Navigation of the drilling capsule

该子项目中的主要课题是仪器位置的自动检测和轨迹控制。将多端口骨科手术的直线路径规划扩展到非线性路径，需要调整仪器监测和轨迹控制。为了精确跟踪仪器的预定轨迹，必须确定钻井舱的六个自由度。在项目的初始阶段，我们开发了使用C形臂锥束计算机断层扫描系统(CBCT)准确确定仪器位置的方法。然而，这些方法仅限于五个自由度的检测。此外，不得违反可接受的辐射水平，因此，不可能进行连续的数据采集。为了克服上述缺点，应考虑增设一个跟踪系统。电磁跟踪(EMT)是合适的，这要归功于使用的小传感器，即使它们被隐藏起来，也可以被连续跟踪。由于EMT的准确性有限，术中CBCT投影被获取并用于确定确切的器械位置，并且基于它，EMT数据在接下来的时间段被调整。在连续的CBCT扫描之间，使用EMT系统连续跟踪仪器。必须调查扫描时间间隔，以便在不危及患者的情况下将辐射暴露降至最低。这些间隔主要取决于EMT系统的准确性、计划轨迹的形状以及到风险结构的距离。将设计一个合适的控制概念来同步和控制各个组件(计划系统、EMT、C形臂和钻井舱)。通过两个跟踪系统(EMT和C-ARM)的有意义的集成，安全的连续监测和控制是可行的。此外，还必须提供视觉反馈--关于器械相对于患者解剖的位置。

Main topics in this subproject are the automatic detection of the instrument position and the trajectory control. The extension of the planning of straight access paths - for multi-port bone surgery - to nonlinear paths requires an adjustment of the instrument monitoring and the trajectory control. In order to follow a pre-planned trajectory with the instrument precisely, the six degrees of freedom of the drilling capsule must be determined. In the initial phase of the project, we developed methods, which allow an accurate determination of the instrument position using a C-arm cone beam computed tomography system (CBCT). However, these methods are limited to the detection of five degrees of freedom. Furthermore, acceptable levels of radiation must not be violated, thus, a continuous data acquisition is not possible. To overcome the aforementioned shortcomings, an additional tracking system should be considered. The electromagnetic tracking (EMT) is suitable, thanks to the used small sensors, which can be continuously tracked, even if they are hidden. Due to the limited EMT accuracy, intra-operative CBCT projections are acquired and used to determine the exact instrument location, and based on it, the EMT data is adjusted for the following time period. Between successive CBCT scans, the instrument is continuously tracked using the EMT system. The scan time intervals have to be investigated in order to minimize the radiation exposure without endangering the patient. These intervals depend principally on the accuracy of the EMT system, the shape of the planned trajectory, and the distances to the risk structures. A suitable control concept will be designed to synchronize and control the various components (planning system, EMT, C-arm, and drilling capsule). By a meaningful integration of the two tracking systems (EMT and C-arm), safe continuous monitoring and control are feasible. Furthermore, a visual feedback - on the instrument position relative to the patient anatomy- has to be offered.