Resample PET image

Hi all, I need to resample my PET image and I have a problem.
When I resample my image in Slicer using the Resample Image (Brains) module, the image ends up correctly resampled except its image activity information, it´s show a different values of the original image. Someone know which could be a problem?

How different are the values? Some small amount of difference is expected due to filtering.

Before at resample the image activity it´s more than 20000 Bq/ml and after resampling it´s 3000 Bq/ml

That sounds pretty big - is there anyway this can be reproduced using shareable data? E.g. what happens if you use public PET data?

I don´t know how to use this public PET data, I´m in the webside but I don´t know where are the example. Can you help me with this?

There’s sample PET data and instructions as part of this tutorial: