Optical windows for head tissues in near‐infrared and short‐wave infrared regions: Approaching transcranial light applications

Abstract

Optical properties of the rat head tissues (brain cortex, cranial bone and scalp skin) are assessed, aiming at transcranial light applications such as optical imaging and phototherapy. The spectral measurements are carried out over the wide spectral range of 350 to 2800 nm, involving visible, near-infrared (NIR) and short-wave infrared (SWIR) regions. Four tissue transparency windows are considered: ~700 to 1000 nm (NIR-I), ~1000 to 1350 nm (NIR-II), ~1550 to 1870 nm (NIR-III or SWIR) and ~2100 to 2300 nm (SWIR-II). The values of attenuation coefficient and total attenuation length are determined for all windows and tissue types. The spectra indicate transmittance peaks in NIR, NIR-II and SWIR-II, with maximum tissue permeability for SWIR light. The use of SWIR-II window for the transcranial light applications is substantiated. Furthermore, absorbance of the head tissues is investigated in details, by defining and describing the characteristic absorption peaks in NIR-SWIR.

Moving tissue spectral window to the deep‐ultraviolet via optical clearing

“…These optical windows turn possible the establishment of new diagnostics and therapeutic procedures, provided that dedicated instrumentation is developed to work at these wavelengths. These new UV‐I and UV‐II tissue spectral windows should, along with the well‐known windows of tissue transparency in the visible and NIR, enter the arsenal of tools for optical imaging and spectroscopy .…”

“…The absorption of light in a tissue is high at wavelengths corresponding to the absorption bands of the tissue components, while strong light scattering is created by the refractive index mismatch between tissue components . Five optical windows have been established for diagnosis and therapeutic purposes at wavelengths, where the light penetration depth presents local maxima . Those windows, designated by roman numerals, are located at: 350‐400 nm (I), 625‐975 nm (II), 1100‐1350 nm (III), 1600‐1870 nm (IV) and 2100‐2300 nm (V) .…”

“…Outside these optical windows, light penetration depth is low as a result of existing absorption bands of tissue components. The main absorption bands for tissue components in the visible to the infrared are centered at: 970, 1180, 1450, 1775, 1930 and 1975 nm (water), approximately 760, 830, 920, 1040, 1210, 1430, 1730, 1760 and from 1900 to 2600 nm (lipids), 420 and 550 nm (deoxygenated hemoglobin, Hb) and 410, 540 and 575 nm (oxygenated hemoglobin, HbO 2 ) . Considering the ultraviolet range, the major absorption bands from common tissue components are observed at: 200 and 230 nm (proteins), 260 nm (DNA and RNA) and 275 and 345 nm (HbO 2 ) and 275 and 360 nm (Hb) .…”

Red and near‐infrared light induces intracellular Ca2+ flux via the activation of glutamate N‐methyl‐D‐aspartate receptors

“…Likewise, other studies demonstrated that visible and NIR light can instigate membrane depolarization without affecting the temperature. In the case of 808 nm at a high intensity of 1.1 W/cm 2 , the temperature rose no more than 0.8°C during laser irradiation for about 30 min (Uozumi et al, 2010), as biological objects weakly absorb light in this spectral range (S. Golovynskyi et al, 2018). Also, it was shown on neurons that green (Reece et al, 2008) of 810 nm with low fluences that do not cause any elevation in temperature (Kharkwal et al, 2011) On the other hand, the thermal mechanism of the membrane depolarization under high-fluence (more than 1 W/cm 2 ) IR light has been better investigated.…”

Core–shell polymeric nanoparticles co-loaded with photosensitizer and organic dye for photodynamic therapy guided by fluorescence imaging in near and short-wave infrared spectral regions

“…However, the efficacy of PDT produced by PS/NIRFD post-loaded poly-AA NPs is decreased by the energy transfer between PS and NIRFD [13]. In addition to the conventional NIR-I window, other optical windows have recently been identified in NIR-II region (or SWIR, as defined by the manufacturers of imaging cameras for ~ 1000-1700 nm range) for in vivo optical imaging [18][19][20]. The reduced tissue scattering and autofluorescence in SWIR spectral region results in a possibility to achieve bioimaging of deeper tissues with imaging camera for short-wave infrared (SWIR) region (~ 1000-1700 nm), which was recently shown to be beneficial for in vivo optical imaging.…”