Spectral Domain Doppler Optical Coherence Tomography Algorithm

Optical coherence tomography (OCT) provides high-resolution cross-sectional images of tissues noninvasively. Combined with Doppler technique, it can measure the flow velocity in tissues, and has important clinical applications due to its noninvasive nature and high spatial resolution. In this dissertation, the work is mainly focused on the research about Spectral domain Doppler OCT algorithms which will improve the accuracy of the measurement. The main contents are as follows:1. Spectral domain Doppler OCT system has been theoretically studied, and the comparison of Phase-resolved method and Joint Spectral and Time domain optical coherence tomography has been shown.2. A method based cross-correlation technique was proposed to acquire and analyse the information about flow velocity with low signal-to-noise ratio (SNR) in Spectral domain OCT. In this method, we cross correlate the adjacent B-lines to suppress the noise which is uncorrelated, thus render an improvement on accuracy. We theoretically studied the procedure of this method, and analysed the correlation between the noises by computer simulation and experiment. The Doppler flow images reconstructed by cross-correlation method were compared with those reconstructed by Joint spectral and time-domain optical coherence tomography (STD-OCT). The results demonstrate that cross-correlation method can significantly suppress the noise under low SNR.3. Higher order cross-correlation method was proposed to further improve the noise suppression based on cross-correlation method. The method is theoretically developed and validated by measurement of moving mirror with known velocities. Standard deviations (STD) of flow velocities of the mirror under different SNRs are determined by the proposed method and compared with those by the modified phase-resolved method. Measurement of flowing particles within glass capillary is also conducted, and Doppler flow velocity maps of glass capillary are reconstructed by both methods. All experimental results demonstrate that the proposed method can significantly suppress noise, thus rendering it suitable for flow measurement under low SNR cases.4. A probe which is capable of two dimensional scanning based on the asymmetry fiber cantilever driven by single piezo bender actuator has been developed for endoscopic optical coherence tomography. However. Lissajous pattern realized by driving signal of sine form is hard to balance between uniformity, coverage and frame frequency, and hence hinders for optimization on scanning pattern. Based on response characteristic of the asymmetry fiber cantilever, the paper presents an amplitude modulated sine function as the driving signal for optimization of the scanning pattern. Simulations on scanning patterns under the same frame rate based on different driving signals are conducted, and evaluations in terms of uniformity and coverage are given. The comparative experiment was conducted too, and the results demonstrated the feasibility of this method.