REVIEW 5 major objections 3 minor 33 references
MS-UMamba: An Improved Vision Mamba Unet for Fetal Abdominal Medical Image Segmentation
T0 review · 5 major / 3 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read MS-UMamba, a hybrid CNN-Mamba U-Net, reports higher mIoU, mDice, and mSE than VM-UNet on a private fetal abdominal ultrasound dataset.
desk verdict A plausible recombined Mamba-UNet for fetal ultrasound, but the core empirical claim is unverifiable as presented: private data, no code, no error bars, and a 1.97-point mIoU margin that the paper itself never shows is outside run-to-run noise. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the SS-MCAT-SSM block, which channel-splits its input into two halves: one goes through a Mamba (selective state-space) branch that models long-range dependencies, and the other through a CNN branch whose BottleNeck block applies Monte Carlo attention, reweighting multi-scale pooled features by association probabilities before 1x1 and 3x3 convolutions, after which the branches are concatenated and channel-shuffled. The second load-bearing piece is the Attention-based Dynamic Feature Fusion (ADFF) module, adapted from the DFF module: it maps encoder and decoder features through 1x1 convolutions, sums them, forms a spatial attention weight with a Sigmoid, concatenates the original features, applies channel attention via a shared MLP on global average and max pooling, and combines both weightings. Together these modules are what the ablation study varies to attribute the performance gain.
What would settle it
Re-run the same comparison on a fixed public fetal ultrasound dataset with patient-disjoint folds and report per-class Dice; if the mIoU gap over VM-UNet drops below the reported 1.97 points, the claimed advantage is an artifact of the private split or labels. Additionally, reporting inter-annotator agreement on the 696 images would show whether label noise explains the small-target errors.
Extended reading notes
Core claim
The paper's central claim is that adding a CNN branch with Monte Carlo attention to a Mamba-based U-Net, together with an attention-weighted dynamic feature fusion module, yields better segmentation of small, overlapping fetal abdominal organs than Mamba-only or CNN-only alternatives. The two proposed modules are named SS-MCAT-SSM, a visual state-space block split into a CNN branch and a Mamba branch, and ADFF, a multi-scale fusion module with spatial and channel attention. Ablation results show the combination reaches the best numbers, while replacing the fused module with the plain DFF module drops mIoU from 67.62% to about 53.54%, which the authors interpret as evidence that the attention-based fusion is what makes the model work. Per-structure results show the largest scores on the L V class and the lowest on SL and UV, the two small-target classes.
Load-bearing premise
The load-bearing premise is that the private 696-image dataset is split and annotated in a way that does not systematically favor MS-UMamba; the paper does not describe how train, validation, and test sets were built or how consistent the technician labels are.
Editorial extensions
If this is right
- If the reported results hold on patient-disjoint data, automated fetal ultrasound screening could measure abdominal structures without manual contouring, reducing the subjectivity and time cost the paper cites as motivation.
- The SS-MCAT-SSM and ADFF modules are described generally enough to be inserted into other encoder-decoder segmentation backbones, giving evidence that hybrid CNN-Mamba fusion is competitive on ultrasound, not only on MRI or CT.
- The ablation says plain DFF fusion hurts performance, implying the attention mechanisms in ADFF are necessary; future hybrid models should expect naive multi-scale fusion to backfire.
- Per-structure results identify small targets (SL, UV) as the bottleneck, so the next natural increment is a loss function or training scheme targeted at small-object recall rather than a larger backbone.
Reading between the lines
- The private dataset has no described patient-disjoint split or inter-annotator agreement; before relying on the 1.97-point mIoU gap over VM-UNet, a reader would want the data released or a public fetal ultrasound benchmark run under identical training settings.
- The table's precision column is internally inconsistent with the prose claim of outperforming all models, because SegMenter shows a higher mPRE, so the defensible claim is the mIoU, mDice, and mSE gain rather than an all-metric win.
- A testable extension would be to ablate only the Monte Carlo attention inside SS-MCAT-SSM while keeping ADFF fixed, to see whether the gain comes from the CNN branch itself or from the attention mechanism.
- If the same architecture transfers to fetal cardiac or head planes, it would support the more general claim that hybrid CNN-Mamba designs handle ultrasound speckle and boundary blur better than either family alone; the paper only tests one plane.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes MS-UMamba, a U-Net-style architecture that combines Vision Mamba state space blocks with a CNN branch (SS-MCAT-SSM) and an attention-based multi-scale feature fusion module (ADFF), for segmenting six fetal abdominal anatomical structures in ultrasound images. The authors report experiments on a private dataset of 696 images, comparing against several existing segmentation models and claiming that MS-UMamba achieves the best performance, with the main result being an mIoU of 67.62% versus 65.65% for VM-UNet. They also provide an ablation study and qualitative visualizations.
Significance. If the reported results are reliable, the proposed hybrid Mamba-CNN architecture and the attention-based fusion module would be a useful contribution to medical image segmentation, particularly for fetal ultrasound where boundary ambiguity and small structures are challenging. The paper includes a reasonable set of baseline comparisons and covers multiple evaluation metrics. However, the significance is currently limited by the use of a private dataset, absence of code and data release, lack of statistical validation (no error bars or significance tests), and incomplete experimental protocol details, all of which make it difficult to verify the claimed architectural advantage.
major comments (5)
- [Section 4.1, Table 1] The dataset split is not described in a way that supports the claimed results. The paper states that 696 images were annotated but does not explain how the train/validation/test sets were constructed, whether the split is patient-disjoint, or whether a single image can contribute to multiple per-structure counts in Table 1. Without this information, the effective test-set size and the independence of per-structure metrics are unclear, so the reported performance gap may be an artifact of the split rather than of the architecture.
- [Section 4.3, Table 2] No run-to-run variance or statistical significance testing is reported for any of the comparisons. A single training run per model on a private dataset cannot establish that the 1.97-point mIoU advantage over VM-UNet is outside the range of random initialization, augmentation order, and batch composition. In addition, the sentence claiming that MS-UMamba 'outperforms all other models in these metrics' is directly contradicted by the next sentence and by Table 2, where SegMenter reports a higher mPRE (76.54% versus 76.11%).
- [Section 3.4, Eq. (9)] The Focal loss equation as printed appears degenerate and consequently the exact loss used for training is not reproducible. In the second term, the factor p^y (1-y) equals 1 for y=0, which removes the focusing term for negative samples, and for y=1 it becomes 0, making the expression inconsistent with the standard focal loss; additionally, the exponent on (1−P) in the first term is ambiguous. The authors need to provide a correct, clearly notated formula that matches their implementation.
- [Table 4, ablation experiment] The DFF-only ablation row shows a catastrophic drop in performance, with mIoU falling from 66.54% in the baseline to 53.54% when the basic DFF module is added, while the text gives no explanation for this behavior. This result is unexpected given that the ADFF module—which is claimed to build on DFF—improves performance when added together with MCAT. The authors should explain what causes this degradation, or the comparison must be considered uncontrolled and the role of the DFF module unclear.
- [Section 4.3, comparison protocol] The experimental protocol for baseline comparisons is under-specified. The manuscript does not state whether all models were trained with identical training budgets, input resolutions, data augmentation, and hyperparameter tuning procedures. Without this information, the relative improvements over baselines cannot be attributed to the proposed SS-MCAT-SSM and ADFF modules rather than to differences in training configuration.
minor comments (3)
- [Section 4.3, Table 2] The last cell of Table 2 reads '99.3176.11' with a missing separator, and the text reports an mPRE of 76.09% while the table shows 76.11%; these values should be reconciled.
- [Throughout] There are several typos and grammatical errors, including 'Blcok' in section headings, 'Sgmiod' in Eq. (4), 'Swim-TransFormer' instead of 'Swin-Transformer', and the abstract's incomplete sentence 'which Integrating feature information from different layers enhances the feature representation ability of the model.'
- [Section 4.1] Table 1 lists per-structure counts for train/validation/test, but it is unclear whether these counts refer to images, instances, or annotated regions; because each image contains multiple structures, the counts may overlap, and the table should be clarified.
Circularity Check
No significant circularity: the paper is an empirical benchmarking study with external baselines and standard metrics, and none of its claims reduce to fitted inputs or self-cited theorems.
full rationale
MS-UMamba is an empirical architecture-comparison paper. The central claim is a measured performance advantage over VM-UNet and other baselines on a non-public fetal ultrasound dataset using standard metrics (mIoU, mDC, mSE, mSP, mPRE). No quantity is defined in terms of another quantity in a way that forces the outcome: the SS-MCAT-SSM block and ADFF fusion module are introduced as architectural proposals with explicit equations for their internal operations, but these equations do not encode the evaluation metrics or the reported results. The baseline comparisons use external published models, and the ablation study compares the proposed model against its own variants, which is a controlled experiment rather than a circular derivation. There are no fitted parameters that are later relabeled as predictions, no uniqueness theorem from the authors' prior work, and no load-bearing self-citation: the reference list contains external prior work, and the present authors do not appear to cite their own earlier results to justify the central premise. The paper's stated limitations--poor small-structure segmentation, scarce data, and large model parameters--are explicit weakness disclosures, not circularity. Concerns about the undocumented train/validation/test split and lack of statistical significance testing are external-validity or reproducibility risks, not circular reasoning. The derivation chain is therefore self-contained as an empirical study, and no circular step can be exhibited with specific equations or self-citations.
Assumptions & free parameters
free parameters (4)
- Focal loss alpha (alpha) =
not reported
- Focal loss gamma (gamma) =
not reported
- Loss combination weight between Focal and Dice loss =
not reported
- Number of attention scales n in Eq. (2) =
not reported
assumptions (4)
- domain assumption Manual annotations of the six fetal structures are correct and consistent.
- domain assumption The train/validation/test split is unbiased and leakage-free.
- domain assumption Baseline models were trained fairly and comparably.
- ad hoc to paper The loss functions in Eqs. (9)-(10) are implemented as intended.
Cite this review
Pith. "Pith review of MS-UMamba: An Improved Vision Mamba Unet for Fetal Abdominal Medical Image Segmentation." pith.science (2026). https://pith.science/paper/JGAQJZ3N
@misc{pith2026250612441,
author = {Pith},
title = {Pith review of: MS-UMamba: An Improved Vision Mamba Unet for Fetal Abdominal Medical Image Segmentation},
year = {2026},
howpublished = {\url{https://pith.science/paper/JGAQJZ3N}},
note = {Machine review of arXiv:2506.12441}
}
read the original abstract
Recently, Mamba-based methods have become popular in medical image segmentation due to their lightweight design and long-range dependency modeling capabilities. However, current segmentation methods frequently encounter challenges in fetal ultrasound images, such as enclosed anatomical structures, blurred boundaries, and small anatomical structures. To address the need for balancing local feature extraction and global context modeling, we propose MS-UMamba, a novel hybrid convolutional-mamba model for fetal ultrasound image segmentation. Specifically, we design a visual state space block integrated with a CNN branch (SS-MCAT-SSM), which leverages Mamba's global modeling strengths and convolutional layers' local representation advantages to enhance feature learning. In addition, we also propose an efficient multi-scale feature fusion module that integrates spatial attention mechanisms, which Integrating feature information from different layers enhances the feature representation ability of the model. Finally, we conduct extensive experiments on a non-public dataset, experimental results demonstrate that MS-UMamba model has excellent performance in segmentation performance.
Figures
Reference graph
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Reviewed August 7, 2026 · model on record in the stance chip above.
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