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[ENH] Add DWI recommended metadata #2309

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[ENH] Add DWI recommended metadata #2309

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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
7af905f
Update field names and units based on feedback
kabilar Jan 26, 2026
eb380c5
Merge branch 'master' of https://github.com/bids-standard/bids-specif…
kabilar Jan 26, 2026
6851fa9
Fix example
kabilar Jan 27, 2026
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2 changes: 2 additions & 0 deletions src/modality-specific-files/magnetic-resonance-imaging-data.md
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Expand Up @@ -912,6 +912,8 @@ JSON example:

```JSON
{
"DiffGradientDuration": 11.0,
"DiffGradientSeparation": 15.2,
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@effigies effigies Jan 16, 2026

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We don't generally use abbreviations. I would say either "DiffusionGradientDuration/Separation" or "GradientDuration/Separation". I would probably prefer the latter if the terms are unambiguous within a diffusion context and wouldn't refer to something else in another context BIDS is likely to touch on.

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@kabilar kabilar Jan 23, 2026

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Thanks @effigies. Just avoid any potential future confusion, I would prefer "DiffusionGradientDuration/Separation".

@ayendiki @Tinggong What do you think?

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@arokem arokem Jan 23, 2026

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I don't necessarily like the word "separation", which to me implies the interval between the end of one pulse and the beginning of the other pulse. Other words to potentially use here are "interval", or "offset". I do wonder if given their prevalence in the literature, BigDelta and SmallDelta wouldn't be clearer. Also, I do believe that this is a redefinition of something that could already be captured by MixingTime: https://bids-specification.readthedocs.io/en/stable/glossary.html#mixingtime-metadata?

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@arokem arokem Jan 23, 2026

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I see this as related to #2311

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@mharms mharms Jan 23, 2026

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I'm not familiar with how diffusion sensitization plays out in a "double spin echo" diffusion weighted sequence, but are MixingTime and BigDelta really the same thing?

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@arokem arokem Jan 23, 2026

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The timing parameters are defined quite differently for "double" or "twice refocused" spin echo sequences, see https://onlinelibrary.wiley.com/doi/10.1002/mrm.10308. IIUC (see Fig 1 therein), there is no "BigDelta" in these sequences, and the intensity of the gradients is somehow integrated across all those small deltas, so I think that's to be handled separately, maybe in the advanced dMRI BEP.

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@mharms mharms Jan 23, 2026

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So then, the existing MixingTime is not appropriate here, right?

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@kabilar kabilar Jan 23, 2026

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I am not too familiar with MixingTime but this paper declares the mixing time, gradient separation, and gradient duration as separate values:

...mixing time TM=173.0 ms, gradient separation Δ=185.8 ms and a gradient duration of δ=5.4ms.

"PhaseEncodingDirection": "j-",
"TotalReadoutTime": 0.095,
"B0FieldSource": ["phasediff_fmap0", "pepolar_fmap0"]
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18 changes: 18 additions & 0 deletions src/schema/objects/metadata.yaml
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Expand Up @@ -882,6 +882,24 @@ 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.
type: number
unit: ms
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.
type: number
unit: ms
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