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Reduced scattering coefficient determination by non-contact oblique angle illumination: methodological considerations
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-6385-6760
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-3454-6576
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
2007 (English)In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6435, 64350I-1-64350I-12 p.Article in journal (Refereed) Published
Abstract [en]

The reduced scattering coefficient, µs, was determined using oblique angle illumination and imaging backscattered light intensity. The distance r between the point of light incidence (hot-spot) and the circular symmetric diffuse reflectance centre, is ~1/µ. Previously, r was obtained analyzing a 1D strip aligned with the laser beam. We improved this method by calculating a 2D intensity image with extended dynamic range by assessing camera linearity, superimposing images with multiple integration times, and compensating for lens vignetting. The hot-spot algorithm utilises several images to minimize speckle variations and account for laser beam shape. Diffuse centre position is obtained by filtering the superimposed image with decreasing thresholds using momentum analysis to determine circular symmetry. The method was evaluated on 18 optical liquid phantoms with µs[1.5, 3.0] mm-1 and µs[0.01, 0.16] mm-1. The 2D method had better linearity with µs and smaller variations due to more stable hot-spot detection, than the 1D method. The anisotropy factor g was obtained by fitting measured and Monte Carlo simulated spatially resolved intensity decays and verified with a laser Doppler flowmetry technique. With an optimal compensation for the µa dependence, the rms error in µ estimation was 2.9%.

Place, publisher, year, edition, pages
2007. Vol. 6435, 64350I-1-64350I-12 p.
Keyword [en]
Reduced scattering coefficient, absorption coefficient, anisotropy factor, optical properties, oblique angle illumination, optical phantoms, Monte Carlo simulations
National Category
Other Industrial Biotechnology
Identifiers
URN: urn:nbn:se:liu:diva-25582DOI: 10.1117/12.698903OAI: oai:DiVA.org:liu-25582DiVA: diva2:246007
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Quantitative diffuse reflectance spectroscopy: myocardial oxygen transport from vessel to mitochondria
Open this publication in new window or tab >>Quantitative diffuse reflectance spectroscopy: myocardial oxygen transport from vessel to mitochondria
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the field of biomedical optics, diffuse reflectance spectroscopy (DRS) is a frequently used technique for obtaining information about the optical properties of the medium under investigation. The method utilizes spectral difference between incident and backscattered light intensity for quantifying the underlying absorption and scattering processes that affects the light-medium interaction.

In this thesis, diffuse reflectance spectroscopy (DRS) measurements have been combined with an empirical photon migration model in order to quantify myocardial tissue chromophore content and status. The term qDRS (quantitative DRS) is introduced in the thesis to emphasize the ability of absolute quantification of tissue chromophore content. To enable this, the photon migration models have been calibrated using liquid optical phantoms. Methods for phantom characterization in terms of scattering coefficient, absorption coefficient, and phase function determination are also presented and evaluated. In-vivo qDRS measurements were performed on both human subjects undergoing routine coronary artery bypass grafting (CABG), and on bovine heart during open-chest surgery involving hemodynamic and respiratory provocations. The application of a hand-held fiber-optic surface probe (human subjects) proved the clinical applicability of the technique as the results were in agreement with other studies. However, problems with non-physiological variations in detected intensity due to intermittent probe-tissue discontact were observed. Also, systematic deviations between modeled and measured spectra were found. By model inclusion of additional chromophores revealing the mitochondrial oxygen uptake ability, an improved model fit to measured data was achieved. Measurements performed with an intramuscular probe (animal subjects) diminished the influence of probe-tissue discontact on the detected intensity. It was demonstrated that qDRS could quantify variations in myocardial oxygenation induced by physiological provocations, and that absolute quantification of tissue chromophore content could be obtained.

The suggested qDRS method has the potential of becoming a valuable tool in clinical practice, as it has the unique ability of monitoring both the coronary vessel oxygen delivery and the myocardial mitochondrial oxygen uptake ability. This makes qDRS suitable for directly measuring the result of different therapies, which can lead to a paradigm shift in the monitoring during cardiac anesthesia.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 92 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1276
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-25587 (URN)978-91-7393-522-7 (ISBN)
Public defence
2009-10-30, Berzeliussalen, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2009-10-15 Created: 2009-10-08 Last updated: 2016-08-31Bibliographically approved

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Lindbergh, TobiasLarsson, MarcusFredriksson, IngemarStrömberg, Tomas

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