To minimize the invasiveness and improve the patient's quality of life, sentinel lymph node (SLN) biopsy with magnetic nanoparticles (MNPs) containing superparamagnetic iron oxide is performed on breast cancer patients. Identifying the first SLN by quantification of the amount of MNPs can help to investigate the cancer metastasis. We developed the device for performing iron quantification during surgery. The compact desktop-size device can be easily introduced into operation rooms, and simple system of the device enables identification of the first SLN. We investigated the optimum nonlinear magnetic responses that are attributed to magnetic relaxations under moderate small ac and dc magnetic fields (1 mT) and found that ac magnetic fields with < 5 kHz are effective in the detection of MNPs. In addition, our clinical trials revealed more iron ( 40μg ) in the first lymph node than in the second lymph node ( 10μg ), clearly indicating intraoperative quantification in the first node.
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