| 1. |
- Briers, David, et al.
(author)
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Laser speckle contrast imaging: theoretical and practical limitations
- 2013
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In: Journal of Biomedical Optics. - : Society of Photo-optical Instrumentation Engineers (SPIE). - 1083-3668 .- 1560-2281. ; 18:6
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Journal article (peer-reviewed)abstract
- When laser light illuminates a diffuse object, it produces a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can provide information about the movement. A simple way of accessing this information is to image the speckle pattern with an exposure time longer than the shortest speckle fluctuation time scale-the fluctuations cause a blurring of the speckle, leading to a reduction in the local speckle contrast. Thus, velocity distributions are coded as speckle contrast variations. The same information can be obtained by using the Doppler effect, but producing a two-dimensional Doppler map requires either scanning of the laser beam or imaging with a high-speed camera: laser speckle contrast imaging (LSCI) avoids the need to scan and can be performed with a normal CCD- or CMOS-camera. LSCI is used primarily to map flow systems, especially blood flow. The development of LSCI is reviewed and its limitations and problems are investigated. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
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| 3. |
- Larsson, Marcus, et al.
(author)
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Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry
- 2002
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In: Journal of Biomedical Optics. - : Journal of Biomedical Optics. - 1083-3668 .- 1560-2281. ; 7:2, s. 236-243
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Larsson, Marcus, 1974-, et al.
(author)
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Influence of tissue phantom optical properties and emitting - receiving fiber distance on Laser Doppler flowmetry
- 2000
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In: Progress in Biomedical Optics and Imaging,2000. - San José : SPIE. - 0819435392 ; , s. 56-63
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Conference paper (peer-reviewed)abstract
- The influence of emitting - receiving fiber distance on the perfusion signal in laser Doppler flowmetry (LDF) for a range of optical properties has been studied. A custom made LDF probe with eight 230 μm fibers arranged in a row was used. Measurements were made on a tissue phantom with three different sets of optical properties (P={μs; μa} [mm-1]; P1={14.7; 0.212}, P2={44.9; 0.226} and P3=(45.6; 0.0532}). A single moving disc simulated flow at four different depths. The noise-corrected perfusion for a given set of optical properties (P), fiber distance (l) and disc depth (d) is defined as Perf(ν,P,d,l)=k(P,d,l) v, where v is the speed of the rotating disc. The relative difference between two slopes, Δk(Pa,Pb,l,d), indicates how sensitive the LDF readings are to changes in optical properties (Pb → Pa) for given disc depth and fiber distance. Evaluation of Δk(P1,P2,d,l) (reflects changes in scattering coefficient, μs) and Δk(P3,P2,d,l) (reflects changes in absorption coefficient, μa) indicated that LDF perfusion was more sensitive to the changes in μs than in μa. The sensitivity also increased with increasing disc depth. A fiber distance of 920 [μm] was found to minimize these effects. E.g. the sensitivity due to the variations in μs, for fiber distance l1=920, l2=230 [μm] and for all disc depths, was Δk(P1,P2,l1)=[0.76, 1.06, 1.58, 2.40] and Δk(P1,P2,l2)=[1.61, 2.98, 5.04, 7.67].
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