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Influence of optical properties on Laser Doppler Flowmetry
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-6385-6760
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser Doppler flowmetry (LDF) is based on the principle that a Doppler shift occurs when coherent light is scattered by a moving object, i.e. red blood cell (RBC). The magnitude of these frequency shifts affects the optical beating that occurs w hen shifted and non-shifted light is mixed. Based on the optical beating, an LDF perfusion measure is calculated. However, the measure is not only sensitive to the RBC velocity and concentration, but also to the photon path Jength in tissue and the scattering characteristics of the RBC. The Jatter two are both govemed by the optical properties (OP), attributes that differ both within and between individuals.

The aim of this thesis was to evaluate how the RBC and tissue OP affect the LDF perfusion measure, and to propose methods that partly correct for these errors. Phantom measurements and Monte Carlo simulations showed that the LDF perfusion was significantly affected by variations in OP relevant to skin, especially when comparing individual readings. Simulations revealed that the variations in OP affected the LDF perfusion and the photon path length in a similar manner. This suggests that a path length normalised measure would decrease the OP induced variations, possibly enabling accurate intra and inter-individual comparisons of LDF perfusion measures in different organs.

A path length estimation technique, based on spatially diffuse reflectance, is proposed and evaluated. Monte Carlo simulations showed that the algorithm predicted the photon path length with an rms error of less than 5%. In vivo measurement (11 subjects) displayed a longer estimated path length (~35%) for the fingertip compared to the forearm. Comparing individual measurements from similar locations, variations up to 40% (max/min) were found. These findings clearly indicate the need for a path length normalization when comparing LDF readings.

The LDF Doppler spectrum is govemed by the RBC velocity distribution and its phase function. In this thesis, an approach is presented where a measured LDF Doppler spectrum is decomposed using a number of theoretical, single-velocity spectra. As a result, a velocity-resolved perfusion measure is achieved. As the blood flow velocity depends on the dimension of the blood vessel, this approach has the potential to differentiate between arteriole/ venule and capillary activity. In addition, the path length estimation technique and the RBC scattering theory, presented in this thesis, provides a promising step towards an absolute perfusion measure.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2004. , 64 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 914
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-28932Local ID: 14139ISBN: 91-85297-04-6 (print)OAI: oai:DiVA.org:liu-28932DiVA: diva2:249744
Public defence
2004-12-17, Sal Eken, Universitetssjukhuset, Linköping, 09:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2016-08-31
List of papers
1. Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry
Open this publication in new window or tab >>Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry
2002 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 7, no 2, 236-243 p.Article in journal (Refereed) Published
Abstract [en]

Microcirculatory blood flow can be measured using a laser Doppler flowmetry (LDF) probe. However, the readings are affected by tissue optical properties (absorption and scattering coefficient; µa and µs) and probe geometry. In this study the influence of optical properties (µa∈[0.053, 0.23] mm-1; µs∈[14.7, 45.7] mm-1) on LDF perfusion and sampling depth were evaluated for different fiber separations. In-vitro measurements were made on a sophisticated tissue phantom with known optical properties, mimicking blood flow at different depths. Monte Carlo simulations were carried out to extend the geometry of the tissue phantom.

A good correlation between measured and simulated data was found. The

simulations showed that, for a fixed flow at a discrete depth, the influence of µs or µa on the LDF perfusion increased with increasing flow depth and decreased with increasing fiber separation. For a homogeneous flow distribution, however, the perfusion varied 40% due to the variations in optical properties, almost independent of fiber separation (0.23-1.61 mm). Therefore, the effect in real tissue is likely to vary due to the unknown heterogeneous blood flow distribution. Further, LDF sampling depth increased with decreasing µs or µa and increasing fiber separation. For a fiber separation of 0.46 mm, the e-1 sampling depth ranged from 0.21-0.39 mm.

Place, publisher, year, edition, pages
Journal of Biomedical Optics, 2002
Keyword
Doppler effect, fiber optics, laser Doppler flowmetry, Monte Carlo, simulations, optical properties, sampling depth
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-11717 (URN)10.1117/1.1463049 (DOI)
Note
Marcus Larsson, Wiendelt Steenbergen and Tomas Strömberg, Influence Of Optical Properties and Fiberseparation on Laser Doppler Flowmetry, 2002, Journal of Biomedical Optics, (7), 236-243. http://spiedigitallibrary.aip.org/journals/doc/JBOPFO-ft/vol_7/iss_2/236_1.html Copyright 2002 Society of Photo-Optical Instrumentation Engineers. This paper was published in Journal of Biomedical Optics and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, 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: 2002-05-02 Created: 2002-05-02 Last updated: 2017-12-13
2. Photon pathlength determination based on spatially resolved diffuse reflectance
Open this publication in new window or tab >>Photon pathlength determination based on spatially resolved diffuse reflectance
2002 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 7, no 3, 478-485 p.Article in journal (Refereed) Published
Abstract [en]

A method for the prediction of the average photon pathlength in turbid media has been developed. The method is based on spatially resolved diffuse reflectance with discrete source detector distances up to 2 mm. Light reflectance was simulated using a Monte Carlo technique with a one-layer model utilizing a wide range of optical properties, relevant to human skin. At a source detector separation of 2 mm, the pathlength can vary sixfold due to differences in optical properties. By applying various preprocessing and prediction techniques, the pathlength can be predicted with a root-mean-square error of approximately 5%. Estimation of the photon pathlength can be used, e.g., to remove the influence of optical properties on laser Doppler flowmetry perfusion readings, which are almost linearly related to the average photon pathlength.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-24559 (URN)10.1117/1.1482378 (DOI)6721 (Local ID)6721 (Archive number)6721 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
3. In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry
Open this publication in new window or tab >>In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry
2003 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 7-8, 124-134 p.Article in journal (Refereed) Published
Abstract [en]

Methods for local photon pathlength and optical properties estimation, based on measured and simulated diffuse reflectance within 2mm from the light source, are proposed and evaluated in vivo on Caucasian human skin. The accuracy of the methods was good (2-7%) for pathlength and reduced scattering but poor for absorption estimation. Reduced scattering and absorption were systematically lower in the fingertip than in the forearm skin (633 nm). A maximum intra-site and inter-individual variation of ~35% in the average photon pathlength was found. The methodology was applied in laser Doppler flowmetry (LDF), where pathlength normalization of the estimated perfusion removed the optical property dependency.

Place, publisher, year, edition, pages
Institutionen för medicinsk teknik, 2003
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-11658 (URN)10.1364/AO.42.000124 (DOI)
Note
Larsson, M., Nilsson, H. & Strömberg, T., In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry, 2003, Applied Optics, (42), 7-8, 124-134. http://dx.doi.org/10.1364/AO.42.000124. This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://ao.osa.org/abstract.cfm?id=70860. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. Copyright OSA., http://www.osa.org/Available from: 2008-04-24 Created: 2008-04-24 Last updated: 2017-12-13
4. Towards a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum
Open this publication in new window or tab >>Towards a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum
2006 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 11, no 1Article in journal (Refereed) Published
Abstract [en]

The tissue microcirculation, as measured by laser Doppler flowmetry (LDF), comprises both capillary, arterial and venous blood flow. With the classical LDF approach, it has been impossible to differentiate between different vascular compartments. We suggest an alternative LDF algorithm that estimates at least three concentration measures of flowing red blood cells (RBCs), each associated with a predefined, physiologically relevant, absolute velocity in mm/s. As the RBC flow velocity depends on the dimension of the blood vessel, this approach might enable a microcirculatory flow differentiation. The LDF concentration estimates are derived by fitting predefined Monte Carlo simulated, single velocity, spectra to a measured, multiple velocity LDF spectrum. Validation measurements, using both single and double-tube flow phantoms perfused with a microsphere solution, showed that it is possible to estimate velocity and concentration changes, and to differentiate between flows with different velocities. The presented theory was also applied to RBC flow measurements. A Gegenbauer kernel phase function (αgk = 1:05; ggk = 0:93), with an anisotropy factor of 0.987 at 786 nm, was found suitable for modelling Doppler scattering by red blood cells diluted in physiological saline. The method was developed for low concentrations of RBCs, but can in theory be extended to cover multiple Doppler scattering.

Place, publisher, year, edition, pages
Institutionen för medicinsk teknik, 2006
Keyword
Doppler effect, biomedical optics, optical properties, anisotropy, laser Doppler
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-11648 (URN)10.1117/1.2166378 (DOI)
Note
Copyright 2006 Society of Photo-Optical Instrumentation Engineers. This paper was published in the Journal of Biomedical Optics, (11), 14024 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. Marcus Larsson and Tomas Strömberg, Towards a velocity resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum, 2006, Journal of Biomdeical Optics, (11), 14024. http://dx.doi.org/10.1117/1.2166378.Available from: 2008-04-23 Created: 2008-04-23 Last updated: 2017-12-13

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