# Diffusion Tensor Imaging

Compute DTI metrics from the eigenvalues of a diffusion tensor online

In this page you can compute any tensor metric from the eigenvalues of a diffusion tensor. Insert the values of the three eigenvalues in decreasing order, then click the **HyperSpatioTensoral Button**.

Lambda 1:

Lambda 2:

Lambda 3:

Metric | Value |
---|---|

Mean Diffusivity | |

Fractional Anisotropy | |

Linearity | |

Planarity | |

Sphericity | |

Volume Ratio |

### Mean Diffusivity

- Used in early stroke detection (it is sensitive to the presence of edema).
- High MD in CSF (\(9.6 \cdot 10^{-3} mm^2/s\)).
- Lower MD in GM and WM (between \(1.95\cdot 10^{-3} mm^2/s\) and \(2.2\cdot10^{-3} mm^2/s\)).
- Water at 37° C has MD = \(9 \cdot 10^{-3} mm^2/s\) .
- In ventricles or edema MD can be higher than in water due to water transportation.

### Fractional Anisotropy

- Measures how much of the observed diffusion is due to the anisotropy.
- A ball has \(FA=0\).
- It is the distance between the tensor`s ellipsoid shape and a spherical isotropic tensor.
- Very often mistaken for a measure of WM integrity, but it is not.

### Linearity

- It measures how much the tensor is elongated along the
*main*axis.

### Planarity

- It measures how much the tensor is close to a plane.
- If \(C_P\) is high, the concept of
*principal fiber direction*is not well defined.

### Sphericity

- It measures how much the tensor is close to being a sphere.
- If \(C_S\) is high, the concept of
*principal fiber direction*is not well defined. - Notice that \(C_L + C_P + C_S = 1\).

### Volume Ratio

- It is the ratio between the volume of the ellipsoid and that of a sphere with the same MD.
- It tells you how much the tensor is far from being a sphere.