tES + fMRI

Magnetic field gradient switching within the fMRI or MRI will generate electrical stimulation artifacts. As the magnetic field shifts, current will be induced in any conductor that crosses the field lines. When combining with electrical stimulation, this induced current will flow in the conductive loop formed between the subject, electrodes, lead wires, and cabling. Soterix Medical solution has been tested for typical tDCS dose (2mA x 20 min) using a current monitor to confirm that artifact stimulation current does not significantly alter programmed current.

The current induced in the conductive loop will also lead to localized heating. The heating increases depending on several factors from thermodynamic and electro-magnetic properties of the electrodes and tissue, stimulation current injected, MRI coil, electrode placement with respect to the coil, blood flow, etc. Soterix Medical solution has been tested for typical tDCS dose (2mA x 20 min) using a standard fiber optic temperature monitoring system. Temperature increases underneath the electrodes were below 0.5 degree Celsius across all conditions tested (phantom and subject).

The final performance metric is image quality, which may deteriorate due to reduced SNR and susceptibility artifacts or B0 field distortions. Soterix Medical solution has been validated via visual inspection for no susceptibility artifacts underneath electrodes and no distortion of EPI images.