Interactions of magnetic resonance imaging radio frequency magnetic fields with elongated medical implants

Magnetic resonance imaging (MRI) is a well established diagnostic technique, one from which all patients should be able to benefit, including those with implanted medical devices. This paper describes an experimental and numerical study of the temperature rise near the ends of wires by the radio frequency (rf) field in MRI. These wires simulate long wires which may be part of a medical implant. Temperature rise as a function of time was measured for wires of different lengths and diameters in a phantom exposed to the 64 MHz rf field inside a MRI body coil. For wires with no or thin insulation, the maximal rise was about seven times background for a wire length of 20 cm; wires with longer and shorter lengths exhibited less temperature rise. The temperature rise was greater for wires with thicker insulation. Computer simulations using a quasistatic model are in reasonable agreement with the measurements on shorter wires. It is concluded that medical implants with long conducting lead wires may result in potentially unsafe temperature rise during MRI imaging.