Elliptical polarization is used to explore the possibility of probing diffuse tissues at selective depths. The results of a recently published Monte Carlo simulations study are exposed. Experimental tests will be presented.
Polarization gating is a popular technique in biomedical optics. It is widely used to inspect the surface of the tissues (under colinear or cocircular detection) or instead to probe the volume (cross-linear detection), without information on the probed depth. Elliptical polarization is introduced to explore the possibility of probing diffuse tissues at selective depths. A thorough Monte Carlo simulation study shows complete correlation between the probed depths and the ellipticity of the polarized light, for a medium with known optical properties. Within a wide range of optical parameters, a linear relation between the backscattered intensity and the depth extension of the probed volume was found whatever the polarization used, but with a controlled extension depending on the ellipticity.
Depth selectivity is crucial for accurate depth volume probing in vivo in a large
number of medical applications such as brain monitoring. Polarization gating has been widely
used to analyze biological tissues. It is shown that using polarized light allows probing tissues
on a specific depth depending on the polarization illumination type (linearly, circularly) and
the tissues properties. However, accurate depth investigation of the tissue requires a high
selectivity of the probed depth. We propose and simulate the use of different elliptically
polarized illuminations for continuous depth examination between linearly and circularly
polarized illumination. Monte Carlo simulations verify that circularly polarized illumination
penetrates deeper than linearly polarized illumination in biological scattering media.
Furthermore, we show that elliptically polarized light can be tuned in its penetration depth
continuously between the penetration depth of linearly polarized light and circularly polarized
light. Experimental results obtained on phantoms mimicking in vivo situations are presented.
A polarization-sensitive Monte Carlo model is used to investigate differently polarized light
illuminations on their degree of polarization (DOP) depth evolution in a semi-infinite scattering
medium. The three-dimensional simulations show that circular polarized light maintains its initial
polarization state longer than elliptical or linear polarized light. It was revealed that elliptical
polarization can be tuned so that its DOP depth evolution can be precisely chosen between the
penetration depths of linearly and circularly polarized light.