REVIEW 4 major objections 5 minor 29 references
MM2CT: MR-to-CT translation for multi-modal image fusion with mamba
T0 review · 4 major / 5 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read This paper claims that fusing T1- and T2-weighted MRI with a Mamba-based module produces synthetic CT images that score higher on PSNR and SSIM than single-modality translation, and that both the Mamba fusion and dynamic enhancement modules
desk verdict A plausible Mamba-based T1+T2 MR-to-CT fusion, but the experiments don't yet support the SOTA claim. 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 argument rides on the Mamba-based fusion module. It alternates channel-swapped T1/T2 features through a cross-modal Mamba block—a selective state space model with a gating mechanism—to project both contrasts into a shared representation. A dynamic local convolution layer and a dynamic difference-aware attention module then amplify subtle differences between modality feature maps. The fused representation is injected as conditioning into a diffusion-based generator, which combines adversarial and cycle-consistency losses. This specific combination is what the paper says enables long-range dependency modeling without quadratic attention cost.
What would settle it
Retrain Syndiff and MM2CT on the same pelvis split with five random seeds each and report mean plus-or-minus standard deviation of PSNR and SSIM. If the 95% confidence intervals overlap, the claimed 0.36 dB PSNR improvement is not established. Additionally, run i2i-mamba, Mambadfuse, and FusionMamba on the identical split; if any of them matches or exceeds 25.72 dB PSNR or 89.54 SSIM, the state-of-the-art claim fails.
Extended reading notes
Core claim
On its own terms, the paper claims that its multi-modal network is the first to meaningfully exploit T1 and T2 together for unpaired MR-to-CT synthesis. It reports that the full MM2CT model reaches 25.72 dB PSNR and 89.54 SSIM on the test split of a public pelvis dataset, beating the best single-modality baseline (25.36 dB, 88.97) and the two cycle-consistency variants. The ablation in Table 2 shows that replacing the Mamba fusion module with the baseline's architecture drops PSNR back to 25.36, and removing only the dynamic enhancement module drops it to 25.49, which the paper interprets as each component contributing. The authors conclude that retaining both Mamba cross-modal fusion and dy
Load-bearing premise
The 0.36 dB PSNR and 0.57% SSIM improvement over the strongest baseline is treated as a real signal despite being within the range that random seed variation could produce, and the state-of-the-art claim would collapse if that difference is noise.
Editorial extensions
If this is right
- If the reported gains are real, multi-modal MR-to-CT translation becomes a practical route to CT-free radiotherapy planning, since routine clinical MR protocols already include T1 and T2.
- The fusion module conditions a diffusion-based generator, so the fused feature representation can in principle be paired with different generation backbones, not only the one used here.
- The paper's ablation places most of the gain on the Mamba fusion module (0.13 dB over baseline) with the dynamic enhancement adding 0.23 dB, so future designs need both to reproduce the reported numbers.
- Because the method is trained on unpaired data, it can be applied to existing clinical MR/CT archives without requiring registration, which is the common acquisition scenario.
Reading between the lines
- The paper cites i2i-mamba, Mambadfuse, and FusionMamba as related multimodal methods but never evaluates them; a head-to-head comparison on the same dataset is the most direct test of the state-of-the-art claim and is left as an open extension.
- The reported margins come from a single run on a 15-subject dataset; repeated runs with different seeds would show whether a 0.36 dB PSNR gap is larger than run-to-run variation, and this check is not present.
- The ablation table reports only three configurations, so the claim that each component is 'necessary' is supported only by pairwise subtraction, not by a full factorial design; a configuration with the dynamic enhancement but without the Mamba module would clarify the interaction.
- The module's generality could be tested by swapping the diffusion generator for a GAN-based one or applying the fusion block to PET-MR synthesis; if the PSNR gain persists, the mechanism is structural, not tied to diffusion conditioning.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes MM2CT, a multi-modal MR-to-CT translation framework that combines T1- and T2-weighted MRI inputs using a Mamba-based fusion module plus a dynamic enhancement module, together with an adversarial diffusion-style generation module adapted from Syndiff. On a public pelvis dataset, the authors report PSNR 25.72 dB and SSIM 89.54, outperforming single-modality CycleGAN and Syndiff baselines. They conclude that the Mamba fusion and dynamic enhancement components are necessary for the improvement and claim state-of-the-art performance. The manuscript includes an architecture overview, loss formulation, quantitative comparison, and a two-row ablation study.
Significance. If the claims were fully supported, the paper would make a useful incremental contribution to multi-modal medical image synthesis: it applies a state-space fusion mechanism to MR-to-CT translation, releases code, and evaluates on a public benchmark with re-trained baselines. However, the evidence as presented is not yet sufficient for the stated claims. The comparison omits all multi-modal baselines, the reported improvements over the strongest baseline are small and are reported without uncertainty quantification, and the ablation table does not actually isolate the proposed components. The core architectural idea is plausible and the paper is clearly written at a high level, but the central 'state-of-the-art' and 'components are necessary' claims require stronger experimental support.
major comments (4)
- [Section 4.3, Table 1] The comparison set contains only single-modality baselines (T1->CT and T2->CT versions of CycleGAN and Syndiff). No method that consumes both T1 and T2 is evaluated, even though Refs. [2], [16], and [25] describe directly relevant multi-modal Mamba-based synthesis/fusion methods. Consequently, the 0.36 dB PSNR and 0.57% SSIM gains over Syndiff could be due simply to the extra input modality or increased model capacity, rather than to the proposed Mamba fusion or dynamic enhancement modules. The authors should compare against i2i-mamba [2], Mambadfuse [16], FusionMamba [25], and, minimally, a control obtained by feeding concatenated T1+T2 inputs to the Syndiff architecture.
- [Section 4.4, Table 2] The ablation study does not isolate the proposed components. The first row ('Mamba module: -, DE: -') reports PSNR 25.36 and SSIM 88.97, which are exactly the T1->CT Syndiff numbers from Table 1, not a version of MM2CT without the Mamba and DE modules. Thus Table 2 compares MM2CT against a single-modality baseline, not against an ablated MM2CT. With only the '+' rows differing by 0.13/0.23 dB PSNR and 0.48/0.09 SSIM, the conclusion that the Mamba fusion and dynamic enhancement modules are 'necessary' is not supported. The text also acknowledges in Section 4.4 that isolating DE is difficult, yet proceeds to claim strong validation; this limitation needs to be addressed with properly designed ablations, e.g., a no-fusion MM2CT with two-channel concatenation and a no-DE version.
- [Section 4.1, Section 4.3] The reported improvements over the strongest baseline are small (0.36 dB PSNR, 0.57% SSIM) and are based on a fixed split with a 4-subject test set, with no multiple random seeds, confidence intervals, or paired statistical tests. Without uncertainty quantification, the claimed state-of-the-art performance cannot be distinguished from run-to-run variation. The authors should report mean and standard deviation over at least several seeds, or use paired tests across test subjects/slices, and should qualify the state-of-the-art claim accordingly.
- [Section 3.1, Section 3.2] The method description is largely qualitative. The diffusive module is described as a 'forward diffusion process' but no diffusion equations, noise schedule, or sampling procedure are given; Eq. (1) only states the overall loss. Similarly, the cross-modal Mamba block and the dynamic difference-aware attention mechanism (Fig. 3) are described in words, but the exact tensor operations and gating formulation are not specified. Because the paper's novelty rests on these modules, this level of detail is insufficient for reproducibility. Adding formulations or precise pseudocode is necessary.
minor comments (5)
- [Section 2.1] The sentence 'CycleGAN uses cycle consistency loss ... [2]' cites Ref. [2], which is i2i-mamba, not CycleGAN. Please correct the citation.
- [Section 4.2] Typo: 'implemeted' should be 'implemented'.
- [Section 5] Typo in 'furtheßr' (should be 'further') in the final paragraph of the conclusion.
- [Table 2] The first row should be labeled explicitly as the single-modality Syndiff baseline, not as an MM2CT variant, to avoid confusion about what is being ablated.
- [Section 3.1] The terminology alternates between 'diffusive module' and 'diffusion module'; please use consistent terminology throughout.
Circularity Check
No significant circularity: the translation performance is measured on held-out test data and no prediction reduces to a fitted input or self-citation chain.
full rationale
The paper is an empirical deep-learning submission. The central result (Table 1) is a quantitative comparison on a fixed public split where the test-set PSNR/SSIM of MM2CT is computed from network outputs versus ground-truth CT; no parameter is fitted to the test metric and then reported as a prediction. The method borrows components (Mamba blocks, channel swapping, cross-modal Mamba) with explicit citations to [16], [25], and [10], and the loss settings are copied from [20], but these are external prior works used as building blocks, not self-citations. The authors' own prior work appears only as related references and is not load-bearing for the SOTA claim. The ablation in Table 2 is imperfect—the first row is Syndiff rather than MM2CT without Mamba/DE—but that is an experimental-design/control concern, not circularity: the reported numbers still come from held-out evaluation, and the paper does not redefine any metric to force its conclusion. Therefore no circular step meets the evidentiary bar of Eq. X = Eq. Y by construction or a fitted parameter renamed as prediction.
Assumptions & free parameters
free parameters (2)
- λl1 =
same as Syndiff [20]
- λgan =
same as Syndiff [20]
assumptions (4)
- domain assumption Mamba blocks capture long-range dependencies effectively in medical images.
- domain assumption T1 and T2 MRI carry complementary information beneficial for CT synthesis.
- domain assumption Unsupervised training on unpaired images transfers to paired registered evaluation.
- domain assumption The diffusion forward process acts as a low-pass filter.
Cite this review
Pith. "Pith review of MM2CT: MR-to-CT translation for multi-modal image fusion with mamba." pith.science (2026). https://pith.science/paper/TVVZ4DCG
@misc{pith2026250805476,
author = {Pith},
title = {Pith review of: MM2CT: MR-to-CT translation for multi-modal image fusion with mamba},
year = {2026},
howpublished = {\url{https://pith.science/paper/TVVZ4DCG}},
note = {Machine review of arXiv:2508.05476}
}
read the original abstract
Magnetic resonance (MR)-to-computed tomography (CT) translation offers significant advantages, including the elimination of radiation exposure associated with CT scans and the mitigation of imaging artifacts caused by patient motion. The existing approaches are based on single-modality MR-to-CT translation, with limited research exploring multimodal fusion. To address this limitation, we introduce Multi-modal MR to CT (MM2CT) translation method by leveraging multimodal T1- and T2-weighted MRI data, an innovative Mamba-based framework for multi-modal medical image synthesis. Mamba effectively overcomes the limited local receptive field in CNNs and the high computational complexity issues in Transformers. MM2CT leverages this advantage to maintain long-range dependencies modeling capabilities while achieving multi-modal MR feature integration. Additionally, we incorporate a dynamic local convolution module and a dynamic enhancement module to improve MRI-to-CT synthesis. The experiments on a public pelvis dataset demonstrate that MM2CT achieves state-of-the-art performance in terms of Structural Similarity Index Measure (SSIM) and Peak Signal-to-Noise Ratio (PSNR). Our code is publicly available at https://github.com/Gots-ch/MM2CT.
Figures
Figures from the paper (1 more)
Reference graph
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Reviewed August 5, 2026 · model on record in the stance chip above.
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