Abstract
BackgroundOver the last decade, the number of neurostimulator systems implanted in patients has been rapidly growing. Nearly 50, 000 neurostimulators are implanted worldwide annually. The most common type of implantable neurostimulators is indicated for pain relief. At the same time, commercial use of other electromagnetic technologies is expanding, making electromagnetic interference (EMI) of neurostimulator function an issue of concern. Typically reported sources of neurostimulator EMI include security systems, metal detectors and wireless equipment. When near such sources, patients with implanted neurostimulators have reported adverse events such as shock, pain, and increased stimulation. In recent in vitro studies, radio frequency identification (RFID) technology has been shown to inhibit the stimulation pulse of an implantable neurostimulator system during low frequency exposure at close distances. This could potentially be due to induced electrical currents inside the implantable neurostimulator leads that are caused by magnetic field coupling from the low frequency identification system.MethodsTo systematically address the concerns posed by EMI, we developed a test platform to assess the interference from coupled magnetic fields on implantable neurostimulator systems. To measure interference, we recorded the output of one implantable neurostimulator, programmed for best therapy threshold settings, when in close proximity to an operating low frequency RFID emitter. The output contained electrical potentials from the neurostimulator system and those induced by EMI from the RFID emitter. We also recorded the output of the same neurostimulator system programmed for best therapy threshold settings without RFID interference. Using the Spatially Extended Nonlinear Node (SENN) model, we compared threshold factors of spinal cord fiber excitation for both recorded outputs.ResultsThe electric current induced by low frequency RFID emitter was not significant to have a noticeable effect on electrical stimulation.ConclusionsWe demonstrated a method for analyzing effects of coupled magnetic field interference on implantable neurostimulator system and its electrodes which could be used by device manufacturers during the design and testing phases of the development process.
Highlights
Over the last decade, the number of neurostimulator systems implanted in patients has been rapidly growing
We found effects of inhibition of one implantable neurostimulator system indicated for incontinence when close to two low frequency radio frequency identification (RFID) emitters
To address the concerns posed by coupling of electromagnetic fields from RFID emitters, we developed a test protocol to assess the interference from coupled magnetic fields on implantable neurostimulator systems
Summary
The number of neurostimulator systems implanted in patients has been rapidly growing. In recent in vitro studies, radio frequency identification (RFID) technology has been shown to inhibit the stimulation pulse of an implantable neurostimulator system during low frequency exposure at close distances. After 10 years of experiments, Michael Faraday and Joseph Henry independently discovered that magnetic fields can produce an electric current in a closed loop, but only if magnetic flux linking the surface area of the loop changes with time. This type of process was named electromagnetic induction. A moving loop in a time varying magnetic field [11]
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