Heating Effects of Magnetic Resonance Imaging on ... - ismrm

6 downloads 0 Views 21KB Size Report
unbreakable) the possibilites of design changes are limited. Changes in the winding configuration are among the proposed developments. The aim of this study ...
Heating Effects of Magnetic Resonance Imaging on Pacemaker Leads: Effect of Lead Types and Positioning Roger Luechinger1, Firat Duru2, Markus B. Scheidegger1, Reto Candinas2, Peter Boesiger1 1

Institute of Biomedical Engineering and Medical Informatics, University and ETH Zurich 2 Division of Cardiology, University Hospital Zurich, Switzerland

Temperature increasing [°C]

25

Circular Linear border Linear middle

20

15

10

5

0 CapSure Fix 4068

CapSure Fix 4568

CapSure CapSure CapSure Z Membrane Tentril DX CapSure Z ThinLine SP 4024 VDD 5032 5034 E 1452T 1388T 4033

Figure 1: Temperature increase of different leads in circular configuration.

In linear configuration the temperature increase depended strongly on whether the lead was placed in the middle of the

reservoir or at the border. 5 leads touching the border were heated by more than 20°C, and the rest showed increases of more than 10°C. Under special configurations, linear at the border with the lead tip at the surface of the saline reservoir, a maximal temperature increase of as much as 69°C was observed. The bipolar ThinLine (Sulzer Intermedics Inc., Angleton, TX) lead with both conductors wound into a single coil showed repeatedly by far the least heating effects. The unipolar lead CapSure Z 4033 (Medtronic Inc., Minneapolis, MN) seemed to be better than the similarly designed bipolar CapSure Z 5034. By moving the lead and reservoir out of the isocenter of the RF coil the temperature changes could be reduced (Figure 2). Temperature increase

Introduction An implanted cardiac pacemaker is usually regarded as a contraindication for magnetic resonance imaging (MRI) due to safety reasons. Nevertheless, at some MRI sites patients with pacemakers underwent MRI examination at different field strengths [1,2]. However, heating of pacemaker leads is still a potentially harmful effect that has drawn recent attention [3,4]. Due to the specific requirements for pacemaker lead design (wires have to be of low resistance, thin, flexible, and unbreakable) the possibilites of design changes are limited. Changes in the winding configuration are among the proposed developments. The aim of this study was to investigate experimentally the heating effects of MRI on old and newer pacemaker leads of varying winding types. The influence of lead positioning and the reproducibility of measurements were analyzed. Methods Heating effects of MRI at 1.5 T (Philips Gyroscan ACS NT) on 9 leads from 3 manufacturers were investigated in vitro. The following categories of lead types were included: unipolar, conventional coaxial bipolar, and coradial bipolar (with both conductors wound into a single coil). The leads were placed inside a 64×33 cm2 large reservoir filled with 20 l saline water and inserted into the scanner. For maximal power irradiation a turbo-spin echo sequence was used. During the measurements (FOV=400mm, matrix 256x205, TE=20 ms, TR=300 ms, 8 slices, flip angle 90°, turbo factor 6, 4 NEX, scan duration 41 sec, SAR=3.8 W/kg) temperature changes at the tip of the different leads were continuously measured by a fiberoptic temperature sensor (Luxtron, Santa Clara, CA). Measurements were repeated on linear and circular lead configurations. The reproducibility of findings were evaluated by performing at least 3 different measurements per type and configuration. Further the dependence of the temperature rises on the position of the RFcoil relative to the lead configuration was examined. Results The temperature increases in the circular configuration (diameter 20cm, in the middle of the reservoir) exceeded 10°C in 2 leads and 15° in one lead (Figure 1). The rise time from room to maximal temperature was less than 10 seconds.

4 3 2 1 0 -50

-40

-30

-20

-10

0

10

20

30

40

Positon of the RF coil relative to the lead [cm ]

Figure 2: Temperature increase at different offsets between reservoir with a lead (circular configuration between -17 and 3 cm, tip at 0cm) and the RF coil isocenter. The marks show the position of the middle of the RF-Coil.

Both screw-in and passive fixation leads were associated with high temperature increases. Shorter leads showed somewhat reduced heating. The temperature changes were independent of whether the leads were isolated or connected to pacemakers. Small changes in the position of the sensor on the lead tip may cause marked changes in the measured temperatures, thus reproducibility of the findings was limited. Discussion MRI at 1.5 T may cause significant heating at the pacemaker lead tip. Special winding constructions, e.g. as used in the coradial ThinLine lead, showed markedly reduced temperature increases, and may represent a way to reduce heating effects. Nevertheless, none of the tested leads appears to be safe under all circumstances. Repeated measurements of limited temperature increases may not guarantee safety against high temperature increases in an individual lead. References 1. Gimbel, J. R., Johanson, D., Levine, P. A., Wilkoff, B. L. Pacing Clin Electrophysiol, 19:913-919, 1996 2. Sommer, T., Lauck, G., Schimpf, R:, Smekal, A. v., Wolke, S., Block, W., Gieseke, J., Schneider, C., Funke, H. D., Schild, H., Rofo Fortschr Geb Rontgenstr, 168(1): 36-43, 1998 3. Hofman, M. B. M., de Cook, C. C., van der Linden, J. C., van Rossum, A. C., Visser, F. C., Sprenger, M., Westerhof, N. Magn Reson Med, 35:413-422, 1996 4. Achenbach, S., Moshage, W., Diem B,. Bieberle, T. Schibgilla, V. and Bachmann, K. Am Heart J, 134(3): 467-473, 1997

Acknowledgments: This research was partly supported by Medtronic Inc. Minneapolis, MN