[Eeglablist] get_chanlocs

Seyed Yahya Shirazi shirazi at ieee.org
Fri Dec 27 14:02:17 PST 2019


Dear Jeff and Andrew,

Glad to hear there is more and more interest in 3D scanning and EEG
digitization/positioning in general. We do digitize EEG electrode locations
using Structure Sensor and iPad Pro 10.5" in our lab.
Our recent paper compared 3D scanning with Zebris and motion capture, and
Structure performed very well both in digitization reliability and also
consistency in finding the same source locations (see
https://www.ncbi.nlm.nih.gov/pubmed/31787866).
Electrode digitization with a 3D scanner has two main steps: 1-
scanning the head 2- marking the electrodes and fiducial locations in a
software (here MATLAB). I would say after learning how to use the scanner,
each step takes about 10 minutes with a 128-channel BioSemi ActiveTwo
system. Gaia Taberna (from Dr. Manitini's lab in KU Leuven) also created a
toolbox for automatically marking the electrodes, and they had the EGI
system (see: https://www.ncbi.nlm.nih.gov/pubmed/31492919). I have not
tried the automatic approach yet because 10 minutes is not a long time to
do mark up the scan.
The original (NOT the core) scanner works with my iPad Air A2152 (it has
the same chassis as iPad Pro 10.5 A1701). I am not sure about the earlier
iPads, but I think as long as the Structure.io website claims the scanner
supports that model, you are good to go. However, make sure that you have
the bracket (adapter) to attach the scanner to the iPad (I checked
strucutre.io, and it seems they don't offer a bracket for A1474).
Structure scanner MarkII is just a better scanner with better resolution.
The core version is supposedly the standalone scanner with a tripod, so I
don't think that's the option you want.
You only need the Scanner app from Apple AppStore (
https://apps.apple.com/us/app/scanner-structure-sdk/id891169722) to do the
scanning. The app is free and would ask you to install its calibrator app
(also free) if you are scanning for the first time. The only downside of
this app is that it can't store the scan on the iPad and only would send it
via email, so you need an internet connection. Both EEGLAB and FieldTrip
toolbox can read outputs of the Scanner app after you unzip it from the
email attachment (see our pipeline, based on FieldTrip, here:
https://github.com/neuromechanist/eLocs).
The Structure sensor has its limitations too. With the original model that
we are currently using, the scanner is susceptible to the lighting
conditions, so we only do the digitization in a specific spot in our lab to
make sure that they are similar. Also, sometimes the scanned point cloud
and the color image that should be overlayed to the point cloud do not
match, or the color image is not clear. So we always check the results on
the iPad to make sure that we have the right quality color image, and the
image matches the point cloud. As I said earlier, using a 3D scanner for
EEG electrode digitization has a learning curve, but once you get used to
the process, it just takes 10 minutes to scan and another 10 minutes to
mark up the locations in MATLAB.

Please do not hesitate to contact me if I can be of more assistance.

Best,
Seyed Yahya Shirazi
Ph.D. Candidate, BRaIN Lab
University of Central Florida


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