A phantom and animal study of temperature changes during fMRI with intracerebral depth electrodes.
BACKGROUND
MRI is routinely used in patients undergoing intracerebral electroencephalography (icEEG) in order to precisely locate the position of intracerebral electrodes. In contrast, fMRI has been considered unsafe due to suspected greater risk of radiofrequency-induced (RF) tissue heating at the vicinity of intracerebral electrodes. We determined the possible temperature change at the tip of such electrodes during fMRI sessions in phantom and animals.


METHODS
A human-shaped torso phantom and MRI-compatible intracerebral electrodes approved for icEEG in humans were used to mimic a patient with four intracerebral electrodes (one parasagittal and three coronal). Six rabbits were implanted with one or two coronal electrodes. MRI-induced temperature changes at the tip of electrodes were measured using a fibre-optic thermometer. All experiments were performed on Siemens Sonata 1.5T scanner.


RESULTS
For coronally implanted electrodes with wires pulled posteriorly to the magnetic bore, temperature increase recorded during EPI sequences reached a maximum of 0.6°C and 0.9°C in phantom and animals, respectively. These maximal figures were decreased to 0.2°C and 0.5°C, when electrode wires were connected to cables and amplifier. When electrode wires were pulled anteriorly to the magnetic bore, temperature increased up to 1.3°C in both phantom and animals. Greater temperature increases were recorded for the single electrode implanted parasagitally in the phantom.


CONCLUSIONS
Variation of the temperature depends on the electrode and wire position relative to the transmit body coil and orientation of the constant magnetic field (B0). EPI sequence with intracerebral electrodes appears as safe as standard T1 and T2 sequence for implanted electrodes placed perpendicular to the z-axis of the magnetic bore, using a 1.5T MRI system, with the free-end wires moving posteriorly, in phantom and animals.
Translational and Integrative Group in Epilepsy Research (TIGER), INSERM, France; U1028, CNRS UMR 5292, Centre de Recherche en Neuroscience de Lyon, Lyon, France. Electronic address: carolina.ciumas@inserm.fr.
Carolina
C
Ciumas
MR:comp GmbH, Testing Services for MR Safety & Compatibility, Gelsenkirchen, Germany.
Gregor
G
Schaefers
Translational and Integrative Group in Epilepsy Research (TIGER), INSERM, France; U1028, CNRS UMR 5292, Centre de Recherche en Neuroscience de Lyon, Lyon, France; CERMEP - Imagerie du Vivant, Lyon, France.
Sandrine
S
Bouvard
CREATIS, CNRS UMR 5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France.
Emmeline
E
Tailhades
CREATIS, CNRS UMR 5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France.
Emmanuel
E
Perrin
U1028, CNRS UMR 5292, Centre de Recherche en Neuroscience de Lyon, Lyon, France.
Jean-Christophe
JC
Comte
CarMeN, INSERM U1060, INSA de Lyon, Université de Lyon, Villeurbanne, France.
Emmanuelle
E
Canet-Soulas
Translational and Integrative Group in Epilepsy Research (TIGER), INSERM, France; U1028, CNRS UMR 5292, Centre de Recherche en Neuroscience de Lyon, Lyon, France.
Chantal
C
Bonnet
CERMEP - Imagerie du Vivant, Lyon, France.
Danielle
D
Ibarrola
Department of Functional Neurosurgery, Hospices Civils de Lyon, Lyon, France.
Gustavo
G
Polo
DIXI, Besançon, France.
Jose
J
Moya
CREATIS, CNRS UMR 5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France.
Olivier
O
Beuf
Translational and Integrative Group in Epilepsy Research (TIGER), INSERM, France; U1028, CNRS UMR 5292, Centre de Recherche en Neuroscience de Lyon, Lyon, France; CERMEP - Imagerie du Vivant, Lyon, France; Department of Functional Neurology and Epileptology, Hospices Civils de Lyon, Lyon, France. Electronic address: ryvlin@cermep.fr.
Philippe
P
Ryvlin
D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism*; D004567:Electrodes, Implanted; D005260:Female; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011817:Rabbits; D013696:Temperature
ASTM; American Society of Testing and Materials; BOLD; EPI; Epilepsy; FOV; HFO; MR; MRI; RF; RF heating; SAR; bold oxygenation level dependency; echo-planar imaging; fMRI; field of view; functional magnetic resonance imaging; high frequency oscillation; icEEG; icEEG/fMRI; intracerebral electroencephalography; magnetic resonance; magnetic resonance imaging; radiofrequency; specific absorption rate