A phantom and animal study of temperature changes during fMRI with intracerebral depth electrodes

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• 作者：Carolina Ciumas ; Gregor Schaefers ; S ; rine Bouvard ; Emmeline Tailhades ; Emmanuel Perrin ; Jean-Christophe Comte ; Emmanuelle Canet-Soulas ; Chantal Bonnet ; Danielle Ibarrola ; Gustavo Polo ; Jose Moya ; Olivier Beuf ; Philippe Ryvlin
• 关键词：BOLD ; bold oxygenation level dependency ; icEEG ; intracerebral electroencephalography ; fMRI ; functional magnetic resonance imaging ; HFO ; high frequency oscillation ; ASTM ; American Society of Testing and Materials ; MRI ; magnetic resonance imaging ; RF ; radiofrequency ; MR ; magnetic resonance ; SAR ; specific absorption rate ; EPI ; echo-planar imaging ; FOV ; field of view
• 刊名：Epilepsy Research
• 出版年：January, 2014
• 年：2014
• 卷：108
• 期：1
• 页码：57-65
• 全文大小：1058 K

文摘

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Summary

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 1.5 T 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 掳C and 0.9 掳C in phantom and animals, respectively. These maximal figures were decreased to 0.2 掳C and 0.5 掳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 掳C in both phantom and animals. Greater temperature increases were recorded for the single electrode implanted parasagitally in the phantom.

Conclusion

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 1.5 T MRI system, with the free-end wires moving posteriorly, in phantom and animals.