Concordance between Centiloid Quantification and Visual Interpretation of Amyloid PET Scans across the Alzheimer Disease Continuum.

Background and purpose: Accurate identification of cerebral β-amyloid (Aβ) accumulation is crucial for diagnosing Alzheimer disease (AD) and determining eligibility for anti-Aβ therapies. The Centiloid (CL) scale has emerged as a standardized method to harmonize Aβ PET quantification across different tracers and sites. We aimed to evaluate the concordance between CL quantification and visual interpretation in a cohort of cognitively impaired (CI) and unimpaired (CU) participants who underwent Aβ PET.

Materials and methods: Two hundred twenty-one participants (mean age 69 ± 12.3 years) were prospectively enrolled in AD studies and underwent 247 Aβ PET scans, including 157 with [¹¹C]-Pittsburgh compound B (PiB) and 90 with [¹⁸F]-florbetaben (FBB). Standardized uptake value ratios (SUVRs) were converted to the CL scale following Global Alzheimer's Association Interactive Network guidelines. Percent agreement and κ statistics were used to evaluate the concordance between CL thresholds and visual interpretation in determining Aβ positivity.

Results: The highest concordance rate for the whole cohort was 93% by using a CL cutoff of 18 (κ coefficient 0.84). Using FBB, the concordance rate was highest by using a CL cutoff of 24 (97%), whereas the concordance rate for PiB peaked at 94% at a CL cutoff of 18. Concordance was higher in negative rather than positive Aβ PET cases, 98% versus 90%. Concordance was slightly higher in CI participants compared with CU (96% versus 93%). Disagreement commonly occurred when focal areas of Aβ positivity were identified on visual interpretation but did not meet the threshold globally by CL quantification.

Conclusions: Global CL quantification of Aβ PET scans is highly concordant with visual interpretation. Combining both methods may provide a more complete assessment of the extent of Aβ deposition in the brain.