In the master thesis, we investigate the use of optical coherence tomography (OCT) to measure the physical and structural properties of samples. OCT is a non-contact optical technique based on the detection of backscattered low-coherence light, which allows determination of the depth distribution of optical scatterers and absorbers in a sample. The technique itself has already found its use in clinical practice in the field of ophthalmology, more precisely in the examination of the retina. In other fields of medicine, the technique is still in experimental use.
In our case, an OCT system at 1300 nm was used with a good penetration depth even in strongly scattering samples, such as skin. First, we performed measurements on tissue phantoms made of silica with different concentrations of scatterers, which were glass microspheres, and absorbers, which was carbon-based ink. We measured the refractive indices of the samples with the OCT system and obtained a very good agreement with the semi-empirical prediction based on measurements with a refractometer. In the next step, we extracted the attenuation coefficients from the OCT signals using two different analysis approaches, where the match with the theoretical prediction was not satisfactory, as the deviation between the measurements and the prediction was more than 100 %. We assume that the reason is the type of scatterers, which also contain very large speheres of 10 μm and more in size. For detailed description of the scattering, knowledge of the scattering phase functions would also be required. However the trend of the measured attenuation coefficients match the planned ones regarding the scatterer and absorber concentration.
Next we used the OCT system to image murine tumors, namely with the usual OCT method and the OCT angiography (OCTA) method. We developed a procedure for determination of the boundary between the tissue and the surrounding area and for determination of the relative effective attenuation coefficients. We have shown that it is possible to extract images of the network of vessels from OCTA images, on which we then superimposed images of relative effective attenuation coefficients, which carry local information about the imaged tissues.
In the master thesis, we showed that the OCT technique is a useful technique both for determinatzion of the physical optical properties of imaged samples, as well as for the structural properties of tissues. The technique is fast and non-contact and therefore useful in both life sciences and medicine.
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