Color Coded Fractional Anisotropy
Compute FA-weighted absolute principal-direction RGB and rounded 8-bit channels; coordinate-axis orientation must match the caller’s image convention.
Description
Direction-encoded color weights absolute principal-direction components by fractional anisotropy.
Direction-encoded color weights absolute principal-direction components by fractional anisotropy. The mapping assigns the three supplied coordinate axes to RGB in their supplied order.
The tool returns fractionalAnisotropy (fractional anisotropy); rgbFractions (rgb fractions); rgb8Bit (rgb8 bit). Input measurements and model parameters are supplied by the caller; the tool computes the stated summary rather than acquiring those measurements.
When to use Color Coded Fractional Anisotropy
Use Color Coded Fractional Anisotropy when you already have eigenvalues, principalDirection and want fractionalAnisotropy, rgbFractions, rgb8Bit. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.
How to use Color Coded Fractional Anisotropy and understand its results
- Enter eigenvalues, principalDirection using the field table below. Match the units, ordering and data boundaries described in the calculation.
- Run the tool after checking the stated bounds and matching paired observations or categories. A malformed request gives a tool error rather than a usable measurement.
- Read fractionalAnisotropy, rgbFractions, rgb8Bit. Use the calculation and interpretation below to distinguish amounts, ratios, signs and decision flags where applicable.
- Review the supplied parameters and assumptions before using the result in a report or comparing it with another observation.
| Input field | Meaning | Value type and bounds | Requirement |
|---|---|---|---|
| eigenvalues | Eigenvalues | list of number | Required |
| principalDirection | Principal direction | list of number | Required |
Require a nonzero three-component direction and three valid nonnegative tensor eigenvalues with nonzero norm. Normalize direction before applying FA.
RGBfractions = FA × abs(direction)/||direction||; RGB8 = round(255×RGBfractions) The symbols refer to the supplied quantities or generated values described above; unit conversions and comparison boundaries follow the stated implementation.
{
"input": {
"eigenvalues": [
2,
0,
0
],
"principalDirection": [
-1,
0,
0
]
},
"output": {
"fractionalAnisotropy": 1,
"rgbFractions": [
1,
0,
0
],
"rgb8Bit": [
255,
0,
0
]
}
}Limitations and assumptions
The eigenvector is supplied and is not checked against the tensor. Axis orientation must be known; direction signs are intentionally discarded.
Numerical inputs must be finite. The tool checks its declared input shape and calculation constraints; those checks do not verify the quality, calibration or representativeness of the supplied observations.
Alternative or Complementary methods
Average Fractional Anisotropy: Compute voxel FA from nonnegative tensor eigenvalues and an ROI-weighted average, rather than averaging tensor eigenvalues before deriving FA. Average Mean Diffusivity: Derive mean diffusivity from each diffusion tensor eigenvalue triplet and aggregate supplied ROI weights; eigenvalues share one caller-selected diffusivity unit.
Methodological background: DTIFIT: diffusion tensor output measures.1
References
-
DTIFIT: diffusion tensor output measures — FMRIB Software Library developers
Similar or alternative tools
- Average Fractional Anisotropy
Compute voxel FA from nonnegative tensor eigenvalues and an ROI-weighted average, rather than averaging tensor eigenvalues before deriving FA.
- Average Mean Diffusivity
Derive mean diffusivity from each diffusion tensor eigenvalue triplet and aggregate supplied ROI weights; eigenvalues share one caller-selected diffusivity unit.