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TractoTransformer: Diffusion MRI Streamline Tractography using CNN and Transformer Networks
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Proposes TractoTransformer, a CNN-plus-decoder-only-Transformer model that predicts conditional fODF directions auto-regressively along streamlines for diffusion MRI tractography.
Problem
White matter tractography from noisy, ambiguous dMRI measurements, where crossing, merging and fanning fiber configurations degrade per-voxel orientation predictions that ignore spatial or sequential structure.
Approach
Treats tractography as autoregressive sequence modeling: a 3D CNN embeds local dMRI neighborhoods of each streamline point, and a decoder-only Transformer predicts a smoothed distribution over 724 sphere directions plus an end-of-fiber class, conditioned on the trajectory so far.
Key results
- On the ISMRM Tractometer benchmark, TractoTransformer reports VC 82%, OL 84%, and F1 75%, the highest among compared methods, with OR 31%.
- Ablation: removing the 3D CNN drops VC from 81.51% to 69.86% (-11.65 points).
- Full-brain inference on one subject takes about 2.5 hours on a single V100 GPU, or about 43 minutes across 4 GPUs.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use TractoTransformer instead of DeepTract | ISMRM 2015 Tractography Challenge · ISMRM 2015 Tractography Challenge | VC (%): 71 -> 82 | Helped |
| Use TractoTransformer instead of RF | ISMRM 2015 Tractography Challenge · ISMRM 2015 Tractography Challenge | OL (%): 75 -> 84 | Helped |
| Use TractoTransformer instead of CTtrack | ISMRM 2015 Tractography Challenge · ISMRM 2015 Tractography Challenge | OR (%): 16 -> 31 | Hurt |
| Use TractoTransformer instead of DeepTract | ISMRM 2015 Tractography Challenge · ISMRM 2015 Tractography Challenge | F1 (%): 70 -> 75 | Helped |
| Add the CNN3D module (ablation) | TractoTransformer · ISMRM 2015 Tractography Challenge | VC (%): 69.86 -> 81.51 | Helped |
| Add reverse-streamline augmentation (ablation) | TractoTransformer · ISMRM 2015 Tractography Challenge | F1 (%): 73.76 -> 74.78 | Helped |
| Add label smoothing (ablation) | TractoTransformer · ISMRM 2015 Tractography Challenge | F1 (%): 74.85 -> 74.78 | No clear effect |
Surprising findings
- Removing label smoothing leaves F1 essentially unchanged (74.85 vs 74.78), and the paper's OR for CTtrack (16%) is better than TractoTransformer's (31%).
Limitations
- CNN3D raises training memory cost, limiting how many subjects fit in memory per batch (ten TractoInferno subjects).
- Full-brain inference is slow (about 2.5 hours per subject on one V100 GPU).
- In vivo evaluation is qualitative only, on one test subject, trained on just ten subjects.
Experimental setup
Datasets: ISMRM 2015 Tractography Challenge phantom TractoInferno
Benchmarks: ISMRM 2015 Tractometer TractoInferno (qualitative)
Metrics: VC OL OR F1
Baselines: RF LearnToTrack DeepTract Entrack TrackToLearn CTtrack
Builds on: Transformer decoder CTtrack DeepTract LearnToTrack
Closest papers by meaning
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