Currently, writing sessions.tsv for converter OASIS-to-BIDS takes two steps :

• creating a dictionary :
  

  clinica/clinica/iotools/converters/oasis_to_bids/oasis_to_bids_utils.py

  Lines 14 to 19 in 6f81685

  	def create_sessions_dict(
  	clinical_data_dir: Path,
  	bids_dir: Path,
  	clinical_specifications_folder: Path,
  	bids_ids: Iterable[str],
  	) -> dict:

• modifying it to be a dataframe and writing it :
  

  clinica/clinica/iotools/converters/oasis_to_bids/oasis_to_bids_utils.py

  Line 103 in 6f81685

  def write_sessions_tsv(bids_dir: Path, sessions_dict: dict) -> None:

Following #1326, the dictionary produced by the first function should not be needed anywhere else so a data frame can be used right away and the steps can be simplified.