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Diffuse reflectance spectroscopy as a tool to evaluate liver tissue

Alburg, Therese LU and Kraus, David (2014) PHYM01 20141
Mathematical Physics
Atomic Physics
Abstract
The shape of a diffuse reflectance spectra can provide knowledge about tissue composition. By analysing this spectra one can, with the right evaluation methods, find out information about the tissue. With known absorption properties of the present tissue chromophores it is possible, with a curve fit algorithm, to find their volume fractions in any measured tissue.

In this work, the usability of diffuse reflectance spectroscopy (DRS) as a tool in tissue diagnostics was investigated. A model based on diffusion theory with a semi-infinite boundary condition and known tissue chromophore data was developed. It was used to evaluate DRS signals in tissue phantoms and on murinae, porcine and human livers. To ease the evaluation, an interface... (More)
The shape of a diffuse reflectance spectra can provide knowledge about tissue composition. By analysing this spectra one can, with the right evaluation methods, find out information about the tissue. With known absorption properties of the present tissue chromophores it is possible, with a curve fit algorithm, to find their volume fractions in any measured tissue.

In this work, the usability of diffuse reflectance spectroscopy (DRS) as a tool in tissue diagnostics was investigated. A model based on diffusion theory with a semi-infinite boundary condition and known tissue chromophore data was developed. It was used to evaluate DRS signals in tissue phantoms and on murinae, porcine and human livers. To ease the evaluation, an interface was developed to run the instruments (one light source and two spectrometers) from the computer and to compute the tissue composition from the provided diffusion model. The tissue composition was computed through a Levenberg-Marquardt least-squares algorithm in MATLAB.

Validation of the diffusion model was performed on tissue phantoms together with Monte Carlo (MC) simulations and a Time-of-Flight Spectroscopy (TOFS) measurement. The results from the validation measurements were varying. Many different kinds of phantoms were created. Commonly used phantoms, containing water, blood and intralipid gave results systematically underestimating the absorption while phantoms with greater fractions of lipid, mixed with agar or Triton-X100, gave results with less good correlation between signals and concentrations. The poor phantom results were discovered to be due to a low haemoglobin concentration in the used blood whilst there was also limitations in the diffusion criteria for these phantoms.

The results from liver measurements gave better correlation between signals and concentrations, and when investigating the criteria for diffusion these were also fulfilled in a greater wavelength region. The liver results also showed an evident difference between healthy and malignant tissue. (Less)
Popular Abstract (Swedish)
I dagens sjukvård finns det många etablerade metoder för att diagnostisera sjukdomar. Vissa av dessa är avbildningstekniker som PET, CT eller MR medan andra, som biopsi, är en annan typ av undersökning som utförs. Dessa metoder har både för- och nackdelar. Gemensamt för dem är att de antingen är dyra, potentiellt kan ha bieffekter eller tar lång tid. Sjukvården har många alternativ, men vilket är egentligen det bästa?

Optiska metoder är inte lika frekvent utnyttjade som diagnostiska verktyg. De är kraftfulla tekniker som varken gör skada, tar tid eller kostar mycket pengar. Genom att i stället använda sig av optiska metoder för diagnostik och terapi kan man både reducera kostnad, tid och i vissa fall förbättra den diagnostiska... (More)
I dagens sjukvård finns det många etablerade metoder för att diagnostisera sjukdomar. Vissa av dessa är avbildningstekniker som PET, CT eller MR medan andra, som biopsi, är en annan typ av undersökning som utförs. Dessa metoder har både för- och nackdelar. Gemensamt för dem är att de antingen är dyra, potentiellt kan ha bieffekter eller tar lång tid. Sjukvården har många alternativ, men vilket är egentligen det bästa?

Optiska metoder är inte lika frekvent utnyttjade som diagnostiska verktyg. De är kraftfulla tekniker som varken gör skada, tar tid eller kostar mycket pengar. Genom att i stället använda sig av optiska metoder för diagnostik och terapi kan man både reducera kostnad, tid och i vissa fall förbättra den diagnostiska informationen. Självklart finns det inte endast positiva saker med de optiska metoderna, en stor nackdel är att ljuset inte når långt ner i vävnaden. Fotonerna når endast en bråkdel av en millimeter till någon centimeter ner i vävnaden, beroende på vilken färg ljuset har.

En optisk metod för att avgöra om viss vävnad är frisk eller skadad bygger på diffus reflektans. Genom att mäta den diffusa reflektansen på specifik vävnad kan man sedan räkna ut vilka komponenter som finns, samt till vilken grad de är närvarande. Detta tillsammans med kunskap om komposition om frisk samt skadad vävnad kan bidra till att ställa en diagnos.

Diffus reflektans har i det här projektet används till att karakterisera vävnad i levern. Applikationerna finns både genom att tekniken kan använadas som ett guidande hjälpmedel under kirurgi samt vid undersökning av kemoterapiskador. I den här rapporten beskrivs den underliggande teorin för hur ljus och vävnad växelverkar med varandra. Med detta som bakgrund har en modell för diffus reflektans utvecklats. Utifrån modellen valideras och evalueras instrument, i form av en optisk prob, en ljuskälla och två spektrometrar. Valideringen har också inkluderat metoder för att karakterisera levervävnad genom en fantomstudie samt genom mätningar på olika levrar. Modellen har också testats genom datorsimuleringar.

Valideringsmätningar av blodfantomerna gav varierande resultat vilket troligen berodde på låga hemoglobinvärden i blodet som användes samt begränsningar i diffusion teori. Levermätningarna gav bra resultat med en tydlig skillnad mellan hälsosam och sjuk vävnad. (Less)
Please use this url to cite or link to this publication:
author
Alburg, Therese LU and Kraus, David
supervisor
organization
course
PHYM01 20141
year
type
H2 - Master's Degree (Two Years)
subject
keywords
diffuse reflectance spectroscopy, drs, biophotonics, medical optics, diffusion, tissue evaluation
language
English
id
4646557
date added to LUP
2014-10-20 14:14:01
date last changed
2015-12-14 13:32:33
@misc{4646557,
  abstract     = {{The shape of a diffuse reflectance spectra can provide knowledge about tissue composition. By analysing this spectra one can, with the right evaluation methods, find out information about the tissue. With known absorption properties of the present tissue chromophores it is possible, with a curve fit algorithm, to find their volume fractions in any measured tissue. 

In this work, the usability of diffuse reflectance spectroscopy (DRS) as a tool in tissue diagnostics was investigated. A model based on diffusion theory with a semi-infinite boundary condition and known tissue chromophore data was developed. It was used to evaluate DRS signals in tissue phantoms and on murinae, porcine and human livers. To ease the evaluation, an interface was developed to run the instruments (one light source and two spectrometers) from the computer and to compute the tissue composition from the provided diffusion model. The tissue composition was computed through a Levenberg-Marquardt least-squares algorithm in MATLAB.

Validation of the diffusion model was performed on tissue phantoms together with Monte Carlo (MC) simulations and a Time-of-Flight Spectroscopy (TOFS) measurement. The results from the validation measurements were varying. Many different kinds of phantoms were created. Commonly used phantoms, containing water, blood and intralipid gave results systematically underestimating the absorption while phantoms with greater fractions of lipid, mixed with agar or Triton-X100, gave results with less good correlation between signals and concentrations. The poor phantom results were discovered to be due to a low haemoglobin concentration in the used blood whilst there was also limitations in the diffusion criteria for these phantoms.

The results from liver measurements gave better correlation between signals and concentrations, and when investigating the criteria for diffusion these were also fulfilled in a greater wavelength region. The liver results also showed an evident difference between healthy and malignant tissue.}},
  author       = {{Alburg, Therese and Kraus, David}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Diffuse reflectance spectroscopy as a tool to evaluate liver tissue}},
  year         = {{2014}},
}