Perfecting and extending the near-infrared imaging window

Area of Science:

• Biomedical Optics
• In Vivo Imaging
• Fluorescence Microscopy

Background:

• Second near-infrared (NIR-II) window imaging offers promise for visualizing mammals.
• Current definitions and mechanisms of NIR-II imaging require refinement.
• Water absorption properties influence photon propagation in near-infrared (NIR) regions.

Purpose of the Study:

• To perfect the definition of the NIR-II window for enhanced intravital imaging.
• To propose a novel third near-infrared (NIR-III) window for improved imaging quality.
• To investigate the role of water absorption in NIR photon propagation.

Main Methods:

• Simulated photon propagation in the NIR region up to 2340 nm.
• Defined the NIR-II window as 900-1880 nm, including NIR-IIx (1400-1500 nm) and NIR-IIc (1700-1880 nm) sub-regions.
• Proposed the NIR-III window as 2080-2340 nm.
• Performed wide-field fluorescence microscopy in the brain within the NIR-IIx region.
• Investigated 1400 nm long-pass detection for off-peak NIR-II imaging.

Main Results:

• Confirmed the beneficial effect of moderate water absorption on intravital imaging.
• Achieved excellent optical sectioning and the greatest imaging depth to date in intravital NIR-II fluorescence microscopy.
• Demonstrated that 1400 nm long-pass detection in off-peak NIR-II imaging surpasses NIR-IIb imaging performance with bright fluorophores.

Conclusions:

• The refined NIR-II window (900-1880 nm) and proposed NIR-III window (2080-2340 nm) offer improved capabilities for in vivo fluorescence imaging.
• The study highlights the importance of water absorption and specific wavelength ranges for optimal imaging.
• Novel detection strategies enhance the performance of intravital NIR-II fluorescence microscopy.