REVIEW 3 major objections 4 minor 13 references
The paper argues that encoding user clicks as Euclidean distance transforms instead of Gaussian kernels improves interactive lesion segmentation in whole-body PET/CT.
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 →
Adding click prompts encoded as Euclidean distance transforms to an nnU-Net improves interactive whole-body PET/CT lesion segmentation over Gaussian encodings and baseline autoPET III models.
T0 review reviewed 2026-08-05 challenge →
load-bearing objection A useful ablation of click encodings for interactive PET/CT segmentation, but the headline ensemble result is not actually reported. the 3 major comments →
Towards Interactive Lesion Segmentation in Whole-Body PET/CT with Promptable Models
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
Core claim
The central claim is that a promptable U-Net-style PET/CT lesion segmenter conditioned by Euclidean Distance Transform (EDT) click channels beats the same model conditioned by Gaussian-kernel click channels. The paper shows this through five-fold cross-validation on the official autoPET/CT IV Task 1 split, where the best EDT variant (Size 2, custom points) achieves the highest Dice and the lowest false-positive and false-negative volumes among the single models. The authors further claim that training-time simulation of clicks is most robust when the official challenge sampler is mixed with a custom sampler that places positive clicks anywhere inside the lesion, favoring the lesion core, and
What carries the argument
The central object is the Euclidean Distance Transform (EDT) click encoding: each user click is expanded into a channel whose values are scaled distances from the clicked voxel, rather than a normalized Gaussian bump. The paper argues EDT wins because Gaussian kernels normalized to unit volume produce very low voxel intensities that the network effectively ignores. The second mechanism is the online prompt simulator, which, after data augmentation, draws 0-10 foreground and 0-10 background clicks per training patch from an 80/20 mixture of the official challenge sampler and a custom sampler, exposing the network to a wider variety of click locations than the official distribution alone.
Load-bearing premise
The gains rest on the assumption that clicks simulated during training resemble the clicks users will actually make at test time; if clinicians click in different places or with different frequency, the reported advantage of EDT encodings and custom point sampling may not transfer.
What would settle it
A direct comparison on the official test set, or in a study where radiologists provide real clicks, in which Gaussian-kernel encodings match or exceed EDT encodings on Dice or false-positive volume under the same five-fold protocol would refute the central claim; the paper already specifies the evaluation setup needed to run that check.
If this is right
- Interactive PET/CT segmenters can be built from existing automated U-Net pipelines by adding two prompt channels, leaving architecture, loss, and hyperparameters untouched.
- Reported reductions in false-positive and false-negative volumes imply that a few user clicks can yield masks that need less manual cleanup in clinical workflows.
- The online simulation recipe offers a way to train promptable models when real clinician clicks are scarce, by generating realistic prompt distributions on the fly.
- The ensemble result suggests combining a strong in-domain baseline with a model trained on additional external data delivers the most robust interactive performance.
Where Pith is reading between the lines
- The EDT-versus-Gaussian outcome is measured on one U-Net encoder; transformer-based promptable models may respond differently to low-intensity Gaussian prompt channels, so the representation result should not be assumed universal without a similar ablation.
- Real clinicians may click lesion boundaries or uncertain regions more often than the simulated sampler does; a reader study with actual clicks would test whether the custom point-sampling advantage survives real-world prompting behavior.
- The logarithmic distribution over click counts implies diminishing returns from additional clicks; an explicit click-budget analysis could give users a stopping rule during interactive refinement.
- Because the external training data spans different tracers, the EDT conditioning could be helping the model combine prompt information with tracer-specific uptake patterns, a hypothesis worth isolating in a per-tracer analysis.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents the authors' submission to the autoPET/CT IV challenge Task 1 (interactive lesion segmentation in whole-body PET/CT). Building on the winning autoPET III nnU-Net pipeline, the authors add two input channels that encode simulated foreground/background clicks, and compare Gaussian-kernel and Euclidean Distance Transform (EDT) encodings. They also propose online simulation of user interactions and a custom point-sampling strategy. Five-fold cross-validation on the official split (Table 1) compares the baseline, several Gaussian variants, EDT variants, and combinations with custom points and additional external data. The abstract and conclusion claim that an ensemble of the two best EDT Size2 models (with and without additional data) achieves the strongest cross-validation performance, while reducing false positives and false negatives. The paper reports code and algorithm details (Table 2).
Significance. If substantiated, the paper provides a practical recipe for turning a strong fully-automatic PET/CT lesion segmentation model into a promptable interactive system, with the specific finding that EDT encodings outperform Gaussian kernels for click conditioning. This is a useful, well-scoped contribution to a challenge and to the broader promptable-segmentation literature. Strengths include the use of a strong, publicly known baseline, a systematic comparison of click-encoding choices, a transparent cross-validation protocol, and the release of code. However, the central claim about the final ensemble is not quantitatively supported, and the reported metrics lack uncertainty quantification, which limits the strength of the conclusions until those gaps are addressed. The work is a credible challenge-report contribution but does not yet provide the evidence needed for a broader methodological claim.
major comments (3)
- [Abstract, §3.1, §4] The abstract and conclusion assert that the ensemble of the EDT Size2 model with custom points and the same model trained with additional data 'achieves the strongest cross-validation performance' and reduces false positives and false negatives compared to baseline models. However, §3.1 does not report the ensemble's Dice, FPvol, or FNvol anywhere; Table 1 lists only individual models. The two ensemble components are best on different metrics ('EDT Size2, custom points' has lowest FPvol of 8.05; 'EDT Size2, more data, custom points' has highest Dice of 76.35), so the ensemble's performance is not inferable from the table. Since the ensemble is the actual submitted method, its quantitative evaluation is essential. Please add the ensemble's metrics computed with the same official evaluation protocol.
- [Table 1, §3] All results are reported as point estimates without error bars, confidence intervals, or significance tests. Multiple model variants are compared on the same fixed cross-validation splits and the best-performing variants are then selected based on these metrics, introducing a selection-bias risk. For example, the gap between the best EDT variant (Dice 76.35) and the best Gaussian variant (Dice 74.59) is about 1.8 Dice points, and the FPvol differences are smaller; without per-fold variability or paired testing, the claim that EDT 'consistently outperforms' Gaussian kernels is not fully supported. Please report per-fold results, standard deviations, and/or paired statistical tests for the key comparisons in Table 1.
- [§3, Table 1] The text states that 'the model with Size 2 and custom points achieves strong performance, reducing FPvol and FNvol compared to other configurations.' This is contradicted by Table 1: while 'EDT Size2, custom points' has the lowest FPvol (8.05), its FNvol (AUC 15.11, Last 4.19) is higher than that of plain 'EDT Size2' (14.46, 3.86) and 'EDT Size4' (13.67, 3.66). Similarly, the claim that the 'custom point sampling strategy provides better generalization to realistic click distributions' is supported only partially (FPvol improves, Dice is similar, FNvol worsens). Please correct the description or provide additional evidence, such as an analysis of the official validation prompt distribution, to support the claim.
minor comments (4)
- [Figure 1 caption] Typography: 'Exemplary' should be 'Example' or 'Exemplar' (the current spelling is not standard).
- [Table 1] The '6,14' in the first Gaussian row appears to be a comma-decimal error; should be '6.14' for consistency with the rest of the table.
- [§3, Table 1] The table header 'Dice↑ FPvol↓ FNvol↓' with subcolumns 'AUC Last' is not fully explained. Please define what 'AUC' and 'Last' refer to (e.g., area under the curve across the number of clicks evaluated at 0, 3, 7, 10, and the value at 10 clicks, respectively), preferably in the caption or in the text.
- [§3, Table 1] The phrase 'AUC calculated using 0, 3, 7, and 10 clicks' is ambiguous: is this the average of the metric across these click counts, or an area under the curve computed across these points? Please clarify.
Circularity Check
No circular derivation: empirical ablations and official validation, though some claims lack reported support.
full rationale
The paper's central claims are empirical comparisons: EDT vs Gaussian click encodings, and variants of prompt simulation/training data. These are supported by five-fold cross-validation on the official challenge splits and the official evaluation implementation (Section 3, Table 1). There is no equation in which an output quantity is defined in terms of itself, no fitted parameter is renamed as a prediction, and no uniqueness theorem is invoked. The EDT representation is said to be 'inspired by nnInteractive' (Section 2), but its superiority is tested against Gaussian kernels rather than assumed from the citation. The model builds on the authors' previous autoPET III pipeline, nnInteractive, and LesionLocator; these are prior independent works, and the autoPET III baseline is externally validated from the earlier challenge. The custom point sampler is trained with an 80/20 mixture and then evaluated on the official precomputed validation prompts, so the comparison is a held-out ablation rather than a self-fulfilling prediction, although the phrase 'better generalization to realistic click distributions' is somewhat subjective. The most notable gap is that the abstract's claim that the ensemble 'achieves the strongest cross-validation performance' is not backed by any row in Table 1; Section 3.1 describes the ensemble but reports no Dice, FPvol, or FNvol value for it, and no error bars or paired tests are provided. This is a missing-evidence/support problem, not a circularity problem. No specific reduction of a result to its inputs by construction was found, so the circularity score is 0.
Axiom & Free-Parameter Ledger
free parameters (5)
- EDT scaling factor (size) =
2
- Gaussian sigma test set =
0.1, 0.25, 0.5, 0.75, 1, 2, 3
- Simulated prompt-count distribution =
logarithmic, 0-10 per class
- Mix ratio between official and custom prompt simulators =
80/20
- Ensemble composition =
5-fold ensemble of EDT Size2 with custom points, with and without extra data
axioms (4)
- domain assumption Simulated user clicks (official challenge simulator plus 20% custom sampling) are representative of real clinician prompts at test time.
- domain assumption Cross-validation on the official challenge training splits is a valid predictor of final challenge test performance.
- domain assumption External datasets (DEEP-PSMA, TCGA-LUAD, NSCLC-Radiogenomics) are label-compatible with the autoPET lesion definition and can be pooled with challenge data.
- domain assumption Adding two prompt channels does not break the assumptions of the nnU-Net normalization, resampling, or loss used in the baseline.
Cite this review
Pith. "Pith review of Towards Interactive Lesion Segmentation in Whole-Body PET/CT with Promptable Models." pith.science (2026). https://pith.science/paper/LK4BDFFQ
@misc{pith2026250821680,
author = {Pith},
title = {Pith review of: Towards Interactive Lesion Segmentation in Whole-Body PET/CT with Promptable Models},
year = {2026},
howpublished = {\url{https://pith.science/paper/LK4BDFFQ}},
note = {Machine review of arXiv:2508.21680}
}
read the original abstract
Whole-body PET/CT is a cornerstone of oncological imaging, yet accurate lesion segmentation remains challenging due to tracer heterogeneity, physiological uptake, and multi-center variability. While fully automated methods have advanced substantially, clinical practice benefits from approaches that keep humans in the loop to efficiently refine predicted masks. The autoPET/CT IV challenge addresses this need by introducing interactive segmentation tasks based on simulated user prompts. In this work, we present our submission to Task 1. Building on the winning autoPET III nnU-Net pipeline, we extend the framework with promptable capabilities by encoding user-provided foreground and background clicks as additional input channels. We systematically investigate representations for spatial prompts and demonstrate that Euclidean Distance Transform (EDT) encodings consistently outperform Gaussian kernels. Furthermore, we propose online simulation of user interactions and a custom point sampling strategy to improve robustness under realistic prompting conditions. Our ensemble of EDT-based models, trained with and without external data, achieves the strongest cross-validation performance, reducing both false positives and false negatives compared to baseline models. These results highlight the potential of promptable models to enable efficient, user-guided segmentation workflows in multi-tracer, multi-center PET/CT. Code is publicly available at https://github.com/MIC-DKFZ/autoPET-interactive
Figures
Reference graph
Works this paper leans on
-
[1]
JGNIHEP5, https://doi.org/10.7937/K9/TCIA.2016.JGNIHEP5, data set
Albertina, B., Watson, M., Holback, C., Jarosz, R., Kirk, S., Lee, Y., Rieger- Christ, K., Lemmerman, J.: The cancer genome atlas lung adenocarcinoma col- lection (tcga-luad) (version 4) (2016).https://doi.org/10.7937/K9/TCIA.2016. JGNIHEP5, https://doi.org/10.7937/K9/TCIA.2016.JGNIHEP5, data set
-
[2]
Scientific data5(1), 1–9 (2018)
Bakr, S., Gevaert, O., Echegaray, S., Ayers, K., Zhou, M., Shafiq, M., Zheng, H., Benson, J.A., Zhang, W., Leung, A.N., et al.: A radiogenomic dataset of non-small cell lung cancer. Scientific data5(1), 1–9 (2018)
work page 2018
-
[3]
Ferdinandus, J., Violet, J., Sandhu, S., Hicks, R.J., Ravi Kumar, A.S., Iravani, A., Kong, G., Akhurst, T., Thang, S.P., Murphy, D.G., et al.: Prognostic biomarkers in men with metastatic castration-resistant prostate cancer receiving [177lu]-psma-
-
[4]
Gatidis, S., Kuestner, T.: A whole-body fdg-pet/ct dataset with manually an- notated tumor lesions (fdg-pet-ct-lesions).https://doi.org/10.7937/GKR0-XV29 (2022), the Cancer Imaging Archive
-
[5]
Nature methods 18(2), 203–211 (2021)
Isensee, F., Jaeger, P.F., Kohl, S.A., Petersen, J., Maier-Hein, K.H.: nnU-Net: a self-configuring method for deep learning-based biomedical image segmentation. Nature methods 18(2), 203–211 (2021). https://doi.org/https://doi.org/10. 1038/s41592-020-01008-z
work page 2021
-
[6]
Isensee, F., Rokuss, M., Krämer, L., Dinkelacker, S., Ravindran, A., Stritzke, F., Hamm, B., Wald, T., Langenberg, M., Ulrich, C., Deissler, J., Floca, R., Maier- Hein, K.: nninteractive: Redefining 3d promptable segmentation (2025),https: //arxiv.org/abs/2503.08373
Pith/arXiv arXiv 2025
-
[7]
arXiv preprint arXiv:2404.09556 (2024)
Isensee, F., Wald, T., Ulrich, C., Baumgartner, M., Roy, S., Maier-Hein, K., Jaeger, P.F.: nnU-Net revisited: A call for rigorous validation in 3d medical image segmen- tation. arXiv preprint arXiv:2404.09556 (2024)
Pith/arXiv arXiv 2024
-
[8]
https://doi.org/10.7937/r7ep-3x37 (2024), the Cancer Imaging Archive
Jeblick, K., et al.: A whole-body psma-pet/ct dataset with manually annotated tu- mor lesions (psma-pet-ct-lesions). https://doi.org/10.7937/r7ep-3x37 (2024), the Cancer Imaging Archive
-
[9]
Kirillov, A., Mintun, E., Ravi, N., Mao, H., Rolland, C., Gustafson, L., Xiao, T., Whitehead, S., Berg, A.C., Lo, W.Y., Dollár, P., Girshick, R.: Segment anything. arXiv:2304.02643 (2023)
Pith/arXiv arXiv 2023
-
[10]
In: Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)
Rokuss, M., Kirchhoff, Y., Akbal, S., Kovacs, B., Roy, S., Ulrich, C., Wald, T., Rotkopf, L.T., Schlemmer, H.P., Maier-Hein, K.: Lesionlocator: Zero-shot universal tumor segmentation and tracking in 3d whole-body imaging. In: Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR). pp. 30872–30885 (June 2025)
work page 2025
-
[11]
Rokuss, M., Kovacs, B., Kirchhoff, Y., Xiao, S., Ulrich, C., Maier-Hein, K.H., Isensee, F.: From fdg to psma: A hitchhiker’s guide to multitracer, multicenter le- sion segmentation in pet/ct imaging (2024),https://arxiv.org/abs/2409.09478
Pith/arXiv arXiv 2024
-
[12]
In: Inter- national Conference on Medical Image Computing and Computer-Assisted Inter- vention
Ulrich, C., Isensee, F., Wald, T., Zenk, M., Baumgartner, M., Maier-Hein, K.H.: Multitalent: A multi-dataset approach to medical image segmentation. In: Inter- national Conference on Medical Image Computing and Computer-Assisted Inter- vention. pp. 648–658. Springer (2023) Interactive Lesion Segmentation in PET/CT 7 Table 2: Algorithm details T eam name a...
work page 2023
-
[617]
European journal of nuclear medicine and molecular imaging47(10), 2322– 2327 (2020)
work page 2020
This paper was first reviewed by deepseek-v4-flash on August 5, 2026.
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.