Pro efficiently witho change in cell  viability and differentiation capacity. Visualization of SPIO-labeled MSCs by 1.5T MRI is feasible.