Optical properties of mice skull bone in the 455- to 705-nm range

Abstract

Abstract. Rodent brain is studied to understand the basics of brain function. The activity of cell populations and networks is commonly recorded in vivo with wide-field optical imaging techniques such as intrinsic optical imaging, fluorescence imaging, or laser speckle imaging. These techniques were recently adapted to unrestrained mice carrying transcranial windows. Furthermore, optogenetics studies would benefit from optical stimulation through the skull without implanting an optical fiber, especially for longitudinal studies. In this context, the knowledge of bone optical properties is requested to improve the quantitation of the depth and volume of imaged or stimulated tissues. Here, we provide experimental measurements of absorption and reduced scattering coefficients of freshly excised mice skull for wavelengths between 455 and 705 nm. Absorption coefficients from 6 to 8 months mice skull samples range between 1.67 AE 0.28 mm −1 at 455 nm and 0.47 AE 0.07 mm −1 at 705 nm, whereas reduced scattering coefficients were in the range of 2.79 AE 0.26 mm −1 at 455 nm up to 2.29 AE 0.12 mm −1 at 705 nm. In comparison, measurements carried out on 4 to 5 weeks mice showed similar spectral profiles but smaller absorption and reduced scattering coefficients by a factor of about 2 and 1.5, respectively. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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

“…Thus, the characteristic hemoglobin bands peaked at~420 and~550 nm dominate in the visible absorption spectra for all the samples. There are some disparities between soft head tissues and bone: the absorption spectra of skin and brain cortex exhibited a single absorption peak at 550 nm related to deoxy-hemoglobin (Hb), while the double-peak absorption at 540 and 575 nm from oxy-hemoglobin (HbO 2 ) is detected for skull bone, as also reported in the literature [13]. In addition, the absorption peak at 410 nm for the bone tissues is seen to be blue-shifted in comparison with the corresponding (A) (B) (C) FIGURE 4 Spectral dependences of the attenuation and absorption coefficients along with fitted scattering for the freshly harvested rat brain cortex (A), skull bone (B) and skin (C) FIGURE 5 Spectral dependences of the absorption coefficient for the brain (blue), skull bone (red) and skin (black) samples after the desiccation.…”

“…The fitting functions are μ s = 12 450· λ −1.05 + 2·10 11 · λ −4 for the brain and μ s = 163· λ −0.28 + 3.4·10 11 · λ −4 for the skin. In contrast, the scattering intensity for the cranial bone slowly decreases following the Mie power law, as reported by other researchers . The fitting function for the cranial bone is μ s = 227· λ −0.23 (Figure B).…”

“…Thus, the characteristic hemoglobin bands peaked at ~420 and ~550 nm dominate in the visible absorption spectra for all the samples. There are some disparities between soft head tissues and bone: the absorption spectra of skin and brain cortex exhibited a single absorption peak at 550 nm related to deoxy‐hemoglobin (Hb), while the double‐peak absorption at 540 and 575 nm from oxy‐hemoglobin (HbO 2 ) is detected for skull bone, as also reported in the literature . In addition, the absorption peak at 410 nm for the bone tissues is seen to be blue‐shifted in comparison with the corresponding peak for the soft head tissues.…”

“…Obviously, our attenuation values should be different from those obtained for the skull surface. In other works [13,14,17,[57][58][59][60], the optical extinction coefficients of mammalian bone tissues were determined in narrow spectral range (mostly for NIR) and a value of reduced attenuation μ 0 t (μ 0 t = μ a + μ 0 s ) was found to be~10 to 30 cm −1 , denoting an increase in the light penetration while moving toward longer wavelengths.…”

“…with optical properties of biological tissues, which results in a limited light penetration. The penetration of light in visible and the shortest near-infrared (NIR-I) ranges of electromagnetic spectrum (ie, 400-700 and~700-1000 nm, respectively) is well characterized for most biological matters [5][6][7][8][9][10][11][12] including head [13][14][15][16][17] and brain [17][18][19][20][21]. NIR light has been found to better propagate through tissue than the visible one, and, in the beginning of 1980th, NIR-I region has been introduced by Parrish and Anderson as the diagnostic or therapeutic window [6,7].…”