Magnetic particle imaging tracers for human applications: preclinical in vivo evaluation of Magtrace, Resotran, and FerroTrace.

Sentinel lymph node (SLN) mapping is essential for cancer staging and treatment planning. Superparamagnetic iron oxides (SPIOs) are used for magnetic SLN localization in breast cancer and are being explored in cancers with complex lymphatic drainage pathways. Magnetic particle imaging (MPI) directly detects SPIOs and has demonstrated feasibility for quantitative lymphography in mouse models. However, most MPI studies have relied on preclinical SPIO formulations not intended for human use. Here, we evaluated three clinically available or investigational SPIOs for MPI, including Magtrace, Resotran, and FerroTrace. SPIOs were characterized in vitro using 2D MPI and relaxometry, benchmarked against the preclinical standard VivoTrax. Magtrace and Resotran demonstrated in vitro performance comparable to VivoTrax, whereas FerroTrace exhibited lower peak signal and resolution by relaxometry. In vivo longitudinal MPI lymphography was performed in healthy C57BL/6 mice following intradermal injection of SPIOs. Magtrace and FerroTrace produced robust lymph node labeling, with MPI signal persisting for at least four weeks across all SPIOs. Feasibility of clinical-scale MPI for complex lymphatic mapping was demonstrated using a human-sized head-and-neck phantom modeling bilateral lymphatic drainage. Together, these results establish Magtrace, Resotran, and FerroTrace as suitable magnetic tracers for MPI lymphography and support their use in future human MPI applications.