P3‐426: REGIONAL AND VOXEL‐WISE SPATIAL RELATIONSHIPS AMONG FLUORINE‐18 AMYLOID PET TRACERS AND PITTSBURGH COMPOUND B
Bibliographic record
Abstract
Historically, the spatial spread of amyloid plaques in studies of Alzheimer's disease (AD) has been quantified with the radioligand [11C]Pittsburgh Compound B (PiB). However, its short half-life limits its viability in clinical and research settings without direct access to radiochemical facilities. [18F]-radioligands, such as florbetapir, florbetaben, and NAV4694, were developed to address this issue but questions remain concerning their comparability to PiB. Using data from two sporadic AD cohorts in the Centiloid project (NAV4694 and florbetaben) and an autosomal AD cohort (florbetapir), we investigated each [18F] tracer's relationship to PiB. PET and T1-weighted head MR images for healthy controls and AD patients were downloaded from the Centiloid project and the Dominantly Inherited Alzheimer's Network-Trial Unit. PET scans using each [18F] tracer were acquired within three months from PiB. MR images were segmented into cortical and subcortical regions of interest (ROIs) using FreeSurfer-5.3. Standard uptake value ratios (SUVrs) were calculated from 90–110 minutes post-injection for florbetaben, and 50–70 minutes post-injection for all other tracers, using cerebellar grey as a reference region. SUVrs between [18F] tracers and PiB were correlated at the ROI level (for cortical/subcortical grey only, and cortical/subcortical grey and subcortical white matter) and at the voxel-wise level. Similarity to PiB across the [18F] tracers was assessed using pairwise t-tests on Fisher's z-transformed values. NAV4694 had the highest correlation with PiB (r=0.95) than either florbetapir (r=0.85) or florbetaben (r=0.90) for cortical and subcortical grey matter (Figure 1). For comparison, PiB test-retest data from a previous report1 showed a regional spatial correlation of >0.91 for cortical and subcortical grey matter. This pattern persisted at the voxel-wise level (Figure 2; NAV4694: r=0.90, florbetapir: r=0.87, florbetaben: r=0.88). Florbetaben showed a significantly stronger relationship with PiB than florbetapir but only at the ROI level.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".