一、SCANNER CHANGES

MR scanners routinely undergo upgrades. These can be relatively minor (SW version) or major (hardware changes, e.g. head coil). In some cases, the scanner itself will be replaced at an ADNI site. We advise the following approach to the issue of scanner changes:

1. Assume that longitudinal within subject data is not compatible before vs after a change in scanner.

2. Assume that longitudinal within subject data is not compatible before vs after a major hardware change – e.g., change in head coil.

3. Assume that longitudinal within subject data maybe compatible before vs after a SW version change, but be advised that this may not be shown to be true eventually for some types of SW changes.

二、Differences between cross-sectional and longitudinal FreeSurfer

FreeSurfer can measure volume of cortical or subcortical structures and compute cortical thicknesses using cross-sectional and longitudinal processing. Longitudinal processing creates within a subject template and initializes each time point with the template to reduce individual variability. The ADNI1 images have been processed both cross-sectionally and longitudinally up to time point 9. ADNIGO/ADNI2 images have been processed using cross-sectional FreeSurfer and are being processed using Longitudinal FreeSurfer for subjects with at least 2 time points within 1 year. ADNIGO/2 longitudinal data will be processed to track longer-term changes as data accumulates. If the researcher is interested in baseline values and their association with some longitudinal or cross-sectional outcome, we recommend using cross-sectional FreeSurfer values. If interest lies in longitudinal change in the volumes or cortical thicknesses, the longitudinal version of FreeSurfer is recommended (when restricting to ADNI1 subjects).