Phantom-based MRI corrections and power to track brain change

The Alzheimer´s Disease Neuroimaging Initiative (ADNI) employed phantom-based scaling of T1-weighted MP-RAGE brain images to improve spatial calibration of scans and longitudinal stability across study sites. Early in ADNI, errors in phantom based scaling were identified due to incorrect acquisition protocols or replacement of phantoms. Images initially made available with questionable scaling factors (scaled) were reprocessed (scaled_2) and made available to the scientific community. As many studies were conducted using images with sub-optimal scaling, we aimed to determine if the power to detect brain change differed between scaled and scaled_2 images. Using tensor-based morphometry, we found a high degree of correlation and no significant difference between scaled and scaled_2 images. We detected no significant differences between effect sizes derived from scaled and scaled_2 images. Our findings support the ADNI MRI core assessment that analyses carried out with either scaled or scaled_2 images may not offer a substantial difference in power.