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- \begin{document}
- Results included in this manuscript come from preprocessing performed
- using \emph{fMRIPrep} 20.1.1+79.g1a72777b (\citet{fmriprep1};
- \citet{fmriprep2}; RRID:SCR\_016216), which is based on \emph{Nipype}
- 1.5.0 (\citet{nipype1}; \citet{nipype2}; RRID:SCR\_002502).
- \begin{description}
- \item[Anatomical data preprocessing]
- A total of 2 T1-weighted (T1w) images were found within the input BIDS
- dataset. All of them were corrected for intensity non-uniformity (INU)
- with \texttt{N4BiasFieldCorrection} \citep{n4}, distributed with ANTs
- 2.2.0 \citep[RRID:SCR\_004757]{ants}. The T1w-reference was then
- skull-stripped with a \emph{Nipype} implementation of the
- \texttt{antsBrainExtraction.sh} workflow (from ANTs), using OASIS30ANTs
- as target template. Brain tissue segmentation of cerebrospinal fluid
- (CSF), white-matter (WM) and gray-matter (GM) was performed on the
- brain-extracted T1w using \texttt{fast} \citep[FSL 5.0.9,
- RRID:SCR\_002823,][]{fsl_fast}. A T1w-reference map was computed after
- registration of 2 T1w images (after INU-correction) using
- \texttt{mri\_robust\_template} \citep[FreeSurfer 6.0.1,][]{fs_template}.
- Brain surfaces were reconstructed using \texttt{recon-all}
- \citep[FreeSurfer 6.0.1, RRID:SCR\_001847,][]{fs_reconall}, and the
- brain mask estimated previously was refined with a custom variation of
- the method to reconcile ANTs-derived and FreeSurfer-derived
- segmentations of the cortical gray-matter of Mindboggle
- \citep[RRID:SCR\_002438,][]{mindboggle}. Volume-based spatial
- normalization to two standard spaces (MNI152NLin2009cAsym,
- MNI152NLin6Asym) was performed through nonlinear registration with
- \texttt{antsRegistration} (ANTs 2.2.0), using brain-extracted versions
- of both T1w reference and the T1w template. The following templates were
- selected for spatial normalization: \emph{ICBM 152 Nonlinear
- Asymmetrical template version 2009c} {[}\citet{mni152nlin2009casym},
- RRID:SCR\_008796; TemplateFlow ID: MNI152NLin2009cAsym{]}, \emph{FSL's
- MNI ICBM 152 non-linear 6th Generation Asymmetric Average Brain
- Stereotaxic Registration Model} {[}\citet{mni152nlin6asym},
- RRID:SCR\_002823; TemplateFlow ID: MNI152NLin6Asym{]},
- \item[Functional data preprocessing]
- For each of the 10 BOLD runs found per subject (across all tasks and
- sessions), the following preprocessing was performed. First, a reference
- volume and its skull-stripped version were generated using a custom
- methodology of \emph{fMRIPrep}. Susceptibility distortion correction
- (SDC) was omitted. The BOLD reference was then co-registered to the T1w
- reference using \texttt{bbregister} (FreeSurfer) which implements
- boundary-based registration \citep{bbr}. Co-registration was configured
- with six degrees of freedom. Head-motion parameters with respect to the
- BOLD reference (transformation matrices, and six corresponding rotation
- and translation parameters) are estimated before any spatiotemporal
- filtering using \texttt{mcflirt} \citep[FSL 5.0.9,][]{mcflirt}. BOLD
- runs were slice-time corrected using \texttt{3dTshift} from AFNI
- 20160207 \citep[RRID:SCR\_005927]{afni}. The BOLD time-series were
- resampled onto the following surfaces (FreeSurfer reconstruction
- nomenclature): \emph{fsaverage}. The BOLD time-series (including
- slice-timing correction when applied) were resampled onto their
- original, native space by applying the transforms to correct for
- head-motion. These resampled BOLD time-series will be referred to as
- \emph{preprocessed BOLD in original space}, or just \emph{preprocessed
- BOLD}. \emph{Grayordinates} files \citep{hcppipelines} containing 91k
- samples were also generated using the highest-resolution
- \texttt{fsaverage} as intermediate standardized surface space. Automatic
- removal of motion artifacts using independent component analysis
- \citep[ICA-AROMA,][]{aroma} was performed on the \emph{preprocessed BOLD
- on MNI space} time-series after removal of non-steady state volumes and
- spatial smoothing with an isotropic, Gaussian kernel of 6mm FWHM
- (full-width half-maximum). Corresponding ``non-aggresively'' denoised
- runs were produced after such smoothing. Additionally, the
- ``aggressive'' noise-regressors were collected and placed in the
- corresponding confounds file. Several confounding time-series were
- calculated based on the \emph{preprocessed BOLD}: framewise displacement
- (FD), DVARS and three region-wise global signals. FD was computed using
- two formulations following Power (absolute sum of relative motions,
- \citet{power_fd_dvars}) and Jenkinson (relative root mean square
- displacement between affines, \citet{mcflirt}). FD and DVARS are
- calculated for each functional run, both using their implementations in
- \emph{Nipype} \citep[following the definitions by][]{power_fd_dvars}.
- The three global signals are extracted within the CSF, the WM, and the
- whole-brain masks. Additionally, a set of physiological regressors were
- extracted to allow for component-based noise correction
- \citep[\emph{CompCor},][]{compcor}. Principal components are estimated
- after high-pass filtering the \emph{preprocessed BOLD} time-series
- (using a discrete cosine filter with 128s cut-off) for the two
- \emph{CompCor} variants: temporal (tCompCor) and anatomical (aCompCor).
- tCompCor components are then calculated from the top 2\% variable voxels
- within the brain mask. For aCompCor, three probabilistic masks (CSF, WM
- and combined CSF+WM) are generated in anatomical space. The
- implementation differs from that of Behzadi et al.~in that instead of
- eroding the masks by 2 pixels on BOLD space, the aCompCor masks are
- subtracted a mask of pixels that likely contain a volume fraction of GM.
- This mask is obtained by dilating a GM mask extracted from the
- FreeSurfer's \emph{aseg} segmentation, and it ensures components are not
- extracted from voxels containing a minimal fraction of GM. Finally,
- these masks are resampled into BOLD space and binarized by thresholding
- at 0.99 (as in the original implementation). Components are also
- calculated separately within the WM and CSF masks. For each CompCor
- decomposition, the \emph{k} components with the largest singular values
- are retained, such that the retained components' time series are
- sufficient to explain 50 percent of variance across the nuisance mask
- (CSF, WM, combined, or temporal). The remaining components are dropped
- from consideration. The head-motion estimates calculated in the
- correction step were also placed within the corresponding confounds
- file. The confound time series derived from head motion estimates and
- global signals were expanded with the inclusion of temporal derivatives
- and quadratic terms for each \citep{confounds_satterthwaite_2013}.
- Frames that exceeded a threshold of 0.5 mm FD or 1.5 standardised DVARS
- were annotated as motion outliers. All resamplings can be performed with
- \emph{a single interpolation step} by composing all the pertinent
- transformations (i.e.~head-motion transform matrices, susceptibility
- distortion correction when available, and co-registrations to anatomical
- and output spaces). Gridded (volumetric) resamplings were performed
- using \texttt{antsApplyTransforms} (ANTs), configured with Lanczos
- interpolation to minimize the smoothing effects of other kernels
- \citep{lanczos}. Non-gridded (surface) resamplings were performed using
- \texttt{mri\_vol2surf} (FreeSurfer).
- \end{description}
- Many internal operations of \emph{fMRIPrep} use \emph{Nilearn} 0.6.2
- \citep[RRID:SCR\_001362]{nilearn}, mostly within the functional
- processing workflow. For more details of the pipeline, see
- \href{https://fmriprep.readthedocs.io/en/latest/workflows.html}{the
- section corresponding to workflows in \emph{fMRIPrep}'s documentation}.
- \hypertarget{copyright-waiver}{%
- \subsubsection{Copyright Waiver}\label{copyright-waiver}}
- The above boilerplate text was automatically generated by fMRIPrep with
- the express intention that users should copy and paste this text into
- their manuscripts \emph{unchanged}. It is released under the
- \href{https://creativecommons.org/publicdomain/zero/1.0/}{CC0} license.
- \hypertarget{references}{%
- \subsubsection{References}\label{references}}
- \bibliography{/usr/local/miniconda/lib/python3.7/site-packages/fmriprep/data/boilerplate.bib}
- \end{document}
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