2.4.3. Multi-Site Harmonization
Matched acquisition protocols were followed across the two imaging centers using custom-coded sequences to help ensure measurement comparability. To assess inter-site consistency of the primary imaging outcomes (relaxometry estimates) across the two imaging centers, a harmonization study was performed using both human “traveling heads” and a commercial quantitative phantom (Essential System phantom from CaliberMRI, which provides 42 NIST-traceable T1 (20–1900 ms), T2 (5–550 ms), and proton density (5–100%) contrast spheres). Matched in vivo and phantom data were acquired at each center with a 1-week inter-visit interval. T1 and T2 measures were calculated for each phantom sphere and throughout the brain. Bland–Altman plots were then calculated for the phantom T1 and T2 results, and a voxel-wise paired t-test was performed between each set of in vivo data collected at the two sites.