Video reflectometry to specify optical properties of tissue in vivo

Abstract

The measurement of tissue optical properties is often required for proper design of therapeutic or diagnostic uses of light in medicine. The ability of light to spread into a tissue and the rate of light absorption by the tissue are two related but distinct processes. The two independent optical parameters which affect these processes are absorption and scattering. To understand light propagation, two independent optical measurements must be made. In this paper, we discuss the measurements of total diffuse reflectance and lateral spread of light in response to a point source of irradiance. In this paper, we call this technique 'video reflectometry'. The video reflectometry technique is a noncontact measurement. Therefore, it can be used with living tissues with their in situ water balance and blood content. The technique includes two measurements: (1) a photodiode measurement of total diffuse reflectance, R_d, and (2) a video camera measurement of the lateral spread of light in the tissue which is expressed as the local diffuse reflectance, R(r). Although it is possible to obtain the value of R_d from the integration of the video R(r) data, the independent photodiode measurement of R_d is more reliable and more easily calibrated. Therefore, we employ the two methods in video reflectometry.

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