magistrsko delo
Črt Keber (Author), Matija Milanič (Mentor), Jošt Stergar (Co-mentor)

Abstract

V magistrskem delu raziščemo uporabo optične koherenčne tomografije (OCT) za merjenje fizikalnih in strukturnih lastnosti vzorcev. OCT je brezdotična optična tehnika, ki temelji na detekciji povratno sipane nizko koherenčne svetlobe, ki omogoča določitev globinske porazdelitve optičnih sipalcev in absorberjev v vzorcu. Sama tehnika je že našla uporabo v klinični praksi na področju oftalmologije, bolj natančno pri preiskavi očesnega ozadja. Na drugih področjih medicine je tehnika še v eksperimentalni uporabi. V našem primeru je bil uporabljen OCT sistem pri 1300 nm, katerega značilnost je dobra vdorna globina tudi v močno sipajoče vzorce, kot je koža. Najprej smo izvedli meritve na tkivnih fantomih iz silikonskega gela z različnimi koncentracijami sipalcev, ki so bile v našem primeru steklene mikrokroglice, in absorberjev, ki je bil v našem primeru črnilo na osnovi ogljika. Z OCT sistemom smo izmerili lomne količnike vzorcev in dobili zelo dobro ujemanje s semiempirično napovedjo na osnovi meritev z refraktometrom. V naslednjem koraku smo z dvema različnima metodama analize iz OCT signalov izluščili atenuacijskje koeficiente, kjer pa ujemanje s teoretično napovedjo ni bilo zadovoljivo, saj je bilo odstopanje med meritvami in napovedjo več kot 100 %. Predvidevam, da je razlog vrsta sipalcev, ki vsebujejo tudi zelo velike kroglice v velikosti 10 μm in več in bi za podroben opis sipanja potrebovali tudi poznavanje sipalnih faznih funkcij. Sami trendi izmerjenih atenuacijskih koeficientov pa se ujemajo z načrtovanih. V nadaljevanju smo z OCT sistemom slikali tumorje mišk in sicer z običajnim OCT načinom in načinom OCT angiografije (OCTA). Razvili smo postopek določanja meje med tkivom in okolico ter določanja relativnih efektivnih atenuacijskih koeficientov. Pokazali smo, da je mogoče iz OCTA slik izluščiti slike omrežja žil, na katere smo potem naložili slike relativnih efektivnih atenuacijskih koeficientov, ki nosijo lokalno informacijo o slikanih tkivih. V magistrskem delu smo pokazali, da je OCT tehnika uporabna tehnika tako za določanje fizikalnih optičnih lastnosti slikanih vzorcev, kot tudi določanje strukturnih lastnosti tkiv. Tehnika je hitra in brezdotična ter zato uporabna s slikanje v živo tako v biologiji kot medicini.

Keywords

medicinska fizika;optična koherenčna tomografija;tkivni fantomi;biološka tkiva;angiografija;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [Č. Keber]
UDC: 616-073:535
COBISS: 121690371 Link will open in a new window
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Downloads: 7
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Other data

Secondary language: English
Secondary title: Determination of optical properties by optical coherence tomography
Secondary abstract: 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.
Secondary keywords: medical physics;optical coherence tomography;tissue phantoms;biological tissues;angiography;
Type (COBISS): Master's thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 68 str.
ID: 16496707