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In Vivo Diffuse Reflectance Spectroscopy of Human Tissue: From Point Measurements to Imaging
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents the non-invasive use of diffuse reflectance spectroscopy (DRS) to provide information about the biochemical composition of living tissue. During DRS measurements, the incident, visible light is partially absorbed by chromophores but also scattered in the tissue before being remitted.

Human skin and heart, the main tissue objects in this thesis, are dependent on a sufficient inflow of oxygenized blood, and outflow of metabolic byproducts. This process could be monitored by DRS using the spectral fingerprints of the most important tissue chromophores, oxyhemoglobin and deoxyhemoglobin.

The Beer-Lambert law was used to produce models for the DRS and has thus been a foundation for the analyses throughout this work. Decomposition into the different chromophores was performed using least square fitting and tabulated data for chromophore absorptivity.

These techniques were used to study skin tissue erythema induced by a provocation of an applied heat load on EMLA-treated skin. The absorbance differences, attributed to changes in the hemoglobin concentrations, were examined and found to be related to, foremost, an increase in oxyhemoglobin.

To estimate UV-induced border zones between provoked and nonprovoked tissue a modified Beer-Lambert model, approximating the scattering effects, was used. An increase of chromophore content of more than two standard deviations above mean indicated responsive tissue. The analysis revealed an edge with a rather diffuse border, contradictory to the irradiation pattern.

Measuring in the operating theater, on the heart, it was necessary to calculate absolute chromophore values in order to assess the state of the myocardium. Therefore, a light transport model accounting for the optical properties, and a calibrated probe, was adopted and used. The absolute values and fractions of the chromophores could then be compared between sites and individuals, despite any difference of the optical properties in the tissue.

A hyperspectral imaging system was developed to visualize the spatial distribution of chromophores related to UV-provocations. A modified Beer-Lambert approximation was used including the chromophores and a baseline as an approximate scattering effect. The increase in chromophore content was estimated and evaluated over 336 hours.

In conclusion, advancing from a restricted Beer-Lambert model, into a model estimating the tissue optical properties, chromophore estimation algorithms have been refined progressively. This has allowed advancement from relative chromophore analysis to absolute values, enabling precise comparisons and good prediction of physiological conditions.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 88 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1210
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:liu:diva-15191ISBN: 978-91-7393-809-9 (print)OAI: oai:DiVA.org:liu-15191DiVA: diva2:113605
Public defence
2008-10-31, Elsa Brändströmsalen, Södra entrén, Campus US, Universitetssjukhuset, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2008-10-22 Created: 2008-10-22 Last updated: 2009-04-30Bibliographically approved
List of papers
1. Reflection Spectroscopy of Analgesized Skin
Open this publication in new window or tab >>Reflection Spectroscopy of Analgesized Skin
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2001 (English)In: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 62, no 3, 392-400 p.Article in journal (Refereed) Published
Abstract [en]

Analgesized skin, when subjected to heat stimuli, responds by increasing skin perfusion. This response does not originate from increased perfusion in superficial capillaries, but rather in the deeper lying vessels. The aim of this study was to assess changes in blood chromophore content, measured by reflection spectroscopy, in relation to the perfusion increase, especially regarding the chromophores oxyhemoglobin and deoxyhemoglobin. Eleven normal subjects were treated with analgesic cream (EMLA) and placebo for 20, 40, 60, 120, and 180 min. Individual reactions to local heating were classified as responses if the change in reflection data or the change in perfusion, as measured by laser Doppler blood flowmetry, exceeded 2 standard deviations of normal variation. The increase in blood perfusion or in blood content gave rise to an increased absorption, interpreted as an increase due mainly to the chromophore oxyhemoglobin. The number of responses increased with increased treatment time for EMLA-treated areas. In general, there was a good agreement between both methods; 44 of 55 classifications coincided for the two methods used. In conclusion, analgesized forearm skin, which had been exposed to local heating, responded with an elevated perfusion consisting of oxygenated blood. This strengthens the hypothesis that the flow increase occurs through dilatation of larger deeper lying skin vessels and not in the capillaries.

Place, publisher, year, edition, pages
ScienceDirect, 2001
Keyword
spectroscopy; laser Doppler flowmetry; EMLA; hemoglobin; analgesia; heat stimuli; skin microcirculation
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:liu:diva-15184 (URN)10.1006/mvre.2001.2358 (DOI)
Available from: 2008-10-22 Created: 2008-10-22 Last updated: 2017-12-14Bibliographically approved
2. A diffuse reflectance spectroscopic study of UV-induced erythematous reaction across well-defined borders in human skin
Open this publication in new window or tab >>A diffuse reflectance spectroscopic study of UV-induced erythematous reaction across well-defined borders in human skin
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2010 (English)In: Skin research and technology, ISSN 0909-752X, E-ISSN 1600-0846, Vol. 16, no 3, 283-290 p.Article in journal (Refereed) Published
Abstract [en]

Introduction The colour of tissue is often of clinicaluse in the diagnosis of tissue homeostasis andphysiological responses to various stimuli.Determining tissue colour changes and borders,however, often poses an intricate problem and visualexamination, constituting clinical praxis, does notallow them to be objectively characterized orquantified. Demands for increased inter- and intraobserverreproducibility have been incentives for theintroduction of objective methods and techniques fortissue colour (e.g. erythema) evaluation. The aim ofthe present paper was to study the border zone of anUVB provoked erythematous response of humanskin in terms of blood volume and oxygenationmeasured by means of diffuse reflectancespectroscopy using a commercial probe.

Material and Methods A provocation model, basedon partial masking of irradiated skin areas, definestwo erythema edges at every skin site responding tothe UV irradiation. In every subject, 5 test sites wereexposed with a constant UV light irradiance (14mW/cm2), but with different exposures times (0, 3,6, 9, 12 seconds). An analysis of the spectral datameasured across the two edges was performed for every scan line. The oxygenized and deoxygenizedhemoglobin contents were estimated in everymeasurement point, using a modified Beer-Lambertmodel.

Results The fit of the experimental data to the model derived by the modified Beer-Lambert law was excellent (R2>0.95). Analyzing data for the chromophore content showed that the erythematous response in provoked areas is dominated by the increase in oxyhemoglobin. The width for the left and right border zone was estimated to 1.81±0.93 mm and 1.90±0.88 mm respectively (M±SD). The unprovoked area between the two edges was estimated to 0.77±0.68 mm.

Conclusion While the chosen data analysis performed satisfactory, the ability of the probe design to differentiate spatial aspects of a reaction with abrupt borders was found to be suboptimal resulting in a probable overestimation of the erythematous edge slope. Probe modification or imaging are possible solutions.

Place, publisher, year, edition, pages
Wiley, 2010
Keyword
Erythema, UV, Spectroscopy, Oxygenation, Human skin
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:liu:diva-15185 (URN)10.1111/j.1600-0846.2010.00424.x (DOI)
Available from: 2008-10-22 Created: 2008-10-22 Last updated: 2017-12-14Bibliographically approved
3. Myocardial tissue oxygenation estimated with calibrated diffuse reflectance spectroscopy during coronary artery bypass grafting
Open this publication in new window or tab >>Myocardial tissue oxygenation estimated with calibrated diffuse reflectance spectroscopy during coronary artery bypass grafting
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2008 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 13, no 5, 054030- p.Article in journal (Refereed) Published
Abstract [en]

We present a study using a method able to assess tissue oxygenation, taking into account the absorption and the level of scattering in myocardial tissue using a calibrated fiber optic probe. With this method, interindividual comparisons of oxygenation can be made despite varying tissue optical properties during coronary artery bypass grafting (CABG). During CABG, there are needs for methods allowing continuous monitoring and prediction of the metabolism in the myocardial tissue. 14 patients undergoing CABG are investigated for tissue oxygenation during different surgical phases using a handheld fiber optic spectroscopic probe with a source-detector distance of less than 1 mm. The probe is calibrated using a light transport model, relating the absorption and reduced scattering coefficients (mu(a) and mu()(s)) to the measured spectra. By solving the inverse problem, absolute measures of tissue oxygenation are evaluated by the sum of oxygenized hemoglobin and myoglobin. Agreement between the model and measurements is obtained with an average correlation coefficient R-2 of 0.96. Oxygenation is found to be significantly elevated after aorta cross-clamping and cardioplegic infusion, as well as after reperfusion, compared to a baseline (p < 0.05). Tissue oxygenation decreases during cardiac arrest and increases after reperfusion.

Keyword
diffuse reflectance spectroscopy, oxygenation, myocardium, tissue, coronary artery bypass grafting
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-16251 (URN)10.1117/1.2976433 (DOI)
Note

Original Publication: Erik Häggblad, Tobias Lindbergh, Daniel Karlsson, Henrik Casimir-Ahn, Göran Salerud and Tomas Strömberg, Myocardial tissue oxygenation estimated with calibrated diffuse reflectance spectroscopy during coronary artery bypass grafting, Journal of Biomedical Optics, (13), 5, 054030, 2008. http://dx.doi.org/10.1117/1.2976433 Copyright 2008 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

Available from: 2009-01-12 Created: 2009-01-09 Last updated: 2017-05-23Bibliographically approved
4. Visible, Hyperspectral Imaging Evaluating the Cutaneous Response to Ultraviolet Radiation
Open this publication in new window or tab >>Visible, Hyperspectral Imaging Evaluating the Cutaneous Response to Ultraviolet Radiation
2007 (English)In: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues V / [ed] Daniel L. Farkas; Robert C. Leif; Dan V. Nicolau, SPIE - International Society for Optical Engineering, 2007, 644103-1-644103-12 p.Conference paper, Published paper (Other academic)
Abstract [en]

In vivo diagnostics of skin diseases as well as understanding of the skin biology constitute a field demanding characterization of physiological and anatomical parameters. Biomedical optics has been successfully used, to qualitatively and quantitatively estimate the microcirculatory conditions of superficial skin. Capillaroscopy, laser Doppler techniques and spectroscopy, all elucidate different aspects of microcirculation, e.g. capillary anatomy and distribution, tissue perfusion and hemoglobin oxygenation. We demonstrate the use of a diffuse reflectance hyperspectral imaging system for spatial and temporal characterization of tissue oxygenation, important to skin viability. The system comprises: light source, liquid crystal tunable filter, camera objective, CCD camera, and the decomposition of the spectral signature into relative amounts of oxy- and deoxygenized hemoglobin as well as melanin in every pixel resulting in tissue chromophore images. To validate the system, we used a phototesting model, creating a graded inflammatory response of a known geometry, in order to evaluate the ability to register spatially resolved reflectance spectra. The obtained results demonstrate the possibility to describe the UV inflammatory response by calculating the change in tissue oxygen level, intimately connected to a tissue's metabolism. Preliminary results on the estimation of melanin content are also presented.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2007
Series
Proceedings of SPIE (Progress in biomedical optics and imaging), ISSN 1605-7422 ; 6441
Keyword
Hyperspectral imaging, Ultraviolet provocation, Erythema, Hemoglobin, CCD camera, Tunable filters
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:liu:diva-15190 (URN)10.1117/12.698165 (DOI)000245855200002 ()9780819465542 (ISBN)
Conference
Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues V, 20 January 2007, San Jose, CA, USA
Available from: 2008-10-22 Created: 2008-10-22 Last updated: 2014-01-30Bibliographically approved

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