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Tyche: Stochastic In-Context Learning for Medical Image Segmentation
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Introduces Tyche, a stochastic in-context learning framework for medical image segmentation that generates multiple plausible masks for unseen tasks without retraining, via a SetBlock architecture (Tyche-TS) or in-context test-time augmentation on existing ICL models (Tyche-IS).
Problem
Medical image segmentation models need retraining for each new task and usually output a single deterministic mask, ignoring annotator disagreement and ambiguity.
Approach
Condition a UNet-like network on a context set and Gaussian noise channels, with SetBlock layers letting candidate predictions interact and a best-candidate Dice loss to encourage diversity; alternatively, apply in-context test-time augmentation to target and context of a deterministic ICL model to get stochastic outputs.
Key results
- On multi-annotator out-of-domain tasks, Tyche-TS reaches LIDC-IDRI max Dice 0.91 and Hippocampus 0.88 versus UniverSeg 0.84 on Hippocampus and 0.67 on LIDC-IDRI.
- Tyche-TS achieves GED of 0.40 on LIDC-IDRI, comparable to stochastic upper bounds such as PhiSeg (0.33) and CIDM (0.42), while using 1.7M parameters.
- Tyche-TS runs in 18.09 ms for 8 predictions versus 2,857 ms for SegGPT, and SetBlock ablation shows it is crucial to best-candidate Dice.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use Tyche-TS rather than Tyche-IS | Tyche · Multi-annotator O.D. datasets | Max Dice: Tyche-IS: 0.87 ± 0.01; Tyche-TS: 0.88 ± 0.01 (Hippocampus) | Helped |
| Use Tyche-TS rather than Tyche-IS | Tyche · Multi-annotator O.D. datasets | GED² | No clear effect |
| Use Tyche-IS rather than Tyche-TS | Tyche · Single-annotator O.D. data | GED² | Helped |
| Use Tyche-IS rather than Tyche-TS | Tyche · Single-annotator O.D. data | Best candidate Dice | No clear effect |
| Remove synthetic multi-annotator training images (ablation) | Tyche-TS · O.D. tasks | Best candidate Dice | No clear effect |
| Add candidate-feature standard deviation to SetBlock (ablation) | Tyche-TS · O.D. tasks | Best candidate Dice | No clear effect |
| Remove SetBlock (ablation) | Tyche-TS · O.D. tasks | Best candidate Dice | Hurt |
| Apply augmentation to both target and context (ablation) | Tyche-IS · O.D. tasks | Segmentation performance | Helped |
| Apply noise to only one of target or context (ablation) | Tyche-IS · O.D. tasks | Segmentation performance | Hurt |
| Increase the number of predictions (ablation) | Tyche-TS · O.D. tasks | Best candidate Dice | Helped |
| Increase context size (ablation) | Tyche-TS · O.D. tasks | Best candidate Dice | Helped |
Surprising findings
- Tyche-IS, a test-time augmentation wrapper with no extra training, is competitive with the trained Tyche-TS on single-annotator best candidate Dice.
- SegGPT performs very poorly on STARE (max Dice 0.02) despite being a large ICL model.
Limitations
- Tyche-TS is slower than some task-specific stochastic models and Tyche-IS needs additional inference time for test-time augmentation.
- GED rewards excessive prediction diversity, so it is an imperfect metric.
- Stochastic upper bounds were trained on the out-of-distribution tasks, which Tyche does not use.
Experimental setup
Datasets: MegaMedical QUBIQ LIDC-IDRI STARE Hippocampus PanDental WBC SCD ACDC SpineWeb
Benchmarks: LIDC-IDRI Hippocampus Prostate QUBIQ STARE PanDental WBC SCD ACDC SpineWeb
Metrics: best candidate Dice Generalized Energy Distance inference time parameter count
Baselines: UniverSeg SegGPT SENet SAM SAM-Med2D Probabilistic UNet PhiSeg CIDM
Builds on: UniverSeg CrossBlock U-Net test-time augmentation
Closest papers by meaning
- Training Like a Medical Resident: Context-Prior Learning Toward Universal Medical Image Segmentation (CVPR 2024 · similarity 0.87)
- Generative Medical Segmentation (AAAI 2025 · similarity 0.86)
- S2S2: Semantic Stacking for Robust Semantic Segmentation in Medical Imaging (AAAI 2025 · similarity 0.86)
- Interactive Medical Image Segmentation: A Benchmark Dataset and Baseline (CVPR 2025 · similarity 0.86)
- ConDSeg: A General Medical Image Segmentation Framework via Contrast-Driven Feature Enhancement (AAAI 2025 · similarity 0.85)
- Show and Segment: Universal Medical Image Segmentation via In-Context Learning (CVPR 2025 · similarity 0.85)
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