Skip to content

Commit

Permalink
Diffusion models: Forbid negative spherical coordinate radius
Browse files Browse the repository at this point in the history
  • Loading branch information
@Lestropie
Lestropie committed Apr 26, 2024
1 parent a2c35b8 commit 8672cbe
Showing 1 changed file with 9 additions and 10 deletions.
19 changes: 9 additions & 10 deletions src/derivatives/05-diffusion-derivatives.md
View file
Original file line number Diff line number Diff line change
Expand Up @@ -129,7 +129,7 @@ see [parameter metadata](#parameter-metadata).
and reference frame for angles:

1. Distance from origin,
encoding some parameter of interest.
encoding some non-negative parameter of interest.

1. Inclination / polar angle in radians,
relative to the zenith direction being the positive direction of the *third* reference axis
Expand Down Expand Up @@ -163,9 +163,8 @@ see [parameter metadata](#parameter-metadata).

1. Value per orientation

The *norm* of the 3-vector encodes some parameter of interest,
The *norm* of the 3-vector encodes some non-negative parameter of interest,
while its normalized form encodes an orientation on the unit sphere.
Note that only non-negative parameters may be encoded in this form.

1. Orientations only

Expand Down Expand Up @@ -279,13 +278,13 @@ Dictionary `"Model["Parameters"]"` has the following reserved keywords that may
The following table defines reserved fields relevant to individual model parameters.
Some fields are applicable only to specific [orientation encoding types](#orientation-encoding-types).

| **Key name** | Relevant [orientation encoding types](#orientation-encoding-types) | **Description** |
| ------------------- | ----------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| BootstrapAxis | Any | OPTIONAL. Integer. If multiple realisations of a given parameter are stored in a NIfTI image, this field nominates the image axis (indexed from zero) along which those multiple realisations are stored. |
| Description | Any | OPTIONAL. String. Text description of what model parameter is encoded in the corresponding data file. |
| NonNegativity | All except [spherical coordinates](#encoding-spherical) and [unit 3-vectors](#encoding-3vector) | OPTIONAL. String. Options are: { `regularized`, `constrained` }. Specifies whether, during model fitting, the parameter was regularised to not take extreme negative values, or was explicitly forbidden from taking negative values. |
| OrientationEncoding | Any | REQUIRED if dimensionality of NIfTI image is greater than three. Dictionary. Provides information requisite to the interpretation of orientation information encoded in each voxel; more details below. |
| ResponseFunction | [Spherical harmonics](#encoding-sh) | OPTIONAL. Dictionary. Specifies a response function that was utilised by a deconvolution algorithm; more details below. |
| **Key name** | Relevant [orientation encoding types](#orientation-encoding-types) | **Description** |
| ------------------- | ------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| BootstrapAxis | Any | OPTIONAL. Integer. If multiple realisations of a given parameter are stored in a NIfTI image, this field nominates the image axis (indexed from zero) along which those multiple realisations are stored. |
| Description | Any | OPTIONAL. String. Text description of what model parameter is encoded in the corresponding data file. |
| NonNegativity | All except [spherical coordinates](#encoding-spherical) and [3-vectors](#encoding-3vector) | OPTIONAL. String. Options are: { `regularized`, `constrained` }. Specifies whether, during model fitting, the parameter was regularised to not take extreme negative values, or was explicitly forbidden from taking negative values. |
| OrientationEncoding | Any | REQUIRED if dimensionality of NIfTI image is greater than three. Dictionary. Provides information requisite to the interpretation of orientation information encoded in each voxel; more details below. |
| ResponseFunction | [Spherical harmonics](#encoding-sh) | OPTIONAL. Dictionary. Specifies a response function that was utilised by a deconvolution algorithm; more details below. |

Dictionary `"OrientationEncoding"` has the following reserved keywords:

Expand Down

0 comments on commit 8672cbe

Please sign in to comment.