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

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.