Application Notes

The results of database comparisons will crucially depend on the parameters used for database creation.

• When calculating the reference value for scaling the pixel values, diseased tissue should always be avoided. Therefore it might be helpful to have databases available with differing reference calculation, for example one using a gray matter mask, and another using a cerebellum mask.
• Resolution mismatches between the database template and the processed patient image and inaccuracies in spatial normalization will result in edge artifacts in the z-score maps. This effect can be reduced by sufficient image smoothing. Again, it might be helpful to have databases available with different smoothing, to be applied depending on the size of the effect one is looking for.

Currently it is not possible to maintain several database definitions with the same set of control samples. However, an easy work-around is the following:

1. Calculate a database with specific settings and an appropriate description, then save.
2. Export the database. In the export dialog, before actually exporting, change the component name.
3. Import the database again. It is now a standalone definition without a relation to the control samples .

To create a modified database change the parameters and recalculate (overwriting the prior definition), and repeat the steps 1. - 3. This procedure can be repeated as many times as required to prepare a collection of databases covering the different situations expected in patient studies.

Note: Functionality for an age correction is not included in the current version of the Brain DB tool.