Imaging data types

This section pertains to imaging data, which characteristically have spatial extent and resolution.

Preprocessed, coregistered and/or resampled volumes

Volumetric preprocessing does not modify the number of dimensions, and so the specifications in Preprocessed or cleaned data apply. In addition, all processed files include the following metadata JSON fields:

Key name Description
SkullStripped REQUIRED. Boolean. Whether the volume was skull stripped (non-brain voxels set to zero) or not.

Masks

Template:

<pipeline_name>/
    sub-<participant_label>/
        anat|func|dwi/
            <source_keywords>[_space-<space>][_desc-<label>]_mask.nii.gz

A binary (1 - inside, 0 - outside) mask in the space defined by <space>. By default (i.e., if no transformation has taken place) the value of space should be set to orig.

JSON metadata fields:

Key name Description
RawSources Same as defined in Introduction, but elevated from OPTIONAL to REQUIRED
Type RECOMMENDED. Short identifier of the mask. Reserved values: Brain - brain mask, Lesion - lesion mask, Face - face mask, ROI - ROI mask

Examples:

func_loc/
    sub-001/
        func/
           sub-001_task-rest_run-1_space-MNI305_desc-PFC_mask.nii.gz
           sub-001_task-rest_run-1_space-MNI305_desc-PFC_mask.json
manual_masks/
    sub-001/
        anat/
            sub-001_desc-tumor_mask.nii.gz
            sub-001_desc-tumor_mask.json

Segmentations and parcellations

Common JSON metadata fields:

Key name Description
Manual OPTIONAL. Boolean. Indicates if the segmenation was performed manually or via an automated process
Atlas OPTIONAL. Which atlas (if any) was used to derive the segmentation.

Discrete Segmentations

Discrete segmentations of brain tissue represent each tissue class with a unique integer label in a 3D volume. See Anatomical Labels for interpretation how integer values map to tissue classes.

Template:

<pipeline_name>/
    sub-<participant_label>/
        anat|func|dwi/
            <source_keywords>[_space-<space>]_dseg.nii.gz

Example:

pipeline/
    sub-001/
        anat/
            sub-001_space-orig_dseg.nii.gz
            sub-001_space-orig_dseg.json

A segmentation could be a binary mask that functions as a discrete label for a single structure. In this case, the label key must be used to specify the corresponding structure. For example:

pipeline/
    sub-001/
        anat/
            sub-001_space-orig_label-GM_dseg.nii.gz

See Anatomical Labels for reserved key values for label.

Probabilistic Segmentations

Probabilistic segmentations of brain tissue represent a single tissue class with values ranging from 0 to 1 in individual 3D volumes or across multiple frames. Similarly to a discrete, binary segmentation, the label key can be used to specify the corresponding structure.

Template:

<pipeline_name>/
    sub-<participant_label>/
        func|anat|dwi/
            <source_keywords>[space-<space>][_label-<label>]_probseg.nii.gz

Example:

pipeline/
    sub-001/
        anat/
            sub-001_space-orig_label-BG_probseg.nii.gz
            sub-001_space-orig_label-WM_probseg.nii.gz

See Anatomical labels for reserved key values for label.

A 4D probabilistic segmentation, in which each frame corresponds to a different tissue class, must provide a label mapping in its JSON sidecar. For example:

pipeline/
    sub-001/
        anat/
            sub-001_space-orig_probseg.nii.gz
            sub-001_space-orig_probseg.json

The JSON sidecar must include the label-map key that specifies a tissue label for each volume:

{
    "LabelMap": [
        "BG",
        "WM",
        "GM"
        ]
}

Values of label need to map to Abbreviations defined in Anatomical Labels.

Surface Parcellations

Discrete parcellations (surface segmentations) of cortical structures should be stored as GIFTI or CIFTI file.

Template:

<pipeline_name>/
    sub-<participant_label>/
        anat/
            <source_keywords>[_hemi-{L|R}][_space-<space>]_dseg.{label.gii|dlabel.nii}

The REQUIRED extension for GIFTI parcellations is .label.gii. The hemi tag is REQUIRED for GIFTI files. For example:

pipeline/
    sub-001/
        anat/
            sub-001_hemi-L_dparc.label.gii
            sub-001_hemi-R_dparc.label.gii

The REQUIRED extension for CIFTI parcellations is .dlabel.nii. For example:

pipeline/
    sub-001/
        anat/
            sub-001_dparc.dlabel.nii
            sub-001_dparc.dlabel.nii

Anatomical Labels

BIDS supplies a standard, generic label-index dictionary, defined in the table below, that contains common tissue classes and can be used to map segmentations (and parcellations) between lookup tables.

Integer value Description Abbreviation (label)
0 Background BG
1 Grey Matter GM
2 White Matter WM
3 Cerebrospinal Fluid CSF
4 Grey and White Matter GWM
5 Bone B
6 Soft Tissue ST
7 Non-brain NB
8 Lesion L
9 Cortical Grey Matter CGM
10 Subcortical Grey Matter SCGM
11 Brainstem BS
12 Cerebellum CBM

These definitions can be overridden (or added to) by providing custom labels in a sidecar <matches>.tsv file, in which <matches> corresponds to segmentation filename.

Example:

pipeline/
    sub-001/
        anat/
            sub-001_space-orig_dseg.nii.gz
            sub-001_space-orig_dseg.tsv

Definitions can also be specified with a top-level dseg.tsv, which propagates to segmentations in relative subdirectories.

Example:

pipeline/
    dseg.tsv
    sub-001/
        anat/
            sub-001_space-orig_dseg.nii.gz

These tsv lookup tables should contain the following columns:

Column name Description
index REQUIRED. The label integer index
name REQUIRED. The unique label name
abbr OPTIONAL. The unique label abbreviation
mapping OPTIONAL. Corresponding integer label in the standard BIDS label lookup
color OPTIONAL. Hexadecimal. Label color for visualization

An example, custom dseg.tsv that defines three labels:

index   name            abbr    color       mapping
100     "Grey Matter"   GM      #ff53bb     1
101     "White Matter"  WM      #2f8bbe     2
102     "Brainstem"     BS      #36de72     11