Effect of coherence length and numerical aperture on the formation of OCT signals from model biotissues

Abstract

Maximal depth of non-distorted imaging is an important characteristic, which shows the efficiency of an application of a certain OCT setup for imaging the given object. This characteristic depends on the setup parameters and the properties of the studied object. The definition of the maximal depth of non-distorted imaging based on the classifications of photons contributing to the signal in dependence on the relations of their optical travel pathlength in the object and maximal reached depth was used in this work. We studied the effect of the coherence length and the detection angle on the formation of OCT signals and images from model biotissues as well as on the maximal depth of non-distorted imaging. The signals and images were obtained by implementing the Monte Carlo technique developed in our earlier works. The following single- and multilayer biotissue phantoms were considered as the studied objects: erythrocyte suspension at physiological hematocrit (35%), 2% intralipid solution reported to have optical properties close to those of skin in optical and NIR range, and multilayer human skin phantoms. For the simulations, the parameters of the OCT setup were chosen in accordance with real ones. The wavelengths of the light sources were chosen 820 and 910 nm. The conducted simulations show that a decrease in the detection angle and an increase in the coherence length increase the maximal probing depth in the studied objects due to smaller role of multiple scattering photons in the formation of the OCT signals. The obtained value of maximal depth of non-distorted imaging varies in the range from 50 to 600 μm depending on the values of the setup parameters.