Purpose

Emerging holographic headsets can be used to register patient-specific virtual models obtained from medical scans with the patient’s body. Maximising accuracy of the virtual models’ inclination angle and position (ideally, ≤ 2° and ≤ 2 mm, respectively, as in currently approved navigation systems) is vital for this application to be useful. This study investigated the accuracy with which a holographic headset registers virtual models with real-world features based on the position and size of image markers.

Methods

HoloLens^® and the image-pattern-recognition tool Vuforia Engine™ were used to overlay a 5-cm-radius virtual hexagon on a monitor’s surface in a predefined position. The headset’s camera detection of an image marker (displayed on the monitor) triggered the rendering of the virtual hexagon on the headset’s lenses. 4 × 4, 8 × 8 and 12 × 12 cm image markers displayed at nine different positions were used. In total, the position and dimensions of 114 virtual hexagons were measured on photographs captured by the headset’s camera.

Results

Some image marker positions and the smallest image marker (4 × 4 cm) led to larger errors in the perceived dimensions of the virtual models than other image marker positions and larger markers (8 × 8 and 12 × 12 cm). ≤ 2° and ≤ 2 mm errors were found in 70.7% and 76% of cases, respectively.

Conclusion

Errors obtained in a non-negligible percentage of cases are not acceptable for certain surgical tasks (e.g. the identification of correct trajectories of surgical instruments). Achieving sufficient accuracy with image marker sizes that meet surgical needs and regardless of image marker position remains a challenge.

中文翻译：

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标记位置和大小对非临床环境中HoloLens配准精度的影响，对高精度外科手术具有影响

目的

新兴的全息头戴式耳机可用于向患者的身体注册从医学扫描获得的特定于患者的虚拟模型。最大化虚拟模型的倾斜角度和位置的精度（理想情况下，如当前批准的导航系统中分别为≤2°和≤2 mm）对于使此应用有用至关重要。这项研究调查了基于图像标记的位置和大小的全息头戴式设备注册具有真实世界特征的虚拟模型的准确性。

方法

HoloLens ^®和图像模式识别工具Vuforia引擎™被用来覆盖在监视器的表面上以5cm半径虚拟六边形在预定位置。头戴式耳机的摄像头检测到图像标记（显示在监视器上），从而触发了头戴式耳机镜头上的虚拟六边形的渲染。使用在9个不同位置显示的4×4、8×8和12×12 cm图像标记。总共在耳机摄像头拍摄的照片上测量了114个虚拟六边形的位置和尺寸。

结果

与其他图像标记位置和较大的标记（8×8和12×12 cm）相比，某些图像标记位置和最小的图像标记（4×4 cm）导致虚拟模型的感知尺寸中的误差更大。分别在70.7％和76％的病例中发现≤2°和≤2 mm的误差。

结论

对于某些外科手术任务（例如，确定手术器械的正确轨迹），在无法忽略的百分比的情况下获得的错误是不可接受的。无论图像标记器的位置如何，如何利用满足手术需要的图像标记器尺寸实现足够的精度仍然是一个挑战。