Magnetic resonance imaging tracing of superparamagnetic iron oxide nanoparticle–labeled mesenchymal stromal cells for repairing spinal cord injury

JOURNAL/nrgr/04.03/01300535-202605000-00037/figure1/v/2025-10-21T121913Z/r/image-tiff Mesenchymal stromal cell transplantation is an effective and promising approach for treating various systemic and diffuse diseases. However, the biological characteristics of transplanted mesenchymal stromal cells in humans remain unclear, including cell viability, distribution, migration, and fate. Conventional cell tracing methods cannot be used in the clinic. The use of superparamagnetic iron oxide nanoparticles as contrast agents allows for the observation of transplanted cells using magnetic resonance imaging. In 2016, the National Medical Products Administration of China approved a new superparamagnetic iron oxide nanoparticle, Ruicun, for use as a contrast agent in clinical trials. In the present study, an acute hemi-transection spinal cord injury model was established in beagle dogs. The injury was then treated by transplantation of Ruicun-labeled mesenchymal stromal cells. The results indicated that Ruicun-labeled mesenchymal stromal cells repaired damaged spinal cord fibers and partially restored neurological function in animals with acute spinal cord injury. T2*-weighted imaging revealed low signal areas on both sides of the injured spinal cord. The results of quantitative susceptibility mapping with ultrashort echo time sequences indicated that Ruicun-labeled mesenchymal stromal cells persisted stably within the injured spinal cord for over 4 weeks. These findings suggest that magnetic resonance imaging has the potential to effectively track the migration of Ruicun-labeled mesenchymal stromal cells and assess their ability to repair spinal cord injury.