Question Posted 02/26/14:
(Sorry for second issue, the form doesn't like messages past a certain length) We also have a scan that may be a scanner change, again with a series that has an unusual series description (the _ND suffix):
ADNI_013_S_4268_MT1__GradWarp__N3m_S206389_I399886.xml "MPRAGE GRAPPA 2_ND"
We think we need to exclude a scanner change from our longitudinal analysis since it relies on image consistency. Is there a particular meaning to the "_ND" series descriptor?
Response posted 02/27/14 by Bret Borowski:
Thank you for your question to the ADNI MRI Core.

The images that you are referring to are indeed from the ADNI protocol. They are from a new Siemens PET/MR Biograph_mMR scanner. The images that contain the "ND". Which stands for No Distortion correction. This system envokes the product inline 3D gradwarp correction, thus provides both 3D gradient correction and non correct sequences. However, ADNI will still provide pre-processed images for this type of system scanner.

Yes, this a significant scanner change, thus it would be advisable exclude these scans from longitudinal analysis.