On-demand calibration and evaluation for electromagnetically tracked laparoscope in augmented reality visualization.
On-demand calibration and evaluation for electromagnetically tracked laparoscope in augmented reality visualization.
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DOI：
10.1007/s11548-016-1406-3
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发表时间：
2016-06
影响因子：
3
通讯作者：
Shekhar R
中科院分区：
文献类型：
--
作者：
Liu X;Plishker W;Zaki G;Kang S;Kane TD;Shekhar R
在当前的腹腔镜增强现实系统中使用的常见摄像机校准方法需要从不同姿势获取整个棋盘图案的多幅图像。这一冗长的程序妨碍了在手术室(OR)进行腹腔镜校准。这项工作的目的是开发一种用于电磁跟踪腹腔镜的快速校准方法，以便可以在OR中按需进行校准。我们设计了一种机械跟踪支架，将EM传感器独特而舒适地定位到传统腹腔镜上的适当位置。开发了一种名为fCalib的工具，用于使用显示特殊目标图案的任意部分的单一图像来校准相机的内部参数、失真系数和外部参数(范围透镜坐标系和EM传感器坐标系之间的转换)。为了快速评估OR中的校准结果，我们集成了一个管状体模和fCalib，并在现场视频场景中叠加了管状模型的虚拟表示。在实验室环境下，比较了常用的OpenCV方法和fCalib方法的空间目标配准误差。此外，我们在临床环境中比较了基于EM跟踪的fCalib和基于光学跟踪的fCalib的校准重投影误差。结果表明，该方法与OpenCV方法具有很好的可比性。然而，改变环境，例如插入或移除手术工具，将影响基于EM跟踪的方法的重新投影精度。FCALIB方法的计算时间平均为14.0 S(范围：3.5 S~22.7 S)。我们开发并验证了一个原型，用于快速校准和评估EM跟踪的常规(前视)腹腔镜。该校准法达到了可接受的准确度，且相对快速，易于按需在OR中执行。
Common camera calibration methods employed in current laparoscopic augmented reality systems require the acquisition of multiple images of an entire checkerboard pattern from various poses. This lengthy procedure prevents performing laparoscope calibration in the operating room (OR). The purpose of this work was to develop a fast calibration method for electromagnetically (EM) tracked laparoscopes, such that calibration can be performed in the OR on demand. We designed a mechanical tracking mount to uniquely and snugly position an EM sensor to an appropriate location on a conventional laparoscope. A tool named fCalib was developed to calibrate intrinsic camera parameters, distortion coefficients, and extrinsic parameters (transformation between the scope lens coordinate system and the EM sensor coordinate system) using a single image that shows an arbitrary portion of a special target pattern. For quick evaluation of calibration result in the OR, we integrated a tube phantom with fCalib and overlaid a virtual representation of the tube on the live video scene. We compared spatial target registration error between the common OpenCV method and the fCalib method in a laboratory setting. In addition, we compared the calibration re-projection error between the EM tracking-based fCalib and the optical tracking-based fCalib in a clinical setting. Our results suggested that the proposed method is comparable to the OpenCV method. However, changing the environment, e.g., inserting or removing surgical tools, would affect re-projection accuracy for the EM tracking-based approach. Computational time of the fCalib method averaged 14.0 s (range 3.5 s – 22.7 s). We developed and validated a prototype for fast calibration and evaluation of EM tracked conventional (forward viewing) laparoscopes. The calibration method achieved acceptable accuracy and was relatively fast and easy to be performed in the OR on demand.