Tissue characterization with optical coherence tomography (OCT)

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Abstract
Tissue spectroscopy and high resolution imaging down to penetration depths of about 1 mm are of great interest for diagnostic purposes. In this paper we cover both disciplines by analyzing detected and simulated heterodyne signals obtained with optical coherence tomography (OCT). The detected signals are affected by photons propagating in forward direction and single-backscattering (dependent on the reflecting target). In the spectroscopic part, we retrieved scattering parameters, which are scattering coefficients (mu) s and mean scattering angles (theta) RMS. We fitted experimentally detected axial point spread functions (PSFs) to simulated curves, obtained by an analytical model described elsewhere. Ballistic photons (coherent component) and multiply forward scattered photons (incoherent component) contribute to the detected signals. In one study, (mu) s and (theta) RMS were retrieved for a slice of 0.5 mm thick tissue. Several simulations about the contrast (obtained from axial PSFs) vs. (theta) RMS and vs. numerical aperture (NA) of the focusing optics were performed for different reflecting targets. In addition, temporal signal fluctuations and the corresponding probability distribution functions (PDFs) are of interest to assess the accuracy of obtained parameters. We show that incoherent averaging provides a means for reducing detected signal fluctuations. Finally in vivo images with a mean resolution of about 20 micrometer are presented.

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