| Summary: | 博士 === 國立臺灣大學 === 光電工程學研究所 === 101 === Abstract
First, an improved image processing procedure for suppressing the phase noise due to a motion artifact acquired during optical coherence tomography (OCT) scanning and effectively illustrating the blood vessel distribution in a living tissue is demonstrated. This new processing procedure and the widely used procedure for micro-angiography application are based on the selection of high-frequency components in the spatial frequency spectrum of B-mode scanning (x-space), which are contributed from the image portions of moving objects. However, by switching the processing order between the x-space and k-space, the new processing procedure shows the superior function of effectively suppressing the phase noise due to a motion artifact. After the blood vessel positions are precisely acquired based on the new processing procedure, the projected blood flow speed can be more accurately calibrated based on a previously reported method. The demonstrated new procedure is useful for clinical microangiography application, in which a stepping motor of generating motion artifacts is usually used in the scanning probe.
Secondary, the significantly less stringent operation of a two-reference swept-source OCT system for suppressing the mirror image is demonstrated based on the spatially localized image processing method. With this method, the phase difference between the two reference signals is not limited to 90 degrees. Based on the current experimental operation, the mirror image can be effectively suppressed as long as the phase difference is larger than 30 degrees. In other words, the adjustment of the beam splitter orientation for controlling the phase difference becomes much more flexible. Also, based on a phantom experiment, the combination the spatially localized mirror image suppression method with the two-reference OCT operation leads to the implementation of full-range optical Doppler tomography.
Finally, the intensity and photothermal images of OCT scanning of agar phantoms with and without the mixture of Au nanorings (NRIs) based on two OCT systems of different operation wavelengths are compared. The Au NRIs have the localized surface plasmon (LSP) resonance peak at ~1320 nm, leading to enhanced coherent scattering for producing clear OCT intensity images with the OCT system of 1310 nm in operation wavelength. Also, the LSP resonance induced absorption results in clear photothermal images through phase signal calibration of OCT scanning with the 1315-nm OCT system and another OCT system of 800 nm in central operation wavelength when a modulated excitation laser is applied. It is found that although the intensity image signal is weak with the 800-nm OCT system, its photothermal signal is quite strong, particularly when bean milk is mixed with agar for enhancing background scattering. The photothermal signal level increases with increasing background scattering when the OCT operation wavelength is located outside the spectral range of LSP resonance of Au NRI. In the viewpoint of practical application of Au nanoparticle (NP) tracking, simultaneous acquirement of clear OCT intensity and photothermal images can help in more precisely identifying the distribution of Au NPs. However, to this goal, the required matching of LSP resonance wavelength and OCT operation wavelength results in lower flexibility of choosing the used Au NP.
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