Sequential scans of 18F-flutemetamol PET using PET/CT and PET/MRI: influence of amyloid burden, scan interval, and age

Visual interpretation showed high agreement between PET/CT and PET/MRI (κ = 0.97), and 98% concordance with CSF findings. SUVr and Centiloid scale demonstrated a strong intraclass correlation coefficient of 0.96-0.98. However, SUVr and Centiloid scale were significantly higher from PET/CT than from PET/MRI, except for SUVr using CGM. Age and Centiloid scale were significant predictors of modality differences. Scan interval was also significant when CGM was used as the reference region. Dynamic PET/MRI revealed time-dependent increases in Centiloid scale among amyloid-positive participants. High concordance in visual and quantitative assessments was seen for ¹⁸F-flutemetamol PET/CT (90 min) and subsequent PET/MRI (120 min). While diagnostic agreement was preserved, quantitative values were influenced by amyloid burden, age, and scan timing. These findings suggest a need for careful consideration when interpreting quantitative metrics across different imaging modalities and time points.