A fourth ADNI site has just replaced their PET scanner (the other 3 sites are listed under “Old Warnings”). As mentioned below, investigators should be aware of resolution differences between scanners, hence should consider analyzing the PET data that has been matched for resolution. This is the 4th of the 4 pre-processed image files that get uploaded to LONI by the QC group. These have a uniform 160x160x96 1.5 mm3 grid and isotropic ~8mm FWHM resolution. Another important consideration is that the apparent size of the brain can be different for different scanners. For example, ’20 cm’ in size on the older Siemens Accel and Exact is smaller than ’20’ cm in the newer BioGraph HiRez scanner. As with the previous 3 PET scanner replacements, all “pre-processed” images for the new scanner have been adjusted to correct for these differences. This is important for within-subject analyses.

*Site 003 USC: All scans acquired prior to 2008 were performed on an Siemens BioGraph LSO scanner, the older 47 slice model. Their new scanner is a BioGraph LSO HiRez 81 slice scanner, and was brought on-line in March 2008. To date (April 2, 2008), two scans have been uploaded to LONI, 003_S_1057 (12m scan) and 003_S_1074 (12m scan). For the new BioGraph HiRez scans, the x,y voxel size is unchanged, while the z dimension of the scans for subjects that have earlier scans on the old scanner has been reduced from 2.0205 to 1.995 mm.

— Bob Koeppe – 02 Apr 2008