A Potential Pitfall in the Interpretation of Microscope-Integrated Fluorescence Angiography: The Center-Periphery Effect.

Background/objectives: Indocyanine green fluorescence angiography (ICG-FA) enables the real-time visualization of tissue perfusion. However, objective research on microscope-integrated fluorescence angiography (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 (WDs) and magnification factors (MFs). The signal was quantified using a tailor-made software in Python 3.8.10.

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 30 cm WD and 3.5× 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 the quantification of tissue perfusion. In clinical practice during reconstructive free-flap surgery, a 30 cm WD, 3.5 MF, and manually opened light beam diameter should be applied to achieve the most homogeneous image.