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Photon pathlength determination based on spatially resolved diffuse reflectance
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-6385-6760
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
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.

Place, publisher, year, edition, pages
2002. Vol. 7, no 3, 478-485 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-24559DOI: 10.1117/1.1482378Local ID: 6721OAI: oai:DiVA.org:liu-24559DiVA: diva2:244880
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Photon migration in tissue: laser induced fluorescence for cancer diagnostics and influence of optical properties on microvascular Doppler spectroscopy
Open this publication in new window or tab >>Photon migration in tissue: laser induced fluorescence for cancer diagnostics and influence of optical properties on microvascular Doppler spectroscopy
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser induced flourescence (LIF) is an "optical biopsy" method, based on the selective accumulation of fluorophores in neoplastic tissue. Two recently developed, non-photosensitizing tumor seeking carotenoporphyrins were assessed regarding tumor selectivity, and biodistribution, in experimental animals. A tumor to peritumoral ratio of 5-6:1 was seen in the background free substance related fluorescence in vivo, as well as ex vivo. Cerebral cortex and skeletal muscle displayed a low, and liver a high substance related fluorescence.

Laser Doppler flowmetry (LDF) is based on the spectral broadening of monochromatic light, that interacts with moving red blood cells in tissue. The power spectral density of the backscattered light can be processed to yield an estimate of microvascular tissue perlusion. Using a Monte Carlo simulation model of human skin, it is demonstt·ated that for a particular light delivery/detection arrangement, Doppler shifted photons that originate from the central core and peripheral parts of blood vessels of physiological dimensions, both contribute to the detected signal. Further, more than 10 times as many photons will interact with the superficial as with the deep vascular plexus. However, due to greater velocities and concentrations of the moving scatterers, the profound circulation still may yield a greater contribution to the LDF perfusion estimate.

A multiple polynomial regression method for prediction of photon pathlength and optical properties in tissue, at surlace source detector separations up to two millimeters, was developed. Using the diffuse, backscattered reflectance profile from an array of optical sensors as predictors in the model resulted in root-meansquare errors of less than three per cent for the estimated pathlength. Caucasian human skin displayed a maximum in vivo variation of ~35 % in the photon pathlength between individuals in similar locations, and within individuals comparing fingertip and forearm skin, as a result of varying optical properties.

Assuming a homogenous tissue perlusion, the pathlength variations will induce a corresponding variation in the LDF petfusion signal, which can be compensated for by linearization and pathlength normalization, making intra- and interindividual comparisons of the LDF perfusion estimate feasible.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2002. 123 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 735
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-29435 (URN)14781 (Local ID)91-7373-179-X (ISBN)14781 (Archive number)14781 (OAI)
Public defence
2002-05-31, Administrationsbyggnadens aula, Universitetssjukhuset, Linköping, 13:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-10-08Bibliographically approved
2. Influence of optical properties on Laser Doppler Flowmetry
Open this publication in new window or tab >>Influence of optical properties on Laser Doppler Flowmetry
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:nbn:se:liu:diva-28932 (URN)14139 (Local ID)91-85297-04-6 (ISBN)14139 (Archive number)14139 (OAI)
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

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Larsson, MarcusNilsson, GertStrömberg, Tomas

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