A technique has been developed, based on magnetic field measurements, to localize, in three dimensions, hypodermic and sewing needles lost in the human body. A theoretical model for the magnetic field generated by needles has been elaborated and experimentally validated. Using this model, the localization technique gives information about needle's centre, orientation and depth. The clinical measurements have been made using a SQUID system, with patients being moved under the sensor with the aid of an X-Y bed. The magnetic field associated with the remanent magnetization of the needle is acquired on-line and mapped over a plane. In all six cases that occurred, the technique allowed surgical localization of the needles with ease and high precision. This procedure can decrease the surgery time for extraction of foreign bodies by a large factor, and also reduce the generally high odds of failure.

A technique had been previously developed, based on magnetic field measurements using a superconducting quantum interference device sensor, to localize in three dimensions steel needles lost in the human body. In all six cases that were treated until now, the technique allowed easy surgical localization of the needles with high accuracy. The technique decreases, by a large factor, the surgery time for foreign body extraction, and also reduces the generally high odds of failure. The method is accurate, noninvasive, and innocuous, and with clear clinical importance. Despite the importance of needle localization, the most prevalent foreign body in the modern society is the firearm projectile (bullet), generally composed of lead, a paramagnetic material, thus not presenting a remanent magnetic field as steel needles do. On the other hand, since lead is a good conductor, eddy current detection techniques can be employed, by applying an alternating magnetic field with the aid of excitation coils. The primary field induces eddy currents on the lead, which in turn generate a secondary magnetic field that can be detected by a magnetometer, and give information about position and volume of the conducting foreign body. In this article we present a theoretical study for the development of a localization technique for lead bullets inside the human body. Initially, we present a model for the secondary magnetic field generated by the bullet, given a known applied field. After that, we study possible excitation systems, and propose a localization algorithm based on the detected magnetic field.

This paper presents the results of investigations recently done by our research group that lead to a new and much better approach to the design of GMI (giant magnetoimpedance) magnetic transducers, which considers the changes in the impedance phase characteristics of GMI sensors due to varying low-intensity magnetic fields, instead of the usual impedance magnitude characteristics considered in the GMI literature. The development process of this new class of magnetic field transducers is discussed, beginning with the definition of the ideal conditioning of the GMI sensor elements (the dc level and frequency of the excitation current and the sample length), proceeding to compare the differences observed between the impedance magnitude and phase of GMI sensors and closing with the electronic circuits that condition ribbon-shaped GMI sensors and read their phase or magnitude variation as a function of the longitudinal magnetic field. Simulation studies, including the full electronic circuit and based on the experimental data obtained from measured GMI curves, have shown that an improvement in the sensitivity of GMI magnetometers larger than ten times can be expected when phase-based transducers are used instead of magnitude-based transducers. Finally, it is also shown that phase-based transducers are highly adequate for miniaturization purposes.

Abstract. The location and surgical removal of foreign bodies in patients is still challenging, especially for firearm projectiles, which are small and non-ferromagnetic. Conventional location techniques use ionizing radiation, posing health risks while the procedures often last several hours and end unsuccessfully. The use of high sensitivity magnetometers provides a noninvasive and innocuous alternative for metallic foreign body location. The developed technique consists of a primary AC magnetic field generator (a solenoid) inducing eddy currents in nonferromagnetic metallic foreign bodies, which results in an ultra-low secondary magnetic field that can be measured. This work compares the initially developed theoretical technique using Superconducting Quantum Interference Device (SQUID) magnetometers with the developed prototypes using lower cost alternatives, namely Giant Magnetoresistance (GMR) and Giant Magnetoimpedance (GMI). The comparison is based on biomedical device requirements for widespread clinical application. The proposed GMI location system is deemed the most qualified for clinical use.

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