In vivo imaging in the second biological window (NIR-II) is in its earlier stages but will undoubtedly push many life science researchers back to the drawing board for their preclinical workflows.
Preclinical optical imaging suffers from the inability to localize signals due to complications associated with light absorption, scattering and autofluorescence in living tissues. In vivo optical imaging can localize a signal well when it is at the surface but not when it is deep in the organism.
Preclinical biologists still strongly desire the ability to rapidly localize optical signals in vivo, but their discussions with imaging physicists often end up in a standstill. Biologists ask: can I use optical imaging to see my mCherry cancer cells in vivo? What about my luciferase cells? The answer is: it depends on many different factors such as the temperature of the animal, the optical properties of organs, how deep they are and how many photons come out.
NIR-II in vivo imaging is not impacted in the same way by drawbacks of light propagation in living tissues, thus enabling real-time imaging of optical probes much deeper in the organism and with much higher resolutions.
One of the breakthroughs in the field of in vivo SWIR imaging has been the demonstration that both NIR-I and NIR-II probes can work well for this application. There is an abundance of probes for the new imaging modality and many of them remain to be validated. The ball is back in the court for biologists to take. No longer will biologists need to accept the “oh well, I guess it depends” answer when asking an optical imaging physicist if it is possible to localize their probes in vivo.