Magnetic sensor for sentinel lymph node biopsy using superparamagnetic beads

The present paper describes a magnetic-sensing device to detect superparamagnetic beads for a sentinel lymph node biopsy. The sentinel lymph node biopsy is a promising method to improve quality of life of patients after surgery of cancer. The sensing device consists of a solenoid coil to excite magnetically the beads and two Hall devices placed on the both ends of the coil. The differential signal between the two Hall devices reflects the existence of magnetic beads near one of the Hall devices. A computer simulation indicates that the signal increases with the increase of magnetic fields from the exciting coil. A prototype is designed based on the simulation of the devices that effectively detect the beads up to the distance of 10 mm from the sensor top. The sensing device detected superparamagnetic iron-oxide beads containing Fe content of 0.5 mg, which are expected to accumulate in lymph nodes, at the distance of 8 mm; the estimated differential magnetic-field between the two Hall devices was 0.026 G.