Characterization of ferromagnetic or conductive properties of metallic foreign objects embedded within the human body with magnetic iron detector (MID): Screening patients for MRI.

ABSTRACT

PURPOSE: A preliminary assessment of the MRI-compatibility of metallic object possibly embedded within the patient is required before conducting the MRI examination. The Magnetic Iron Detector (MID) is a highly sensitive susceptometer that uses a weak magnetic field to measure iron overload in the liver. MID might be used to perform a screening procedure for MRI by determining the ferromagnetic/conductive properties of embedded metallic objects. METHODS: The study was composed by (i) definition of MID sensitivity threshold; (ii) application of MID in a procedure to characterize the ferromagnetic/conductive properties of metallic foreign objects in 958 patients scheduled for MID examination. RESULTS: The detection threshold for ferromagnetic objects was found to be the equivalent of a piece of wire of length 2 mm and gauge 0.8 mm(2) and, representing purely conductive objects, an aluminum sheet of area 2 × 2 cm(2) . Of 958 patients, 165 had foreign bodies of unknown nature. MID was able to detect those with ferromagnetic and/or conducting properties based on fluctuations in the magnetic and eddy current signals versus control. CONCLUSION: The high sensitivity of MID makes it suitable for assessing the ferromagnetic/conductive properties of metallic foreign objects embedded within the body of patients scheduled for MRI.