Purpose: Intraoperative ultrasound (US) can enhance real-time visualization in transoral robotic surgery. The surgeon creates a mental map with a pre-operative scan. Then, a surgical assistant performs freehand US scanning during the surgery while the surgeon operates at the remote surgical console. Communicating the target scanning plane in the surgeon's mental map is difficult. Automatic image retrieval can help match intraoperative images to preoperative scans, guiding the assistant to adjust the US probe toward the target plane. Methods: We propose a self-supervised contrastive learning approach to match intraoperative US views to a preoperative image database. We introduce a novel contrastive learning strategy that leverages intra-sweep similarity and US probe location to improve feature encoding. Additionally, our model incorporates a flexible threshold to reject unsatisfactory matches. Results: Our method achieves 92.30% retrieval accuracy on simulated data and outperforms state-of-the-art temporal-based contrastive learning approaches. Our ablation study demonstrates that using probe location in the optimization goal improves image representation, suggesting that semantic information can be extracted from probe location. We also present our approach on real patient data to show the feasibility of the proposed US probe localization system despite tissue deformation from tongue retraction. Conclusion: Our contrastive learning method, which utilizes intra-sweep similarity and US probe location, enhances US image representation learning. We also demonstrate the feasibility of using our image retrieval method to provide neck US localization on real patient US after tongue retraction.

翻译：目的：术中超声（US）可增强经口机器人手术中的实时可视化效果。外科医生通过术前扫描构建心理地图。随后，在手术过程中，当外科医生在远程手术控制台操作时，由手术助手进行自由手超声扫描。传达外科医生心理地图中的目标扫描平面具有挑战性。自动图像检索可帮助将术中图像与术前扫描进行匹配，从而引导助手调整超声探头朝向目标平面。方法：我们提出一种自监督对比学习方法，用于将术中超声视图与术前图像数据库进行匹配。我们引入一种新颖的对比学习策略，该策略利用帧内扫描相似性和超声探头位置来改进特征编码。此外，我们的模型采用灵活阈值来拒绝不理想的匹配结果。结果：我们的方法在模拟数据上实现了92.30%的检索准确率，并优于最先进的基于时间的对比学习方法。消融研究表明，在优化目标中使用探头位置可改善图像表示，这表明可从探头位置中提取语义信息。我们还在真实患者数据上展示了我们的方法，以证明所提出的超声探头定位系统在舌牵拉导致组织变形情况下的可行性。结论：我们利用帧内扫描相似性和超声探头位置的对比学习方法，增强了超声图像表示学习。我们还证明了使用我们的图像检索方法在舌牵拉后的真实患者超声图像上提供颈部超声定位的可行性。