MRI RF-Induced Pacemaker Lead Heating: Effect of Single vs Dual-lead Systems
Shi Feng1, Shiloh Sison2, Jazmine Garcia3, Gabriel Mouchawar3, and Richard Williamson3

1Hardware development, St. Jude Medical, Sylmar, CA, United States, 2St. Jude Medical, Sunnyvale, CA, United States, 3St. Jude Medical, Sylmar, CA, United States

Synopsis

Metallic leads of an implanted electronic device such as a pacemaker may behave as antennae in the strong radio frequency electromagnetic field of MRI. The induced current surrounding the electrodes may heat the local tissue. The MRI-induced tissue heating around the electrodes of a pacemaker have only been investigated for pacemakers employing a single lead. In this paper, we examine the MRI-induced temperature rise (TR) of the tip electrode(s) associated with a pacemaker system with two St. Jude Medical Tendril 2088 STS leads, and compare it to the single result. Both transfer function and in vitro temperature rise are investigated.

Introduction

When subjected to MRI and its radio frequency (RF) field, metallic leads of an implanted electronic device such as a pacemaker may behave as antennae. The induced current surrounding the electrodes may heat the local tissue [1]. The MRI-induced tissue heating around the electrodes of a pacemaker have only been investigated for pacemakers employing a single lead [2], [3]. In this paper, we examine the MRI-induced temperature rise (TR) of the tip electrode(s) associated with a pacemaker system with two St. Jude Medical Tendril 2088 STS leads.

Method

Due to the complex and tiny pacemaker leads structure, it has an established transfer function (TF) modeling the conversion of the incident electric field to an induced current which may be employed in analyzing the electrode/tissue heating effect [4]. The tip TR can be estimated by squaring the inner product of the incident electrical field along the lead pathway and the TF. Consequently, the lead heating impact of adding a second lead to a pacemaker system can be estimated by comparing the TFs of pacemaker systems with 1 V.S. 2 leads. We measured the TFs using established means [2], [3] of 1 and 2-lead pacemaker systems in a saline bath phantom with electrical conductivity of 1.2 S/m and a relative permittivity of 80 at 64 MHz, approximating the electrical characteristics of blood. TR measurements were performed with leads located along several phase reversal pathways in the ELIT1.5 phantom filled with HEC gel with the same electrical parameters as the saline used in the TF measurement. The two leads are separated at 3cm from distal end to avoid the interference to the local SAR (Specific Absorption Rate) distribution from each other. The phantom was loaded in the MITS 1.5 T vertical RF coil as show in Figure 1.

Result

The TF of a pacemaker system with two Tendril 2088 58cm STS leads was measured, scaled and compared with that of a system with a single lead. The magnitude of the two lead TF was clearly lower than that of the single lead, and the shape was also changed, as show in Figure 2 (a); meanwhile, the TF phase of the dual lead system was almost identical to that of the single lead system, as shown in Figure 2 (b). Based on the TF value, a much lower TR would be expected for the dual lead system, which was verified by the in vitro measurement result as shown in Figure 3. The triangle marks and the circular marks represent the measured TR from a single lead and dual leads, respectively. On average, a 47% drop in TR was achieved with the dual lead system. However, this heating from the dual lead pacemaker system cannot be directly predicted by scaling the single lead result because the transfer function shape was also changed. A careful TF validation process was accomplished by comparing the predicted and measured TR on each lead pathway as shown in Figure 4.

Conclusions

We compared the MRI-induced lead heating resulting from pacemaker systems employing one and two leads. The dual lead system experienced significantly reduced tip heating compared to the single lead system. We have shown that the RF heating TF methodology specified in ISO/TS 10974 can be extended to dual lead TF and that the accuracy of dual lead TFs are comparable to single lead TFs.

Acknowledgements

No acknowledgement found.

References

[1] S. Pisa, G. Calcagnini, M. Cavagnaro, E. Piuzzi, E. Mattei, and P. Bernardi, “A study of the interaction between implanted pacemakers and the radio frequency field produced by magnetic resonance imaging apparatus,” IEEE Trans. Electromag. Compat, vol. 50, no. 1, pp. 35-42, February 2008.

[2] S. Feng, R. Qiang, W. Kainz, and J. Chen, “A Technique to Evaluate MRI-induced Electric Fields at the Ends of Practical Implanted Lead,” Microwave Theory and Techniques, IEEE Transactions on, vol. 63, no.1, pp.305,313, Jan. 2015

[3] J. A. Nyenhuis, S.-M. Park, R. Kamondetdacha, A. Amjad, F. G. Shellock, and A. R. Rezai, “MRI and Implanted Medical Devices: Basic Interactions With an Emphasis on Heating,” IEEE Transactions on Device and Materials Reliability, vol. 5, no. 3, pp. 467-480, September 2005

[4] S.-M. Park, R. Kamondetdacha, and J. A. Nyenhuis, “Calculation of MRI-Induced Heating of an Implanted Medical Lead Wire With an Electric Field Transfer Function,” Journal of Magnetic Resonance Imaging, vol. 26, no. 5, pp. 1278-1285, November 2007

Figures

Figure 1 In vitro temperature rise measurement experimental set up

Figure 2 Measured TF comparisons between single Tendril 2088 STS leads and dual Tendril 2088 STS leads

Figure 3 Measured in vitro lead tip temperature rise for different phase reversal lead pathways (the TR of two 2088 leads tip electrodes are the same in dual lead system)

Figure 4 Comparison between predicted temperature rise and measured temperature rise



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
0919