Influence of dense-array EEG cap on fMRI signal

Area of Science:

• Neuroimaging
• Biophysics

Background:

• Dense-array electroencephalography (EEG) systems are increasingly used with functional magnetic resonance imaging (fMRI).
• Increasing EEG channel count can cause MRI signal dropout due to radiofrequency shielding effects.
• The impact of dense-array EEG caps on MRI image quality and fMRI signal detection needs investigation.

Purpose of the Study:

• To investigate the influence of a 256-channel EEG cap on MRI image quality.
• To assess the effect of dense-array EEG caps on blood oxygen level dependent (BOLD) fMRI signal detection sensitivity.

Main Methods:

• Established a theoretical model for EEG cap effects on MRI signal, noise, SNR, and CNR.
• Scanned seven subjects comparing T(2)-weighted image quality and fMRI detection sensitivity with and without the 256-channel EEG cap.
• Utilized an auditory/visual/sensorimotor task during simultaneous EEG-fMRI acquisition.

Main Results:

• Dense-array EEG caps substantially reduced anatomic signal in brain areas near wires (e.g., visual cortex, ~38% decrease).
• Image signal-to-noise ratio (SNR) remained comparable with and without the EEG cap (decrease < 8%, not significant).
• No statistically significant difference was found in BOLD fMRI activation extent.

Conclusions:

• Dense-array EEG caps cause localized anatomic signal reduction in MRI.
• Despite signal dropout, image SNR and fMRI detection sensitivity are largely unaffected.
• Simultaneous EEG-fMRI studies can reliably use dense-array EEG systems without compromising fMRI signal detection.