We study an ultrasound-first, radiation-preserving policy for developmental dysplasia of the hip (DDH) that requests a radiograph only when needed. We (i) pretrain modality-specific encoders (ResNet-18) with SimSiam on a large unlabelled registry (37186 ultrasound; 19546 radiographs), (ii) freeze the backbones and fit small, measurement-faithful heads on DDH-relevant landmarks and measurements, (iii) calibrate a one-sided conformal deferral rule on ultrasound predictions that provides finite sample marginal coverage guarantees under exchangeability, using a held-out calibration set. Ultrasound heads predict Graf alpha, beta, and femoral head coverage; X-ray heads predict acetabular index (AI), center-edge (CE) angle and IHDI grade. On our held out labeled evaluation set, ultrasound measurement error is modest (e.g., alpha MAE ~= 9.7 degrees, coverage MAE ~= 14.0%), while radiographic probes achieve AI and CE MAEs of ~= 7.6 degrees and ~= 8.9 degrees, respectively. The calibrated US-only policy is explored across rule families (alpha-only; alpha OR coverage; alpha AND coverage), conformal miscoverage levels, and per-utility trade-offs using decision-curve analysis. Conservative settings yield high coverage with near-zero US-only rates; permissive settings (e.g., alpha OR coverage at larger deltas) achieve non-zero US-only throughput with expected coverage tradeoffs. The result is a simple, reproducible pipeline that turns limited labels into interpretable measurements and tunable selective imaging curves suitable for clinical handoff and future external validation.

翻译：本研究探讨一种以超声优先、辐射防护的髋关节发育不良诊疗策略，仅在必要时才申请X光检查。我们（i）使用SimSiam方法在大型无标注数据集（37186例超声；19546例X光）上预训练模态特异性编码器（ResNet-18），（ii）冻结主干网络并在DDH相关解剖标志点和测量参数上拟合小型、测量保真度高的预测头，（iii）基于可交换性假设，利用预留校准集对超声预测结果进行单侧保形延迟决策校准，提供有限样本边际覆盖保证。超声预测头输出Graf α角、β角及股骨头覆盖率；X光预测头输出髋臼指数、中心边缘角及国际髋关节发育不良学会分级。在预留标注评估集上，超声测量误差处于可接受范围（如α角平均绝对误差≈9.7度，覆盖率平均绝对误差≈14.0%），而X光测量探针分别获得髋臼指数与中心边缘角平均绝对误差≈7.6度与≈8.9度。通过决策曲线分析，在规则族（仅α角；α角或覆盖率；α角与覆盖率）、保形误覆盖水平及效用权衡三个维度对校准后的纯超声策略进行探索。保守设置可实现高覆盖率和接近零的纯超声决策率；宽松设置（如在较大Δ值下的α角或覆盖率规则）能以预期覆盖率为代价获得非零纯超声通过率。最终构建的流程简洁可复现，能将有限标注转化为可解释的测量结果和可调节的选择性成像曲线，适用于临床交接及未来外部验证。