Non-invasive characterization of scattering properties of human skin

doctoral thesis

Neža Golmajer Zima (Author), Boris Majaron (Mentor)

Abstract

The objective of my doctoral research was the characterization of the scattering properties of the human skin and their changes due to aging and injury. In this thesis, I combined two non-invasive optical techniques to characterize the skin's optical properties: diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR). DRS measurements were made in the visible part of the spectrum, while PPTR involves measurements of mid-infrared emission from the sample surface after irradiating it with a light pulse. The two measurements are then fitted and compared with the predictions from a Monte Carlo model of light-tissue interaction. Using different types of skin models, I obtained a good match between the model and experimental data. Using a numerical forward model (inverse Monte Carlo, IMC) I iteratively got up to 14 sample model parameters. I showed that modification to the DRS measurements and additional corrections in the analysis have to be done to properly evaluate skin parameters. This was especially true with measurements of the tattooed skin, where I showed better results after corrections were made. In the context of a skin aging study, it was demonstrated that the scattering amplitude of the dermis decreases with the person’s age. However, no influence of the person’s age was observed on the thickness of the epidermis and dermis, nor on the scattering amplitude of the epidermis. I demonstrated that blood content influences the assessed scattering properties and that by eliminating the blood we can compensate for the smaller sample size in skin aging studies. I show that our method is effective in noninvasive measurements of burned skin. I show that the scattering properties of the skin change after a burn injury and that difference between severity of the burn can be seen. With this method we were able to measure the exact same part of the burns during the healing process. In the end, I also tried to validate the method using phantoms. While the assessed values of dye and scatterers concentrations were found to be proportional to the theoretical values, there was no absolute agreement. I found that many problems arise during validation, especially in the preparation of samples. The nanoparticles adhere to the walls of the containers, potentially forming aggregates, which could be a contributing factor to the observed discrepancies. All this reduces the accuracy of assessing scattering properties. In the case of absorption, the differences between assessed and theoretically predicted values are much smaller and consistent.

Keywords

medical physics;human skin;aging;burn wunds;tattoos;single beam substitution error;pulsed photothermal radiometry;diffuse reflectance spectroscopy;

Data

Language:	English
Year of publishing:	2025
Typology:	2.08 - Doctoral Dissertation
Organization:	UL FMF - Faculty of Mathematics and Physics
Publisher:	[N. Golmajer Zima]
UDC:	543.4:616-073(043.3)
COBISS:	239671811
Views:	173
Downloads:	51
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary title:	Neinvazina karakterizacija sipalnih lastnosti človeške kože
Secondary abstract:	Cilj doktorskega dela je bila določitev sipalnih lastnosti kože in njihovih sprememb zaradi staranja in ob poškodbah. V delu sem združila dve neinvazivni optični tehniki za karakterizacijo sipalnih lastnosti človeške kože: difuzno refleksijsko spektroskopijo (DRS) in sunkovno fototermalno radiometrijo (SFTR). DRS meritve so bile opravljene v vidnem delu spektra, SFTR obsega meritve srednjega infrardečega sevanja s površine vzorca po obsevanju s svetlobnim sunkom. Obe meritvi se nato prilagodita in primerjata z napovedmi iz Monte Carlo modela interakcije svetlobe in tkiva. Z uporabo različnih tipov modelov kože sem dosegla dobro ujemanje med modelom in eksperimentalnimi podatki. Z uporabo inverznega numeričnega modela (inverzni Monte Carlo, IMC) sem iterativno določila do 14 parametrov vzorčnega modela. Pokazala sem, da so za pravilno ovrednotenje fizikalnih parametrov človeške kože potrebne spremembe meritev DRS in dodatne korekcije v analizi. To je še posebej veljalo za meritve tetovirane kože, kjer sem po popravkih pokazala izboljšane rezultate. Pri študiji staranja kože sem pokazala, da se s starostjo sipalna amplituda dermisa manjša, vpliva na debelino epidermisa in dermisa ter na sipalno amplitudo epidermisa nismo opazili. Poleg tega vsebnost krvi vpliva na ocenjene lastnosti sipanja, pri čemer z našo metodo izločanja krvi lahko kompenziramo tudi manjšo velikost vzorca v študijah staranja kože. Naša metoda se je izkazala za učinkovito tudi pri neinvazivnih meritvah opečene kože. Pokazali smo, da se sipalne lastnosti opečene kože spremenijo in spremljali zdravljenje. Metoda lahko pomaga določiti stopnjo opekline ali pomaga pri izvajanju objektivnih longitudinalnih študij celjenja opeklinske rane. Na koncu sem poskusila metodo tudi validirati s pomočjo fantomov. Ocenjene vrednosti koncentracije barvila in sipalcev so sicer proporcionalne s teoretično določenim, vendar se absolutno ne ujemajo. Ugotovila sem, da se pri validaciji pojavljajo številni problemi, predvsem s pripravo vzorcev. Nanodelci, ki jih uporabljamo, se lepijo na stene posod, in sumimo, da nastajajo skupki. Vse to zmanjšuje točnost napovedovanja sipalnih lastnosti. Pri absorpciji so razlike med ocenjenimi vrednostmi in teoretično napovedanimi precej manjše in konsistentne.
Secondary keywords:	medicinska fizika;človeška koža;staranje;opekline;tetovaže;artefakt zamenjave vzorca;sunkovna fototermalna radiometrija;difuzijska refleksijska spektroskopija;Koža;Disertacije;Poškodbe;Karakterizacija;
Type (COBISS):	Doctoral dissertation
Study programme:	0
Thesis comment:	Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages:	162 str.
ID:	26594149