Optical coherence tomography (OCT) is an emerging alternative imaging tool to confocal microscopy. In layers beyond about 200 - 300 micrometers depth, an increasing fraction of multiple scattered photons begins to deteriorate diffraction limited axial and lateral resolution curves, which otherwise can be obtained only in very superficial layers (single-scatter regime). At greater depths, the contrast and resolution from OCT (and confocal microscopy) are determined by the parameters of the turbid medium rather than by the focusing optics. We have developed an analytical model to describe spatial resolution curves in homogeneous turbid media employing the heterodyne interferometric principle. Analogous to basic ideas from theoretical work done in the atmospheric LIDAR (Light Detecting and Ranging) community we derived the heterodyne detector signal from a mutual coherent function (MCF). The MCF is a function of the parameters of the focusing optics, the object position and the degree of coherence (lateral coherence length), which in turn characterizes the turbid medium. Axial resolution curves were acquired with our interferometer in reflection mode to characterize various turbid media by fitting the experimental data to simulation curves. Particularly when light propagates through suspensions of large particles before impinging on the object, a considerably loss in contrast (and even resolution) of the curves is noticeable. We studied the effects of a mirror and a diffuse plate serving as reflecting targets. In ex vivo tissue, we obtained a lateral coherence length on the order of 1 micrometers under the assumption of the validity of the model used.

Date Published: 10 April 1996
PDF: 13 pages
Proc. SPIE 2655, Three-Dimensional Microscopy: Image Acquisition and Processing III, (10 April 1996); doi: 10.1117/12.237484

Published in SPIE Proceedings Vol. 2655:
Three-Dimensional Microscopy: Image Acquisition and Processing III
Carol J. Cogswell; Gordon S. Kino; Tony Wilson, Editor(s)