REVIEW 4 major objections 5 minor 20 references
Analysis of Quantitative Angiography using Projection Foreshortening Correction and Injection Bias Removal
T0 review · 4 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read Two-dimensional quantitative angiography can be made view- and injection-independent by dividing the angiogram by a 3D-derived path-length map, then deconvolving the dome curve with the arterial input function.
desk verdict A legitimate integration of the group's own PLC and SVD methods with clear self-consistency evidence, but the clinical claims outrun the validation, especially on 3D-2D registration and ground truth. 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 path-length weight matrix: for each detector ray, the length of its intersection with the co-registered 3D vessel mask, obtained by forward-projecting the reconstruction onto the DSA geometry and ray tracing. Dividing the log-angiogram by this weight matrix converts the signal from path-length-weighted absorption into a concentration-like signal, which is what removes view dependence. The second mechanism is SVD deconvolution of the aneurysm dome time-density curve by the arterial input function, which removes the injection waveform; the paper compares sSVD, bSVD, and oSVD variants. The corrected impulse response function then yields the three parameters that the paper treats as the stable hemodynamic readouts.
What would settle it
Acquire DSA in two views at two injection rates for a single phantom, then deliberately mis-register the 3D mask by increasing translational offsets (for example, 1, 2, and 5 mm) and recompute the mean transit time; if the mean-transit-time-versus-duration slope grows with mis-registration rather than staying flat, the claimed injection independence is bounded by registration accuracy and fails outside that tolerance.
Extended reading notes
Core claim
The authors' central claim is that the projection and injection biases that make quantitative angiography unstable are not intrinsic to the hemodynamics, and that they can be corrected with a co-registered 3D geometry plus deconvolution. After ray tracing through the 3D vessel mask to build a path-length weight matrix, each logarithmically subtracted angiographic frame is divided by that matrix to remove foreshortening. Then the dome time-density curve is deconvolved by the arterial input function with one of three SVD variants (standard Tikhonov-regularized, block-circulant, and oscillation-index), producing an impulse response function whose peak height, area under the curve, and mean transit time are reported. The paper presents RMSE reductions between arterial input curves from frontal and lateral views after path-length correction, and $\mathrm{MTT}$-versus-injection-duration slopes near zero after the combined correction: $0.015 \pm 0.017$, $0.014 \pm 0.032$, and $0.013 \pm 0.025$ for sSVD, bSVD, and oSVD in silico, and $0.031 \pm 0.015$, $0.047 \pm 0.031$, and $0.013 \pm 0.004$ in vitro.
Load-bearing premise
The entire correction rests on the 3D vessel geometry being accurately co-registered with the 2D DSA frame; if that alignment is off, the ray-traced path-length map is wrong and the correction could inject new artifacts instead of removing bias.
Editorial extensions
If this is right
- Post-correction arterial input functions from frontal and lateral views agree, so angiographic comparisons no longer need to be restricted to a single projection angle.
- Mean transit time stays nearly flat over injection durations from 0.25 to 2 seconds, so the speed of a 5 ml bolus does not change the hemodynamic readout.
- The pipeline was demonstrated on both CFD-generated virtual angiograms and a physical patient-specific phantom, suggesting it can be transferred to clinical C-arm DSA data.
- Stable parameters allow pre- and post-treatment comparisons to be made even when the C-arm angle or injection settings differ between runs, which is the common intraoperative situation.
- All three SVD variants flattened the mean-transit-time dependence, so the choice among them can be made on noise handling, computational cost, or other practical grounds.
Reading between the lines
- A testable extension would use the residual mean-transit-time-versus-duration slope as a per-case quality check: a large slope after correction would flag a failed 3D-to-2D co-registration or an incomplete vessel mask.
- The same path-length weight matrix could be applied to other DSA-derived biomarkers, such as parametric color maps or wash-in/wash-out indices, not just the three impulse-response parameters studied here.
- Registration accuracy is the unquantified tolerance: perturbing the 3D-to-2D alignment by millimeters and measuring the resulting mean-transit-time drift would define the clinical geometry requirement.
- The method depends on having a pre-existing 3D volume, so workflows that acquire only biplane DSA would need a surrogate depth model before this correction could be applied.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This manuscript proposes a pipeline that combines path-length correction (PLC) with singular value decomposition (SVD) based deconvolution to reduce projection-induced foreshortening and injection-related variability in two-dimensional quantitative angiography. The PLC step co-registers a 3D vascular mask or reconstruction with the 2D DSA projection, ray-traces vessel-intersection lengths, and divides the logarithmic angiogram by this path-length map. Three SVD variants (sSVD, bSVD, oSVD) are then used to deconvolve the aneurysm time-density curve with an arterial input function, yielding impulse response parameters PH_IRF, AUC_IRF, and MTT. The method is evaluated in three in-silico intracranial aneurysm models and one in-vitro patient-specific phantom under different views, flow velocities, and injection durations. The authors report reduced RMSE between AIFs from different views/locations after PLC and flattening of MTT versus injection-duration slopes after PLC+SVD, and conclude that the combination significantly enhances the reliability of quantitative angiographic measurements.
Significance. If the proposed method truly removes projection and injection biases, it would fill a practical clinical need for stable quantitative angiographic measurements during neurovascular procedures. The paper's strengths are its combined in-silico and in-vitro experimental design, the systematic comparison of three standard SVD deconvolution variants, and a workflow that relies on routinely acquired 3D rotational angiography. However, the current validation is almost entirely based on self-consistency metrics—agreement between AIFs and constancy of MTT across injection durations—rather than on comparisons with independent ground truth. In addition, the in-vitro branch of the pipeline depends on an unquantified 3D-to-2D registration step. The contribution is therefore promising and potentially useful, but the central claim of enhanced reliability requires stronger validation before it can be considered established.
major comments (4)
- [Section 2.2] The accuracy of the PLC pipeline in the in-vitro experiments depends on the co-registration between the forward-projected 3D reconstruction and the averaged DSA frame, but the paper reports no quantitative registration error (e.g., target registration error, Dice overlap, or manual landmark distances) and no sensitivity analysis to misalignment. Because PLC divides each pixel by a ray-traced path length, even small registration errors could nonuniformly scale the time-density curves and potentially produce or mask the RMSE reductions and slope flattening reported in Section 3. The in-silico experiments assume perfect alignment by construction and therefore cannot rule out such artifacts. Please add a registration accuracy metric and a perturbation study (e.g., applying realistic translations or rotations to the projected mask) to show that the correction is robust.
- [Section 3 (Table 1 and Figures 5-6)] The validation is based entirely on self-consistency metrics: RMSE between AIFs from different views/locations and the flattening of MTT versus injection-duration slopes. There is no comparison to a gold-standard measurement, even though the in-silico CFD simulations provide an independent ground-truth transit time that could be computed directly from particle trajectories, and the in-vitro phantom could potentially be assessed with an independent measurement technique. Without such a comparison, the claim that PLC+SVD 'significantly enhances the reliability of quantitative angiographic measurements' is not fully supported; the method could be imposing an internally consistent but biologically or physically incorrect result. Please include direct comparisons with ground-truth MTT or other independent quantities where available.
- [Section 2.3] The SVD truncation threshold is described as 'determined empirically, retaining singular values above a certain percentage of the maximum value,' but the manuscript does not specify the exact selection rule, the range of thresholds tested, or whether the same threshold was applied across all cases. If the threshold was chosen by inspecting the same datasets used to compute the MTT slopes, the reported flattening could partly reflect tuning rather than genuine removal of injection bias. Please provide a principled threshold selection criterion (e.g., based on noise level or the L-curve) and report the sensitivity of the MTT results to the threshold choice.
- [Section 3 (in-vitro results)] The in-vitro conclusions are derived from a single patient-specific phantom, two views, and no repeated acquisitions, and the reported MTT slopes are means across views without measures of variability or statistical tests. The statement that the method 'nearly eliminated' injection effects is therefore based on a very small sample. Please report per-view slopes, standard errors, and formal tests of whether the slopes are consistent with zero, or explicitly state the exploratory nature of these in-vitro results.
minor comments (5)
- [Abstract and Section 1] The phrase 'path-length correction (PLC) correction' is redundant; the second 'correction' should be deleted.
- [Section 2.2 and Figure 3 captions] The term 'corregistration' is used in several places; it should be 'co-registration.'
- [Table 1] The caption states that RMSEs are averaged across three in-silico models but does not indicate the spread of the values; please include standard deviations or error bars so the reader can assess consistency across models.
- [Section 2.4] The hypothesis tests are described only qualitatively (e.g., 'significant reduction in RMSE') without statistical tests; please add confidence intervals or p-values, or soften the wording to describe observed reductions rather than significant effects.
- [Figures 5 and 6] The captions do not define the line colors and styles in the figures (e.g., which lines correspond to 'without PLC and deconvolution,' 'SVD alone,' and 'PLC+SVD'); please ensure every plot element is identified in the caption or legend.
Circularity Check
No significant circularity: the in-vitro PLC validation is independent of the fitted geometry, and no QA parameter is optimized to the reported endpoints.
full rationale
The paper's central claim is that path-length correction plus SVD deconvolution makes QA parameters stable across projection views and injection durations. The load-bearing evidence includes in-vitro experiments in which the PLC map is obtained by co-registering a 3D rotational DSA reconstruction with 2D DSA frames (Section 2.2), then dividing the angiogram by the ray-traced path-length matrix; this is a physical normalization, not a fit to the AIF RMSE or MTT endpoints. The SVD truncation threshold is described only as 'determined empirically' (Section 2.3), with no statement that it was selected to minimize the reported MTT slopes, so a fitted-input-called-prediction step cannot be established from the paper text. The in-silico PLC test (Section 2.1) is indeed nearly an identity: virtual DSA is generated by cone-beam forward projection whose weights are the same ray-intersection lengths used for correction, so dividing by the weight matrix is the inverse of the forward model and the RMSE reduction is mathematically guaranteed. However, the authors explicitly acknowledge the geometry is 'already aligned' in the in-silico case, and the in-vitro arm provides the independent empirical test of the method. Self-citations (Refs. 6, 8, 14) are method and feasibility references for PLC and SVD variants; the present paper contains its own in-vitro measurements of the corrected parameters. The acknowledged limitation that PLC requires high-quality 3D imaging and accurate co-registration (Discussion) is a robustness concern, not a circularity: the paper does not define PLC in terms of the outcomes it predicts. No specific equation or quoted passage reduces the central derivation to a fitted parameter or to a self-citation chain.
Assumptions & free parameters
free parameters (2)
- SVD truncation threshold =
not reported
- Registration hyperparameters =
grid spacing 128 to 0.01, 4-5 resolutions, LBFGS, etc.
assumptions (5)
- domain assumption The recorded DSA gray values after logarithmic subtraction are linearly proportional to the integrated contrast concentration along the X-ray path (Beer-Lambert law).
- domain assumption The co-registration between the 3D vascular mask and the 2D DSA projection is accurate enough that the ray-traced path-length matrix faithfully represents the true X-ray paths through the vessel.
- domain assumption SVD deconvolution with the AIF recovers the true impulse response function of the aneurysm dome.
- domain assumption MTT invariance across injection durations is a valid indicator that injection bias has been removed.
- domain assumption In-silico CFD simulations using steady-state laminar flow with parabolic inlet profiles adequately represent the hemodynamics of the aneurysms for validating the correction method.
Cite this review
Pith. "Pith review of Analysis of Quantitative Angiography using Projection Foreshortening Correction and Injection Bias Removal." pith.science (2026). https://pith.science/paper/P345WQSA
@misc{pith2026241108185,
author = {Pith},
title = {Pith review of: Analysis of Quantitative Angiography using Projection Foreshortening Correction and Injection Bias Removal},
year = {2026},
howpublished = {\url{https://pith.science/paper/P345WQSA}},
note = {Machine review of arXiv:2411.08185}
}
read the original abstract
This study aims to mitigate these biases and enhance QA analysis by applying a path-length correction (PLC) correction, followed by singular value decomposition (SVD)-based deconvolution, to angiograms obtained through both in-silico and in-vitro methods. We utilized DSA data from in-silico and in-vitro patient-specific intracranial aneurysm models. To remove projection bias, PLC for various views were developed by co-registering the pre-existing 3D vascular geometry mask with the DSA projections, followed by ray tracing to determine paths across 3D vessel structures. These maps were used to normalize the logarithmic angiographic images, correcting for projection-induced foreshortening across different angles. Subsequently, we focused on eliminating injection bias by analyzing the corrected angiograms under varied projection views, injection rates, and flow conditions. Regions of interest at the aneurysm dome and inlet were placed to extract Time Density Curves for the lesion and the arterial input function, respectively. Using three standard SVD methodologies, we extracted the aneurysm Impulse Response function (IRF) and its associated parameters Peak Height (PHIRF), Area Under the Curve (AUCIRF), and Mean Transit Time (MTT). Our methodology employing PLC and SVD-based deconvolution ensures reliable quantitative angiographic measurements across varying conditions, supporting consistent assessments of disease severity and treatment efficacy. This approach significantly enhances intrapatient and intraprocedural reliability in neurovascular diagnostics.
Figures
Figures from the paper (2 more)
Reference graph
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Reviewed August 12, 2026 · model on record in the stance chip above.
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