Electrical and Thermal Behavior of Intracranial Electrodes during Magnetic Resonance Imaging: A Quantitative Study.
Abstract number :
1.196
Submission category :
Year :
2001
Submission ID :
265
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
N.C. Bhavaraju, Ph.D., Flint Hills Scientific, LLC, Lawrence, KS; V. Nagaraddi, MBBS, Comprehensive Epilepsy Center, KU Medical Center, Kansas City, KS; I. Osorio, MD, Comprehensive Epilepsy Center, KU Medical Center, Kansas City, KS
RATIONALE: Localization of brain targets and verification of electrode placement benefit from MRI, but concerns exist about patient safety because of the potential for heating of and induction of electrical currents in implanted devices even if made of non-ferrous metals. This study attempts to quantify these phenomena.
METHODS: MRI scans (1.5 T, Siemens MAGNETOM Vision) were performed on a phantom brain made out of 0.9 % saline gelled with agar and implanted with depth and surface grid electrodes (AdTech 6-contact needle, 32-contact surface grid, and Medtronic-3387 DBS electrodes). Induced voltages (V) were measured with an oscilloscope (TDS 220, Tektronix, Inc., OR) and temperature (T) with a fluoroptic thermometer (Model 790, Luxtron Corp., CA) during various MRI scan sequences. Number of electrodes and their positions were varied to study the effects on V and T.
RESULTS: Maximal change in T was 0.4 [degree]C. V depended on the number of electrodes, their position, slice thickness and scan sequences. Maximal V measured in the absence of lead wire loops was [lt]10 V, but thin slices and T1 axial sequences increased it to 12 V. Lead wire loops raised V to 70 V and degraded MR images. The estimated currents because of the induced voltages due to possible leakage and single fault conditions resulted in charge densities well within the safety limit of 30 [mu]C/cm2 for the electrodes used.
CONCLUSIONS: MRI scans may be safely performed in patients with intracranial electrodes made of non-ferrous metals provided the leads do not form a closed circuit. Moreover, this conclusion applies only if the subject can lay still and only for the electrode types/configurations used in this study. The number of MR sequences performed should be the minimum required for diagnostic or localization purposes; the same considerations apply to the selection of slice thickness. Although in this study lead wire loops of up to 700 cm2 induced voltages at safe levels, it is strongly recommended that loops be eliminated.
Mark Rise, Greg Hrdlicka, David Po, Edward Murray and Mark Smith provided technical assistance.