Brain surface electrode co-registration using MRI and x-ray

Electrocorticographic recording is now being used in a wide variety of experimental settings. We present a simple method which can be used to estimate electrode position with respect to brain gyral anatomy using a pre-implantation MRI and post-implantation coronal and sagittal x-rays. It is semi-automated, with the user manually rotating and scaling an x-ray to fit brain outline, identifying threshold values for brain surface rendering, and clicking on electrodes on an x-ray. Electrode positions can be rapidly identified and rendered in about 20 minutes from start to finish. This approach is useful when the MRI quality is poor, there is no quality CT, but one would like to understand the relationship between experimental result and brain anatomy.