Magnetic particle imaging (MPI) is an emerging cross-sectional imaging technique that in the future may be a new clinical imaging modality offering high resolution, dynamic functional imaging without utilizing ionizing radiation.
Magnetic particle imaging is a tracer imaging technique, which relies on superparamagnetic iron oxide nanoparticles (SPION) to generate signal. It uses a homogeneous magnetic field (termed a selection field) which saturates all SPIONs except in a select field-free region (field free line (FFL)). During an MPI scan the FFL rapidly sweeps over the imaging region, during which only SPIONs in the FFL generate a voltage in the receiver coil of the system, from which the amount of SPIONs in the FFL can be calculated 1.
Current use, potential future applications and benefits
Currently magnetic particle imaging scanners are only utilized in preclinical small animal imaging, however there is no known theoretical obstacle that would limit the construction of clinical systems. If the techniques tested in preclinical settings can be scaled up for clinical use (the main difficulty being the required extremely homogeneous drive field), magnetic particle imaging as a tracer-based imaging modality could be utilized for a diverse array of functional imaging applications similarly to PET/SPECT without ionizing radiation. As biologic tissues (including those with endogenous iron) do not generate any signal in an MPI system, the modality offers a very high intrinsic contrast, and low detection limits. To this date MPI has been tested in preclinical models for blood perfusion imaging and angiography using free SPIONs. Construction of targeted SPIONs for a variety of future applications (oncology, inflammation, stem cell tracking) is an area of active research 1,2.
- 1. L.C. Wu, Y. Zhang, G. Steinberg, H. Qu, S. Huang, M. Cheng, T. Bliss, F. Du, J. Rao, G. Song, L. Pisani, T. Doyle, S. Conolly, K. Krishnan, G. Grant, M. Wintermark. A Review of Magnetic Particle Imaging and Perspectives on Neuroimaging. (2019) American Journal of Neuroradiology. 40 (2): 206. doi:10.3174/ajnr.A5896 - Pubmed
- 2. M. Graeser, F. Thieben, P. Szwargulski, F. Werner, N. Gdaniec, M. Boberg, F. Griese, M. Möddel, P. Ludewig, D. van de Ven, O. M. Weber, O. Woywode, B. Gleich, T. Knopp. Human-sized magnetic particle imaging for brain applications. (2019) Nature Communications. 10 (1): 1. doi:10.1038/s41467-019-09704-x - Pubmed