Garcia Garrido Marina, Mühlfriedel Regine L, Beck Susanne C, Wallrapp Christine, Seeliger Mathias W
Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.
BTG International Germany GmbH, Alzenau, Germany.
PLoS One. 2015 Jun 25;10(6):e0131154. doi: 10.1371/journal.pone.0131154. eCollection 2015.
To address the problem of unequal scales for the measurement of two-dimensional structures in OCT images, and demonstrate the use of intra¬ocular objects of known dimensions in the murine eye for the equal calibration of axes.
The first part of this work describes the mathematical foundation of major distortion effects introduced by X-Y scaling differences. Illustrations were generated with CorelGraph X3 software. The second part bases on image data obtained with a HRA2 Spectralis (Heidelberg Engineering) in SV129 wild-type mice. Subretinally and intravitreally implanted microbeads, alginate capsules with a diameter of 154±5 μm containing GFP-marked mesenchymal stem cells (CellBeads), were used as intraocular objects for calibration.
The problems encountered with two-dimensional measurements in cases of unequal scales are demonstrated and an estimation of the resulting errors is provided. Commonly, the Y axis is reliably calibrated using outside standards like histology or manufacturer data. We show here that intraocular objects like dimensionally stable spherical alginate capsules allow for a two-dimensional calibration of the acquired OCT raw images by establishing a relation between X and Y axis data. For our setup, a correction factor of about 3.3 was determined using both epiretinally and subretinally positioned beads (3.350 ± 0.104 and 3.324 ± 0.083, respectively).
In this work, we highlight the distortion-related problems in OCT image analysis induced by unequal X and Y scales. As an exemplary case, we provide data for a two-dimensional in vivo OCT image calibration in mice using intraocular alginate capsules. Our results demonstrate the need for a proper two-dimensional calibration of OCT data, and we believe that equal scaling will certainly improve the efficiency of OCT image analysis.
解决光学相干断层扫描（OCT）图像中二维结构测量尺度不均的问题，并展示如何利用小鼠眼中已知尺寸的眼内物体进行轴的等比例校准。
本研究的第一部分描述了由X - Y缩放差异引入的主要失真效应的数学基础。插图由CorelGraph X3软件生成。第二部分基于使用HRA2 Spectralis（海德堡工程公司）在SV129野生型小鼠中获得的图像数据。视网膜下和玻璃体内植入的微珠，即直径为154±5μm、含有绿色荧光蛋白标记的间充质干细胞的海藻酸盐胶囊（细胞珠），被用作眼内校准物体。
展示了尺度不均情况下二维测量中遇到的问题，并给出了由此产生的误差估计。通常，使用组织学或制造商数据等外部标准可可靠地校准Y轴。我们在此表明，尺寸稳定的球形海藻酸盐胶囊等眼内物体可通过建立X轴和Y轴数据之间的关系，对采集的OCT原始图像进行二维校准。对于我们的设置，使用视网膜表面和视网膜下放置的珠子分别确定了约3.3的校正因子（分别为3.350±0.104和3.324±0.083）。
在本研究中，我们强调了由X和Y尺度不均引起的OCT图像分析中与失真相关的问题。作为一个示例，我们提供了使用眼内海藻酸盐胶囊对小鼠进行二维体内OCT图像校准的数据。我们的结果表明需要对OCT数据进行适当的二维校准，并且我们相信等比例缩放肯定会提高OCT图像分析的效率。
