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Critical design parameters in laser Doppler perfusion imaging
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
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: 0000-0002-0012-7867
1996 (English)In: Proc. SPIE 2678: Optical Diagnostics of Living Cells and Biofluids / [ed] Daniel L. Farkas; Robert C. Leif; Alexander V. Priezzhev; Toshimitsu Asakura; Bruce J. Tromberg, SPIE Proceedings Series , 1996, Vol. 2678, 401-408 p.Conference paper, Published paper (Refereed)
Abstract [en]

Laser Doppler Perfusion Imaging (LDPI) is a method for visualization of tissue blood perfusion. A low power laser beam is used to step-wise scan a tissue area of interest and a perfusion estimate based on the backscattered, partially Doppler broadened, light is generated. Although the basic operating principle of LDPI is the same as that of conventional Laser Doppler Perfusion Monitoring (LDPM), significant differences exist between the implementation of the methods which must be taken into account in order to generate high quality perfusion images. The purpose of this study is to investigate the relevance of a number of LDPI design parameters, such as:

(1) The influence of artifact noise when using a continuously moving laser beam instead of a step-wise moving beam to scan the image.

(2) The signal processor output's dependency on the distance between the measurement object and the scanner head when using collimated laser light.

(3) The speed and mode of the scanning.

The results show a substantial rise in the noise level when using a continuously moving beam as opposed to a step-wise. Skin measurements using a collimated laser beam demonstrated an amplification factor dependency on the distance between the skin surface and the scanner head not present when using a divergent laser beam. The scanning speed is limited by the trade-off between the Doppler signal lower cut-off frequency and the image quality.

Place, publisher, year, edition, pages
SPIE Proceedings Series , 1996. Vol. 2678, 401-408 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-33211DOI: 10.1117/12.239527Local ID: 19198ISBN: 9780819420527 (print)OAI: oai:DiVA.org:liu-33211DiVA: diva2:254034
Conference
Optical Diagnostics of Living Cells and Biofluids, San Jose, CA | January 27, 1996
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2016-05-04
In thesis
1. Origin and processing of laser Doppler spectra
Open this publication in new window or tab >>Origin and processing of laser Doppler spectra
2000 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser Doppler Flowmetry (LDF) is a technique for studying microvascular blood flow. Laser light is guided to the tissue and the backscattered light, after being Doppler shifted by moving Red Blood Cells (RBCs), is detected using a heterodyne process. In Laser Doppler Perfusion Monitoring, the light is guided to and from the tissue using optical fibers, whilst in Laser Doppler Perfusion Imaging (LDPI), a freely impinging laser beam is used. The Power Spectral Density (PSD) of the photodetector current constitutes the LDF spectrum and can be processed to yield an estimate of the tissue perfusion.

The aim of this thesis was to study the origin and suggest adequate processing of the LDF spectra from both a technical and a physiological perspective.

The orientation and length of the average scattering vector resulting from a RBC/photon interaction, are altered when changing the laser source wavelength. It has been shown theoretically that the change in the orientation and length do not alter the average frequency shift of the scattering event. In vivo measurements on a low and a high perfused area using the wavelengths 632.8 nm and 780 nm respectively, confirm the theoretical findings. The heterodyne efficiency of the detector increases for longer wavelengths, giving higher photodetector signal amplitude.

A method for differentiating high velocity flows, by changing the filtering of the LDF spectra is presented. Emphasis is given to higher frequencies, including information from higher flow velocities.

The scanning mode and the shape of the laser beam. influence the spectral signature in LDPI. In order to maintain a high signal quality, a stepwise mode is to be preferred. The continuous mode induces large spectral components that depend on the scanning speed and the tissue surface roughness. Using a slightly divergent beam minimizes the inlluence of the distance between the detector and the tissue surface.

The physiological perspective includes two randomized and placebo controlled studies of the rela tionship between topical skin analgesia and the perfusion response to different local stimuli. In the first study, it was shown that analgesia using EMLA® cream during local heating, changes the dynamic flow regulation to a persistent and delayed perfusion increase. This was not observed in untreated or placebo treated skin. In the second study, this heating response was positively related to longer treatment times and. hence. to higher intradermal concentrations of the analgesics. By using capillary microscopy. it was shown that analgesic cream treatment for at least one hour reduces the number of physiologically active capillaries by 50%, while LDf perfusion remains unaltered. After local heating, the LDF perfusion increased, in 9/11 subjects by an average of 8.7 times, while the number of capillaries remained decreased. These findings suggest a low capillary influence of the LDF signal in human skin.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2000. 44 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 644
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-29444 (URN)14791 (Local ID)91-7219-805-2 (ISBN)14791 (Archive number)14791 (OAI)
Public defence
2000-09-11, Berzeliussalen, Universitetssjukhuset, Linköping, 09:15 (Swedish)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-02-27

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Nilsson, GertWårdell, Karin

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