Imaging Tissue In SWIR

Small animal imaging plays a vital role in drug discovery by allowing real-time, non-invasive tracking of therapeutic effects in living organisms. A powerful technique involves the use of photoluminescent taggants that attach to tumor cells and fluoresce when excited by near-infrared (NIR) laser light. For example, an 808 nm laser deeply penetrates tissue due to low absorption but scatters diffusely. Despite this scattering, it delivers sufficient energy to excite taggants that emit light at longer wavelengths, such as 1310 nm. These longer wavelengths face only one tissue pass to reach the surface and benefit from reduced scattering, which better preserves the spatial shape of internal structures.

A one-minute video illustrates this phenomenon using the SU320HX camera, the most sensitive room-temperature InGaAs camera available. After injecting nanotubes responsive to 808 nm into a sedated mouse, emitted light at 1300 nm revealed organ and vascular details. The glow pulses during breathing suggest oxygen intake affects emission intensity. Over time, light distribution changes, and a 16-minute post-injection image shows nanotube accumulation in specific regions, like the ear—highlighted by the presence of a metal ID tag.

This deep imaging is made possible by the “therapeutic window” (650–1400 nm), where tissue absorbance is minimized and Rayleigh scattering decreases with wavelength. A second optimal window (1000–1350 nm) enables deeper imaging due to less autofluorescence and scattering. Techniques like optical coherence tomography (OCT) at 1050 nm leverage this for high-resolution views of blood vessels and optic nerves, aiding diagnosis of conditions like macular degeneration and glaucoma.