Single-sided Magnetic Particle Imaging for in vivo applications

Magnetic Particle Imaging (MPI) is an emerging tracer-based biomedical imaging technique that detects the magnetic response of superparamagnetic iron oxide  nanoparticles (SPION). Similar to other tracer-based modalities, PET or SPECT, MPI generates quantitative tracer concentration maps, however, using non-radioactive nanoparticles instead of ionizing radiation. The technique offers excellent sensitivity and high spatial resolution, making it promising for applications like tumor detection and cell tracking. Although promising for clinical use, MPI has not yet been adopted into clinical practice. One major challenge is scaling the hardware to human size. MPI relies on electromagnetic coils to generate magnetic fields, but building a closed-bore MPI system capable of whole-body imaging would require prohibitively high power. To address this, we are developing a single-sided MPI scanner that contains all field-generating hardware on one side of the imaging volume, enabling low-power imaging of near-surface anatomies.

Here we present the next-generation field-free line (FFL) single-sided MPI system, which demonstrates substantial improvements in spatial resolution, imaging sensitivity, and field of view. The achieved resolution now matches that of human-head-scale MPI systems, which typically operate with gradients of 0.2–1.1 T/m and provide 12–3 mm resolution. The two-dimensional field of view has been expanded to an 8 × 8 cm² linear region. The enhanced sensitivity also reaches the threshold required for detecting SPION-labeled tumors. We further demonstrate imaging of artificial tumors embedded in a large anatomical breast phantom, an object size exceeding the capacity of most closed-bore MPI systems. In addition, we report the first in vivo imaging of mice using a single-sided MPI scanner. Following intravenous injection of Synomag-D SPIONs, delayed imaging revealed SPION uptake by internal organs. Together, these results represent important milestones toward scalable MPI systems, bridging the gap between preclinical and human-scale imaging. This approach shows strong potential for breast cancer imaging and other near-surface clinical applications, areas that remain largely unexplored within the MPI community.