Optical coherence tomography (OCT) uses near-infrared light to generate high-resolution images of coronary arteries in vivo and can be considered an optical analog of intravascular ultrasound, which uses light instead of sound. The near-infrared light with a wavelength of about 1.3 μm is invisible to the human eye. OCT uses low-coherence interferometry by measuring the echo time delay and intensity of the light reflected from internal structures in tissue to generate cross-sectional images. The light beam from an OCT system is split by an interferometer into two arms, a sample arm and a reference arm. The sample arm light travels to the sample tissue, then is being reflected, refracted, or absorbed by the tissue and fnally travels back to the interferometer. The reference arm is directed to a mirror, which reflects it back to the interferometer, combined with the sample arm light and detected by a detector. The OCT image is built based on the interaction between these two light waves, depending on whether there is constructive or destructive interference between the waves . Cross-sectional images are generated by measuring the delay time and intensity of light reflected or backscattered from internal structures in biologic tissue .