Spectroscopic OCT

Overview

Spectroscopic OCT (S-OCT) extends conventional OCT by extracting wavelength-dependent tissue optical properties from the broadband interference signal. This enables quantitative characterization of material composition — distinguishing molecular species without additional imaging modalities.

Technical Approach

The system uses a swept-source OCT VCSEL laser operating at 1310 nm center wavelength with 100 nm bandwidth. The key pieces:

Inverse algorithm design. We developed a Tikhonov-regularized spectral fitting framework that extracts depth-resolved scattering and absorption coefficients from the OCT signal. The algorithm handles the ill-posed nature of the inverse problem through joint regularization across wavelengths, exploiting the spectral smoothness of biological chromophores as a physical prior.

Polarization-sensitive extension. By incorporating Jones matrix analysis of the polarization state evolution through the catheter and tissue, we add birefringence as a third contrast mechanism alongside scattering and absorption. This is particularly valuable for characterizing collagen organization in fibrous caps.

Current Status

The inverse algorithm has been validated on tissue-mimicking phantoms with known optical properties, achieving relative reconstruction error below 5%.

Impact

Reliable, quantitative material characterization during imaging could transform a range of fields including biomedical imaging. Current clinical OCT provides structural images but cannot quantify tissue composition meaning that clinicians must infer plaque vulnerability from morphological features alone. S-OCT would provide direct biochemical contrast, enabling more accurate identification of vulnerable plaques and better-informed treatment decisions.