A potential pitfall in the interpretation of microscope-integrated fluorescence angiography: the center-periphery effect. - raw data

<b>Background/Objectives</b>: Indocyanine green fluorescence angiography (ICG-FA) enables real-time visualization of tissue perfusion. However, objective research microscope-integrated FA has not been conducted before. This study aims to evaluate the fluorescence light distribution in images formed by ICG-FA in two surgical microscopes using a phantom, and to provide recommendations for their application. <b>Methods</b>:<i> </i>An 11.8 by 6.8 cm ICG and Intralipid phantom was made to evaluate overall spatial fluorescence sensitivity in two surgical microscopes in multiple working distances (WD) and magnification factors (MF). The signal was quantified using tailor-made software in Python. <b>Results</b>: A clear center-periphery effect was present in most settings in both microscopes, with the highest peripheral fluorescence signal loss in the lowest MF: 100% in the Tivato and 83% in the Pentero. Increasing the MF improved homogeneity where the biggest difference was seen between the first and second MF. A 30cm WD and 3.5x MF produced the most homogeneous images suitable for free-flap surgery. Manually opening the light beam diameter also reduced the center-periphery effect. <b>Conclusions</b>: Peripheral signal loss in microscope-integrated ICG-FA must be considered during clinical interpretation and for quantification of tissue perfusion. In clinical practice during reconstructive free-flap surgery, a 30cm WD, 3.5 MF and manually opened light beam diameter should be applied to achieve the most homogeneous image.

**背景与研究目标**：吲哚菁绿荧光血管造影（Indocyanine green fluorescence angiography, ICG-FA）可实现组织灌注的实时可视化。然而，此前尚未开展针对科研级集成式显微镜的ICG-FA相关研究。本研究旨在借助体模，评估两款手术显微镜搭载ICG-FA所成图像中的荧光光线分布情况，并为其临床应用提供参考建议。
**研究方法**：制作了11.8×6.8cm的吲哚菁绿-脂肪乳体模，用于评估两款手术显微镜在不同工作距离（working distance, WD）与放大倍率（magnification factor, MF）下的整体空间荧光灵敏度。采用Python语言编写的定制化软件对荧光信号进行定量分析。
**研究结果**：两款显微镜的多数成像参数设置下均呈现显著的中心-外周效应，其中最低放大倍率下的外周荧光信号衰减最为严重：Tivato显微镜的信号衰减达100%，Pentero显微镜达83%。提升放大倍率可改善图像均匀性，其中首次与第二次放大倍率间的均匀性差异最为显著。采用30cm工作距离与3.5倍放大倍率时，可获得最均匀的成像效果，适用于游离皮瓣手术。手动增大光束直径也可缓解中心-外周效应。
**结论**：显微镜集成式ICG-FA存在外周信号衰减问题，临床解读图像及定量分析组织灌注时必须予以考虑。在重建游离皮瓣手术的临床实践中，应采用30cm工作距离、3.5倍放大倍率并手动增大光束直径，以获得最均匀的成像效果。