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[ENH] Add combined DWI scheme #2320

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5ef201d
Add recommended DWI metadata
kabilar Jan 16, 2026
69fc18f
Update metadata
kabilar Jan 16, 2026
e81113f
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jan 16, 2026
6feca23
Add extensions
kabilar Jan 22, 2026
d5c4660
Add combined DWI scheme
kabilar Jan 22, 2026
431658c
Fix format
kabilar Jan 22, 2026
b002ea8
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jan 22, 2026
f45379c
Merge branch 'dwi-parameters' of https://github.com/kabilar/bids-spec…
kabilar Jan 23, 2026
789df67
Update data types
kabilar Jan 23, 2026
a9dcba4
Remove extensions
kabilar Jan 23, 2026
5345f35
Move values from paired files to the sidecar JSON file
kabilar Jan 23, 2026
836818d
Merge branch 'dwi-combined' of https://github.com/kabilar/bids-specif…
kabilar Jan 23, 2026
9a3ae7b
Remove extensions
kabilar Jan 23, 2026
177d1a7
Merge branch 'master' of https://github.com/bids-standard/bids-specif…
kabilar Jan 23, 2026
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34 changes: 34 additions & 0 deletions src/modality-specific-files/magnetic-resonance-imaging-data.md
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Expand Up @@ -900,6 +900,38 @@ A guide for using macros can be found at
}
) }}

### Combined DWI schemes

Some DWI schemes are acquired by varying parameters including the
[echo time (TE)](../glossary.html#objects.metadata.EchoTime),
[duration of the diffusion-encoding gradient pulse (δ)](../glossary.md#diffgradientduration-metadata),
the [time between the leading edges of two successive diffusion-encoding gradient pulses (Δ)](../glossary.md#diffgradientseparation-metadata);
in addition to varying the diffusion-encoding weightings (b-values) and
gradients (b-vectors).

For instance, in a single run the
[Connectome 2.0 scanner](https://doi.org/10.1016/j.neuroimage.2021.118530)
collects DWI volumes where the TE, δ, and Δ parameters can be varied. The DWI
volumes are concatenated in a single file and processed together with the TE, δ,
and Δ values.

BIDS permits saving the TE, δ, and Δ values corresponding to the *N*
volumes in the NIfTI file. The TE, δ, and Δ values MAY be stored as an array in the sidecar JSON file using the `EchoTime`, `DiffGradientDuration`, and `DiffGradientSeparation` fields, respectively.
If a single TE, δ, or Δ value is used for the entire acquisition, the value
MAY be stored as a single number in the sidecar JSON file using the `EchoTime`, `DiffGradientDuration`, or `DiffGradientSeparation` fields, respectively.
The TE, δ, and Δ values are specified in seconds, milliseconds, and
milliseconds, respectively.

The `EchoTime`, `DiffGradientDuration`, and `DiffGradientSeparation` fields MAY be
saved in the sidecar JSON file on any level of the directory structure and thus define those values for
all sessions and/or subjects in one place (see
[the inheritance principle](../common-principles.md#the-inheritance-principle)).

As an exception to the [common principles](../common-principles.md#definitions)
that parameters are constant across runs, the TE, δ, and Δ values (stored
within the `EchoTime`, `DiffGradientDuration`, and `DiffGradientSeparation`
fields) MAY change across the DWI run.

### Other RECOMMENDED metadata

<!-- This block generates a metadata table.
Expand All @@ -922,6 +954,8 @@ JSON example:

```JSON
{
"DiffGradientDuration": 11.0,
"DiffGradientSeparation": 15.2,
"PhaseEncodingDirection": "j-",
"TotalReadoutTime": 0.095,
"B0FieldSource": ["phasediff_fmap0", "pepolar_fmap0"]
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32 changes: 32 additions & 0 deletions src/schema/objects/metadata.yaml
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Expand Up @@ -929,6 +929,38 @@ DewarPosition:
`"upright"`, `"supine"` or `"degrees"` of angle from vertical:
for example on CTF systems, `"upright=15°, supine=90°"`.
type: string
DiffGradientDuration:
name: DiffGradientDuration
display_name: Diffusion Gradient Duration
description: |
In the context of a diffusion-weighted pulsed gradient spin echo sequence,
corresponds to the duration of a diffusion-encoding gradient pulse (δ),
specified in milliseconds.
anyOf:
- type: number
unit: ms
exclusiveMinimum: 0
- type: array
items:
type: number
unit: ms
exclusiveMinimum: 0
DiffGradientSeparation:
name: DiffGradientSeparation
display_name: Diffusion Gradient Separation
description: |
In the context of a diffusion-weighted pulsed gradient spin echo sequence,
corresponds to the time between the leading edges of two successive
diffusion-encoding gradient pulses (Δ), specified in milliseconds.
anyOf:
- type: number
unit: ms
exclusiveMinimum: 0
- type: array
items:
type: number
unit: ms
exclusiveMinimum: 0
DigitizedHeadPoints:
name: DigitizedHeadPoints
display_name: Digitized Head Points
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2 changes: 2 additions & 0 deletions src/schema/rules/sidecars/dwi.yaml
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Expand Up @@ -16,5 +16,7 @@ MRIDiffusionOtherMetadata:
- suffix == "dwi"
- match(extension, "^\.nii(\.gz)?$")
fields:
DiffGradientDuration: recommended
DiffGradientSeparation: recommended
PhaseEncodingDirection: recommended
TotalReadoutTime: recommended