REVIEW 3 major objections 5 minor 33 references
Brightness-Invariant Tracking Estimation in Tagged MRI
T0 review · 3 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read BRITE separates anatomy from fading tags, yielding accurate motion and strain estimates in tagged MRI.
desk verdict BRITE is a well-built tracking method, but 'brightness-invariant' is only shown for global brightness changes; local variations are not modeled or tested. 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 factorized forward model $g^{h,v}_t = \tilde a_t \otimes \tilde p^{h,v}_t$, where $\tilde p^{h,v}_t = [A_t \sin(2\pi \tilde\mu s_{h,v} + \tilde\varphi^{h,v}) + B_t] \circ \phi_t^{-1}$, with $s_h=x$ and $s_v=y$. This factorization lets brightness change be absorbed by the two scalar parameters $A_t$ and $B_t$ instead of leaking into the motion field. The second essential piece is the deformation representation: a physics-informed neural network maps coordinates $(x,y)$ to a stationary velocity field $u_t$, and scaling-and-squaring exponential integration converts $u_t$ into the smooth, invertible deformation $\phi_t$ and its inverse. Because $\phi_t^{-1}$ warps both the anatomy and the tag pattern into the current frame, the same motion explains both image components, which is why no explicit smoothness penalty is needed.
What would settle it
Run BRITE on a tagged sequence with known deformation in which part of the field of view undergoes a local brightness change (for instance, a spatially varying T1 or flip-angle map, or an inflow of contrast agent) while the rest stays uniform; if the estimated displacement near that local region deviates from ground truth but is accurate elsewhere, the global-fading, constant-anatomy assumption is the reason.
Extended reading notes
Core claim
The central claim is that the ill-posed problem of jointly recovering the underlying anatomy, the fading tag pattern, and the Lagrangian motion (motion of each material point relative to the first frame) from a tagged MRI sequence has a tractable solution when the forward model is factored as $g^{h,v}_t = \tilde a_t \otimes \tilde p^{h,v}_t$. The anatomy is required to be constant in material coordinates, $\tilde a_t = \tilde a_0 \circ \phi_t^{-1}$, while the tag pattern is a sinusoid whose frequency and phase are fixed from the first frame and whose amplitude $A_t$ and offset $B_t$ are the only time-varying quantities. A diffusion model pretrained on anatomical images provides the prior that makes recovering $\tilde a_0$ from the product well-posed, and a physics-informed neural network outputs a stationary velocity field whose exponential map produces the deformation $\phi_t$, a smooth, invertible warping. The paper reports that on gel phantom data, this disentanglement yields more accurate displacement and strain estimates than the compared methods, with the advantage largest when tag fading and spectral overlap are severe.
Load-bearing premise
The method's forward model assumes the anatomy is exactly carried along by the motion, with only a single global amplitude and offset changing in the tag pattern; if real tissue brightness changes locally rather than globally, the optimizer can translate that brightness change into a spurious apparent deformation.
Editorial extensions
If this is right
- If BRITE's reported accuracy holds, tagged MRI motion tracking can be made brightness-invariant without extra acquisitions, removing a major practical argument for CSPAMM or TruHARP.
- Because the tag frequency is estimated from the data rather than assumed from the pulse sequence, the method can tolerate gradient imperfections that shift or blur the spectral peaks.
- Initializing each frame's velocity-field network from the previous frame's solution lets the tracker follow motion larger than half a tag period without tag-jumping, and avoids error accumulation from composing pairwise registrations.
- Resistance to tag fading should extend the usable time window of a single tagged acquisition, exactly where HARP and intensity-based methods degrade most.
- The reported processing time of about 8.4 seconds per frame with modest GPU memory suggests 2D clinical workflows are feasible today, and the paper argues 3D extension is straightforward.
Reading between the lines
- A test the paper does not run is a spatially nonuniform brightness change, since its fading model has only global $A_t$ and $B_t$; one would expect local T1 variation or inflow to be absorbed as apparent deformation, which would set the boundary of the method's applicability.
- The diffusion prior is trained only on synthetic ovals, and the paper's own limitations section restricts the tag model to sinusoids and validation to a 2D static gel phantom with simulated deformations; applying the method to textured human organs with independent motion measurements will show how much the prior and tag model must be generalized.
- The same factorization could be carried over to other amplitude-modulated tagging schemes, such as grid tags or higher-order SPAMM, by swapping the sinusoidal tag model while keeping the PINN tracking stage.
- A direct comparison against CSPAMM and TruHARP on the same phantom with the same ground truth would quantify how much accuracy is gained or lost by avoiding their extra acquisitions.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces BRITE, a two-stage tracking method for SPAMM-tagged MRI. In the first stage, the method disentangles the anatomical image from the horizontal and vertical tag patterns at the reference frame by jointly optimizing a DDPM latent code and a CNN-predicted sinusoidal tag model (Eq. 1). In the second stage, for each subsequent frame a PINN produces a stationary velocity field whose exponential map defines a diffeomorphic Lagrangian deformation, while a Tag Fading Module estimates two global scalars A_t and B_t per frame; all unknowns are fit by minimizing the reconstruction MSE in Eq. (6). The method is evaluated on a silicone gel phantom with eight SPAMM acquisitions (tag periods 9, 12, 18, 26 mm; flip angles 5 and 10 degrees) under simulated non-rigid deformations (N=20), one rigid rotation, and a static case, comparing EPE and eMPS against HARP, SinMod, DRIMET, SyN variants, and DeepTag. The paper claims that BRITE is more accurate than these baselines and is resistant to tag fading.
Significance. If the claims survive closer quantitative scrutiny, BRITE would be a useful contribution: it attacks tag fading and spectral overlap simultaneously, requires no extra acquisitions beyond the standard horizontal/vertical SPAMM pair, and the validation design has real merit because the phantom images carry natural T1-driven tag fading while the ground-truth deformations come from external simulation. The runtime and memory figures are modest. The main evidence, however, is global-fading-only phantom data, and the quantitative support is incomplete (no error bars or significance tests, and no numbers for the rotation/static cases), so the strength of the central claim is currently larger than the evidence.
major comments (3)
- [§3, Eqs. (4)–(6); §5, Limitations] The forward model represents brightness evolution by only two global scalars per frame, A_t and B_t, in the Tag Fading Module. The phantom is a homogeneous gel, so its T1-driven fading is spatially uniform and exactly matches this model. Real tissue has spatially varying T1, B1 inhomogeneity, inflow, and off-resonance; none of these are exercised by the experiments, and the manuscript's Limitations section does not discuss them. Under the pixel-wise MSE objective of Eq. (6), a spatially varying brightness change could be absorbed as spurious deformation, which is precisely the failure mode the title promises to avoid. Please either narrow the claim to global tag fading or add a validation with spatially varying brightness modulation (e.g., synthetic local intensity scaling on the acquired phantom data) and report EPE/eMPS for that case.
- [§5, Fig. 5] The main quantitative evidence is reported only as curves without error bars, confidence intervals, or significance tests across the 20 non-rigid deformations. The claim that BRITE 'generally outperforms' all other methods cannot be verified statistically from the figures. Please provide per-sequence results, summary statistics with error bars, and, if appropriate, paired tests (e.g., Wilcoxon) on EPE and eMPS.
- [§5, Fig. 7] The rigid-rotation and static no-motion experiments are central to the tag-fading-resistance claim, yet the text states that 'quantitative results are omitted due to limited space.' In particular, the static case directly measures spurious motion caused by fading (cf. Fig. 2), so omitting its numbers weakens the main claim. Please include EPE and eMPS values for the rotation and static scenarios, alongside the qualitative images.
minor comments (5)
- [§4, Evaluation Metrics] Please specify how MPS is computed from the estimated displacement field (e.g., finite-difference strain and Lagrangian strain tensor), since eMPS is a central metric.
- [§4, Datasets] Please report the B-spline control-point spacing and displacement magnitudes used to generate the 20 non-rigid deformations, as these parameters determine the difficulty of the test.
- [§3, Implementation Details] The text says 'a multilayer perception' (should be 'perceptron'), and the notation for the tag-pattern CNN and the PINN weights should be made consistent (f_{\theta_{tag}} versus f_{\theta_{pinn,t}}).
- [§5, Figs. 5–7] The figure captions contain garbled strings such as '10-12mm-15-18mm-2' and the legends in Fig. 5 are difficult to read; please clean up all figures and make the per-method plotting conventions explicit.
- [Overall] No code or data availability statement is present; please add one or state that the phantom data can be shared on request.
Circularity Check
No significant circularity: BRITE's motion and strain estimates are validated against externally simulated ground-truth deformations, and its fitted brightness parameters are nuisance variables rather than disguised predictions.
full rationale
The central derivation chain is not circular. BRITE fits an anatomical prior (DDPM over synthetic ovals), tag-pattern parameters, per-frame fading scalars (At, Bt), and PINN velocity fields by minimizing reconstruction error (Eqs. 1 and 6), but its motion outputs are evaluated against simulated rigid and non-rigid ground-truth deformations that are not used in the fitting objective. The per-frame At and Bt in Eqs. (5)-(6) are nuisance parameters that absorb global tag fading, and the validation shows that this fitted brightness model does not prevent accurate motion recovery on the phantom data, including a static no-motion case. Self-citations (e.g., ref. [8], DRIMET baseline) are present but not load-bearing: they motivate prior work and provide baselines rather than justify the core inverse problem. The paper's own limitation passage correctly notes the sinusoidal tag-pattern assumption and the need for human validation. The residual concern—that spatially varying brightness changes not captured by two global scalars could be absorbed as spurious deformation (Eqs. 4-6)—is a generalization risk, not an internal circularity, and is not exercised by the homogeneous gel phantom experiments.
Assumptions & free parameters
free parameters (5)
- DDPM latent code z =
optimized, no closed form
- Tag pattern parameters (A0, B0, mu, phi_h, phi_v) =
A0,B0 initialized 0.45/0.55; phi at 2pi; mu from pulse sequence, all refined by CNN
- Per-frame fading parameters (A_t, B_t) =
initialized 0.5 for each t
- PINN velocity field weights theta_pinn,t =
fully connected net, 3x128 hidden; trained per frame
- CNN encoder weights theta_tag =
4-layer ResNet, trained with Eq (1)
assumptions (5)
- domain assumption Tagged MR image equals element-wise product of anatomy and sinusoidal tag pattern (g = a ⊗ p)
- domain assumption Anatomy is materially constant: a_t = a0 ∘ phi_t^{-1}
- domain assumption Tag pattern remains a single sinusoid with fixed frequency and phase after t=0
- domain assumption DDPM trained on synthetic random ovals generalizes to real phantom anatomy
- standard math Exponential map (scaling and squaring) produces diffeomorphic deformations
Cite this review
Pith. "Pith review of Brightness-Invariant Tracking Estimation in Tagged MRI." pith.science (2026). https://pith.science/paper/5EEWMD2G
@misc{pith2026250518365,
author = {Pith},
title = {Pith review of: Brightness-Invariant Tracking Estimation in Tagged MRI},
year = {2026},
howpublished = {\url{https://pith.science/paper/5EEWMD2G}},
note = {Machine review of arXiv:2505.18365}
}
read the original abstract
Magnetic resonance (MR) tagging is an imaging technique for noninvasively tracking tissue motion in vivo by creating a visible pattern of magnetization saturation (tags) that deforms with the tissue. Due to longitudinal relaxation and progression to steady-state, the tags and tissue brightnesses change over time, which makes tracking with optical flow methods error-prone. Although Fourier methods can alleviate these problems, they are also sensitive to brightness changes as well as spectral spreading due to motion. To address these problems, we introduce the brightness-invariant tracking estimation (BRITE) technique for tagged MRI. BRITE disentangles the anatomy from the tag pattern in the observed tagged image sequence and simultaneously estimates the Lagrangian motion. The inherent ill-posedness of this problem is addressed by leveraging the expressive power of denoising diffusion probabilistic models to represent the probabilistic distribution of the underlying anatomy and the flexibility of physics-informed neural networks to estimate biologically-plausible motion. A set of tagged MR images of a gel phantom was acquired with various tag periods and imaging flip angles to demonstrate the impact of brightness variations and to validate our method. The results show that BRITE achieves more accurate motion and strain estimates as compared to other state of the art methods, while also being resistant to tag fading.
Figures
Figures from the paper (4 more)
Reference graph
Works this paper leans on
-
[1]
Magnetic Resonance in Medicine64(2), 574–585 (2010)
Agarwal, H.K., Prince, J.L., Abd-Elmoniem, K.Z.: Total removal of unwanted harmonic peaks (TruHARP) MRI for single breath-hold high-resolution myocardial motion and strain quantification. Magnetic Resonance in Medicine64(2), 574–585 (2010)
work page 2010
-
[2]
Journal of Magnetic Resonance 137(1), 247 (1999)
Aletras, A.H., Ding, S., Balaban, R.S., Wen, H.: DENSE: displacement encoding with stimulated echoes in cardiac functional MRI. Journal of Magnetic Resonance 137(1), 247 (1999)
work page 1999
-
[3]
In: American Associ- ation for Artificial Intelligence (AAAI) Spring Symposium Series
Amini, A., Curwen, R., Constable, R.T., Gore, J.C.: MR physics-based snake tracking and dense deformations from tagged cardiac images. In: American Associ- ation for Artificial Intelligence (AAAI) Spring Symposium Series. Applications of Computer Vision in Medical Image Processing. pp. 126–129 (1994)
work page 1994
-
[4]
Arsigny, V., Commowick, O., Pennec, X., Ayache, N.: A log-euclidean framework for statistics on diffeomorphisms. In: MICCAI. pp. 924–931. Springer (2006)
work page 2006
-
[5]
IEEE Transactions on Medical Imaging29(5), 1114–1123 (2010)
Arts, T., Prinzen, F.W., Delhaas, T., Milles, J.R., Rossi, A.C., Clarysse, P.: Mapping displacement and deformation of the heart with local sine-wave modeling. IEEE Transactions on Medical Imaging29(5), 1114–1123 (2010)
work page 2010
-
[6]
Radiology172(2), 349–350 (1989)
Axel, L., Dougherty, L.: Heart wall motion: improved method of spatial modulation of magnetization for MR imaging. Radiology172(2), 349–350 (1989)
work page 1989
-
[7]
Annals of Biomedical Engineering49, 2677–2692 (2021)
Bayly, P.V., Alshareef, A., Knutsen, A.K., Upadhyay, K., Okamoto, R.J., Carass, A., Butman, J.A., Pham, D.L., Prince, J.L., Ramesh, K.T., Johnson, C.L.: MR imaging of human brain mechanics in vivo: New measurements and applications to the development of computational models of brain injury. Annals of Biomedical Engineering49, 2677–2692 (2021)
work page 2021
-
[8]
Bian, Z., Alshareef, A., Wei, S., Chen, J., Wang, Y., Woo, J., Pham, D.L., Zhuo, J., Carass, A., Prince, J.L.: Is registering raw tagged-MR enough for strain estimation in the era of deep learning? In: Medical Imaging 2024: Image Processing. vol. 12926, pp. 79–85. SPIE (2024)
work page 2024
Show all 33 references
-
[9]
In: Medical Imaging with Deep Learning
Bian, Z., Xing, F., Yu, J., Shao, M., Liu, Y., Carass, A., Woo, J., Prince, J.L.: DRIMET: Deep registration-based 3d incompressible motion estimation in tagged- MRI with application to the tongue. In: Medical Imaging with Deep Learning. pp. 134–150. PMLR (2024) 14 Bian et al
2024
-
[10]
In: International Conference on Machine Learning
Bora, A., Jalal, A., Price, E., Dimakis, A.G.: Compressed sensing using generative models. In: International Conference on Machine Learning. pp. 537–546. PMLR (2017)
2017
-
[11]
IEEE Transactions on Medical Imaging18(4), 359–363 (1999)
Dougherty, L., Asmuth, J.C., Blom, A.S., Axel, L., Kumar, R.: Validation of an optical flow method for tag displacement estimation. IEEE Transactions on Medical Imaging18(4), 359–363 (1999)
1999
-
[12]
Magnetic Resonance in Medicine30(2), 191–200 (1993)
Fischer, S.E., McKinnon, G., Maier, S., Boesiger, P.: Improved myocardial tagging contrast. Magnetic Resonance in Medicine30(2), 191–200 (1993)
1993
-
[13]
The University of Iowa (1990)
Fisher, D.J.: Automatic tracking of cardiac wall motion using magnetic resonance markers. The University of Iowa (1990)
1990
-
[14]
In: Information Processing in Medical Imaging
Gupta, S.N., Prince, J.L.: On variable brightness optical flow for tagged MRI. In: Information Processing in Medical Imaging. vol. 3, pp. 323–334. Kluwer Dordrecht (1995)
1995
-
[15]
Journal of Cardiovascular Magnetic Resonance13(1), 36 (2011)
Ibrahim, E.S.H.: Myocardial tagging by cardiovascular magnetic resonance: evolu- tion of techniques–pulse sequences, analysis algorithms, and applications. Journal of Cardiovascular Magnetic Resonance13(1), 36 (2011)
2011
-
[16]
Journal of Biomechanics 47(14), 3475–3481 (2014)
Knutsen, A.K., Magrath, E., McEntee, J.E., Xing, F., Prince, J.L., Bayly, P.V., Butman, J.A., Pham, D.L.: Improved measurement of brain deformation during mild head acceleration using a novel tagged MRI sequence. Journal of Biomechanics 47(14), 3475–3481 (2014)
2014
-
[17]
Journal of Magnetic Resonance Imaging36(6), 1490–1495 (2012)
Mannelli, L., Wilson, G.J., Dubinsky, T.J., Potter, C.A., Bhargava, P., Cuevas, C., Linnau, K.F., Kolokythas, O., Gunn, M.L., Maki, J.H.: Assessment of the liver strain among cirrhotic and normal livers using tagged MRI. Journal of Magnetic Resonance Imaging36(6), 1490–1495 (2012)
2012
-
[18]
IEEE Transactions on Medical Imaging40(4), 1240–1252 (2021)
Mella, H., Mura, J., Wang, H., Taylor, M.D., Chabiniok, R., Tintera, J., Sotelo, J., Uribe, S.: HARP-I: a harmonic phase interpolation method for the estimation of motion from tagged MR images. IEEE Transactions on Medical Imaging40(4), 1240–1252 (2021)
2021
-
[19]
Medical Physics39(4), 1793–1810 (2012)
Moerman, K.M., Sprengers, A.M., Simms, C.K., Lamerichs, R.M., Stoker, J., Nederveen, A.J.: Validation of continuously tagged MRI for the measurement of dynamic 3D skeletal muscle tissue deformation. Medical Physics39(4), 1793–1810 (2012)
2012
-
[20]
Radiology191(2), 578–580 (1994)
Niitsu, M., Kumada, M., Campeau, N.G., Niimi, S., Riederer, S.J., Itai, Y.: Tongue displacement: visualization with rapid tagged magnetization-prepared MR imaging. Radiology191(2), 578–580 (1994)
1994
-
[21]
Magnetic Resonance in Medicine42(6), 1048–1060 (1999)
Osman, N.F., Kerwin, W.S., McVeigh, E.R., Prince, J.L.: Cardiac motion track- ing using CINE harmonic phase (HARP) magnetic resonance imaging. Magnetic Resonance in Medicine42(6), 1048–1060 (1999)
1999
-
[22]
Magnetic Resonance in Medicine46(2), 324–334 (2001)
Osman, N.F., Sampath, S., Atalar, E., Prince, J.L.: Imaging longitudinal cardiac strain on short-axis images using strain-encoded MRI. Magnetic Resonance in Medicine46(2), 324–334 (2001)
2001
-
[23]
The Journal of the Acoustical Society of America121(1), 491–504 (2007)
Parthasarathy, V., Prince, J.L., Stone, M., Murano, E.Z., NessAiver, M.: Measuring tongue motion from tagged cine-MRI using harmonic phase (HARP) processing. The Journal of the Acoustical Society of America121(1), 491–504 (2007)
2007
-
[24]
IEEE Transactions on Medical Imaging11(2), 238–249 (1992)
Prince, J.L., McVeigh, E.R.: Motion estimation from tagged MR image sequences. IEEE Transactions on Medical Imaging11(2), 238–249 (1992)
1992
-
[25]
In: 2006 International Conference of the IEEE Engineering in Medicine and Biology Society
Qian, Z., Metaxas, D.N., Axel, L.: Extraction and tracking of MRI tagging sheets using a 3D Gabor filter bank. In: 2006 International Conference of the IEEE Engineering in Medicine and Biology Society. pp. 711–714. IEEE (2006) BRITE: Brightness-Invariant Tracking Estimation 15
2006
-
[26]
In: Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat
Qian, Z., Montillo, A., Metaxas, D.N., Axel, L.: Segmenting cardiac MRI tagging lines using Gabor filter banks. In: Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No. 03CH37439). vol. 1, pp. 630–633. I...
2003
-
[27]
Journal of Computational Physics378, 686–707 (2019)
Raissi, M., Perdikaris, P., Karniadakis, G.E.: Physics-informed neural networks: A deep learning framework for solving forward and inverse problems involving nonlinear partial differential equations. Journal of Computational Physics378, 686–707 (2019)
2019
-
[28]
arXiv preprint arXiv:2010.02502 (2020)
Song, J., Meng, C., Ermon, S.: Denoising diffusion implicit models. arXiv preprint arXiv:2010.02502 (2020)
2020 arXiv
-
[29]
In: IEEE Conference on Computer Vision and Pattern Recognition (CVPR)
Ulyanov, D., Vedaldi, A., Lempitsky, V.: Deep image prior. In: IEEE Conference on Computer Vision and Pattern Recognition (CVPR). pp. 9446–9454 (2018)
2018
-
[30]
IEEE Transactions on Medical Imaging36(10), 2116–2128 (2017)
Xing, F., Woo, J., Gomez, A.D., Pham, D.L., Bayly, P.V., Stone, M., Prince, J.L.: Phase vector incompressible registration algorithm for motion estimation from tagged magnetic resonance images. IEEE Transactions on Medical Imaging36(10), 2116–2128 (2017)
2017
-
[31]
In: IEEE Conference on Computer Vision and Pattern Recognition (CVPR)
Ye, M., Kanski, M., Yang, D., Chang, Q., Yan, Z., Huang, Q., Axel, L., Metaxas, D.: Deeptag: An unsupervised deep learning method for motion tracking on cardiac tagging magnetic resonance images. In: IEEE Conference on Computer Vision and Pattern Recognition (CVPR). pp. 7261–7...
2021
-
[32]
In: Proceedings of SPIE Medical Imaging (SPIE-MI 2023), San Diego, CA, February 19 – 23, 2023
Yu, J., Shao, M., Bian, Z., Liang, X., Zhuo, J., Stone, M., Prince, J.L.: New starting point registration method for tagged MRI tongue motion estimation. In: Proceedings of SPIE Medical Imaging (SPIE-MI 2023), San Diego, CA, February 19 – 23, 2023. p. 1246429 (2023)
2023
-
[33]
Medical Physics23(8), 1359–1369 (1996)
Zhang, S., Douglas, M.A., Yaroslavsky, L., Summers, R.M., Dilsizian, V., Fanana- pazir, L., Bacharach, S.L.: A Fourier based algorithm for tracking SPAMM tags in gated magnetic resonance cardiac images. Medical Physics23(8), 1359–1369 (1996)
1996
Reviewed August 7, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.