Development of Magnetic Particle Imaging (MPI) for Cell Tracking and Detection

Introduction: Magnetic particle imaging (MPI ) is a new imaging modality that sensitively and specifically detects superparamagnetic iron oxide nanoparticles (SPIONs) within a sample. SPION-based MRI cell tracking has very high sensitivity, but low specificity and quantification of iron labeled cells is difficult. MPI cell tracking could overcome these challenges. Methods: MDM-AB-231BR cells labeled with MPIO, mice were intracardially injected with either 2.5 x 105 or 5.0 x 105 cells. MRI was performed in vivo the same day at 3T using a bSSFP sequence. After mice were imaged ex vivo with MPI. In a second experiment Mice received an intracardiac injection of either 2.5 x105 or 5.0 x 104 MPIO-labeled 231BR cells. In a third experiment, mice were injected with 5 x 104 4T1BR cells, labelled with either MPIO or the SPION Vivotrax. MRI and MPI was performed in vivo. Results: Signal from MPI and signal voids from MRI both showed more iron content in mice receiving an injection of 5.0 x 105 cells than the 2.5 x 105 injection. In the second experiment, Day 0 MRI showed signal voids and MPI signal was detected in all mouse brains. The MPI signal and iron content measured in the brains of mice that were injected with 2.5 x 105 cells were approximately four times greater than in brains injected with 5.0 x 104 cells. In the third experiment, in vivo MRI was able to detect signal voids in the brains of mice injected with Vivotrax and MPIO, although voids were fainter in Vivotrax labeled cells. In vivo MPI signal was only detectable in mice injected with MPIO-labeled cells. Conclusion: This is the first example of the use of MPIO for cell tracking with MPI. With an intracardiac cell injection, approximately 15% of the injected cells are expected to arrest in the brain vasculature. For our lowest cell injection of 5.0 x 104 cells this is ~10000 cells.