SPIO Detection and Distribution in Biological Tissue—A Murine MPI-SLNB Breast Cancer Model

Surgical breast cancer related staging with radical axillary lymph node extraction was mandatory in past times. High morbidity and significant loss of quality of life was inevitable. By introduction of the concept of sentinel lymph node biopsy (SLNB), these adverse effects decreased. Detection of sentinel lymph nodes (SNLs) is realized by the use of dyes and radio nuclides as tracer substances. These tracers can be replaced by superparamagnetic iron oxide nanoparticles (SPIOs) in the near future. Magnetic particle imaging (MPI) guided 3-D real-time imaging and a distinct localization of SPIOs can be achieved in SLNB by the use of MPI. However, qualitative and quantitative enrichment of SPIOs in biologic tissue, in particular, the axillary lymphatic tissue is unexplored until now. We aim to prove the principle of SLNB with MPI within a healthy and than in a tumor bearing mouse model with metastatic axillary lymph nodes in breast cancer. Axillary tissue, surrounding tissues, and tissue from the whole body are analyzed with the following techniques: histology, Prussian blue staining, electron microscopy, atomic absorption spectrometry, and magnetic particle spectroscopy. We found that the SPIOs moves from the injection site through the lymph-fat tissue to the axillary region and finally into the axillary lymph nodes. SPIOs follow traces of lymphatic vessels, respecting borders, and spaces between different tissues. They accumulate near collagen fibers and distinct regions. We present our results of the approach of SLNB with MPI. Application of SPIOs and tracer detection in SNLs with MPI as a new SLNB technology could be less complex and incriminating for patient and staff and could make SLNB more accurate. To realize this approach, an MPI hand probe for intraoperative use is under construction. This will simplify SNL detection and helps to reduce axillary exploration morbidity by avoidance of intensive surgical quest. The tracer for MPI is easy to obtain and this make- the method accessible to many patients. The concept of SLNB by MPI may be applied in principle in all solid tumors.