Risk Assessment & Mitigation

How Can We Ensure Implantable Medical Devices Allow for Life-Saving Imaging?

Exponent provides wide-ranging testing support to improve the safety and performance of medical devices and innovative healthcare.

Testing MRI Safety for an Implanted Medical Device

A promising new therapy for stroke recovery pairs Vagus Nerve Stimulation (VNS) with rehabilitation therapy to help patients regain function in their upper extremities. Our client needed to understand the effect of the MRI environment on its device and to develop safety labeling providing the conditions under which patients can be safely imaged.

The Challenge 

Millions of stroke survivors experience lasting brain damage that results in lost motor function, such as arm and hand impairment. In 2021, the FDA approved a new treatment approach that pairs neuroplasticity-inducing VNS stimulation with rehabilitation therapy to help the body reroute neural pathways around impacted areas of the brain. Over time, this therapy helps the brain strengthen control of the arm and hand, allowing stroke survivors to improve their ability to engage in everyday tasks and hobbies.

MicroTransponder developed the Vivistim® Paired VNSTM System to deliver this treatment. Vivistim uses a small generator placed in the patient's chest, similar to a pacemaker.  The generator contains a battery connected to wires that extend through the torso and toward the neck. The wires are then placed in contact with the vagus nerve, which leads to targeted areas of the brain.  Once activated, most patients cannot feel the stimulation.

One important safety consideration for devices like this is to understand whether patients can undergo magnetic resonance imaging (MRI) — and if so, whether special considerations might be needed. The electromagnetic field of the MRI system can have a range of consequences on a device's metal components, circuits, or batteries. Similarly, certain types of electromagnetic fields used during MRI can create interactions that may lead to a device heating and cause components to fail or deliver unintended stimulation.

Implanted devices are required to have MRI safety labeling to prevent these types of occurrences. "MRI Conditional" labeling provides the instructions and conditions for care providers under which a patient can have an MRI performed.


Given the risks to patient safety, manufacturers must evaluate every aspect of an implant's MRI compatibility — and Exponent is one of the few consultancies providing rigorous, broad risk-based assessments for active implants. Exponent gathered the right experts into a project team that efficiently gave MicroTransponder the answers they needed. 

EXPONENT's Impact 

Exponent's tests supported the conclusion that it was appropriate to label the VNS device as "MRI Conditional," given some expected restrictions. With these tests concluded and a safety label developed, MicroTransponder entered clinical trials and has now received FDA approval and begun commercialization.

Exponent has helped numerous clients develop their "MRI Conditional" labeling, ensuring that patients and doctors can confidently take advantage of new therapies without losing critical options for diagnostic imaging. Our consultants are also supporting the development of consensus standards to ensure the techniques we use can be recognized as industry best practice for assessing risks in the device development process. Exponent's unique multidisciplinary approach helps clients obtain regulatory approvals for new and groundbreaking medical technologies.