Vagus nerve stimulation therapy system: in vitro evaluation of magnetic resonance imaging-related heating and function at 1.5 and 3 tesla.

Objectives.  To evaluate magnetic resonance imaging-related (MRI-related) heating for the VNS Therapy System at 1.5 and 3 tesla (T) using various device configurations and MRI conditions and to assess device function before and after MRI. Methods.  The VNS Therapy System (pulse generator, Model 102; leads Models 300 and 302; Cyberonics, Inc., Houston, Tex, USA) underwent assessment of MRI-related heating at 1.5 and 3 T using different positioning configurations, leads, transmit radiofrequency (RF) coils (body and head), RF power levels, and scans on different body regions. The function of the VNS Therapy System was evaluated before and after scanning. Results.  At 1.5 T using a transmit RF body coil, excessive temperature changes were associated with scans of the C-spine/shoulder (+11.5°C, complete system; +29.5°C, lead without pulse generator). The lowest temperature change occurred for the scan of the L-spine. At 1.5 T using a transmit/receive RF head coil, temperature changes did not exceed +0.2°C under the conditions studied. At 3 T using a transmit RF body coil, the highest temperature change occurred with the scan of the C-spine/shoulder (+14.5°C) with the lead configured with no strain relief loops at the vagus nerve. MRI performed using various conditions at 1.5 and 3 T produced no significant alterations in the function of the VNS Therapy System. Conclusions.  MRI-related heating was characterized for a variety of scenarios, identifying unsafe as well as safe conditions. Device function was unaffected by MRI procedures at 1.5 and 3 T. By following specific conditions, safety guidelines for the VNS Therapy System may be expanded beyond those currently indicated by the manufacturer.