Mark3D -A semi-automated open-source toolbox for head-surface reconstruction and electrode position registration using a smartphone camera video

Source localization in EEG necessitates aligning EEG sensor coordinates with the subject's MRI, typically done through electromagnetic tracking or 3D scanning.Both methods have drawbacks-electromagnetic tracking is slow and immobile, while 3D scanners are expensive.Photogrammetry offers a cost-effective alternative, but requires multiple photos to sample the head, with good spatial sampling.Post-reconstruction, existing tools for electrode position labelling on the 3D head-surface have limited visual feedback and an inability to accommodate customized montages, typical in multi-modal measurements.Mark3D is an open-source, integrated tool for 3D head reconstruction from phone camera videos.Its eliminates the need for precise spatial sampling during image capture.It includes blur detection algorithms, a user-friendly interface for electrode and tracking, and integrates with popular toolboxes like FieldTrip and MNE Python.The accuracy of the proposed method was benchmarked with the head-surface derived from a handheld 3D scanner ("ground truth").The derived head shapes were used to reconstruct source information and the source estimates from the ground truth and video-based models were compared.The error in source reconstruction using the photogrammetry model was found to be 0.033 ± 0.016 mm and 0.037 ± 0.017 mm in the left and right cortical hemispheres respectively.