The incidence of patients receiving implanted neurostimulation or neuromodulation systems for treatment of neurological disorders and other conditions continues to increase. Because of the inherent design and intended function of neurostimulation systems, [including those used for deep brain stimulation (DBS), spinal cord stimulation (SCS), vagus nerve stimulation (VNS), and other similar devices], the electromagnetic fields used for MR procedures may produce a variety of problems. For example, altered function of a neurostimulation system that results from exposure to the electromagnetic fields of an MR system may cause discomfort, pain, or serious injuries to patients.
MRI-related heating has been reported to create the greatest concern for various devices used for neuromodulation. Variables that impact heating include, but are not limited to, the following:
- The specific type of neuromodulation system
- The electrical characteristics of the specific neuromodulation system
- The field strength and RF wavelength of the MR system
- The type of transmit RF coil (i.e. transmit head vs transmit body RF coil) used for MRI
- The amount of RF energy delivered (i.e., the RF power level, SAR)
- The technique used to calculate or estimate SAR used by the MR system
- The patient’s anatomy undergoing MR imaging
- The landmark position or body part undergoing MRI relative to the transmit RF coil
- Theorientation and configuration of the implantable pulse generator (IPG), extension (e.g., the cable connecting the pulse generator (PG) to the implanted lead), and the lead relative to the source of RF energy (i.e. the transmit RF coil)
Importantly, the exact criteria for the particular neurostimulation system with regard to the pulse generator, leads, electrodes, and operational aspects of the device as well as the MR system conditions must be defined by comprehensive testing and carefully followed to ensure patient safety. On-going investigations continue to define the acceptable criteria to permit MR examinations, including those involving 1.5- and 3-Tesla MR systems, to be performed in patients with neurostimulation systems. Importantly, various device manufacturers now have certain neurostimulation systems that have been specially designed to be MR Conditional which have fewer limitations for MR imaging procedures compared to older devices.
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