arXiv:2609.03981cs.CVcs.LG2026-09

用结构相似性优化的残差修正器,让脑部MRI修复更清晰。

Sharpening the Ensemble: An SSIM-Aligned Residual Refiner for Brain-MRI Inpainting Post-Processing

论文配图:Sharpening the Ensemble: An SSIM-Aligned Residual Refiner for Brain-MRI Inpainting Post-Processing
图 1 · 摘自论文原文
  • 构建双模型集成,用含结构相似项的损失训练轻量残差修正器
  • 在测试集上SSIM从0.8767提升至0.8780,MSE基本不变
  • 无需重新训练,适合已有的高性能修复模型后处理

脑部MRI修复需将掩码区域替换为解剖上合理的健康组织,使本应拒绝的图像能使用针对健康脑设计的分析工具。在BraTS局部合成基准上,当前最强模型虽准确,但常出现模糊合成区域,归因于训练损失中ℓ₁与MSE项的均值追逐行为。本文在后处理阶段提出解决方案:整合2025年并列第一的两个模型构成深度集成,基于其输出训练一个轻量级残差修正器,损失函数加入结构相似性(SSIM)项,权重λ可调。在适中λ下,修正器使集成在保留数据集上的SSIM从0.8767提升至0.8780,在官方验证榜单上从0.8555升至0.8572,而MSE几乎无变化。提升微小但稳定,在62.6%的样本中改善,符号秩检验p=2.2×10⁻⁷;过强结构项则导致性能下降。消融实验表明:加入第三模型会损害集成效果,传统未锐化掩膜方法最佳仅达0.8765,低于原集成的0.8767,证明提升源于学习而非盲目锐化。该方法成本低、可复现,可在不重训练前提下提升已有强大集成模型的表现。

原文摘要 · Abstract (English)

Brain-MRI inpainting replaces a masked region of a scan with synthesized, anatomically plausible healthy tissue, so that analysis tools built for healthy brains can be applied to images they would otherwise reject. On the BraTS local-synthesis benchmark, which ranks submissions on the structural similarity index (SSIM), the peak signal-to-noise ratio, and the mean squared error (MSE) jointly, the strongest recent models are accurate, but several report blurry synthesized regions and attribute this to the mean-seeking behavior of the $\ell_1$ and MSE terms in their training losses. We address this in post-processing, forming a deep ensemble of the two co-first-place 2025 models and training a lightweight residual refiner on the ensemble's own outputs under an $\ell_1$ loss augmented with a structural-similarity term whose weight $\lambda$ we vary. At a moderate $\lambda$ the refiner improves SSIM over the ensemble, from $0.8767$ to $0.8780$ on a held-out reproduction of the official scorer and from $0.8555$ to $0.8572$ on the official validation leaderboard, with essentially no change in MSE. The gain is small but consistent, improving $62.6\%$ of the held-out cases with a signed-rank $p=2.2\times10^{-7}$, whereas over-weighting the structural term reverses it. Two ablations bound the effect. Adding any third model to the two-model ensemble degrades it, and classical unsharp masking fails to improve SSIM at any strength (best $0.8765$ against $0.8767$), so the gain reflects learned rather than indiscriminate sharpening. The result is a cheap, reproducible post-processing stage that improves an already strong ensemble without any large-scale retraining.

MRI修复结构相似性后处理轻量模型

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