Computationally efficient model of OCT scan formation by focused beams and its usage to demonstrate a novel principle of OCT-angiography

Abstract

A computationally highly efficient full-wave model of OCT-scan formation by focused beams in spectral-domain optical coherence tomography (OCT) is presented. Similarly to some previous models, it is based on summation of fields scattered by discrete sub-resolution scatterers and enables accounting for axial and lateral inhomogeneity of the illuminating Gaussian beam. The main feature ensuring high computational efficiency of the described model is that instead of numerical integration of the scattered signal over the receiving aperture we apply analytical description of both the illuminating-beam focusing and collection of the scattered signals over the receiving aperture. Elimination of numerical integration over the receiving aperture has increased the computation speed by a factor of ~3 10. This is of key importance for practical feasibility of simulations of 3D OCT data volumes for large amounts (~7 5 10 10 ) of scatterers corresponding to realistic densities of cells in biological tissues. We demonstrate the model possibilities by simulating digital refocusing of strongly focused OCT beams in the presence moving scatterers. A novel principle of contrast-agent-free visualization of scatterer flows with velocities typical of blood microcirculation is demonstrated.

Simulation of multimodal optical coherence tomography for biomedical diagnostics: comprehensive full-wave description based on ballistic scattering of arbitrary-profile beams

“…Even using such simplified beam geometries as in 13,16 , it is already possible to simulate important features of real OCT-scans formed by beams with weak focusing/divergence and obtain useful results for developing new OCT modalities such as elastography 20,21,22,23 . For weakly focused beams, the validity of such simplified models is also confirmed by similarity with physical experiments and results of more advanced models like 17,18 that belong to full-wave approaches and are based on rigorous consideration of Gaussian beams with allowance for pronounced focusing.…”

“…In what follows we demonstrate that using the same basic approximations (i.e., the use of discrete scatterers and ballistic scattering) as in 17,18 and many other models, e.g. 9,14 , it is possible to reformulate the OCT-scan formation model, such that the above-mentioned limitations can be completely lifted.…”

“…The use of discrete scatterers concerns all three groups of simulation methods (e.g. 9,16,17,18 ). This is quite a meaningful approximation, even if real scatterers are not literally point-like objects; nevertheless, they still can be treated as discrete sub-resolution particles in OCT scans and be reasonably corresponded to cells in biological tissues.…”

“…In this context utilization of Gaussian beams in modeling is rather attractive because of the possibility to describe their forward propagation analytically. Collection of the backpropagated waves over the receiving aperture can be made either using numerical integration (like in 17 ), or even analytically for non-diaphragmed beams 18 . Certainly, the possibility to pass from numerical integration to analytical description of the back-propagated wave and its collection over the receiving aperture like in 18 dramatically improved the computational efficiency.…”

“…Collection of the backpropagated waves over the receiving aperture can be made either using numerical integration (like in 17 ), or even analytically for non-diaphragmed beams 18 . Certainly, the possibility to pass from numerical integration to analytical description of the back-propagated wave and its collection over the receiving aperture like in 18 dramatically improved the computational efficiency. However, this improvement was enabled at the expense of a limitation: the Gaussian beam diameter should be significantly smaller than the illuminating/receiving aperture.…”