Evaluation of MR-driven versus MR-free PET/CT spatial normalization approaches for quantification of regional uptake...

Spatial normalization is a critical preprocessing step in PET imaging. While MR-driven normalization represents the gold standard, MR-free approaches offer an alternative that may enhance accessibility.

This study aims to evaluate the performance of MR-free normalization compared to MR-driven normalization across three PET modalities (18F-FDG, early-phase amyloid, and late amyloid PET), examinating regional agreement.

56 patients with dementia performing MR and the three PET modalities were retrospectively enrolled in the study. Three different spatial normalization methods were performed: MR-driven and two MR-free (¹⁵O-H₂O template and site-specific PET template). The agreement among different methods was pair-wise compared using intraclass correlation coefficients (ICCs).

MR-free normalization showed strong agreement with MR-driven methods for FDG and early amyloid PET, with ICCs > 0.99 in cortical regions. The spatial normalization with early-phase amyloid site-specific template had a median ICC of 0.927, confirming its agreement with MR-driven approach. The performance was slightly lower with late amyloid-derived templates (ICC = 0.822) compared to the ¹⁵O-H₂O template. The worst reproducibility was observed in cerebellar and thalamic sub-regions, though aggregating sub-ROIs in parent regions brought to strong ICCs (> 0.920).

MR-free normalization is a viable alternative to MR-driven approaches, particularly for FDG and early amyloid PET. In addition, the results confirm the similarity of early amyloid and FDG tracers distributions.