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

Abstract

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.

Repurposing Cyanine NIR‐I Dyes Accelerates Clinical Translation of Near‐Infrared‐II (NIR‐II) Bioimaging

“…As we observed, the emission spectrum of NIR‐I dyes did not follow the Franck–Condon principle (i.e., mirror image rule), in which the emission spectra should approximate the mirror image of their absorption spectra . The missing shoulder in the emission spectrum originated from the low detection efficiency of silicon‐based detectors over 900 nm.…”

“…IRDye800CW‐guided surgery trials have been completed with successes, but imaging depth is still limited in the NIR‐I region . Recently, several groups found that some of the clinically approved and commercially available NIR‐I cyanine dyes may function as NIR‐II fluorophores with emission tails extending into the NIR‐II region . However, the mechanism of tail emission was never investigated and it is indeed interesting to establish a general rule to explore conventional NIR‐I dyes with bright NIR‐II tail emission for NIR‐II imaging.…”

Shortwave infrared fluorescence imaging with the clinically approved near-infrared dye indocyanine green

“…The results reported in this manuscript were initially posted by the authors on April 28, 2017, in the online archive, bioRxiv (65). During the manuscript review process, the authors became aware that ICG fluorescence in the SWIR was independently reported by another group in PLoS One on November 9, 2017 (66 …”

Flavylium Polymethine Fluorophores for Near‐ and Shortwave Infrared Imaging

“…[13] Despite impressive F F values,the quantum efficiencies of the D-A-D chromophores are limited by their low absorption coefficients.R ecently,t he effect of high e values has been highlighted by off-peak SWIR detection of ICG fluorescence surpassing the brightness of early-generation benzobisthiadiazoles. [14] Theh igh absorption coefficient of ICG is mirrored in other members of its chromophore class,t he polymethine dyes.T hese dyes are charged molecules composed of heterocycles linked by am ethine chain ( Figure 1). Nitrogencontaining polymethines (cyanine dyes) with 1-5 methine units span the visible region, while 7-methines,s uch as ICG, reach NIR wavelengths.…”