Three sites have replaced their PET scanner during the ADNI project. Investigators should be aware of resolution differences between scanners, and should consider analyzing the PET data that has been matched for resolution. This is the 4th of the pre-processed image files that get uploaded to LONI. 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. In each case the voxel size of scans from the replacement scanner has been adjusted to match that of the earlier scans if there was a scanner change for the subject.

• Site 016 Wien: subjects 0354 and 0359 had their BV scans on an Siemens Accel. Their 6m and 12m scans were acquired on a Siemens BioGraph HiRez scanner. The voxel size of scans for these two subjects acquired on the repalcement scanner have been made smaller, multiplied by 0.965 in the x,y dimensions, and by 0.970 in the z dimension.
• Site 100 Boston: subjects 0047 BV, 6m, 12m; 0743 BV and 6m; 0747 BV and 6m; 0892 BV; 0930 BV; 0995 BV; 1062 BV, and 1154 BV were performed on a Siemens BioGraph. Subjects 0747 12m; 0892 6m; 0930 6m; 0995 6m; 1062 6m, and 1154 6m have been performed on a GE Discovery STE scanner. The x,y voxel size is unchanged. The z dimension of the STE scans for subjects that have earlier BioGraph scans has been reduced to 0.325 cm.
• Site 114 CWRU: subjects 0173 BV; 0228 BV; 0374 BV; 0378 BV; 0410 BV; 0416 BV were performed on a Philips Allergo scanner. All other scans at this site have been performed on a Philips Gemini-TF scanner. The voxel sizes for the new scanner did not need to be adjusted, and are unchanged.

— Bob Koeppe – 03 Oct 2007