Molecular contrast optical coherence tomography: SNR comparison of techniques and introduction of ground state recovery pump-probe OCT

Abstract

Molecular contrast OCT (MCOCT) is an extension of OCT in which specific molecular species are imaged based on their spectroscopic characteristics. In order to improve the sensitivity and specificity of MCOCT, several techniques have recently been introduced which depend upon coherent detection of inelastically scattered light from molecules of interest in a sample. These techniques include harmonic generation, coherent anti-Stokes Raman scattering, and several different forms of pump-probe spectroscopy. We have developed a theoretical framework to facilitate the comparison of different inelastic scattering-based contrast mechanisms for molecular contrast OCT. This framework is based upon the observation that since the noise floor is defined by the reference arm power in a shot-noise limited heterodyne detection system, the relevant comparison among the techniques is isolated to the available molecular-specific signal power. We have derived the value of the molecular contrast signal power for second harmonic generation OCT (SHOCT) and three different pump-probe OCT (PPOCT) techniques. Motivated by this analysis, we have constructed a preliminary ground state recovery pump-probe OCT system, and demonstrated its performance using rhodamine 6G as the MCOCT contrast agent.