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MODELIRANJE ŠIRJENJA SVETLOBE V SIPAJOČIH MEDIJIH ZA REFLEKTANČNO SPEKTROSKOPIJO Z OPTIČNIMI SONDAMI
ID Naglič, Peter (Avtor), ID Buermen, Miran (Mentor) Več o mentorju... Povezava se odpre v novem oknu

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Izvleček
Reflektančna spektroskopija je eksperimentalna metoda za zajem in analizo povratno sipane svetlobe iz snovi. Na snov navadno posvetimo s širokospektralnim svetilom v vidnem in bližnje infrardečem področju. Vpadna svetloba se glede na lomni količnik snovi bodisi odbije neposredno od površine, bodisi lomi v snov. V snovi je svetloba podvržena procesom absorpcije in sipanja. Zaradi sipanja, ki spreminja smer širjenja svetlobe, znaten del svetlobe povsem spremeni začetno smer širjenja in zapusti snov. Eksperimentalno lahko to svetlobo zaznamo z optičnimi sondami [1] in integracijskimi sferami [2], služi pa tudi kot glavni vir informacije pri hiperspektralnem slikanju [3]. Rezultat zajema in analize povratno sipane svetlobe z reflektančno spektroskopijo je reflektančni spekter, ki nosi informacijo o strukturi in kemijski sestavi opazovane sipajoče snovi. Reflektančna spektroskopija se najpogosteje uporablja za določanje optičnih lastnosti snovi (tj. absorpcijskih in sipalnih lastnosti) na področju biomedicine [4]. Prednost reflektančne spektroskopije je osvetljevanje in zbiranje svetlobe z iste strani snovi, pri čemer uporabljamo svetila nizkih intenzitet, kar med drugim omogoča tudi neinvazivno določanje lastnosti snovi [5–8]. Optične lastnosti snovi določimo s pomočjo modeliranja reflektančnih spektrov, ki jih prilegamo na izmerjene spektre. Pri tem spreminjamo parametre modela, tj. optične lastnosti, dokler ne najdemo optimalnega ujemanja med modelom in meritvijo [7,9–16]. Namen naših študij bo nadaljnji razvoj modelov za simulacijo in analizo reflektančnih spektrov pridobljenih s pomočjo optičnih sond ter njihovo objektivno vrednotenje na eksperimentalni ravni.

Jezik:Slovenski jezik
Ključne besede:sipajoči medij, simulacije Monte Carlo, sipanje svetlobe, modeliranje širjenja svetlobe, reflektančna spektroskopija, sipalna fazna funkcija, optične sonde, sub-difuzijski režim, sipajoči fantomi
Vrsta gradiva:Doktorsko delo/naloga
Organizacija:FE - Fakulteta za elektrotehniko
Leto izida:2017
PID:20.500.12556/RUL-92376 Povezava se odpre v novem oknu
COBISS.SI-ID:11759700 Povezava se odpre v novem oknu
Datum objave v RUL:25.05.2017
Število ogledov:1897
Število prenosov:536
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Sekundarni jezik

Jezik:Angleški jezik
Naslov:MODELING OF LIGHT PROPAGATION IN TURBID MEDIA FOR FIBER OPTIC REFLECTANCE SPECTROSCOPY
Izvleček:
Reflectance spectroscopy is an experimental technique for acquisition and analysis of light backscattered from a turbid medium. In the field of biomedical optics, reflectance spectroscopy is most commonly used for estimation of turbid medium optical properties, which carry information about the structural and chemical composition of a biological tissue. As such, reflectance spectroscopy has the potential to provide insight into various diseases and malformations that affect the biological tissue and could thus aid to better understanding and evaluation of a disease. The main advantage of the reflectance spectroscopy lies in the convenient experimental setting that allows illumination and light detection to be performed on the same side of the turbid medium. A broadband light source in the visible and near-infrared spectral range is usually used to illuminate the turbid medium. The incident light is then either reflected from the turbid medium or refracted into the turbid medium, where it is subjected to physical processes such as absorption and scattering. Due to scattering in the turbid medium, the propagation direction of light changes. Consequently, some light is backscattered from the turbid medium, where it can be detected by optical fiber probes, integrating spheres or by using hyperspectral imaging systems. The detected backscattered light forms the so-called reflectance spectrum. The optical properties of the turbid medium can be estimated by modeling the reflectance spectra using a light propagation model and subsequently computing the free parameters of the model by minimizing the difference between the modeled and measured reflectance spectra. The estimation of optical properties utilizing reflectance spectroscopy is complex and often requires the use of simplified light propagation models. However, such simplifications may limit the applicability of the models. Namely, many studies tend to substantially simplify the geometrical and structural description of the experimental setup. This especially holds for the optical fiber probes, where the probe-medium interface is often assumed to be a simple laterally uniform boundary between two media with mismatched refractive indices. Additionally, proper description of the scattering phase function, which defines the angular properties of scattering, is often overlooked in the models that are used to estimate optical properties. The role of scattering phase function becomes increasingly important with decreasing distance between the light source and detector. In this case, the acquired reflectance, in addition to the absorption and scattering coefficients, significantly depends on the scattering phase function. Although incorporating the scattering phase function into the estimation of optical properties presents a difficult task, the shape of the scattering phase function carries important information about the turbid medium microstructure. As such, estimation of any additional information associated to the scattering phase function could yield information about biological tissues on a cellular level. This thesis focuses on accurate estimation of optical properties from reflectance spectra acquired with optical fiber probes. Firstly, we quantitatively evaluate the impact of commonly used simplified geometrical and structural properties of the optical fiber probes in the simulation of light propagation in turbid media utilizing the Monte Carlo method. We find that in order to accurately estimate the optical properties, the materials that form the optical fiber probe tip and their arrangement have to be taken into account. Subsequently, we objectively evaluate the existing models for estimation of optical properties from reflectance spectra. We prove that the scattering phase function plays an important role in the estimation procedure. By accounting for some of the scattering phase function information, we show that the models can be substantially improved and thus yield more accurate estimates of the optical properties such as the absorption and reduced scattering coefficients and the additional scattering phase function related parameters.

Ključne besede:turbid medium, Monte Carlo simulations, light scattering, light propagation modeling, reflectance spectroscopy, scattering phase function, optical fiber probes, sub-diffusive regime, turbid phantoms

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