Question Posted 04/27/17:
Dear PET Core,

after downloading PET AV45 images ( VISCODE2 = bl, RID = 5126, 5162, 5222 ) I realized that they present negative uptake values. Is this an isolated problem or it can be present in other images? How can I fix it?

Thanks in advance.
Response posted 05/02/17 by Bob Koeppe:
I would need more information than this. I don't think there should be any negative values, and certainly not in any actual brain regions.
Can you give me the site and subject ID for some examples. Are these the original or pre-processed images, and in what format did you download them? There have been some problems at times using the nifti formatted files. Please e-mail me at
Response posted 05/02/17 by Susan Landau:
No PET images should have negative voxel values. I checked the image you mentioned and I do not see any negative values. Please feel free to contact me with more specific information about where you are seeing the negative values.