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Final Report - Google Summer of Code 2019


TL;DR (abstract)

In my GSoC, I bridged the data standard "BIDS" and the analyis software "MNE-Python" to facilitate automatic data analysis in the domain of neuro-electrophysiology.

Description

With the emergence of the Brain Imaging Data Structure (BIDS) in 2016, the scientific community received a standard to organize and share data in the broad domain of Neuroscience / Neuroimaging.

BIDS prescribes how the highly complex data that results from experiments should be structured and which metadata should be encoded next to the raw data. Through this, there are several benefits that can be reaped:

  1. sharing data within a lab and between labs: Through the structured specification, everybody who has read the basics can understand any BIDS dataset without requiring specialist knowledge.
  2. data validation: Use software to check whether everything is documented or whether there are missing data (see bids-validator)
  3. automatic data analysis pipelines: Through the use of REQUIRED, RECOMMENDED, and OPTIONAL flags for data in BIDS, analysis software can perfectly know which data to expect and where to search for it. Data reading and processing are facilitated and can be automated to a much higher degree than with non-standard data structures.

... and many more benefits - I recommend reading the original publication on BIDS.

The objective in my Google Summer of Code (GSoC) 2019 was to harness BIDS to simplify common workflows in the analysis of neuroimaging data and specifically in the analysis of electrophysiology data such as EEG, MEG, and iEEG.

Inititally, the idea of Mainak Jas, Alexandra Gramfort (my mentors) was to program a versatile analysis pipeline drawing on BIDS and several other existing packages that already make interfaces between BIDS and Python.

However, after a few early discussions, we decided against programming a new analysis pipeline from scratch and instead determined to focus on revamping the existing mne-study-template to draw on BIDS.

The mne-study-template is a set of processing files that form a complete pipeline for automatic processing of MEG and EEG datasets. So far, the study template had relied on some unspecified data structure, that was still relatively rigid. Through BIDS, the expected input for the study template can become much more transparent ... and the code base can be significantly reduced through reading the data from metadata files that we know MUST be present in BIDS.

Preparing the mne-study-template to be BIDS compatible involved several key points, such as:

  • preparing testing datasets
  • testing CI setups
  • working on the study-template itself
  • changes to MNE-BIDS and MNE-Python along the way

All of these points have been part of my GSoC, and as an outcome of the overall project work, the mne-study-template is now usable with BIDS formatted data, MNE-BIDS version 0.3 is released, and lots of other benefical outcomes are usable to the community at large.

Usable outcomes: Highlights

Here I list the highlights of my contributions in several projects that are interrelated. Somewhat ordered by importance (but feel free to disagree!)

Unfinished business

A single Google Summer of Code is not enough to fix all problems that appear along the way. Right below I list some work that can be picked up by other community members, or even myself at the next convenient time. As before, this is not an exhaustive list, it merely highlights the most pressing issues.

  • MNE-Python has the "reports" feature that can provide html reports for analysis steps that have been run. This feature should be integrated into the mne-study-template, but it's not working so far. (issue #47 in mne-study-template)

  • MNE-BIDS has a read_raw_bids function. Unfortunately, this function does currently not read any digitization files such as the headshape, electrode positions, or head position coils. (issue #203 in mne-bids)

  • MNE-BIDS has the function to write anatomical data with its write_anat function. This function depends on reading fiducial points from an MNE raw object. In the future, it should be possible for the function to get fiducial information from a BIDS coordsystem.json file (issue #214 in mne-bids)

Complete documentation

Throughout my GSoC, I have written a changelog with all work I have done each day. The changelog is structured by weeks and days with the most recent dates on top of the document.

The document can be found in this repository: changelog.md

The blog that I wrote during my GSoC can be found here.

Acknowledgements

I have received a lot of support by my mentors @jasmainak and @agramfort, both of which helped me to write clean code and to stay practical.

I am furthermore grateful to @larsoner and @massich for providing guidance and advise in topics surrounding MNE-Python, code testing, and Python in general.

Both the MNE-Python community and BIDS community made my time during the GSoC very enjoyable and productive.

Lastly, I think that Google Open Source is doing a great job with their Google Summer of Code program and I consider myself lucky to have been a part of this.

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