To cite package 'freesurferformats' in publications use:

Tim Schäfer (2020). freesurferformats: Read and Write 'FreeSurfer'
Neuroimaging File Formats. R package version 0.1.9.
https://CRAN.R-project.org/package=frees...

A BibTeX entry for LaTeX users is

@Manual{,
title = {freesurferformats: Read and Write 'FreeSurfer' Neuroimaging File Formats},
author = {Tim Schäfer},
year = {2020},
note = {R package version 0.1.9,
url = {https://CRAN.R-project.org/package=freesurferformats},
doi = {10.5281/zenodo.3540434},
url = {https://dx.doi.org/10.5281/zenodo.3540434},
}