High-Sensitivity Ferrite Magnetometer for Low-Dose Magnetic Sentinel Lymph Node Detection.

Abstract

Magnetic tracer-guided sentinel lymph node (SLN) biopsy offers a radiation-free alternative for nodal staging in breast cancer and other solid tumors. However, current handheld magnetometers often require high superparamagnetic iron oxide nanoparticle (SPION) doses due to limited sensitivity and detection depth, leading to skin staining and MRI artifacts. We developed FerriMag, a handheld ferrite magnetometer integrating a central high-permeability Mn-Zn ferrite core to enhance magnetic excitation and signal reception. Lock-in amplification and bandpass filtering were employed to suppress interference. The ferrite core increased the excitation field strength by 11-fold and receiving-coil sensitivity by 1.7-fold. FerriMag achieved a detection limit of 21.6 ng Fe and reliably detected 0.5 μg Fe at a depth of 10 mm. In a rabbit model, accurate SLN localization was obtained with only 0.05 mL (0.5 mg Fe) of SPIONs, without visible skin staining. Metastatic nodes exhibited significantly reduced SPION uptake (p = 0.0005) and slower signal rise(p = 0.038) compared to non-metastatic nodes. FerriMag improves the sensitivity and detection depth of handheld magnetic SLN detection, enabling reliable low dose SPION-based SLN localization in vivo. This system provides a low-cost, radiation-free, and clinically translatable platform for low-dose magnetic SLN detection, with potential applicability beyond breast cancer and possible utility for intraoperative nodal assessment.