Fast Dynamic Whole-Body In Vivo Cytometry Using Magnetic Particle Imaging

Rapid quantification of the immediate organ accumulation of injected stem cells remains a major challenge. We performed in vivo cytometry (non-invasive cell counting) with magnetic particle imaging (MPI) to track magnetically labeled cells in real-time on a time scale of minutes with high sensitivity, zero background signal, and simple linear quantification. Human mesenchymal stem cells (hMSCs, ~25 µm in diameter) and human neural precursor cells (hNPCs, ~10 µm in diameter) were labeled with ferucarbotran or Synomag®-D70 as superparamagnetic iron oxide (SPIOs), and tracked with MPI in mice to map their whole-body cell biodistribution after intravenous (IV) or intra-arterial (IA) injection. The organ site of cell accumulation and retention were dependent on cell type, injection route, and frequency of administration, with the lung and liver acting as the major entrapment organs. In vivo MPI enabled quantitative tracking of the dynamic clearance and redistribution of labeled cells, showing major differences between larger hMSCs and smaller hNPCs. Co-registered MRI/CT and histological validation confirmed the anatomical localization of SPIO-labeled cells including the brain following IA injection. Integrating MPI cytometry with preclinical and translational studies may aid in further optimization of the route, dose, and frequency of stem cell administration.