REVIEW 2 major objections 2 minor 1 cited by
Self-supervised pretraining on large unlabeled brain MRI datasets produces models that generalize better to heterogeneous clinical data than supervised models trained directly on the target domain.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · grok-4.3
2026-05-25 06:27 UTC pith:5CHYGABH
load-bearing objection FOMO25 delivers a clean multi-team benchmark on SSL pretraining for clinical brain MRI but the three tasks leave the broader clinic-deployment claim under-supported. the 2 major comments →
Towards Brain MRI Foundation Models for the Clinic: Findings from the FOMO25 Challenge
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Self-supervised pretraining improves generalization on clinical data under domain shift, with the strongest models trained out-of-domain surpassing supervised baselines trained in-domain. No single pretraining objective benefits all tasks: masked autoencoding favors segmentation while hybrid reconstruction-contrastive objectives favor classification. Strong performance was achieved by small pretrained models, and scaling model size or training duration did not yield reliable benefits across the evaluated tasks.
What carries the argument
The FOMO25 challenge protocol that compares self-supervised models pretrained on the FOMO60K unlabeled dataset against supervised baselines on out-of-domain clinical tasks covering infarct classification, meningioma segmentation, and brain age regression.
Load-bearing premise
The three chosen clinical tasks and their evaluation datasets serve as representative proxies for the heterogeneity and labeling costs encountered in actual hospital brain MRI deployment.
What would settle it
A new set of clinical brain MRI scans from a different hospital network on which in-domain supervised models trained from scratch achieve higher accuracy than the top FOMO25 self-supervised entries on the same three tasks.
If this is right
- MAE-based pretraining should be prioritized when the downstream task is segmentation.
- Hybrid reconstruction-contrastive objectives should be prioritized when the downstream task is classification.
- Model scaling and extended pretraining can be deprioritized in favor of careful objective selection for brain MRI foundation models.
Where Pith is reading between the lines
- The same pretraining strategy may transfer to other MRI contrasts or body regions if the unlabeled data distribution matches the target clinical workflow.
- Deployment pipelines could start with a small pretrained model and add task-specific fine-tuning rather than training large models from scratch.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports findings from the FOMO25 MICCAI challenge, in which 19 foundation models submitted by 16 teams were evaluated via a standardized containerized pipeline on three clinical brain MRI tasks (infarct classification, meningioma segmentation, brain age regression) using the FOMO60K pretraining dataset. The central claims are that self-supervised pretraining improves out-of-domain generalization on clinical data, that the strongest out-of-domain SSL models surpass in-domain supervised baselines, that no single pretraining objective is optimal across tasks, and that scaling model size or training duration yields no reliable gains.
Significance. If the empirical comparisons hold, the work supplies a reproducible, multi-team benchmark demonstrating practical benefits of SSL for clinical brain MRI under domain shift and label scarcity. The containerized evaluation protocol and task-specific objective findings constitute concrete, falsifiable guidance for foundation model development.
major comments (2)
- [Results] Results section: the claim that out-of-domain SSL models surpass in-domain supervised baselines is presented without error bars, confidence intervals, or statistical significance tests on the performance differences, which is load-bearing for the central generalization claim given the known variability of medical imaging metrics.
- [Introduction/Evaluation] Introduction and Evaluation sections: no quantitative characterization of domain-shift severity (e.g., distribution distances between FOMO60K and the three clinical test sets, or in-domain vs. out-of-domain performance drops) is provided, leaving the representativeness of the chosen tasks for broader clinical deployment unverified and weakening the interpretation of the reported outperformance.
minor comments (2)
- [Abstract] Abstract: the description of the containerized pipeline would benefit from a brief statement of the exact metrics and few-shot protocols used for each task.
- [Tables/Figures] Tables/figures: performance tables should consistently report standard deviations across runs or folds to allow direct visual assessment of the surpassing claim.
Simulated Author's Rebuttal
We thank the referee for the positive evaluation and recommendation for minor revision. The comments highlight important opportunities to strengthen the statistical presentation and domain-shift analysis. We address each point below.
read point-by-point responses
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Referee: [Results] Results section: the claim that out-of-domain SSL models surpass in-domain supervised baselines is presented without error bars, confidence intervals, or statistical significance tests on the performance differences, which is load-bearing for the central generalization claim given the known variability of medical imaging metrics.
Authors: We agree that measures of variability and formal statistical tests are necessary to support the central claim. In the revised manuscript we will add error bars (standard deviation across repeated evaluations or bootstrap estimates) to all reported metrics and include paired statistical significance tests (Wilcoxon signed-rank or McNemar as appropriate) for the key comparisons between the strongest out-of-domain SSL models and the in-domain supervised baselines. revision: yes
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Referee: [Introduction/Evaluation] Introduction and Evaluation sections: no quantitative characterization of domain-shift severity (e.g., distribution distances between FOMO60K and the three clinical test sets, or in-domain vs. out-of-domain performance drops) is provided, leaving the representativeness of the chosen tasks for broader clinical deployment unverified and weakening the interpretation of the reported outperformance.
Authors: We acknowledge the value of quantifying domain shift. Computing full high-dimensional distances (MMD, Wasserstein) on raw 3-D MRI volumes at the scale of FOMO60K is computationally prohibitive within the challenge setting. In the revision we will add quantitative proxies—differences in mean voxel intensity, intensity histogram overlap, and variance between FOMO60K and each clinical test set—together with explicit in-domain versus out-of-domain performance gaps for the supervised baselines where such data exist. These additions will improve interpretability without altering the core experimental design. revision: partial
Circularity Check
No circularity: empirical challenge results with external evaluation
full rationale
The paper reports outcomes from the FOMO25 challenge involving 19 models evaluated via standardized pipeline on clinical tasks (infarct classification, meningioma segmentation, brain age regression) using FOMO60K pretraining data. Central claims rest on direct empirical comparisons of SSL vs supervised performance under domain shift, with no equations, fitted parameters renamed as predictions, self-definitional constructs, or load-bearing self-citations. The derivation chain consists solely of observed performance metrics from independent teams and external test sets; no step reduces by construction to its inputs.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption The FOMO60K pretraining dataset and clinical test sets are representative of real clinical workflows and domain shifts.
read the original abstract
Clinical deployment of automated brain MRI analysis faces a fundamental challenge: clinical data is heterogeneous and noisy, and high-quality labels are prohibitively costly to obtain. Self-supervised learning (SSL) can address this by leveraging the vast amounts of unlabeled data produced in clinical workflows to train robust \textit{foundation models} that adapt out-of-domain with minimal supervision. However, the development of foundation models for brain MRI has been limited by small pretraining datasets and in-domain benchmarking focused on high-quality, research-grade data. To address this gap, we organized the FOMO25 challenge as a satellite event at MICCAI 2025. FOMO25 provided participants with a large pretraining dataset, FOMO60K, and evaluated models on data sourced directly from clinical workflows in few-shot and out-of-domain settings. Tasks covered infarct classification, meningioma segmentation, and brain age regression, and considered both models trained on FOMO60K (method track) and any data (open track). Nineteen foundation models from sixteen teams were evaluated using a standardized containerized pipeline. Results show that (a) self-supervised pretraining improves generalization on clinical data under domain shift, with the strongest models trained \textit{out-of-domain} surpassing supervised baselines trained \textit{in-domain}. (b) No single pretraining objective benefits all tasks: MAE favors segmentation, hybrid reconstruction-contrastive objectives favor classification, and (c) strong performance was achieved by small pretrained models, and improvements from scaling model size and training duration did not yield reliable benefits.
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