Phase-sensitive signal processing in the DiffMag handheld probe

Sentinel Lymph Node Biopsy (SLNB) is a surgical procedure that employs a tracer and a handheld detection device to assess lymphatic metastasis. Superparamagnetic iron oxide nanoparticles (SPIONs) have been used as tracers, with handheld magnetometers utilised for detection. The differential magnetometry processing technique (DiffMag) effectively suppresses interference from stationary magnetic materials. However, movement of magnetic materials introduces signal artefacts---referred to as motion artefact---due to the sequential nature of the processing technique. Continuous manoeuvring of surgical equipment during SLNBs generates such artefact, potentially extending surgery time. To address this drawback, we propose an extension of DiffMag using phase-sensitive signal processing to measure phase lag---a property unique to signals from SPIONs. This extension demonstrates potential to differentiate SPION signals from motion artefacts. In this study, we examined phase lag across various SPION types (Magtrace, Resotran, Resovist, Ferrotrace) within clinically relevant parameter for SLNB, including low SPION concentrations and increased environmental viscosity. Implementing the processing technique in the DMH yielded highly stable phase measurements characterised by low noise levels and negligible drift. Notably, SPIONs across all tested conditions exhibited a distinct measurable phase difference to those of motion artefacts. In conclusion, phase-sensitive signal processing utilised in the DMH-probe demonstrates strong potential for differentiating SPION signals from motion artefacts.