Leibniz Universität Hannover, Institute of Mechatronic Systems, Appelstr. 11a, 30167 Hanover, Germany.
Leibniz Universität Hannover, Institute of Mechatronic Systems, Appelstr. 11a, 30167 Hanover, Germany.
Med Image Anal. 2017 Aug;40:80-95. doi: 10.1016/j.media.2017.06.004. Epub 2017 Jun 8.
Recent research has revealed that image-based methods can enhance accuracy and safety in laser microsurgery. In this study, non-rigid tracking using surgical stereo imaging and its application to laser ablation is discussed. A recently developed motion estimation framework based on piecewise affine deformation modeling is extended by a mesh refinement step and considering texture information. This compensates for tracking inaccuracies potentially caused by inconsistent feature matches or drift. To facilitate online application of the method, computational load is reduced by concurrent processing and affine-invariant fusion of tracking and refinement results. The residual latency-dependent tracking error is further minimized by Kalman filter-based upsampling, considering a motion model in disparity space. Accuracy is assessed in laparoscopic, beating heart, and laryngeal sequences with challenging conditions, such as partial occlusions and significant deformation. Performance is compared with that of state-of-the-art methods. In addition, the online capability of the method is evaluated by tracking two motion patterns performed by a high-precision parallel-kinematic platform. Related experiments are discussed for tissue substitute and porcine soft tissue in order to compare performances in an ideal scenario and in a setup mimicking clinical conditions. Regarding the soft tissue trial, the tracking error can be significantly reduced from 0.72 mm to below 0.05 mm with mesh refinement. To demonstrate online laser path adaptation during ablation, the non-rigid tracking framework is integrated into a setup consisting of a surgical Er:YAG laser, a three-axis scanning unit, and a low-noise stereo camera. Regardless of the error source, such as laser-to-camera registration, camera calibration, image-based tracking, and scanning latency, the ablation root mean square error is kept below 0.21 mm when the sample moves according to the aforementioned patterns. Final experiments regarding motion-compensated laser ablation of structurally deforming tissue highlight the potential of the method for vision-guided laser surgery.
最近的研究表明，基于图像的方法可以提高激光微创手术的准确性和安全性。本研究讨论了使用手术立体成像的非刚性跟踪及其在激光烧蚀中的应用。最近开发的基于分段仿射变形建模的运动估计框架通过网格细化步骤和考虑纹理信息进行了扩展。这补偿了由于不一致的特征匹配或漂移可能导致的跟踪不准确。为了方便该方法的在线应用，通过并发处理和跟踪与细化结果的仿射不变融合，降低了计算负载。通过在视差空间中考虑运动模型，基于卡尔曼滤波器的上采样进一步最小化了与残留滞后相关的跟踪误差。在具有挑战性的条件下，如部分遮挡和显著变形的腹腔镜、跳动心脏和喉序列中评估了准确性，这些条件包括挑战性的条件。将性能与最先进的方法进行了比较。此外，通过跟踪高精度并联运动平台执行的两种运动模式，评估了该方法的在线能力。为了比较在理想情况下和模拟临床条件的设置中的性能，进行了相关的组织替代物和猪软组织的实验。关于软组织试验，通过网格细化可以将跟踪误差从 0.72mm 显著降低到 0.05mm 以下。为了演示在烧蚀过程中的非刚性跟踪框架的在线激光路径自适应，将该非刚性跟踪框架集成到由手术 Er:YAG 激光、三轴扫描单元和低噪声立体相机组成的设置中。无论误差源如何，例如激光到相机的配准、相机校准、基于图像的跟踪和扫描延迟，当样品根据上述模式移动时，烧蚀均方根误差都保持在 0.21mm 以下。关于结构变形组织的运动补偿激光烧蚀的最终实验突出了该方法用于视觉引导激光手术的潜力。
