A handheld SPIO-based sentinel lymph node mapping device using differential magnetometry

Abstract

Sentinel lymph node biopsy has become a staple tool in the diagnosis of breast cancer. By replacing the morbidity-plagued axillary node clearance with removing only those nodes most likely to contain metastases, it has greatly improved the quality of life of many breast cancer patients. However, due to the use of ionizing radiation emitted by the technetium-based tracer material, the current sentinel lymph node biopsy has serious drawbacks. Most urgently, the reliance on radioisotopes limits the application of this procedure to small parts of the developed world, and it imposes restrictions on patient planning and hospital logistics. Magnetic alternatives have been tested in recent years, but all have their own drawbacks, mostly related to interference from metallic instruments and electromagnetic noise coming from the human body. In this paper, we demonstrate an alternative approach that utilizes the unique nonlinear magnetic properties of superparamagnetic iron oxide nanoparticles to eliminate the drawbacks of both the traditional gamma-radiation centered approach and the novel magnetic techniques pioneered by others. Contrary to many other nonlinear magnetic approaches however, field amplitudes are limited to 5 mT, which enables handheld operation without additional cooling. We show that excellent mass sensitivity can be obtained without the need for external re-balancing of the probe to negate any influences from the human body. Additionally, we show how this approach can be used to suppress artefacts resulting from the presence of metallic instruments, which are a significant dealbreaker when using conventional magnetometry-based approaches.

A comprehensive literatures update of clinical researches of superparamagnetic resonance iron oxide nanoparticles for magnetic resonance imaging

“…Meng et al (63) suggested that if MRI could accurately diagnose axillary lymph node metastases in early stage breast cancer, the most cost-effective strategy was to replace sentinel lymph node biopsy with axillary MRI. Detection of sentinel lymph nodes with SPIO can be done by a simple hand-hold probe ( Figure 3) (64)(65)(66)(67). A number of studies with the combination of Sienna plus ® and SentiMag ® (Endomagentics Ltd) have been reported.…”

Handheld magnetic probe with permanent magnet and Hall sensor for identifying sentinel lymph nodes in breast cancer patients

“…We should also note that, there are sensors with higher sensitivities, which work at room temperature, such as the giant magneto-resistance (GMR) and magneto-impedance (MI) sensors. However, these sensors do not work successfully in the vicinity of a magnet because their magnetic characteristics may change due to the nonuniformity of the strong magnetic field 28 , 29 .

Figure 2 Numerical results: ( a ) Two-dimensional distribution of the longitudinal magnetic field B Z of the permanent magnet.

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“…The other uses a permanent magnet for generating a direct magnetic field 19 (as demonstrated by M. Shiozawa et al .). The benefit of using an electromagnetic coil is that the strength of magnetic field can be adjusted and the nonlinear magnetic characteristics can be utilized 27 , 28 . However, the disadvantage of this method is that it requires a large power supply to generate strong magnetic fields, which in turn leads to the need for a countermeasure for Joule heating.…”

A novel characterization technique for superparamagnetic iron oxide nanoparticles: The superparamagnetic quantifier, compared with magnetic particle spectroscopy

“…Consequently, the tracer will accumulate in the first nodes it encounters, namely, the sentinel nodes. The sentinel nodes can then be identified using a dedicated probe 6,7 and examined for metastases following surgical removal.…”

“…9 For in vivo SNB, a handheld probe is used. 7 Localization of SPIONs in vivo can also be useful in different applications, such as intraoperative assessment of tumor boundaries. 10 SPION detection can be optimized by matching the magnetic properties of the particle with the excitation parameters of the handheld probe.…”