Center for Laryngeal Surgery and Voice Rehabilitation, Massachusetts General Hospital, Boston, Massachusetts, USA; Department of Speech, Language & Hearing Sciences, Boston University, Boston, Massachusetts, USA; Department of Communicative Sciences and Disorders, Michigan State University, East Lansing, Michigan, USA.
Department of Civil & Environmental Engineering, Michigan State University, East Lansing, Michigan, USA.
J Voice. 2024 Jul;38(4):803-815. doi: 10.1016/j.jvoice.2021.12.017. Epub 2022 Feb 1.
Evidence-based practice and precision medicine can significantly benefit from the ability to perform calibrated spatial measurements (eg, mm) from endoscopic images. However, calibrated measurements are not readily available from laryngeal images. Laser-projection endoscopes can provide the required information for performing calibrated spatial measurements, but their applications require a process known as calibration. During calibration, a set of benchtop recordings are used to determine the effect of confounding factors of spatial measurements, and also to learn their proper compensation strategies. Calibration benchtop recordings are acquired from flat surfaces and at a perpendicular imaging angle which is significantly different from in-vivo situations, where a three-dimensional (3D) surface gets recorded at a semi-unknown imaging angle. The aim of this study was to quantify changes in calibrated vertical and horizontal measurement accuracies as we move from the controlled condition of calibration to more realistic and uncontrolled settings.
A flat surface was positioned in front of a calibrated laser-projection transnasal fiberoptic endoscope at different working distances and imaging angles. Calibrated vertical and horizontal measurement errors were computed from each condition. Multiple linear regression analyses were used to quantify the dependence of vertical and horizontal measurement errors on the imaging angle and working distance. Next, a 3D-printed surface was positioned in front of the laser-projection endoscope at different working distances. Calibrated vertical and horizontal measurement errors were computed from each condition and then they were compared to measurement errors from a flat surface positioned at comparable working distances.
The outcome of analyses supported a significant effect of imaging angle on calibrated vertical measurement accuracy, while no significant effect of imaging angle on calibrated horizontal measurement accuracy was established. Additionally, the result of multiple linear regression analyses showed that the coefficient of imaging angle was two times larger than the working distance, which further highlights the significant effect of imaging angle on vertical measurement accuracy. Comparing the magnitude of calibrated vertical and horizontal measurement errors between the 3D surface and a flat surface suggested a significant effect of surface topology on calibrated measurement accuracies.
The mean percent magnitude of error of vertical and horizontal measurement errors from the 3D surface were respectively around 6% and 11%, at most working distances, which are acceptable for many applications. However, the significant effect of imaging angle and surface topology on measurement errors highlights the need for further research on these confounding factors. It also suggests that significant improvements in measurement accuracies may be achieved if these factors are properly accounted for during the calibration process. Last but not least, this study highlights the need for the evaluation of laser-projection endoscopes in uncontrolled and more realistic settings. Specifically, evaluations of laser-projection endoscopes in very controlled settings could significantly overestimate their accuracies and hence it will not represent their actual performances during in-vivo data acquisitions.
循证实践和精准医学可以从对内镜图像进行校准空间测量（例如毫米）的能力中显著受益。然而，喉部图像无法提供校准的测量值。激光投影内窥镜可以提供进行校准空间测量所需的信息，但它们的应用需要一个称为校准的过程。在校准过程中，使用一组台式记录来确定空间测量的混杂因素的影响，并学习适当的补偿策略。校准台式记录是从平面表面获取的，并且以与体内情况明显不同的垂直成像角度获取，其中三维（3D）表面以半未知成像角度记录。本研究的目的是量化从校准的受控条件到更现实和不受控制的设置时，校准垂直和水平测量精度的变化。
将一个平面放置在经过校准的激光投影经鼻纤维内窥镜的不同工作距离和成像角度前。从每种条件计算校准的垂直和水平测量误差。使用多元线性回归分析来量化垂直和水平测量误差对成像角度和工作距离的依赖关系。接下来，将 3D 打印表面放置在激光投影内窥镜前的不同工作距离处。从每种条件计算校准的垂直和水平测量误差，然后将其与放置在可比工作距离处的平面表面的测量误差进行比较。
分析结果支持成像角度对校准垂直测量精度有显著影响，而未建立成像角度对校准水平测量精度有显著影响。此外，多元线性回归分析的结果表明，成像角度的系数是工作距离的两倍，这进一步突出了成像角度对垂直测量精度的显著影响。比较 3D 表面和平面之间校准的垂直和水平测量误差的大小表明，表面拓扑结构对校准测量精度有显著影响。
在大多数工作距离下，3D 表面的垂直和水平测量误差的平均百分比误差分别约为 6%和 11%，对于许多应用来说是可以接受的。然而，成像角度和表面拓扑结构对测量误差的显著影响突出表明需要进一步研究这些混杂因素。这也表明，如果在校准过程中适当考虑这些因素，测量精度可能会显著提高。最后但并非最不重要的是，本研究强调了需要在不受控制和更现实的环境中评估激光投影内窥镜。具体来说，在非常受控的环境中评估激光投影内窥镜可能会显著高估其精度，因此无法代表其在体内数据采集期间的实际性能。
