REVIEW 4 major objections 7 minor 1 cited by
Dynamic-Computed Tomography Angiography for Cerebral Vessel Templates and Segmentation
T0 review · 4 major / 7 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read Dynamic CTA can supply the training labels that make automatic artery and vein segmentation on conventional CTA feasible.
desk verdict Genuinely new CT angiographic atlases, but the DL-vs-atlas comparison is inflated by sensitivity-only metrics and shared iCafe labels. 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 central mechanism is a voxel-wise conditional subtraction rule. After rigidly registering the arterial-phase and venous-phase CTA series, the algorithm keeps a subtracted arterial voxel only when its intensity exceeds the corresponding venous value, suppressing veins, and keeps a subtracted venous voxel only in the reverse comparison, suppressing arteries. This produces an artery-only volume and a vein-only volume for every patient. Those volumes serve two roles: they are inputs to the iterative multivariate template-construction pipeline that yields the first arterial and venous CTA atlases, and they are the images on which the semi-automatic vessel tracer produces the labels used to train and evaluate the deep learning models.
What would settle it
Have two expert neuroradiologists manually annotate arteries and veins on the same 11 test scans, then recompute the modified Dice alongside a symmetric metric such as full Dice or precision; if precision is much lower than the reported sensitivity, or if inter-rater agreement is poor, the claimed accuracy is not a reliable measure of segmentation quality.
Extended reading notes
Core claim
The paper's central claim is that the temporal information in dynamic CTA can be converted into high-quality vascular ground truth for conventional CTA. By subtracting the pre-contrast baseline and then comparing arterial-phase and venous-phase intensities voxel by voxel, the authors isolate arteries and veins into separate volumes, which allows them to construct, for the first time, dedicated CT angiographic atlases of intracranial arteries and veins. Using these vessel-separated volumes as input to a semi-automatic MRA tracing tool, they generate 20 arterial labels plus venous labels with only modest manual correction, and train deep learning models to predict all vessels directly from bone-in CTA images. On an 11-patient test set, the deep learning models exceeded template-registration segmentation by a wide margin on the sensitivity-oriented modified Dice metric (0.856 versus 0.324 for arteries, 0.743 versus 0.495 for veins), with the largest gains on proximal vessels including the internal carotid, middle cerebral M1, posterior cerebral P1, and anterior cerebral A1 segments.
Load-bearing premise
The whole comparison depends on the labels produced by a semi-automatic MRA vessel-tracing tool applied to the subtracted CTA images and checked only qualitatively by a neuroradiologist, with a sensitivity-oriented metric that never penalizes predictions that add false vessels.
Editorial extensions
If this is right
- A model trained on a modest dynamic-CTA cohort can segment proximal arteries and major veins on bone-in CTA images that were never manually annotated.
- The first CT angiographic atlases can serve as population templates for automated labeling of the ICA, vertebrobasilar, M1, A1, and P1 territories, although distal branches are not reliably captured.
- Artery-vein separation is achievable from temporal information alone, making dynamic acquisition a source of ground truth rather than requiring expert manual tracing on static CTA.
- Registration-based segmentation is competitive only when aligned to subtracted or vessel-separated volumes, not to raw CTA, so atlas guidance for routine CTA will need the deep learning route or an intermediate subtraction step.
Reading between the lines
- The evaluation is sensitivity-focused, so the reported gap would likely shrink under a symmetric metric that counts false-positive vessels; a precision-aware comparison could test this, and the paper does not report one.
- Because the deep learning model is trained on bone-in CTA across multiple contrast phases, a direct deployment path is conventional single-phase CTA acquired near peak arterial timing; the paper demonstrates phase robustness but does not test that transfer.
- Distal-vessel segmentation remains weak (M2+, A2+, P2+), suggesting that the next bottleneck is small-vessel annotation rather than artery-vein separation; centerline supervision or topology-aware losses are natural extensions.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes two automatic vessel segmentation approaches for conventional CTA: (1) construction of population-averaged arterial and venous CT angiographic templates from 4D-CTA data, followed by nonlinear registration to segment vessels via template-derived ROIs, and (2) deep learning segmentation models (nnU-Net and NexToU) trained on labels produced by the semi-automatic MRA tool iCafe applied to vessel-separated dynamic CTA volumes. The authors evaluate both approaches on 11 test patients using branch-wise metrics (modified Dice coefficient mDC, average directed Hausdorff distance adHD, and topology sensitivity tSens), reporting that deep learning outperforms atlas-based registration (arterial amDC 0.856 vs 0.324; venous amDC 0.743 vs 0.495). The main contributions claimed are the first angiographic CT atlases and a practical pipeline for generating CTA vessel ground truth with reduced manual effort.
Significance. If the claims are substantiated, the work would provide a useful contribution: the first CT angiographic templates, a method for leveraging dynamic CTA to separate arteries and veins, and a deep learning approach that may reduce annotation burden for CTA vessel segmentation. The use of public tools (ANTs, nnU-Net, iCafe) and a clearly described preprocessing pipeline are strengths. However, the central quantitative claim (DL superiority over atlas) rests on a sensitivity-only metric and on evaluation labels derived from the same iCafe pipeline used for training labels. The paper does not report precision, standard Dice, or any false-positive measure, nor a statistical comparison between DL and atlas results. The small, single-scanner, all-female evaluation cohort further limits generalizability. The novelty of the atlas construction is credible, but the segmentation claim as currently supported is fragile.
major comments (4)
- [§2.6.1 and §3.3] The modified Dice coefficient defined in §2.6.1 is mDC(Aj,P) = |Aj∩P|/|Aj|, which is pure recall (sensitivity). The headline comparisons in the abstract and §3.3, e.g., amDC 0.856 vs 0.324 for arteries, therefore penalize the atlas for missing ground-truth voxels but do not penalize either method for over-prediction. A prediction covering the entire image volume would achieve an mDC of 1.0 for every label. To support the claim that DL 'outperforms' atlas-based segmentation, the paper must report a precision-aware metric (e.g., standard Dice, precision, or volume overlap) or a false-positive-sensitive surface metric (e.g., bidirectional Hausdorff distance). Without this, the observed difference could reflect different recall/precision trade-offs rather than overall segmentation quality.
- [§2.5, §2.6.2, §3.3] There is a partial circularity in the DL evaluation: the training labels and the evaluation ground truth are both produced by the same iCafe pipeline applied to vessel-separated dynamic CTA volumes (§2.5). The deep learning model is therefore trained and scored on fidelity to iCafe, not on independent anatomical truth. The atlas-based segmentation is built independently of iCafe, making the DL-vs-atlas comparison asymmetric in label source. The limitations section (§4.3.2) acknowledges that iCafe was designed for MRA, required manual editing for veins, and that inter-rater studies are needed, but the paper does not quantify how much of the reported 0.856 vs 0.324 gap is attributable to reproducing iCafe-specific biases. The authors should evaluate the DL models on an independent manually annotated test set (or a subset at least) and report the agreement between iCafe-derived labels and manual expert labels.
- [§3.2, §3.3] The headline claim that DL outperforms atlas registration is not accompanied by any statistical comparison. The atlas results are presented in Figure 8 and Supplemental Table 2 (per-label mDC for Groups 1–3), while the DL results are given in Table 2 (per-phase averages). No paired test, confidence interval, or per-patient comparison between the two methods is reported. Given N=11 and the high variance visible in the atlas box plots, the observed differences may not be statistically robust. The authors should report per-label, per-patient paired comparisons (e.g., Wilcoxon signed-rank test) or at least confidence intervals for the amDC differences.
- [§2.4, §4.2, Table 1] The number of training patients is inconsistent across the manuscript. The abstract states that iCafe was used to segment vessels in 29 patients; §4.2 states 'a dataset with 102 training images from 27 patients'; Table 1 lists 'Training (27)'. Section 2.5 and Figure 4 do not specify the training cohort size. These numbers must be reconciled. The discrepancy affects the reader's ability to assess the claims about data scale and generalizability.
minor comments (7)
- [Abstract] The sentence 'Dynamic CTA is a type of imaging that captures temporal information about the We aim to develop' is grammatically broken; it should be revised.
- [§2.2] 'NifTi' should be 'NIfTI'.
- [§2.5.1] The label 'V A' (with a space) is used inconsistently; elsewhere it is 'VA'. Also 'Pcomm' vs 'PComm' capitalization should be made consistent.
- [§4.1] 'Smaller distal vessels appeared to be diffused' should likely be 'diffuse'.
- [§4.2] The phrase 'metrics that focused on sensitively' contains a typo; it should be 'sensitivity'.
- [Figure 2] '1937 imaged by the institution' should be '1937 images'.
- [§2.6.2] The metric adHD is defined as a sum over ground-truth surface points only (directed toward the predicted surface), so it does not penalize spurious predictions. This should at least be stated explicitly in the main text, not only in the Discussion, to avoid over-interpretation.
Circularity Check
No significant circularity: held-out evaluation of DL against iCafe-derived labels is a standard supervised generalization test, not a derivation equivalent to its inputs; the atlas comparison is independent of training labels.
full rationale
Walking the derivation chain, the only candidate circular link is that both training and evaluation labels for the DL models are produced by the same semi-automatic iCafe pipeline (Sections 2.4, 2.5, 2.6.2). This is a limitation in anatomical validity, not a circular derivation: the DL model never sees the evaluation patients' labels during training; patient-level splitting is stated in Section 2.4, and the test mDC therefore measures out-of-sample generalization of the learned mapping from bone-in CTA to iCafe-style labels. No equation in the paper defines the predictions in terms of the test labels, and no fitted parameter is re-evaluated on the data that produced it. The atlas-based comparison is also not circular because the atlas is built from a separate 25-patient cohort and its ROIs are threshold/manual, not derived from iCafe labels. The sensitivity-only mDC and the MRA-oriented iCafe tool are validity concerns explicitly acknowledged in Sections 2.6.1 and 4.3.2, but they do not make the reported DL-vs-atlas comparison equivalent to its inputs. There are no load-bearing self-citations: iCafe [16], nnU-Net [17], NexToU [18], and the template pipelines [24, 10] are external prior work with no author overlap. Hence no circular step meets the quoted-evidence bar.
Assumptions & free parameters
free parameters (2)
- Template ROI threshold =
30 HU
- Template convergence selection rule =
DSC cutoff 98%; iteration with lowest RMSE, iteration 10
assumptions (4)
- domain assumption Scanner baseline subtraction removes bone and soft tissue accurately across all dynamic phases.
- domain assumption A voxel brighter in the arterial phase than in the venous phase is artery, and vice versa.
- domain assumption iCafe vessel traces on subtracted CTA are valid ground truth for arteries and veins.
- ad hoc to paper Sensitivity-only modified Dice is a sufficient comparison metric.
Cite this review
Pith. "Pith review of Dynamic-Computed Tomography Angiography for Cerebral Vessel Templates and Segmentation." pith.science (2026). https://pith.science/paper/KR436RPA
@misc{pith2026250209893,
author = {Pith},
title = {Pith review of: Dynamic-Computed Tomography Angiography for Cerebral Vessel Templates and Segmentation},
year = {2026},
howpublished = {\url{https://pith.science/paper/KR436RPA}},
note = {Machine review of arXiv:2502.09893}
}
read the original abstract
Background: Computed Tomography Angiography (CTA) is crucial for cerebrovascular disease diagnosis. Dynamic CTA is a type of imaging that captures temporal information about the We aim to develop and evaluate two segmentation techniques to segment vessels directly on CTA images: (1) creating and registering population-averaged vessel atlases and (2) using deep learning (DL). Methods: We retrieved 4D-CT of the head from our institutional research database, with bone and soft tissue subtracted from post-contrast images. An Advanced Normalization Tools pipeline was used to create angiographic atlases from 25 patients. Then, atlas-driven ROIs were identified by a CT attenuation threshold to generate segmentation of the arteries and veins using non-linear registration. To create DL vessel segmentations, arterial and venous structures were segmented using the MRA vessel segmentation tool, iCafe, in 29 patients. These were then used to train a DL model, with bone-in CT images as input. Multiple phase images in the 4D-CT were used to increase the training and validation dataset. Both segmentation approaches were evaluated on a test 4D-CT dataset of 11 patients which were also processed by iCafe and validated by a neuroradiologist. Specifically, branch-wise segmentation accuracy was quantified with 20 labels for arteries and one for veins. DL outperformed the atlas-based segmentation models for arteries (average modified dice coefficient (amDC) 0.856 vs. 0.324) and veins (amDC 0.743 vs. 0.495) overall. For ICAs, vertebral and basilar arteries, DL and atlas -based segmentation had an amDC of 0.913 and 0.402, respectively. The amDC for MCA-M1, PCA-P1, and ACA-A1 segments were 0.932 and 0.474, respectively. Conclusion: Angiographic CT templates are developed for the first time in literature. Using 4D-CTA enables the use of tools like iCafe, lessening the burden of manual annotation.
Figures
Figures from the paper (9 more)
Forward citations
Cited by 1 Pith paper
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Reference graph
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