→ Both doctors and researchers want EEG hardware that can go into an MRI!
→ Interactions between EEG connecting wires and RF fields need to be investigated!
→ Heating of wires/adjacent AGAR and signal artifacts were measured as a function of EEG wire length
→ Interactions showed a resonance length pattern
→ Discussion of implications for EEG in MR environment
Long Version
Surgical resection is effective in treating pharmaceutically resistant partial epilepsy patients. The possibility of surgery is contingent on localization of the epileptogenic tissue. Both EEG and MRI techniques are utilized in the clinical localization regime, and thus MR-compatible EEG hardware is desirable to avoid logistical challenges such as repeated application of the EEG electrodes, which demands additional technician time and increases the risk of scalp irritation/infection. Further need for MR-compatible hardware comes from the research sector, in which imultaneous
EEG/MRI studies have shown potential for localizing epileptogenic tissue based on irregular hemodymanics. Electrically conductive hardware can interact with the electromagnetic (EM) fields of a MR scanner, creating potential safety and signal quality concerns that scale with the resonance frequency of the scanner. Although EEG electrodes and their connecting wires are both present within the data acquisition volume during head scans, previous work has confirmed that the effects of the electrodes are insignificant given that appropriate materials are used in their construction. However, capacitive energy coupling between the wires and the electric field components of the radiofrequency (RF) pulses may produce significant tissue heating and signal loss. To investigate the energy coupling between conductive wires and RF pulses as evidenced by heat induction in the wires and adjacent tissue, as well as induced signal artifacts. Specifically, the interaction dependence on the length of the conductive wires will be examined, and safety criteria will be established for 4.0 T scanners. Experiments were performed on the 4.0 T scanner at Robarts, using a cylindrical saline AGAR phantom to mimic human tissue. Heating of the wires and adjacent AGAR were monitored while applying high-power RF pulses, and signal artifacts were characterized in GE images; all measures were examined as a function of wire length. Both heating and signal artifacts varied as a function of wire length, showing definite ‘resonance length’ phenomena. Implications for EEG in the MR environment will be discussed.