# Quantify voxel overlap

### Calculate dice coefficient

Voxalign also has a built-in function to verify the accuracy of longitudinal voxel placement. This tool takes as input session 1 and session 2 T1 and spectroscopy DICOMs or NIFTIs, coregisters the two T1s and applies the same transform to the session 1 spectroscopy voxel, and then calculates the dice coefficient between the two spectroscopy voxels. A dice coefficient of 1 reflects perfect overlap.

<figure><img src="https://4276957606-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LtSg7ZEM6EHbi9iE84a%2Fuploads%2FG5UgBb6Bg5gSbTNTX6Ta%2Fvoxalign_overlap.png?alt=media&#x26;token=0a9e245e-f353-4187-8025-fc7cf63d47dd" alt=""><figcaption><p>Voxalign multi-session voxel placement results. Light blue is the session 1 voxel and the dark blue outline is the session 2 voxel outline.</p></figcaption></figure>

1. Launch the dice coefficient GUI with `dice-coef`&#x20;
2. Click "Select output folder" and choose a folder. If you previously ran `dice-coef` for this same participant, you can choose the same output folder and the skull-stripped T1s and linear coregistration will be re-used.&#x20;
3. Provide all other files.
4. Click "Calculate dice coefficient"
5. The dice coefficient will be printed to the terminal, and a fsleyes window will be opened, with the coregistered T1s and MRS voxels overlaid.