Myelin Water Fraction
Sum short-T2 component amplitudes relative to a supplied fitted relaxometry spectrum; the short-pool cutoff is caller supplied and amplitudes are not fitted here.
Description
A fitted relaxation spectrum distributes signal amplitude among T2 components.
A fitted relaxation spectrum distributes signal amplitude among T2 components. A short-component fraction can serve as a myelin-water measure under an appropriate acquisition and model.
The tool returns shortComponentAmplitude (short component amplitude); totalComponentAmplitude (total component amplitude); myelinWaterFraction (myelin water fraction). Input measurements and model parameters are supplied by the caller; the tool computes the stated summary rather than acquiring those measurements.
When to use Myelin Water Fraction
Use Myelin Water Fraction when you already have componentT2Ms, componentAmplitudes, shortT2UpperMs and want shortComponentAmplitude, totalComponentAmplitude, myelinWaterFraction. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.
How to use Myelin Water Fraction and understand its results
- Enter componentT2Ms, componentAmplitudes, shortT2UpperMs 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 shortComponentAmplitude, totalComponentAmplitude, myelinWaterFraction. 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 |
|---|---|---|---|
| componentT2Ms | Component t2 ms | list of number | Required |
| componentAmplitudes | Component amplitudes | list of number | Required |
| shortT2UpperMs | Short t2 upper ms | number | Required |
Require strictly increasing positive T2 values, nonnegative aligned amplitudes and positive total amplitude. Include components exactly at the supplied short-T2 cutoff.
fraction = Σamplitudes where T2≤cutoff / Σall amplitudes The symbols refer to the supplied quantities or generated values described above; unit conversions and comparison boundaries follow the stated implementation.
{
"input": {
"componentT2Ms": [
10,
30,
100
],
"componentAmplitudes": [
2,
3,
5
],
"shortT2UpperMs": 40
},
"output": {
"shortComponentAmplitude": 5,
"totalComponentAmplitude": 10,
"myelinWaterFraction": 0.5
}
}Limitations and assumptions
The tool neither fits a relaxation spectrum nor validates a myelin interpretation or acquisition-specific cutoff.
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
Myelination Index: Compute reference-normalized T1w/T2w ROI ratios as an explicit myelin-sensitive imaging index; intensity bias correction is external and this is not a myelin fraction. G-Ratio: Compute the aggregate g-ratio sqrt(AVF/(AVF+MVF)) from calibrated volume fractions; not an arithmetic average of individual axon diameter ratios.
Methodological background: Whole-Brain In-vivo Measurements of the Axonal G-Ratio in a Group of 37 Healthy Volunteers.1
References
-
Whole-Brain In-vivo Measurements of the Axonal G-Ratio in a Group of 37 Healthy Volunteers — Mohammadi et al.; Frontiers in Neuroscience
Similar or alternative tools
- Myelination Index
Compute reference-normalized T1w/T2w ROI ratios as an explicit myelin-sensitive imaging index; intensity bias correction is external and this is not a myelin fraction.
- G-Ratio
Compute the aggregate g-ratio sqrt(AVF/(AVF+MVF)) from calibrated volume fractions; not an arithmetic average of individual axon diameter ratios.