RF-induced temperature elevation along metallic wires in clinical magnetic resonance imaging: influence of diameter and length.

With the development of interventional MRI, heating of biological tissues along the metallic wires in the MRI scanner has become an important issue. To assess thermal response to RF exposure during MRI, we studied the temperature elevation near nonmagnetic metallic wires. All tests were performed on a 1.5 T clinical scanner. Four experiments were conducted to investigate the effects of the wire diameter, the excitation flip angle, the temperature distribution along the wire, and the wire length. Electromagnetic simulations of the experimental setup were made with the use of commercial method of moments (MoM) software and numerical simulations of Hallen's equations. Comparisons between measured and calculated values of the electric field are presented. This study demonstrates that 1) temperature decreases with the diameter of the wire,2) temperature increases quadratically with the excitation flip angle, 3) heating occurs not only at the tip but also along the wire, and 4) the heating peaks are not obtained for the classical resonant length multiple of lambda/4 (where lambda is the RF field wavelength). In addition, significant and rapid heating increases were observed in the close vicinity of the wire. (c) 2004 Wiley-Liss, Inc.