Method for Locating a Small Magnetic Object in the Human Body

摘要

A piece of a thin acupuncture needle lodged under the right scapula of a patient could not be found in surgical procedures accompanied by studies of 30 standard X-ray images. To locate it, the authors mapped the magnetic field component normal to a plane lying above the object, using a superconducting quantum interference device (SQUID). Assuming that the needle could be modelled as a magnetic dipole, the authors were able to infer its lateral position, depth, orientation, and magnetic moment. With this information, directed CT scans, high-resolution X-ray films, and the subsequent surgical removal of the needle proved that it could be located in the body with an accuracy of about three millimeters.