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 IR (SWIR; 1,000–2,000 nm) promises higher contrast, sensitivity, and penetration depths compared with conventional visible and near-IR (NIR) fluorescence imaging. However, adoption of SWIR imaging in clinical settings has been limited, partially due to the absence of US Food and Drug Administration (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. Even though their emission spectra peak in the NIR, these dyes outperform commercial SWIR fluorophores and can be imaged in the SWIR, even beyond 1,500 nm. We show real-time fluorescence imaging using ICG at clinically relevant doses, including intravital microscopy, noninvasive imaging in blood and lymph vessels, and imaging of hepatobiliary clearance, and show increased contrast compared with NIR fluorescence imaging. Furthermore, we show tumor-targeted SWIR imaging with IRDye 800CW-labeled trastuzumab, an NIR dye being tested in multiple 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-based SWIR cameras. Using ICG in particular opens the possibility of translating SWIR fluorescence imaging to human clinical applications. Indeed, our findings suggest that emerging SWIR-fluorescent in vivo contrast agents should be benchmarked against the SWIR emission of ICG in blood.

An IR820 Dye–Protein Complex for Second Near‐Infrared Window and Photoacoustic Imaging

“…Spectroscopic characterization of this NIR‐I (650–900 nm) dye reveals a long‐emission tail that stretches into the NIR‐II region over 1000 nm. This finding highlights the possibility of using conventional NIR‐I dyes for NIR‐II imaging . Further imaging studies using commercially available NIR‐I dyes clearly demonstrate the success of this strategy, opening an entirely new route to realize NIR‐II imaging in preclinical research and even clinical imaging .…”

Multiplexed NIR‐II Probes for Lymph Node‐Invaded Cancer Detection and Imaging‐Guided Surgery

“…Although the peak emission of donor–acceptor–donor (D‐A‐D) dyes and the tail emission of cyanine dyes can be both used for NIR‐II imaging, the benefit of NIR‐II imaging is better realized in the NIR‐IIb sub‐window (>1500 nm), where light can penetrate nearly all tissues . Imaging in the NIR‐IIb window can minimize photon scattering and simultaneously avoid high absorbance by water, affording high resolution of mouse vasculature at depths of several millimeter in the brain or other tissues .…”

NIR-II fluorescence microscopic imaging of cortical vasculature in non-human primates

“…1a), a probe that is readily available and is approved by US Food and Drug Administration (FDA). ICG has been previously used in humans as a typical NIR-I fluorophore (for studies of liver and retina) 2,3,40 , and, as been previously shown, also offers the advantage of bright NIR-II fluorescence emission 31 .…”

“…Here, we report the development of two NIR-II fluorescence microscopes adapted to brain imaging of large animals. Using a clinically approved dye named indocyanine green (ICG) as a bright NIR-II fluorescent probe 31,32 in rhesus macaques, we demonstrate that the wide-field NIR-II fluorescence microscope offers high temporal resolution 23 , sufficient for realizing real-time imaging of cerebral blood vessels and achieving measurement of CBF velocity and cardiac cycle. The second microscope, a confocal NIR-II fluorescence microscope, offers high spatial resolution and high SBR (signal to background ratio) via optical sectioning capability 33 , enabling reconstruction of a clear three-dimensional volume of cortical vasculature up to an imaging depth of ~500 μm.…”