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

Haleh Soleimanzad,Frédéric Pain,Hirac Gurden

doi:10.1117/1.jbo.22.1.010503

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 ± 0.28 ?? mm ? 1 at 455 nm and 0.47 ± 0.07 ?? mm ? 1 at 705 nm, whereas reduced scattering coefficients were in the range of 2.79 ± 0.26 ?? mm ? 1 at 455 nm up to 2.29 ± 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.

Highlights

Several in vivo optical techniques used to study rat and mouse brain have been recently adapted to minimally invasive approaches in which imaging or stimulation is carried out through thinned bone skull without exposing the dura-matter or the brain tissues
A hypothesis that requires further investigation would be that H2O2 treatment leads to structural denaturation of bone, for example, by increasing bone porosity leading to the increase of the reduced scattering coefficient
The ex vivo optical properties of mouse skull bone were determined in the 455- to 705-nm window

Summary

Introduction

Several in vivo optical techniques used to study rat and mouse brain have been recently adapted to minimally invasive approaches in which imaging or stimulation is carried out through thinned bone skull without exposing the dura-matter or the brain tissues. These transcranial approaches allow repeated imaging of brain tissues over intervals ranging from seconds to months.[1,2] In this context, the knowledge of skull bone’s optical properties would allow (i) to better quantify the biophysical origins of the recorded optical signals and (ii) to quantify the volume and depths of tissues that are photostimulated.

Methods

Results

Conclusion