Lu Yiming, Son Taeyoon, Kim Tae-Hoon, Le David, Yao Xincheng
Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA.
Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, USA.
Quant Imaging Med Surg. 2021 Mar;11(3):1060-1069. doi: 10.21037/qims-20-542.
High resolution imaging is desirable for advanced study and clinical management of retinal diseases. However, spatial resolution of retinal imaging has been limited due to available numerical aperture and optical aberration of the ocular optics. This study is to develop and validate virtually structured detection (VSD) to surpass diffraction limit for resolution improvement in retinal imaging of awake human.
A rapid line scanning laser ophthalmoscope (SLO) was constructed for retinal imaging. A high speed (25,000 kHz) camera was used for recording the two-dimensional (2D) light reflectance profile, corresponding to each focused line illumination. VSD was implemented to the 2D light reflectance profiles for super-resolution reconstruction. Because each 2D light reflectance profile was recorded within 40 μs, the intra-frame blur due to eye movements can be ignored. Digital registration was implemented to further compensate for inter-frame eye movements, before the VSD processing. Based on digital processing, the modulation transfer function (MTF) of the imaging system was derived for objective identification of the cut-off frequency of ocular optics, which is essential for robust VSD processing to ensure reliable super-resolution imaging. Dynamic motility analysis of the super-resolution images was implemented to further enhance the imaging contrast of retinal rod and cone photoreceptors.
The VSD based super-resolution SLO significantly improved image quality compared with equivalent wide-field imaging. observation of individual retinal photoreceptors has been demonstrated unambiguously. Dynamic motility analysis of the super-resolution images enhanced the contrast of retinal rod and cone photoreceptors, and revealed sub-cellular structures in cone photoreceptors.
In conjunction with rapid line-scan imaging and digital registration to minimize the effect of eye movements, VSD enabled resolution improvement to observe individual retinal photoreceptors without the involvement of adaptive optics (AO). An objective method has been developed to identify MTF to enable quantitative estimation of the cut-off frequency required for robust VSD processing.
高分辨率成像对于视网膜疾病的深入研究和临床管理至关重要。然而，由于眼屈光系统的可用数值孔径和光学像差，视网膜成像的空间分辨率一直受到限制。本研究旨在开发并验证虚拟结构检测（VSD）技术，以突破衍射极限，提高清醒人类视网膜成像的分辨率。
构建了一台用于视网膜成像的快速线扫描激光眼科显微镜（SLO）。使用高速（25,000 kHz）相机记录与每条聚焦线照明相对应的二维（2D）光反射轮廓。将VSD应用于2D光反射轮廓进行超分辨率重建。由于每个2D光反射轮廓在40微秒内记录，因此可忽略因眼球运动引起的帧内模糊。在VSD处理之前，进行数字配准以进一步补偿帧间眼球运动。基于数字处理，推导了成像系统的调制传递函数（MTF），以客观识别眼屈光系统的截止频率，这对于稳健的VSD处理以确保可靠的超分辨率成像至关重要。对超分辨率图像进行动态运动分析，以进一步增强视网膜视杆和视锥光感受器的成像对比度。
与等效的宽视野成像相比，基于VSD的超分辨率SLO显著提高了图像质量。已明确证明能够观察到单个视网膜光感受器。超分辨率图像的动态运动分析增强了视网膜视杆和视锥光感受器的对比度，并揭示了视锥光感受器中的亚细胞结构。
结合快速线扫描成像和数字配准以最小化眼球运动的影响，VSD能够在不涉及自适应光学（AO）的情况下提高分辨率，从而观察单个视网膜光感受器。已开发出一种客观方法来识别MTF，以便对稳健的VSD处理所需的截止频率进行定量估计。
