Radial Diffusivity MRI Calculator

Actual radial diffusivity RD=(λ2+λ3)/2, independently fit positive-semi definite diffusion tensor λ1≥λ2≥λ3≥0, units retained. Not mean of all3or eigen fit from signal.

Description

Radial diffusivity averages the two smaller eigenvalues of an independently fitted diffusion tensor.

Radial diffusivity averages the two smaller eigenvalues of an independently fitted diffusion tensor.^[1]

This tool accepts exactly three descending nonnegative eigenvalues and returns that average in their unit.

When to use Radial Diffusivity MRI Calculator

This tool accepts exactly three descending nonnegative eigenvalues and returns that average in their unit.

How to use Radial Diffusivity MRI Calculator and how it works

Prepare ordered tensor eigenvalues, using the input definitions and matching units below.
Enter the required fields and run Radial Diffusivity MRI Calculator.
Read result.value using the units, signs and ordering explained below.
Correct any rejected inputs and rerun; interpret the result within the stated model and its assumptions.

Input field	Meaning	Value type	Requirement
actualOrderedTensorEigenvalues	Exactly [lambda1,lambda2,lambda3] in descending nonnegative order, retaining diffusivity units.	array of number	Required; other constraints below

Require exactly three nonnegative independently fitted diffusion-tensor eigenvalues in descending order, allowing ties. Return the mean of the second and third in the supplied diffusivity unit. No signal fitting, eigendecomposition or tissue interpretation occurs.

radialDiffusivity=(lambda2+lambda3)/2

Apply the input ordering, units and branch conditions stated above.

Output field	Meaning	Value type
result	Object containing the calculated or selected fields below.	object
result.value	Mean of the two smaller eigenvalues in their original diffusivity unit.	number

json

{
  "input": {
    "actualOrderedTensorEigenvalues": [
      3,
      2,
      1
    ]
  },
  "output": {
    "result": {
      "value": 1.5
    }
  }
}

Limitations and assumptions

The calculation uses the supplied observations and model inputs. It does not collect measurements, select a reference population or coefficient, or establish that the model applies to the actual case. The stated branch conditions and output units remain part of the result.

All fields require explicit values. Unexpected fields, wrong types, nonfinite numbers and sparse arrays are rejected. Alignment, bounds and supported-token rules are explained above; extremely large inputs or nonfinite results can also fail. Input errors differ from successful false comparisons, unavailable-domain flags and empty match lists.

Alternative or Complementary methods

Use Diffusion Time Calculator for a complementary operation: For rectangular pulsed-gradient spin-echo timing, effective diffusion time differs from the leading-edge separation.

Use Voxel Volume Calculator for a complementary operation: Rectangular voxel volume combines readout size, phase size and actual slice thickness.

References

Radial Diffusivity MRI Calculator — tool.io

Similar or alternative tools

Diffusion Time Calculator
For rectangular pulsed-gradient spin-echo timing, effective diffusion time differs from the leading-edge separation.
Voxel Volume Calculator
Rectangular voxel volume combines readout size, phase size and actual slice thickness.