Intraoperative localization of retained metallic fragments in missile wounds

Patients with missile wounds often retain fragments of different materials within their bodies. They are usually of no clinical consequence, but sometimes they can cause complications. Furthermore, the presence of metallic objects is a contraindication for magnetic resonance imaging. Therefore, the fragments should be removed whenever possible. A new metal detector designed for intraoperative use and a method that allows exact localization and removal of conductive fragments is presented.

Practical experience shows that the volume of missile fragments varies by a factor of 1,000. Different materials can be detected and located at distances usually not greater than 50 mm. An adaptive electronic amplifier was used in this instrument to locate missile fragments of different sizes and magnetic properties at different distances. Environmental disturbances such as electrical wires and external magnetic fields, and the limited dynamics of human perception, were compensated for by the spatial selectivity and adaptive sensitivity of the instrument. The source of the alternating magnetic field was placed in a hand-held probe connected to the instrument, with which small changes in the magnetic field were detected and exploited for the location of metallic fragments.

The boundaries of detectability and localizability by the device have been determined for different missile fragments to demonstrate the diagnostic feasibility and limitations of the method.

The successful use of the method, in cases where other imaging procedures are either not available or ineffective, is demonstrated by two cases of patients with gunshot wounds.