Toward Absorption Contrast Imaging of biological tissues In Vivo by using Photothermal Optical Coherence Tomography

摘要

Optical coherence tomography has been proven in the last two decades its clinical value by providing 3D non-invasive in vivo biopsy of the biological samples. In addition to structural information given by the backscattered intensity, the optical absorption will also provide another powerful contrast. Optical absorbers in biological tissues exhibits important role such as hemoglobin and melanin. However, current methods of absorption contrast take long time and not suitable for in vivo imaging. Toward in vivo absorption contrast imaging, we developed photothermal OCT system by combining swept-source OCT system and excitation laser. A swept-source OCT system is used with a wavelength swept laser at 1310 nm with a scanning rate and range of 47 kHz and of 100 nm, respectively. Photocurrents from balanced photoreceivers are sampled by a high-speed digitizer by using k-clock from the source to sample optical spectrum in k-linear domain. The sensitivity of 107 dB for two polarization channels is achieved. At the sample arm, the OCT probe beam and an excitation laser are combined by a dielectric mirror. The fiber-coupled laser diode of 406 nm wavelength is used for excitation since the absorption of hemoglobin has peak around this wavelength. In order to evaluate the ability of this system, phase stability of the system was measured. The standard deviation of the phase shift is measured as 0.0028 radians, where the signal-to-noise-limited value is approximately 0.001. Several issues for in vivo case, motion, blood flow, thermal damage, and etc. will be addressed here.