Reconstruction-dependent differences in brain [18F]FDG PET: a large-scale same-acquisition comparison of Q.Clear and VUE Point FX.

OBJECTIVE: To determine whether Q.Clear and VUE Point FX (VPFX) reconstructions obtained from the same brain [18 F]fluorodeoxyglucose positron emission tomography ([18 F]FDG PET) acquisition are quantitatively interchangeable, and to characterise the regional, reference-region and noise-texture dependence of any differences. METHODS: We retrospectively analysed paired Q.Clear and VPFX reconstructions from 1,145 clinical brain PET folders. The reviewed protocol used a 10-min acquisition, Q.Clear QCFX-S with beta 150, SharpIR and no z-axis filter, and VPFX-S with 3 iterations, 16 subsets and a 4.0-mm filter. Digital Imaging and Communications in Medicine metadata were audited, and 1,022 readable same-examination pairs were processed in MATLAB R2026a and statistical parametric mapping version 25. A common transform estimated from mean(Q.Clear, VPFX) was applied to both reconstructions. Absolute and standardised uptake value ratio (SUVR) differences normalised to whole brain, cerebellum and pons were assessed voxel-wise and in Automated Anatomical Labelling atlas 3 regions. DICOM-derived local high-frequency and robust global coefficients of variation (CVs) were also compared. RESULTS: Q.Clear increased the whole-brain, cerebellar and pontine reference means by 0.953%, 0.595% and 0.818%, respectively. Absolute regional differences were heterogeneous; after normalisation, most cortical and limbic Q.Clear-minus-VPFX differences were negative. The medial temporal whole-brain-normalised difference was - 0.00625 (Cohen dz -2.09), equivalent to approximately - 0.69% at an illustrative VPFX SUVR of 0.90. Covariate-adjusted voxel-wise T maps were nearly identical to no-covariate maps (r = 0.9996-0.9999; sign concordance > = 99.96%). Local high-frequency CV was lower with VPFX in 689 pairs and with Q.Clear in 333, whereas robust global CV was lower with Q.Clear in 903 pairs, with one tie. CONCLUSIONS: Q.Clear and VPFX were not quantitatively interchangeable under the evaluated protocol. The study establishes protocol-specific reconstruction-dependent differences, not the direction of quantitative accuracy, because no ground truth was available. Harmonised reconstruction and validation are required when quantitative brain PET data are compared or pooled.