Hummel Johann B, Bax Michael R, Figl Michael L, Kang Yan, Maurer Calvin, Birkfellner Wolfgang W, Bergmann Helmar, Shahidi Ramin
Center of Biomedical Engineering and Physics, Medical University of Vienna, Vienna, Austria, Image Guidance Laboratories, Stanford University School of Medicine, Stanford, California and Ludwig-Boltzmann Institute of Nuclear Medicine, Vienna, Austria.
Image Guidance Laboratories, Stanford University School of Medicine, Stanford, California.
Med Phys. 2005 Jul;32(7Part1):2371-2379. doi: 10.1118/1.1944327.
This paper defines a simple protocol for competitive and quantified evaluation of electromagnetic tracking systems such as the NDI Aurora (A) and Ascension microBIRD with dipole transmitter (B). It establishes new methods and a new phantom design which assesses the reproducibility and allows comparability with different tracking systems in a consistent environment. A machined base plate was designed and manufactured in which a 50 mm grid of holes was precisely drilled for position measurements. In the center a circle of 32 equispaced holes enables the accurate measurement of rotation. The sensors can be clamped in a small mount which fits into pairs of grid holes on the base plate. Relative positional/orientational errors are found by subtracting the known distances/rotations between the machined locations from the differences of the mean observed positions/rotation. To measure the influence of metallic objects we inserted rods made of steel (SST 303, SST 416), aluminum, and bronze into the sensitive volume between sensor and emitter. We calculated the fiducial registration error and fiducial location error with a standard stylus calibration for both tracking systems and assessed two different methods of stylus calibration. The positional jitter amounted to 0.14 mm(A) and 0.08 mm(B). A relative positional error of 0.96mm±0.68mm, range -0.06 mm; 2.23 mm(A) and 1.14mm±0.78mm, range -3.72 mm; 1.57 mm(B) for a given distance of 50 mm was found. The relative rotation error was found to be 0.51° (A)/0.04° (B). The most relevant distortion caused by metallic objects results from SST 416. The maximum error 4.2mm(A)∕⩾100mm(B) occurs when the rod is close to the sensor(20 mm). While (B) is more sensitive with respect to metallic objects, (A) is less accurate concerning orientation measurements. (B) showed a systematic error when distances are calculated.
本文定义了一种简单的协议，用于对电磁跟踪系统（如NDI Aurora（A）和带偶极发射器的Ascension microBIRD（B））进行竞争性和量化评估。它建立了新的方法和新的体模设计，可评估再现性，并能在一致的环境中与不同的跟踪系统进行比较。设计并制造了一个加工基板，其中精确钻出了一个50毫米的孔网格用于位置测量。在中心有一个由32个等距孔组成的圆，可实现旋转的精确测量。传感器可夹在一个小支架中，该支架可装入基板上的成对网格孔中。通过从平均观测位置/旋转的差异中减去加工位置之间的已知距离/旋转来发现相对位置/方向误差。为了测量金属物体的影响，我们将由钢（SST 303、SST 416）、铝和青铜制成的棒插入传感器和发射器之间的敏感区域。我们使用标准探针校准计算了两种跟踪系统的基准配准误差和基准位置误差，并评估了两种不同的探针校准方法。位置抖动分别为0.14毫米（A）和0.08毫米（B）。对于给定的50毫米距离，发现相对位置误差为0.96毫米±0.68毫米，范围为-0.06毫米；2.23毫米（A）和1.14毫米±0.78毫米，范围为-3.72毫米；1.57毫米（B）。发现相对旋转误差为0.51°（A）/0.04°（B）。由金属物体引起的最相关失真来自SST 416。当棒靠近传感器（20毫米）时，最大误差为4.2毫米（A）∕⩾100毫米（B）。虽然（B）对金属物体更敏感，但（A）在方向测量方面不太准确。在计算距离时，（B）显示出系统误差。
