Locating steel needles in the human body using a SQUID magnetometer

A technique has been developed, based on magnetic field measurements, to lo calize, in three dimensions, hypodermic and sewing needles lost in the huma n body. A theoretical model for the magnetic field generated by needles has been elaborated and experimentally validated. Using this model, the locali zation technique gives information about needle's centre, orientation and d epth. The clinical measurements have been made using a SQUID system, with p atients being moved under the sensor with the aid of an X-Y bed. The magnet ic field associated with the remanent magnetization of the needle is acquir ed on-line and mapped over a plane. In all six cases that occurred, the tec hnique allowed surgical localization of the needles with ease and high prec ision. This procedure can decrease the surgery time for extraction of forei gn bodies by a large factor, and also reduce the generally high odds of fai lure.