Finite-difference time-domain analysis of refractive index tomography of melanin measured by optical coherence tomography
Date Issued
2015
Date
2015
Author(s)
Huang, Shi-Hao
Abstract
Melanin is a widely distributed natural pigment in creature, but the exact refractive index of melanin is still not clear. Optical coherence tomography (OCT) is with the advantage of high-speed scan and much higher resolution, but with low image penetration. Therefore, it is very appropriate to apply the tomography to superficial in vivo sample like epidermis tissue and the structure of retina in the eye. The numerical electromagnetic simulation method: finite-difference time domain (FDTD) can easily simulate the axial scan (A-scan) from OCT experiment carrier raw data. We assumed that the mechanism of light reflected from sample is incident Fresnel’s equation and simulated the OCT carrier raw data by 1D-FDTD. The method we propose is to use the signal which are with absorption to reconstruct the sample without absorption structure first. After getting the structure without absorption, the structure can be a simulation scenario to get another reflection signal without absorption to compare with the first reflection. In conclusion, the absorption coefficient (α) can be calculated from the decay of second reflection and the result shows that the reconstructed sample with some defects can be attributed to the slight boundary that is with thin thickness in lateral direction. Therefore, we compare to the result with double sized structure, the difference shows that the larger geometry can reduce the reconstruct error caused by the thickness under the resolution.
Subjects
Optical coherence tomography
Michelson’s interferometry
finite-difference time domain method
absorptive tissue
melanin
Type
thesis
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