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Optical windows for head tissues in near-infrared and short-wave infrared regions

12 Mar | By Biophotonics.World
Optical windows for head tissues in near-infrared and short-wave infrared regions
Four optical transparency windows are indicated: ~700-1000 nm (NIR-I), ~1000-1350 nm (NIR-II), ~1550-1870 nm (NIR-III or SWIR) and ~2100-2300 nm (SWIR-II) on spectra of attenuation coefficient for head tissues, as brain cortex, cranial bone and skin. Image source: Journal of Biophotonics By: Sergii Golovynskyi et al.

In  new research from Shenzhen University, China and Taras Shevchenko National University of Kyiv, Ukraine, four transparency windows in near-infrared (NIR) and short-wavelength infrared (SWIR) spectral ranges were identified for freshly excised rat head tissues (brain cortex, cranial bone and scalp skin). The study of Golovunskyi et al, which  has been recently published as an article in Journal of Biophotonics, defines windows at ~700-1000 nm (NIR-I), ~1000-1350 nm (NIR-II), ~1550-1870 nm (NIR-III or SWIR) and ~2100-2300 nm (SWIR-II).

It is known that NIR light better penetrates through tissue than the visible one. By now, the penetration of light in NIR-I region is well characterized for most biological matters including head and brain. Over the last decades, this window has been employed for noninvasive optical bioimaging, optical imaging guided therapy and drug delivery. Recently, NIR-II, NIR-III (or SWIR) optical windows have been identified and use of NIR-SWIR light for the in vivo optical bioimaging, including transcranial brain imaging, has actively been advanced. The use of the SWIR-II window at ~2100-2300 nm has also been assessed for imaging of soft tissues. 

In the paper by Golovynskyi et al, an investigation of the head tissue optical properties has been performed in the broad spectral range of 350-2800 nm. The obtained spectra of attenuation coefficient and total attenuation length exhibit NIR-I, NIR-II (SWIR) and SWIR-II transparency windows, with maximal tissue permeability in SWIR range. An absorbance of the head tissues has also been investigated in details, with defining and describing the characteristic absorption peaks in NIR-SWIR. Taking into account the rapid development of new SWIR imaging detectors; the reduced scattering and absence of autofluorescence in SWIR windows can provide major benefits for optical bioimaging, as the reduced scattering results in the improved imaging contrast and resolution. The authors point that attenuation of light by skull bone and other head tissues is similar between SWIR-II and  NIR-I, where tissues exhibit lower absorption but higher scattering. In contrast, lower scattering (and higher absorption) in SWIR-II means that the collimated (ballistic) light can relatively better propagate through a tissue, suggesting a promising potential of SWIR-II window for transcranial imaging. In addition, based on the NIR-SWIR absorption spectra obtained for the head tissues, the authors accentuate that the distinctive spectral features of the tissue constituents in NIR-II, SWIR and SWIR-II (e.g., close but spectrally distinctive absorption peaks of lipids at ~2165 nm, proteins at ~ 2300 nm and water at ~ 2480 nm) can provide endogenous contrast for optical tissue imaging.  

Original article: 

S. Golovynskyi, I. Golovynska, L.I. Stepanova, O.I. Datsenko, L. Liu, J. Qu, T.Y.  Ohulchanskyy, Optical windows for head tissues in near and short-wave infrared regions: approaching transcranial light applications. Journal of Biophotonics, e201800141 (2018). https://doi.org/10.1002/jbio.201800141


Authors: Dr. Sergii Golovynskyi and Prof. Tymish Y. Ohulchanskyy


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