@@ -7,7 +7,7 @@ Outputs of *PETPrep*
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---------------------
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*PETPrep * outputs conform to the :abbr: `BIDS ( brain imaging data structure ) `
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Derivatives specification (see `BIDS Derivatives `_, along with the
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- upcoming `BEP 011 `_ and `BEP 012 `_).
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+ upcoming `BEP 011 `_ and `BEP 023 `_).
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*PETPrep * generates three broad classes of outcomes:
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1. **Visual QA (quality assessment) reports **:
@@ -20,9 +20,9 @@ upcoming `BEP 011`_ and `BEP 012`_).
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have been applied.
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For example, :abbr: `INU ( intensity non-uniformity ) `-corrected versions
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of the T1-weighted image (per subject), the brain mask,
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- or :abbr: ` BOLD ( blood-oxygen level dependent ) `
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- images after head-motion correction, slice-timing correction and aligned into
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- the same-subject's T1w space or in some standard space.
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+ or dynamic PET series after motion correction (and optional partial volume
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+ correction) aligned into the same-subject's T1w space or in some
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+ standard space.
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3. **Confounds **: this is a special family of derivatives that can be utilized
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to inform subsequent denoising steps.
@@ -57,14 +57,14 @@ The log directory contains `citation boilerplate`_ text.
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``dataset_description.json `` is a metadata file in which PETPrep
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records metadata recommended by the BIDS standard.
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- This layout, now the default, may be explicitly specified with the
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+ This default layout , may be explicitly specified with the
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``--output-layout bids `` command-line option.
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- For compatibility with versions of PETPrep prior to 21.0, the
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+ For compatibility with versions of fMRIPrep prior to 21.0, the
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`legacy layout `_ is available via ``--output-layout legacy ``.
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Processing level
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----------------
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- As of version 23.2.0 , PETPrep supports three levels of derivatives:
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+ As of version 0.0.1 , PETPrep supports three levels of derivatives:
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* ``--level minimal ``: This processing mode aims to produce the smallest
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working directory and output dataset possible, while enabling all further
@@ -73,13 +73,9 @@ As of version 23.2.0, PETPrep supports three levels of derivatives:
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preprocessing can be assessed. Because no resampling is done, confounds
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and carpetplots will be missing from the reports.
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* ``--level resampling ``: This processing mode aims to produce additional
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- derivatives that enable third-party resampling, resampling PET series
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+ derivatives that enable third-party resampling, resampling PET data
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in the working directory as needed, but these are not saved to the output
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directory.
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- The ``--me-output-echos `` flag will be enabled at this level, in which
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- case the individual echos will be saved to the working directory after
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- slice-timing correction, head-motion correction, and susceptibility
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- distortion correction.
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* ``--level full ``: This processing mode aims to produce all derivatives
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that have previously been a part of the PETPrep output dataset.
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This is the default processing level.
@@ -197,7 +193,7 @@ and lookup tables are provided. ::
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desc-aparcaseg_dseg.tsv
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Copies of the ``fsaverage `` subjects distributed with the running version of
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- FreeSurfer are copied into this subjects directory, if any functional data are
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+ FreeSurfer are copied into this subjects directory, if any PET data are
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sampled to those subject spaces.
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Note that the use of ``sourcedata/ `` recognizes FreeSurfer derivatives as an input to
@@ -206,16 +202,14 @@ This is strictly true when pre-computed FreeSurfer derivatives are provided eith
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the ``sourcedata/ `` directory or passed via the ``--fs-subjects-dir `` flag;
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if PETPrep runs FreeSurfer, then there is a mutual dependency.
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- Functional derivatives
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+ PET derivatives
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~~~~~~~~~~~~~~~~~~~~~~
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- Functional derivatives are stored in the ``func/ `` subfolder.
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- All derivatives contain ``task-<task_label> `` (mandatory) and ``run-<run_index> `` (optional), and
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- these will be indicated with ``[specifiers] ``::
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+ PET derivatives are stored in the ``pet/ `` subfolder.
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sub-<subject_label>/
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func/
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- sub-<subject_label>_[specifiers] _space-<space_label>_desc-brain_mask.nii.gz
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- sub-<subject_label>_[specifiers] _space-<space_label>_desc-preproc_pet.nii.gz
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+ sub-<subject_label>_space-<space_label>_desc-brain_mask.nii.gz
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+ sub-<subject_label>_space-<space_label>_desc-preproc_pet.nii.gz
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.. note ::
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@@ -251,27 +245,6 @@ image and affine transform::
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Coregistration outputs are part of the *minimal * processing level.
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- **Fieldmap registration **.
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-
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- If a fieldmap is used for the correction of a PET series, then a registration
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- is calculated between the PET series and the fieldmap. If, for example, the fieldmap
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- is identified with ``"B0Identifier": "TOPUP" ``, the generated transform will be named::
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-
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- sub-<subject_label>/
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- func/
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- sub-<subject_label>_[specifiers]_from-petref_to-TOPUP_mode-image_xfm.txt
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-
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- If the association is discovered through the ``IntendedFor `` field of the
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- fieldmap metadata, then the transform will be given an auto-generated name::
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-
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- sub-<subject_label>/
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- func/
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- sub-<subject_label>_[specifiers]_from-petref_to-auto000XX_mode-image_xfm.txt
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-
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- .. note ::
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-
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- Fieldmap registration outputs are part of the *minimal * processing level.
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-
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**Regularly gridded outputs (images) **.
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Volumetric output spaces labels (``<space_label> `` above, and in the following) include
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``T1w `` and ``MNI152NLin2009cAsym `` (default).
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func/
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sub-<subject_label>_[specifiers]_space-T1w_desc-aparcaseg_dseg.nii.gz
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sub-<subject_label>_[specifiers]_space-T1w_desc-aseg_dseg.nii.gz
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- sub-<subject_label>_[specifiers]_hemi-[LR]_space-<space_label>_bold .func.gii
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+ sub-<subject_label>_[specifiers]_hemi-[LR]_space-<space_label>_pet .func.gii
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Surface output spaces include ``fsnative `` (full density subject-specific mesh),
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``fsaverage `` and the down-sampled meshes ``fsaverage6 `` (41k vertices) and
@@ -361,30 +334,25 @@ also included.
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Confounds
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---------
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- The :abbr: `BOLD ( blood-oxygen level dependent ) ` signal measured with fMRI is a mixture of fluctuations
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- of both neuronal and non-neuronal origin.
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- Neuronal signals are measured indirectly as changes in the local concentration of oxygenated hemoglobin.
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- Non-neuronal fluctuations in fMRI data may appear as a result of head motion, scanner noise,
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- or physiological fluctuations (related to cardiac or respiratory effects).
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- For a detailed review of the possible sources of noise in the BOLD signal, refer to [Greve2013 ]_.
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+ The PET signal is a mixture of fluctuations of both neuronal and non-neuronal origin.
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+ Non-neuronal fluctuations in PET data may appear as a result of head motion or scanner noise.
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*Confounds * (or nuisance regressors) are variables representing fluctuations with a potential
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non-neuronal origin.
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- Such non-neuronal fluctuations may drive spurious results in fMRI data analysis,
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- including standard activation :abbr: `GLM ( General Linear Model ) ` and functional connectivity analyses.
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+ Such non-neuronal fluctuations may drive spurious results in PET data analysis.
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It is possible to minimize confounding effects of non-neuronal signals by including
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them as nuisance regressors in the GLM design matrix or regressing them out from
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- the fMRI data - a procedure known as *denoising *.
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- There is currently no consensus on an optimal denoising strategy in the fMRI community.
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+ the PET data - a procedure known as *denoising *.
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+ There is currently no consensus on an optimal denoising strategy in the PET community.
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Rather, different strategies have been proposed, which achieve different compromises between
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how much of the non-neuronal fluctuations are effectively removed, and how much of neuronal fluctuations
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are damaged in the process.
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The *PETPrep * pipeline generates a large array of possible confounds.
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The most well established confounding variables in neuroimaging are the six head-motion parameters
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(three rotations and three translations) - the common output of the head-motion correction
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- (also known as *realignment *) of popular fMRI preprocessing software
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- such as SPM _ or FSL _ .
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+ (also known as *realignment *) of popular PET preprocessing software
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+ such as SPM _ or FreeSurfer _ .
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Beyond the standard head-motion parameters, the PETPrep pipeline generates a large array
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of possible confounds, which enable researchers to choose the most suitable denoising
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strategy for their downstream analyses.
@@ -397,7 +365,7 @@ Such tabular files may include over 100 columns of potential confound regressors
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Do not include all columns of ``~_desc-confounds_timeseries.tsv `` table
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into your design matrix or denoising procedure.
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Filter the table first, to include only the confounds (or components thereof)
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- you want to remove from your fMRI signal.
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+ you want to remove from your PET signal.
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The choice of confounding variables may depend on the analysis you want to perform,
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and may be not straightforward as no gold standard procedure exists.
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For a detailed description of various denoising strategies and their performance,
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- ``dvars `` - the derivative of RMS variance over voxels (or :abbr: `DVARS ( derivative of
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RMS variance over voxels ) `) [Power2012 ]_;
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- ``std_dvars `` - standardized :abbr: `DVARS ( derivative of RMS variance over voxels ) `;
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- - ``non_steady_state_outlier_XX `` - columns indicate non-steady state volumes with a single
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- ``1 `` value and ``0 `` elsewhere (*i.e. *, there is one ``non_steady_state_outlier_XX `` column per
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- outlier/volume).
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Detected outliers can be further removed from time series using methods such as:
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volume *censoring * - entirely discarding problematic time points [Power2012 ]_,
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Legacy layout
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-------------
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- Prior to PETPrep 21.0, the following organizational structure was used::
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+ Prior to tools such as fMRIPrep 21.0, the following organizational structure was used::
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<output_dir>/
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- petprep /
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+ fmriprep /
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freesurfer/
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Although this has the advantage of keeping all outputs together,
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- it ensured that the output of PETPrep could not itself be a BIDS derivative dataset,
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+ it ensured that the output of fMRIPrep could not itself be a BIDS derivative dataset,
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only contain one.
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To restore this behavior, use the ``--output-layout legacy `` command-line option.
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