Using an obliquely incident laser beam to measure optical properties of turbid media

Abstract

A simple and quick approach was invented to measure optical properties of tissue-like turbid media. A laser beam with oblique incidence to the medium causes the center of the diffuse reflectance that is several transport mean free paths away from the incident point to shift from the point of incedence. The amount of shift is used to compute the reduced scattering coefficient by a simple formula. This formula is a function of the refractive index of the turbid medium divided by that of the incident medium and the angle of incidence off the surface normal for a semi-infinite turbid medium having a much smaller absorption coefficient than the reduced scattering coefficient. For a turbid medium having a comparable absorption coefficient with the reduced scattering coefficient, a revision to the above formula was made. The slope of the diffuse reflectance can be used to compute the penetration depth. Both the computation of the reduced scattering coefficient and penetration depth are based on simple and quick algorithms. the validity condition of the algorithms for slabs of turbid media are studied. This technique has potential for noninvasive, in vivo, real-time diagnosis of disease or monitoring of treatments.