Kenneth Baker PhD, Presenter: Nothing to Disclose

Ali R. Rezai MD, Abstract Co-Author: Nothing to Disclose

Jean A. Tkach PhD, Abstract Co-Author: Nothing to Disclose

Purpose:  To determine, using a phantom model, the effect of lead routing and configuration of an elongated, conductive neurostimulation system used for deep brain stimulation (DBS) on MRI-related heating. Materials and Methods: The Activa (Medtronic, Inc.) hardware system used for DBS therapy was configured bilaterally within a gel-filled phantom of the human head and torso.  Temperature changes at the most proximal and distal electrode contacts of bilaterally-placed leads were measured using fluoroptic thermometry during different levels of RF power delivery.  MR imaging was performed using the Tx/Rx head coils and the Tx body/Rx head coils of two different-generation 1.5-Tesla MR systems.  The routing of the excess lead as it exited the skull burr hole was reconfigured arbitrarily to examine the effect of lead routing on the heating profile.  Similarly, the position of the phantom itself was shifted slightly (1.5- or 2-cm) on the patient table to examine the effect of relative patient positioning.  Analyses were performed on temperature changes, taken at two-minutes following onset of RF delivery, normalized to console-reported values of SAR in the head (DT/SAR-H). Results:  The greatest change, as high as 50% (p < 0.01) was observed with reconfiguration of the excess lead in the subcutaneous pocket emulated on the phantom skull.  Shifting the entire phantom 2.0-cm caudally or 1.5-cm laterally produced a change of up to 29% (p < 0.01) and 8% (p < 0.01), respectively.  Importantly, the magnitude, and in the case of the lateral shift the direction, of the observed effects varied depending upon the contact of the DBS lead being monitored.Conclusion:  Attempts to establish MR safety guidelines related to RF-induced heating of elongated, conductive implants is complicated by inter-patient variability in implant routing and configuration as well as positioning on the MR table.  The data presented underscore the potential for significant changes in the RF-induced heating as a result of these clinically-relevant differences.  Such variability must be considered and accounted for in any recommendations concerning the MR safety and compatibility of a given implant.

Baker, K, Rezai, A, Tkach, J, Hot Topic: Impact of Configuration/Routing of Neurostimulation Systems on RF-Induced Heating.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4425791.html