Summary: For patients with implanted cuff electrodes—devices commonly used to treat epilepsy, depression, and inflammatory disorders—an MRI scan might come with an unexpected side effect. A new study warns that these metallic implants can trigger unintended nerve stimulation during a scan.
The research shows that the fast-switching magnetic fields and radiofrequency (RF) heating of an MRI significantly lower the threshold required to activate a nerve, potentially causing pain or discomfort. This discovery suggests that current MRI safety guidelines may be outdated for the growing number of people with bioelectronic implants.
Key Facts
- Unintended Stimulation: Gradient magnetic fields in an MRI can interact with metallic cuff electrodes to trigger nerve responses that are not part of the patient’s therapy.
- Lowered Threshold: The presence of the cuff electrode makes it much easier for external electrical fields to “fire” the nerve, meaning even standard MRI settings could be risky.
- RF Heating Factor: Radiofrequency-induced heating further decreases the activation threshold, especially during short pulse durations common in high-resolution scans.
- Common Devices at Risk: The warning applies to cuff electrodes placed around the vagus nerve, which are widely used for managing chronic conditions like epilepsy and depression.
- Need for New Guidelines: Researchers argue that safety protocols must be refined to account for different human body models, implantation pathways, and MRI polarizations.
Source: University of Houston
A University of Houston engineering professor is warning that implanted cuff electrodes – widely used in therapy for epilepsy, depression and inflammatory disorders – could trigger unintended nerve stimulation for patients undergoing an MRI scan.
The implanted electrodes, which stimulate the vagus nerve, are metallic and positioned near the nerve bundle, so their presence in an MRI environment raises concerns about nerve stimulation due to fast-switching gradient coils and radio frequency coil-induced heating near nerve fibers.
The study, led by Ji Chen, professor of electrical and computer engineering at UH, used detailed computer simulations to examine how MRI fields interact with the cuff electrodes.
“We found that patients with implantable devices may experience unintended nerve stimulation during MRI, which could cause discomfort or pain,” Chen said.
“This suggests that current MRI safety guidelines may not fully account for implanted nerve cuffs, and that more refined guidelines and careful safety considerations are needed.” Chen reported his findings in the journal Magnetic Resonance in Medicine.
The results indicate that the presence of the cuff electrode significantly reduces the activation threshold, or minimum electrical level needed to trigger a nerve response, under gradient field exposure, while RF-induced heating further decreases the threshold for stimulations with short pulse durations.
Chen said the findings should be interpreted as preliminary indications of safety under controlled conditions and future testing is needed.
“For RF-induced heating safety assessment, multiple human body models, more imaging landmarks, more implantation pathways, and different polarizations should all be considered,” he said.
Chen’s team is developing methods and new designs to mitigate these risks in future cuff electrodes.
Key Questions Answered:
A: This research is a warning for doctors and engineers rather than a total ban. While “MRI-conditional” implants exist, this study suggests the safety margins might be thinner than we thought. Always consult your neurologist and radiologist before a scan.
A: The MRI fields don’t send a literal electric shock through the device, but they create electrical currents in the tissue around the metal cuff. This can trick the nerve into “firing,” which can feel like a sharp pain, twitching, or discomfort.
A: Yes. The University of Houston team is already developing new electrode designs and mitigation methods to ensure that future bioelectronic devices are 100% compatible with high-powered MRI machines.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neurotech research news
Author: Laurie Fickman
Source: University of Houston
Contact: Laurie Fickman – University of Houston
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Unintended Vagus Nerve Stimulation From Cuff Electrode During MRI: Combined Effects of Gradient and Radiofrequency Fields” by Lijian Yang, Xiaolin Yang, Ao Shen, Mir Khadiza Akter, Hui Ye, Norbert Kaula, Jianfeng Zheng, Ji Chen. Magnetic Resonance in Medicine
DOI:10.1002/mrm.70261
Abstract
Unintended Vagus Nerve Stimulation From Cuff Electrode During MRI: Combined Effects of Gradient and Radiofrequency Fields
Purpose
Emissions generated during magnetic resonance imaging (MRI)—including gradient coil induced electric fields and radiofrequency coil induced heating near nerve fiber—may alter neural activation inside patients. This study investigates the combined effects of these emissions on vagus nerve activation in the presence of cuff electrodes.
Methods
Electromagnetic, thermal, and neurophysiological simulations were performed to quantify activation thresholds under MRI-induced fields. The study examined the impact of gradient field exposure and RF-induced heating, particularly for the trapezoidal waveform of the gradient coil with short pulse duration.
Results
The results indicate that the presence of the cuff electrode significantly reduces the activation threshold under gradient field exposure, while RF-induced heating further decreases the threshold for stimulations with short pulse durations. In some scenarios, the reduced neuron activation threshold can be lower than peripheral nerve stimulation limits defined in IEC 60601-2-33.
Conclusion
These findings indicate the potential risk of unintended vagus nerve stimulation in MRI environments, emphasizing the need for safety considerations in patients with implantable vagus nerve stimulators.
