Abstracts

Rationale: Patients with partial seizures can be successfully treated for medically intractable epilepsy with brain-responsive neurostimulation. Monitoring and diagnosis with Magnetic Resonance Imaging (MRI) post-implant has multiple advantages over Computerized Tomography (CT) imaging. MRI of the brain, and importantly all other body regions, can be safely performed in these patients. Our aim is to provide case-based experience with safe performance of MRI on patients implanted with the RNS® System¹ (NeuroPace, Inc.). We demonstrate the diagnostic utility of MRI in these patients and the MRI artifacts due to the implanted components. We also highlight safe MRI performance and artifact reduction techniques on a patient who underwent MRI within the FDA-approved guidelines.

1 Only the RNS-320 model of the RNS System and NeuroPace leads are MRI Conditional. The RNS-300M is MRI Unsafe. See MRI Guidelines for the RNS System for more information.

Methods: Patient: A 65-year-old female presented with back pain and confusional state following a vertebroplasty at an outside center. Desire for MRI evaluation prompted request for brain and spine imaging at our institution. Imaging: Key guidelines for MRI with the RNS System require a field strength of 1.5 T with a horizontal field and cylindrical system. Maximal gradient amplitudes of 30 T/m and slew rate of 200 T/m/s per axis can be performed using the body quadrature coil for transmission with any receive coil. T/R head or T/R extremity coils are not approved. RF power (B1+RMS) is limited superior to the T2 vertebra to ≤2.95μT, and below T2 to 4.67μT. Fast-spin-echo imaging was utilized within parameters provided. Repetition time of 6230ms, echo train length of 18, receiver bandwidth of >32kHz and reduced phase encoding steps to 220 reduced susceptibility artifact. Imaging was conducted with an interleaved slice prescription. Full guidelines are available at https://www.neuropace.com/providers/rns-system-mri-guidelines/. Analysis: Brain MRI and exams of other body regions were qualitatively assessed in a binary fashion as diagnostic or non-diagnostic. Extent of the artifact around the electrodes and neurostimulator were recorded. The patient was surveyed for any physical signs or symptoms of complication

Results: Brain imaging was diagnostic with some limitation around the areas of greatest susceptibility. Artifact near the electrodes extended 2-3 mm from the center of the lead. Artifact from the cranial neurostimulator extended 1-2 cm from its edge. Spinal MRI was unaffected by artifact from the RNS System implant. There were no complications or adverse events.

Conclusions: MRI in patients with the RNS System within the FDA-approved guidelines can safely provide useful diagnostic information. Artifact from depth lead electrodes are small. Artifacts from the neurostimulator obscure imaging up to a distance of 1-2 cm from the neurostimulator. Body imaging is feasible and is unaffected by implanted components of the RNS System.

Funding: Please list any funding that was received in support of this abstract.: None.