Epilepsia open · 2026
Safety of postimplantation MRI with Dixi microdeep electrodes in situ: An in vitro evaluation of MRI-related heating at 1.5T.
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Tuura Ruth O'Gorman, Luechinger Roger, Heule Rahel, Kottke Raimund, Rona Sabine, Krayenbühl Niklaus, Ramantani Georgia
Аннотация
OBJECTIVE: Postimplantation assessment of the position of depth EEG electrodes for intracerebral recordings in patients with refractory focal epilepsy can be performed with MRI or with CT after coregistration to a preimplantation MRI. While both methods offer risks and advantages, postimplantation MRI risks depend on the electrode heating profile under different MRI conditions. We aimed to assess the MRI-related heating of Dixi microdeep electrodes at 1.5T in multiple electrode configurations and with varying levels of radiofrequency (RF) power.
METHODS: In vitro tests of heating due to RF power deposition were performed according to the F2182-19e2 standard from the ASTM (American Society for Testing and Materials International). A 10-contact Dixi microdeep electrode was inserted into the gel within the ASTM head-torso phantom, and the temperature was recorded from selected electrode contacts during MRI. Tests were performed with the electrode positioned in various locations in straight and coiled configurations, with coil diameters from 6 to 25 cm. MRI was conducted on a 1.5T Philips Achieva scanner using the transmit-receive body coil.
RESULTS: Significant heating was observed for all configurations where more than 12 cm of the electrode was in the RF coil, apart from those with an applied specific absorption rate (SAR) ≤0.16 W/kg and with additional coiling of the electrode lead using a diameter of ≤6 cm. The worst-case configurations, reaching a maximum temperature of 70°C (temperature rise 48°C), occurred where the electrode end was straight or looped with a large-diameter (25 cm) loop. Heating was greatest in the contact furthest from the tip.
SIGNIFICANCE: Dixi microdeep electrodes demonstrate heating levels capable of causing serious injury during MRI, but using a conservative SAR limit of 0.1 W/kg and coiling the electrode lead to a diameter of ≤6 cm appears to reduce the heating risk.
PLAIN LANGUAGE SUMMARY: Electrodes positioned within the brain for planning epilepsy surgery can heat up during MRI. Using a standard test object mimicking the electrical properties of the human body, we measured heating of Dixi microdeep depth electrodes in different positions and orientations and with varying levels of radiofrequency power. We found substantial heating apart from when the radiofrequency power was greatly restricted or when the lead was tightly coiled. Different electrode contacts showed drastically different heating, and heating levels capable of causing serious injury were measured during MRI.
METHODS: In vitro tests of heating due to RF power deposition were performed according to the F2182-19e2 standard from the ASTM (American Society for Testing and Materials International). A 10-contact Dixi microdeep electrode was inserted into the gel within the ASTM head-torso phantom, and the temperature was recorded from selected electrode contacts during MRI. Tests were performed with the electrode positioned in various locations in straight and coiled configurations, with coil diameters from 6 to 25 cm. MRI was conducted on a 1.5T Philips Achieva scanner using the transmit-receive body coil.
RESULTS: Significant heating was observed for all configurations where more than 12 cm of the electrode was in the RF coil, apart from those with an applied specific absorption rate (SAR) ≤0.16 W/kg and with additional coiling of the electrode lead using a diameter of ≤6 cm. The worst-case configurations, reaching a maximum temperature of 70°C (temperature rise 48°C), occurred where the electrode end was straight or looped with a large-diameter (25 cm) loop. Heating was greatest in the contact furthest from the tip.
SIGNIFICANCE: Dixi microdeep electrodes demonstrate heating levels capable of causing serious injury during MRI, but using a conservative SAR limit of 0.1 W/kg and coiling the electrode lead to a diameter of ≤6 cm appears to reduce the heating risk.
PLAIN LANGUAGE SUMMARY: Electrodes positioned within the brain for planning epilepsy surgery can heat up during MRI. Using a standard test object mimicking the electrical properties of the human body, we measured heating of Dixi microdeep depth electrodes in different positions and orientations and with varying levels of radiofrequency power. We found substantial heating apart from when the radiofrequency power was greatly restricted or when the lead was tightly coiled. Different electrode contacts showed drastically different heating, and heating levels capable of causing serious injury were measured during MRI.