Shortwave Infrared Fluorescence Imaging with the Clinically Approved Near-Infrared Dye Indocyanine Green

Fluorescence imaging is a method of real-time molecular tracking in vivo that has enabled many clinical technologies. Imaging in the shortwave infrared region (SWIR, 1-2 μm) promises higher contrast, sensitivity, and penetration depths compared to conventional visible and near-infrared (NIR) fluorescence imaging. However, adoption of SWIR imaging in clinical settings has been limited, due in part to the absence of FDA-approved fluorophores with peak emission in the SWIR. Here, we show that commercially available NIR dyes, including the FDA-approved contrast agent indocyanine green (ICG), exhibit optical properties suitable for in vivo SWIR fluorescence imaging. Despite the fact that their emission reaches a maximum in the NIR, these dyes can be imaged non-invasively in vivo in the SWIR spectral region, even beyond 1500 nm. We demonstrate real-time fluorescence angiography at wavelengths beyond 1300 nm using ICG at clinically relevant doses. Furthermore, we show tumortargeted SWIR imaging with trastuzumab labeled with IRDye 800CW, a NIR dye currently being tested in multiple phase II clinical trials. Our findings suggest that high-contrast SWIR fluorescence imaging can be implemented alongside existing imaging modalities by switching the detection of conventional NIR fluorescence systems from silicon-based NIR cameras to emerging indium gallium arsenide (InGaAs) SWIR cameras. Using ICG in particular opens the possibility of translating SWIR fluorescence imaging to human clinical applications.