Variability in RF‐induced heating of a deep brain stimulation implant across MR systems

Purpose To compare the MRI‐related heating per unit of specific absorption rate (SAR) profile of a conductive implant between two 1.5‐Tesla/64 MHz MR systems using a transmit/receive (t/r) head coil configuration. Materials and Methods Deep brain stimulation (DBS) leads were configured within a gel‐filled phantom of the human head and torso. Temperature variation at each of four contacts of the bilaterally‐placed leads was monitored using fluoroptic thermometry. MRI was performed using the t/r head coils of two different‐generation 1.5‐Tesla MR systems from the same manufacturer. Temperature changes were normalized to SAR values for the head (ΔT/SAR‐H), and the slope of this ΔT/SAR‐H by time relationship was compared between the two scanners. Results The ΔT/SAR‐H for the implant ranged from 3.5 to 5.5 times higher on one MR system as compared to the other ( P < 0.01) depending on the measurement site. Conclusion The findings support previous observations that console‐reported SAR does not constitute a reliable index of heating for elongated, conductive implants, such as the DBS hardware system tested. In contrast to our previous findings using a t/r body coil, the data presented here reveal marked differences between two MR systems using t/r head coils (the coil configuration was consistent with the implant manufacturer's imaging guidelines). J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.