Modelling of light propagation in diffusive media with applications to tissue spectroscopy, tomography and photodynamic therapy
Šušnjar, Stefan LU
(2026)
In Lund Reports on Atomic Physics, LRAP
- Abstract
- This thesis introduces the field of biomedical or diffuse optics and covers basic principles of light propagation in highly scattering media. Physics is well supported by mathematical derivations and equations, which is essential for the development of analytical models. These models are applied to three main fields.
First, in photodynamic therapy (PDT) — a promising approach, based on a dynamic interaction between light, photosensitiser (PS) and oxygen — for the treatment of prostate cancer. Real-time feedback based on three key components can be beneficial for better outcomes. The first component is tissue absorption, and measurements of tissue absorption have already been applied in clinical trials. The second is the spatial... (More) - This thesis introduces the field of biomedical or diffuse optics and covers basic principles of light propagation in highly scattering media. Physics is well supported by mathematical derivations and equations, which is essential for the development of analytical models. These models are applied to three main fields.
First, in photodynamic therapy (PDT) — a promising approach, based on a dynamic interaction between light, photosensitiser (PS) and oxygen — for the treatment of prostate cancer. Real-time feedback based on three key components can be beneficial for better outcomes. The first component is tissue absorption, and measurements of tissue absorption have already been applied in clinical trials. The second is the spatial distribution of PS concentration. In this work, we develop models and methods to monitor PS distribution during treatment. The models are based on diffuse fluorescence tomography (DFT). Developed methods include numerical simulations, inverse problem solving in two stages, preparation of tissue-mimicking phantoms with PS, and experimental validation. The third parameter is oxygen concentration, which could be a subject of future work.
After the basics of inverse problem solving in diffuse optical tomography (DOT), the fundamental principles of ultrasound optical tomography (UOT) are introduced. Mechanisms that cause the frequency of light to shift in the presence of ultrasound are discussed, and simplified modelling, based on the diffusion equation and perturbation approach, is presented. The developed model enables rapid simulation of UOT images of media with inhomogeneous absorption, which is essential for inverse problem solving and clinical translation of the technique.
Finally, within the field of diffuse optics, where mainly elastic scattering of light is discussed, inelastic Raman scattering is introduced for the purpose of spectroscopic applications with excellent chemical specificity. Diffuse Raman spectroscopy (DRS) for two-layered media is supported with thorough mathematical derivation and suggestions for further refinement.
In conclusion, this thesis connects three seemingly different fields of application (DFT in PDT, UOT, and DRS) by one common thread –– analogy in mathematical modelling. Raman scattered light, PS fluorescence, and ultrasound-modulated light are all kinds of “tagged’’ light that “carries information’’ about where this “tagging” has occurred. This is beneficial for spatial resolution in DFT and UOT, and is also used to separate Raman spectra of layered media. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/f4e74501-aed6-476a-958c-3052f0091bfa
- author
- Šušnjar, Stefan
LU
- supervisor
- opponent
-
- Prof. Lilge, Lothar, University of Toronto, Canada.
- organization
- publishing date
- 2026-03
- type
- Thesis
- publication status
- published
- subject
- keywords
- diffuse optics, photodynamic therapy (PDT), photosensitiser (PS) fluorescence, diffuse optical tomography (DOT), inverse problems, ultrasound optical tomography (UOT), tissue-mimicking phantoms, Raman spectroscopy
- in
- Lund Reports on Atomic Physics, LRAP
- issue
- 622
- publisher
- Department of Physics, Lund University
- defense location
- Lecture Hall Rydbergsalen, Department of Physics, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund.
- defense date
- 2026-04-24 13:15:00
- ISSN
- 0281-2762
- ISBN
- 978-91-8104-923-7
- 978-91-8104-924-4
- language
- English
- LU publication?
- yes
- id
- f4e74501-aed6-476a-958c-3052f0091bfa
- date added to LUP
- 2026-03-28 16:00:32
- date last changed
- 2026-04-01 03:20:07
@phdthesis{f4e74501-aed6-476a-958c-3052f0091bfa,
abstract = {{This thesis introduces the field of biomedical or diffuse optics and covers basic principles of light propagation in highly scattering media. Physics is well supported by mathematical derivations and equations, which is essential for the development of analytical models. These models are applied to three main fields.<br/><br/>First, in photodynamic therapy (PDT) — a promising approach, based on a dynamic interaction between light, photosensitiser (PS) and oxygen — for the treatment of prostate cancer. Real-time feedback based on three key components can be beneficial for better outcomes. The first component is tissue absorption, and measurements of tissue absorption have already been applied in clinical trials. The second is the spatial distribution of PS concentration. In this work, we develop models and methods to monitor PS distribution during treatment. The models are based on diffuse fluorescence tomography (DFT). Developed methods include numerical simulations, inverse problem solving in two stages, preparation of tissue-mimicking phantoms with PS, and experimental validation. The third parameter is oxygen concentration, which could be a subject of future work.<br/><br/>After the basics of inverse problem solving in diffuse optical tomography (DOT), the fundamental principles of ultrasound optical tomography (UOT) are introduced. Mechanisms that cause the frequency of light to shift in the presence of ultrasound are discussed, and simplified modelling, based on the diffusion equation and perturbation approach, is presented. The developed model enables rapid simulation of UOT images of media with inhomogeneous absorption, which is essential for inverse problem solving and clinical translation of the technique.<br/><br/>Finally, within the field of diffuse optics, where mainly elastic scattering of light is discussed, inelastic Raman scattering is introduced for the purpose of spectroscopic applications with excellent chemical specificity. Diffuse Raman spectroscopy (DRS) for two-layered media is supported with thorough mathematical derivation and suggestions for further refinement.<br/><br/>In conclusion, this thesis connects three seemingly different fields of application (DFT in PDT, UOT, and DRS) by one common thread –– analogy in mathematical modelling. Raman scattered light, PS fluorescence, and ultrasound-modulated light are all kinds of “tagged’’ light that “carries information’’ about where this “tagging” has occurred. This is beneficial for spatial resolution in DFT and UOT, and is also used to separate Raman spectra of layered media.}},
author = {{Šušnjar, Stefan}},
isbn = {{978-91-8104-923-7}},
issn = {{0281-2762}},
keywords = {{diffuse optics; photodynamic therapy (PDT); photosensitiser (PS) fluorescence; diffuse optical tomography (DOT); inverse problems; ultrasound optical tomography (UOT); tissue-mimicking phantoms; Raman spectroscopy}},
language = {{eng}},
number = {{622}},
publisher = {{Department of Physics, Lund University}},
school = {{Lund University}},
series = {{Lund Reports on Atomic Physics, LRAP}},
title = {{Modelling of light propagation in diffusive media with applications to tissue spectroscopy, tomography and photodynamic therapy}},
url = {{https://lup.lub.lu.se/search/files/246068187/Thesis_Stefan_Susnjar_LUCRIS.pdf}},
year = {{2026}},
}