Magnetic microspheres can be used for magnetic particle imaging of cancer cells arrested in the mouse brain

Purpose: Magnetic particle imaging (MPI) is a new imaging modality that sensitively and specifically detects superparamagnetic iron oxide nanoparticles (SPIOs). MRI cell tracking with SPIOs has very high sensitivity, but low specificity and quantification is difficult. MPI could overcome these limitations. There are no reports of micron-sized iron oxide particles (MPIO) for cell tracking by MPI. Therefore, the goal was to evaluate if MPIO can be used for in vivo detection and quantification of cancer cells distributed in the mouse brain by MPI. Methods: In the first experiment mice were injected with either 2.5 x 10(5) or 5.0 x 10(5) MPIO-labeled cancer cells and MPI was performed ex vivo. In a second experiment, mice received either 2.5 x 10(5) or 5.0 x 10(4) MPIO-labeled cells and MPI was performed in vivo. In a third experiment, mice were injected with 5.0 x 10(4) cells, labeled with either MPIO or ferucarbotran, and MPI was performed in vivo. Results: MPIO-labeled cells were visible in all MPI images of the mouse brain. The MPI signal and iron content measurements were greater for brains of mice that were injected with higher numbers of MPIO-labeled cells. Ferucarbotran-labeled cells were not detected in the brain by MPI. Conclusion: This is the first example of the use of MPIO for cell tracking with MPI. With an intracardiac cell injection, similar to 15% of cells will arrest in the brain vasculature. For our lowest cell injection of 5.0 x 10(4) cells, this was similar to 10 000 cells, distributed throughout the brain.

Automated summary

MPI is a new imaging modality that detects SPIOs sensitively and specifically. MPIO labeled cells were visible in mouse brain images, with signal and iron content measurements increasing with higher numbers of injected cells.