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

Background/Objectives: 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. Methods: 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. Results: 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. Conclusions: 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.