# PPMI DTI
###### tags: `CVC Lab` `Aaron - 2024`
### PPMI Additional Hacks:(https://hackmd.io/D3JsvYx1TPut1h7uslxLVQ)
#### DTI

The basic concept behind DTI is that water molecules diffuse differently along the tissues depending on its type, integrity, architecture, and presence of barriers, giving information about its orientation and quantitative anisotropy. With DTI analysis it is possible to infer, in each voxel, properties such as the molecular diffusion rate (Mean Diffusivity (MD)) and the directional preference of diffusion (Fractional Anisotropy (FA)). Both of which have already been calculated by PPMI and provided to us as an image. There are other metrics such as the axial (diffusion rate along the main axis of diffusion), and radial (rate of diffusion in the transverse direction) diffusivity which we are not provided directly. Diffusion in White Matter (WM) is less restricted along the axon and tends to be anisotropic (directionally-dependent) whereas in Gray Matter (GM) is usually less anisotropic and in the Cerebrospinal fluid (CSF) is unrestricted in all directions (isotropic)

A raw DTI image is provided in the same dimensions as the MRI image. The pixel values in a DTI image are the three eigenvalues. Which are then converted into the above values through the following equations.

Recent papers have linked changes to MA and FA in certain regions of the brain to changes in the disease state of Parkinsons.

> MD progressively increased over time and was higher in the putamen (p < 0.001) and globus pallidus (p = 0.002). FA increased (p < 0.05) in the thalamus at year six, and decreased in the putamen and globus pallidus at year 12. Putaminal (p = 0.0210), pallidal (p = 0.0066) and caudate MD (p < 0.0001) correlated with disease duration. Caudate MD (p < 0.05) also correlated with UPDRS-III and H&Y scores. [1]

A DTI scan can reveal whether or not the water molecules in the axons are flowing properly along axonal directions. There are currently 3670 DTI images with a resolution of (1044,1044,65) and a pixel spacing of 2mm.

For DTI there were 380,1655,637 images for the control, PD, and prodromal groups respectivly.
* For the prodromal group and looking at time unique images, there are 159 patients with 1 image, 23 patients with 2 images, 24 patients with 3 images and 5 patients with 4 images.
* For the PD group and looking at time unique images, there are 169 patients with 1 image, 44 patients with 2 images, 53 patients with 3 images, 95 patients with 4 images and 1 patient with 5 images.
* For the control group and looking at time unique images, there were 41 patients with 1 image, 49 patients with 2 images, 14 patients with 3 images, and 3 patients with 4 images.

**Figure** FA image overlaid on a T1 Weighted MRI

**Figure** MD image overlaid on a T1 Weighted MRI

## References
[1] https://www.frontiersin.org/articles/10.3389/fnagi.2023.1169254/full