Abstract
An accurate knowledge of tissue optical properties (absorption coefficients, μa, and reduced scattering coefficients, μs’) is critical for precise modeling of light propagation in biological tissue, essential for developing diagnostic and therapeutic optical techniques that utilize diffusive photons. A great number of studies have explored the optical properties of various tissue, and these values are not known in detail due to difficulties in the experimental determination and significant variations in tissue constitution. Especially, in situ estimates of the optical properties of brain tissue, a common measurement target in optical imaging, is a challenge because of its layer structure (where the thin gray matter covers the white matter). Here, we report an approach to in situ estimates of the μa and μs’ of the gray and white matter in living rat and monkey brains by using femtosecond time-resolved measurements and Monte Carlo simulation. The results demonstrate that the μa of the gray matter is larger than that of the white matter, while there was no significant difference in the μs’ between the gray and white matter. The optical properties of the rat brain were very similar to those of the monkey brain except for the μa of the gray matter here.
Highlights
Recent advances in optical imaging and optogenetic modulation techniques have greatly contributed to the evolution of life sciences[1,2,3]
The optical properties can be determined by fitting the measured temporal point spread function (TPSF) and theoretical data derived from numerical models of light propagation in biological tissue, such as the radiative transfer equation (RTE) and the photon diffusion equation (PDE), the diffusion approximation of the RTE18,19
The phantom is homogeneous, the TPSFs vary with depth for reasons thought to be mainly due to the reflection at the liquid-air interface
Summary
Recent advances in optical imaging and optogenetic modulation techniques have greatly contributed to the evolution of life sciences[1,2,3]. It has long been challenging to image and modulate biological processes deep within living tissue, and optical diagnostic (e.g. diffuse optical tomography, DOT6) and therapeutic techniques (e.g. photodynamic therapy, PDT7) with near-infrared light remain under development. Brain tissue is one of the most common measurement targets in optical imaging and in situ estimates of its optical properties is a challenge because of its layer structure (where the thin gray matter covers the white matter). The gray and white matter are not separately measured and average optical properties of a large volume of tissue are estimated Unlike these conventional approaches, Bevilacqua et al.[17] tried to optically differentiate a small tissue heterogeneity. We used time-resolved measurements as an approach to in situ separate measurements of the optical properties of cerebral gray and white matter. Prior to the measurements of rat and monkey brains, the validity of our approach was examined by measurements of a liquid phantom
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