clean up PET spreadsheet

[Remi-Gau]

Comparing the published PET-guidelines table and the BIPS PET BEP, here are a few things that could be done to improve the PET google spreadsheet:

TO DO

• add new items that are in BIDS specs but not in the original guideline (e.g PET modality, manufacturer, scanner...)
• make sure that output units are mentioned in the spreadsheet
• improve the lists of responses choices based on the suggestions from the BIDS PET
• improve the lists of responses choices for units based on the suggestions from the BIDS PET
• use the key from the BIDS PET jsons as item names facilitate things down the line

BIDS PET section: done

• info
• radiochem
• time
• recon
• blood

BIDS PET section: cross-checked

• info
• radiochem
• time
• recon
• blood