Magnetic resonance imaging of live particle-loaded cells. (A) One slice from a 3-dimensional MR data set showing a single chamber of a culture dish containing live, labeled MSCs in culture media. Single cells are present where there are dark spots in the dish, owing to the susceptibility effect of the endocytosed particles. (B) Representative confocal image of the area within the white box in panel A from the same chamber slide showing highly efficient labeling (green fluorescence) of nearly 100% of the plated cells (nuclei counterstained with DAPI). Original magnification for panel B, × 100.