AI检测肺结节的敏感性受重建间隔与结节大小比值影响，比值≥1时位置效应成主要变因。
Reconstruction Interval Z-Phase Dependence of AI Detection Sensitivity in CT Lung Nodule Screening
- 按结节大小与重建间隔比值分层分析检测敏感性
- 当比值≥1.0时，敏感性下降至61.4%，且受z相位影响显著
- 该效应无法通过常规质量指标或置信度反映，对临床筛查有隐性风险
背景：深度学习辅助肺结节检测系统的敏感性已知受辐射剂量、重建核函数和层厚等扫描参数影响。然而，目前尚无研究系统刻画检测概率随重建周期内结节位置（z相位）的变化关系。方法：基于LIDC-IDRI数据集，对先前验证过的154例扰动研究结果进行再分析。针对每位共识结节（≥4名阅片者一致），将结节中心在重建周期中的相对位置定义为z相位，并折叠至[0, 0.5]区间。按z相位分组、重建间隔（1mm、3mm、5mm）及重建间隔与结节直径比值（d/D）分层评估检测敏感性。结果：在5mm重建间隔下，敏感性为71.6%，而1mm基准下为84.8%；在5mm条件下，不同z相位组间敏感性差异达17.6个百分点。按d/D分层显示：d/D < 0.5时敏感性为92.4%，0.5 ≤ d/D < 1.0时为78.0%，d/D ≥ 1.0时为61.4%，且仅在d/D ≥ 1.0组中观察到明显的系统性z相位效应。结论：AI检测敏感性依赖于重建间隔与结节直径的比值。当该比值接近或超过1.0（如3–6mm结节在5mm重建下），z相位成为每例研究中检测变异性的主导因素。此随机效应无法被协议级质量指标捕捉，也未体现在AI置信度评分中。
原文摘要 · Abstract (English)
Background: Sensitivity of AI-assisted lung nodule detection systems is known to vary with CT acquisition parameters including radiation dose, reconstruction kernel, and slice thickness. However, the dependence of detection probability on nodule position within the reconstruction cycle -- the z-phase -- has not, to the author's knowledge, been characterized for deep learning-based detection systems. Methods: A retrospective analysis was performed using the LIDC-IDRI dataset. Detection results from a previously validated 154-case perturbation study were re-analyzed. For each consensus nodule (>=4-reader agreement), z-phase was defined as the fractional position of the nodule center within the reconstruction cycle, folded to [0, 0.5]. Detection sensitivity was stratified by z-phase bin, reconstruction interval (1mm, 3mm, 5mm), and by the ratio of reconstruction interval to nodule diameter (d/D). Results: At 5mm reconstruction interval, sensitivity was 71.6% vs 84.8% at 1mm baseline. Within the 5mm condition, sensitivity varied by 17.6 percentage points across z-phase bins. Stratified by d/D ratio, sensitivity was 92.4% for d/D < 0.5, 78.0% for 0.5 <= d/D < 1.0, and 61.4% for d/D >= 1.0, with a systematic z-phase effect present only in the d/D >= 1.0 stratum. Conclusions: AI detection sensitivity depends on the ratio of reconstruction interval to nodule diameter. When this ratio approaches or exceeds 1.0 -- as occurs for 3-6mm nodules at 5mm reconstruction -- z-phase becomes the dominant source of per-study detection variance. This stochastic effect is invisible to protocol-level quality metrics and not reflected in AI confidence scores.
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