Cuff Electrodes Not Always Compatible With MRI Scans

Implanted cuff electrodes—widely used in therapy for epilepsy, depression and inflammatory disorders—could trigger unintended nerve stimulation for patients undergoing MRI scans, a University of Houston engineering professor has warned.

Designed to stimulate the vagus nerve, the implanted electrodes are metallic and positioned near the nerve bundle. Their presence during MRIs raises concerns about nerve stimulation due to fast-switching gradient coils and radio frequency coil-induced heating near nerve fibers.

A study led by Ji Chen, professor of electrical and computer engineering at UH, used detailed computer simulations to examine the ways in which MRI fields interact with the cuff electrodes.

“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,” the study concluded. Chen reported his findings in the journal Magnetic Resonance in Medicine.

The study results show 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. Future testing most certainly will be 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 commented.

Chen’s team is developing methods and new designs to mitigate these risks in future cuff electrodes.