通过空间自适应温度调节,让模型更关注病灶区域,提升CT病灶检测效果。
Lesion Detection in CT with Frozen Self-Distilled Features: SALT, a Spatially Adaptive Label-Guided Temperature

- 用弱标注框定义区域,动态增强病灶处的训练信号
- 在4个CT队列上实现小病灶3D检测性能显著提升
- 方法可适配任意弱空间标注,适合医疗图像预训练
自监督预训练目标在空间上是均匀的:教师温度和每块损失权重在整个图像中一致,因此仅几块大小的病灶对训练信号的贡献与周围正常组织相同。以往工作通过偏向标注区域来改变模型所见,但未改变目标本身。我们提出一种新方法SALT(空间自适应标签引导温度),通过条件化自蒸馏的目标:在预训练阶段,仅有的弱框标注定义编码器补丁网格上的紧凑区域,在该区域内教师softmax温度被锐化,掩码补丁损失权重被提高。其余目标、掩码策略和中心统计均保持不变,下游使用时编码器为纯特征提取器,无需标签或条件。我们在四个CT队列上冻结编码器,仅训练轻量级多深度CenterNet风格头进行3D病灶检测,并对比了架构、预训练数据、调度和标签引导裁剪完全相同的基线,但无目标条件。报告了补丁级可分性、按队列和病灶大小分层的3D检测结果、框质量,以及无需注册、掩码或微调的探测器自由探针——单个冻结补丁嵌入即可在随访扫描中重识别病灶。由于条件通过空间指示而非标签语义表达,该框架可适配任意弱空间标注;我们以病灶为例进行了实例化与验证。
原文摘要 · Abstract (English)
Self-supervised pretraining objectives are spatially uniform: the teacher temperature and the per-patch loss weight are identical everywhere in the image, so a lesion a few patches wide contributes no more to the training signal than the surrounding parenchyma. Prior work biases the views toward annotated regions, which changes what the model sees but adds no pressure on the objective. We instead condition the targets of self-distillation, a method we call SALT (Spatially Adaptive Label-guided Temperature). Weak, box-derived labels, available only during pretraining, define a compact region on the encoder's patch grid, inside which the teacher's softmax temperature is sharpened and the masked-patch loss is up-weighted. The objectives, the masking policy and the centering statistics are otherwise unchanged, and at every downstream use the encoder is a plain feature extractor with no labels and no conditioning. We evaluate by freezing the encoder and training only a lightweight multi-depth CenterNet-style head, detecting lesions in 3D on four CT cohorts, and we isolate the mechanism against a backbone identical in architecture, pretraining data, schedule and label-guided cropping but with no target conditioning. We report patch-level separability, 3D detection stratified by cohort and by lesion size, box quality, and a detector-free probe in which a single frozen patch embedding re-identifies a lesion in a follow-up scan without registration, masks or fine-tuning. Because the conditioning is expressed through a spatial indicator rather than through label semantics, the formulation admits any weak spatial annotation; we instantiate and validate it for lesions.
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