Direct Cell Labeling to Image Transplanted Stem Cells in Real Time Using a Dual-Contrast MRI Technique

Exogenous direct cell labeling with superparamagnetic iron oxide nanoparticles (SPIONs) is currently the most employed cell-labeling technique for tracking transplanted cells using magnetic resonance imaging (MRI). Although SPION-based cell labeling is effective for monitoring cell delivery and migration, monitoring cell survival is still a challenge. This unit describes an MRI technique that permits detection of the delivery, migration, and death of transplanted cells. This dual-contrast technique involves labeling cells with two different classes of MRI contrast agents, possessing different diffusion coefficients: SPIONs (T₂/T₂ ^* contrast agents, with lower diffusion coefficients) and gadolinium chelates (T₁ contrast agents, with higher diffusion coefficients). In live cells, where both agents are in close proximity, the T₂/T₂ ^* contrast predominates and the T₁ contrast is quenched. In dead cells, where the cell membrane is breached, gadolinium chelates diffuse from the SPIONs and generate a signature T₁ contrast enhancement in the vicinity of dead cells.