Where should I store additional session information, if not in participants.tsv?

Hello BIDS-experts,

I run a two-session MRI study and, of course, I am converting my data to BIDS.

I have a bunch of data about the participants for each session that I would like to include, e.g., what time of time day they were scanned, who scanned them, temperature, etc. but I am not quite sure where to best include it.

First, I thought about adding columns to the participants.tsv file but I didn’t like the idea that I would need separate columns for each session, e.g., temperature_ses-01 and temperature_ses-02 since I generally prefer the long table format, so something like:

participant_id session temperature_celcius
sub-01 ses-01 21.5
sub-01 ses-02 22.0
sub-02 ses-01 20.9

But, according to the relevant section in the BIDS specification

Each participant MUST be described by one and only one row.

So I MUST do something like this:

participant_id session temperature_s1 temperature_s2
sub-01 ses-01 21.5 22.0

Of course, this is not the end of the world, but I still wondered if anyone could recommend another option. For example, I thought about creating additional behavioral data files where I would have more freedom to choose the data organization. Then again, the data I want to document here are not really an additional behavioral experiment, so maybe that’s not ideal either.

I only have two sessions here, so even a wide format (as shown above) would not hurt, but for longitudinal datasets this seems even more relevant, so maybe someone has figured out a good solution.

Thanks in advance and best,
Lennart

Use a sessions file for this case.

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Thanks for your quick response @effigies!

Perfect, that’s exactly what I need. Sorry for failing to find this option myself.

Thanks again and cheers,
Lennart

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