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| 2. |
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| 3. |
- Nilsson, Henrik, et al.
(författare)
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Monte Carlo simulations of the light interaction with blood vessels in human skin in the red wavelength region
- 1998
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Ingår i: Proceedings of SPIE, 3252(06),44-53. - San José : SPIE. - 9780819426918 ; , s. 44-53
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Konferensbidrag (refereegranskat)abstract
- An attempt was made at determining if the elastically backscattered Doppler shifted light from cutaneous blood vessels merely emanates from the peripheral parts, or also from the more central core of these vessels, after illumination by red laser light (632 nm). A multilayered, semi-infinite Monte Carlo model of human skin was constructed accordingly, with separate layers or epidermis, dermis including blood, inferior vascular plexus and subcutaneous fat. Two concentric cylinders of infinite length and with varying diameters, representing core and peripheral parts of a blood vessel, were located at various depths in the skin model, either in the superior or inferior vascular plexus. In order to test the stability of the model predictions, widely varying values of the optical properties were employed in the calculations, trying to encompass most of the extreme values found in the literature. The number of photons Doppler shifted by a fixed size central core of a small blood vessel, is independent of the volume of blood surrounding this core in the rest of the blood vessel, provided the total number of detected photons is maintained constant, and the vessel dimensions are within human physiological limits. For the source/detector system simulated (one optical fiber 700 micrometer diameter), backscattered light Doppler shifted in superficial blood vessels constituted almost all the photons detected, with only very few photons having interacted with the inferior plexus.
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| 4. |
- Nilsson, Henrik, et al.
(författare)
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Photon pathlength determination based on spatially resolved diffuse reflectance
- 2002
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Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 7:3, s. 478-485
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
- Arildsson, Mikael, 1967-, et al.
(författare)
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Critical design parameters in laser Doppler perfusion imaging
- 1996
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Ingår i: <em>Proc. SPIE</em> 2678. - : SPIE Proceedings Series. - 9780819420527 ; , s. 401-408
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Arildsson, Mikael, 1967-, et al.
(författare)
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Effects on skin blood flow by provocation during local analgesia
- 2000
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Ingår i: Microvascular Research. - : Elsevier BV. - 0026-2862 .- 1095-9319. ; 59:1, s. 122-130
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Tidskriftsartikel (refereegranskat)abstract
- Although topical analgesia cream has been used for several years, little is known about its effects on the microcirculation. Previous studies have shown a vasoconstrictive effect after short application times and a vasodilatation after longer application. It has also been shown that vasomotion does not occur in the analgesized skin. The present study was undertaken to investigate the alterations in skin blood perfusion following local cooling, local heating and pin-pricking after the establishment of analgesia. In 11 healthy volunteers, skin analgesia was attained by use of a eutectic mixture of lidocaine and prilocaine (EMLA, Astra Pain Control AB, Sweden) applied to the skin three hours prior to provocation. The changes in skin blood perfusion, after applying three different provocation methods, were studied using the laser Doppler technique. Local cooling and heating to temperatures of +10 and +45°C, respectively, were applied for 9 s by use of a copper probe (Ø12 mm). In the pin-prick provocation method, a combined effect of deflection and penetration of the skin to in total 3 mm was attained. Identical provocation methods were applied to placebo treated and untreated skin areas. After heat provocation, significant differences in the perfusion response between the treatments were seen (P < 0.0001). Skin areas treated with analgesia cream responded with a slow increase in perfusion that persisted beyond the four minute measurement period. Placebo and untreated areas decreased their perfusion over time. After cooling a significant reduction in skin perfusion was seen, irrespective of the treatment. Similarly, after pin-pricking a perfusion increase was seen for all treatments. The findings indicate that topical analgesia influences the myogenic control of the blood flow in those vascular plexa measured by laser Doppler following heat provocation. No differences could be seen in the response to pin-pricking and cooling for the different treatments.
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| 11. |
- Arildsson, Mikael, et al.
(författare)
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Spectral signature and heterodyne efficiency for different wavelengths in laser Doppler flowmetry
- 2002
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 40:1, s. 85-89
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler perfusion monitoring and imaging technologies generate time traces and two-dimensional flow maps of the microcirculation. With the goal of reaching different tissue depths, these technologies are equipped with lassers operating at different wavelengths λ. The fact that the average scattering angle, at a single scattering event, between a photon and a red blood cell increases with λ is compensated for by a 1/λ effect in the scattering vector, rendering the average frequency shift virtually independent of the choice of wavelength. Monte Carlo simulations showed that the corresponding spectral signature of the Doppler signals for λ=632.8nm and 780nm were close to identical. The theoretical predictions were verified by calculating the centre-of-gravity (COG) frequency of the laser Doppler power spectral density for the two wavelengths from forearm and finger skin, representing a low and high perfusion area, respectively (forearm COG=123 against 121Hz, finger COG=220 against 212 Hz). When the wavelength changes from 632.8nm to 780nm, the heterodyne efficiency of the detector and, thereby, the inherent system amplifcation increase. For tissues with identical microvascular flow conditions, the output signal therfore tends to increase in magnitude when shifting to longer wavelengths.
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| 16. |
- Clancy, Neil T., et al.
(författare)
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Analysis of skin recovery from mechanical indentation using diffuse lighting and digital imaging
- 2007
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Ingår i: Diffuse Optical Imaging of Tissue. - : SPIE - International Society for Optical Engineering. ; , s. 66291G-1-66291G-10
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Skin behaves as a viscoelastic material, having mechanical properties composed of elastic and fluid components. Upon indentation, the fibres are stretched and fluid displaced from the compressed region. The rate of recovery from this imprint is therefore dependent on the hydration and elasticity of the skin. A reliable measurement could be applied to the assessment of clinical conditions such as oedema, rare genetic disorders such as cutis laxa and the evaluation of the 'effective age' of skin in vivo . This paper describes a new approach to the non-invasive indentation technique and a novel method of analysis. A method is proposed that tracks the skin's recovery optically from an initial strain made using a mechanical indentor, diffuse side-lighting and a CCD video-capture device. Using the blue colour plane of the image it is possible to examine the surface topography only, and track the decay of the imprint over time. Two algorithms are discussed for the extraction of information on the skin's displacement and are analysed in terms of reliability and reproducibility.
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| 17. |
- Clancy, Neil T., et al.
(författare)
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Analysis of skin recovery from mechanical indentation using diffuse lighting and digital imaging. in Diffuse Optical Imaging of Tissue.
- 2007
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Ingår i: Proceedings of SPIE - Diffuse Optical Imaging of Tissue. - Bellingham, WA, United States : SPIE - International Society for Optical Engineering. - 9780819467737 ; , s. 66291G-1-66291G-10
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Konferensbidrag (refereegranskat)abstract
- Skin behaves as a viscoelastic material, having mechanical properties composed of elastic and fluid components. Upon indentation, the fibres are stretched and fluid displaced from the compressed region. The rate of recovery from this imprint is therefore dependent on the hydration and elasticity of the skin. A reliable measurement could be applied to the assessment of clinical conditions such as oedema, rare genetic disorders such as cutis laxa and the evaluation of the 'effective age' of skin in vivo . This paper describes a new approach to the non-invasive indentation technique and a novel method of analysis. A method is proposed that tracks the skin's recovery optically from an initial strain made using a mechanical indentor, diffuse side-lighting and a CCD video-capture device. Using the blue colour plane of the image it is possible to examine the surface topography only, and track the decay of the imprint over time. Two algorithms are discussed for the extraction of information on the skin's displacement and are analysed in terms of reliability and reproducibility.
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| 18. |
- Golster, Helena, et al.
(författare)
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Red Blood Cell Velocity and Volumetric Flow Assessment by Enhanced High-Resolution Laser Doppler Imaging in Separate Vessels of the Hamster Cheek Pouch Microcirculation
- 1999
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Ingår i: Microvascular Research. - : Elsevier BV. - 0026-2862 .- 1095-9319. ; 58:1, s. 62-73
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Tidskriftsartikel (refereegranskat)abstract
- An enhanced high-resolution laser Doppler imager (EHR-LDI), configured to fit the demands of a measurement area containing separate microvessels, was evaluated for perfusion measurements in hamster cheek pouch preparations during ischemia, reperfusion, and pharmacologically induced vasodilation and vasoconstriction. Measurements in separate microvessels where the laser beam was smaller than the vessel diameter were referred to as red blood cell (RBC) velocity estimates, as previously validated in vitro, whereas a relative flow index, RFI (mean RBC velocity/tissue area), was introduced as a volumetric flow measure. Microvessel diameter and RBC velocity changes during ischemia, reperfusion, as well as during vasoconstriction and vasodilation correlated to the data obtained from the microscope. Correspondingly, during the described provocations anticipated volumetric flow changes were registered as changes in the RFI. When data on intravessel RBC velocity profiles are presented they reflect a parabolic flow profile usually seen in this size microvessel. The EHR-LDI appears a promising tool for investigation of the microvasculature, as it almost simultaneously provides information on relative changes of both in vivo RBC velocity and volumetric flow (RFI), although the latter estimate needs to be further refined.
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| 19. |
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| 20. |
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| 21. |
- Leahy, MJ., et al.
(författare)
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Diffuse reflection imaging of sub-epidermal tissue haematocrit using a simple RGB camera
- 2007
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Ingår i: Optical Technologies in Biophysics and Medicine VIII. - : SPIE - International Society for Optical Engineering. ; , s. 653503-1-653503-17
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes the design and evaluation of a novel easy to use, tissue viability imaging system (TiVi). The system is based on the methods of diffuse reflectance spectroscopy and polarization spectroscopy. The technique has been developed as an alternative to current imaging technology in the area of microcirculation imaging, most notably optical coherence tomography (OCT) and laser Doppler perfusion imaging (LDPI). The system is based on standard digital camera technology, and is sensitive to red blood cells (RBCs) in the microcirculation. Lack of clinical acceptance of both OCT and LDPI fuels the need for an objective, simple, reproducible and portable imaging method that can provide accurate measurements related to stimulus vasoactivity in the microvasculature. The limitations of these technologies are discussed in this paper. Uses of the Tissue Viability system include skin care products, drug development, and assessment spatial and temporal aspects of vasodilation (erythema) and vasoconstriction (blanching).
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| 24. |
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| 25. |
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| 26. |
- Liebert, Adam, et al.
(författare)
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Estimation of scattering volume in short distance reflectance measurements by Monte Carlo modelling
- 2002
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Ingår i: Optica Applicata. - : Politechnika Wroclawska. - 0078-5466 .- 1899-7015. ; 32:4, s. 709-720
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The depth of light penetration is an interesting issue in various tissue optics experiments. The measurements of remitted light distribution was shown to allow for estimation of optical properties. However, in case of measurements with a short distance between the emitter and the detector, the diffusion equation fails, and the proposed methods cannot be applied. The aim of this study was to develop a simple method for estimation of the light penetration depth for short-distance measurements of remitted light. The idea is based on the analysis of the diffusely back-scattered light distribution adjacent to the emitter for the assessment of the scattering volume. The Monte Carlo method was used for theoretical estimation of the relationship between the light distribution around emitting fiber and the depth of light scattering volume. Two series of Monte Carlo simulations were performed: the first one with limited and the second one with unlimited scattering volume. In both series the values of absorption and scattering coefficients were altered within ranges typical of human tissues. The results of this study show that: the diffuse reflectance is strongly dependent on the absorption and scattering properties of the tissue and it is possible to estimate the depth of the scattering volume by use of the short distance profile of diffusely back-scattered light as measured at the surface of the tissue.
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| 27. |
- Lindén, Maria, 1965-, et al.
(författare)
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Evaluation of Enhanced High-Resolution Laser Doppler Imaging in an in Vitro Tube Model with the Aim of Assessing Blood Flow in Separate Microvessels
- 1998
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Ingår i: Microvascular Research. - : Elsevier BV. - 0026-2862 .- 1095-9319. ; 56:3, s. 261-270
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Tidskriftsartikel (refereegranskat)abstract
- An enhanced high-resolution laser Doppler imaging (EHR-LDI) technique intended for visualization of separate microvessels was evaluated by use ofin vitroflow models. In EHR-LDI, a laser beam focused to a half-power diameter less than 40 μm successively scans the tissue under study in steps of 25 μm. Spatial blood flow variations within microvascular structures of 1.5 × 1.5 mm are rendered by 64 × 64 measurement sites. Individual microvessel diameters could be estimated and an average difference of 11 μm compared to microscopic measurements was obtained. For the flow algorithm used, the LDI output signal was found to scale linearly with average velocity (0–3.5 mm/s) when a plastic tube of inner diameter 175 μm was perfused with human blood (correlation coefficient 0.99). The LDI output signal was further found insensitive to hematocrit variations in the range 16–44%. Due to the limited laser light penetration in blood, a reduction in the LDI output signal was observed as the inner tube diameters were successively changed from 280 to 1400 μm.
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| 28. |
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| 29. |
- Litscher, G., et al.
(författare)
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Changed skin blood perfusion in the fingertip following acupuncture needle introduction as evaluated by Laser Doppler Perfusion Imaging
- 2002
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Ingår i: Lasers in Medical Science. - : Springer Science and Business Media LLC. - 0268-8921 .- 1435-604X. ; 17:1, s. 19-25
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Tidskriftsartikel (refereegranskat)abstract
- Rapidly repeated imaging of the left middle fingertip skin blood perfusion was performed in 51 healthy volunteers (mean age ▒ SD: 25.3 ▒ 7.6 years) prior to, immediately after and in the early reperfusion phase following introduction of an acupuncture needle at the Neiguan point (Pe. 6) and at a placebo point respectively, using a Laser Doppler Perfusion Imager (LDPI). The average skin perfusion of the fingertip was calculated for each image and used as an indicator of the microvascular response to the acupuncture needle introduction. The results of this randomised, placebo-controlled, cross-over study showed significant differences (p = 0.001) in the immediate skin blood perfusion response when needling is performed in an acupuncture point (Neiguan) and a placebo point, with a more pronounced reduction in skin blood perfusion when needling the acupuncture point. In the early reperfusion phase, however, a substantial increase in skin perfusion was observed that amounted to about 18% of the level prior to needle introduction, irrespective of the site of needle application. In a single individual it was demonstrated that the vasodilatation following needling in the acupuncture point persisted for a more extended time period. These results suggest that the LDPI technology may be useful in visualising and quantifying the peripheral vascular effects of acupuncture on the microcirculation.
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| 30. |
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| 31. |
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| 32. |
- Möller, K.O, et al.
(författare)
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Introduction to Laser Doppler Flowmetry
- 1999
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Ingår i: Technology and Health Care. - : I O S Press. - 0928-7329 .- 1878-7401. ; 7
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Tidskriftsartikel (refereegranskat)
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| 33. |
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| 34. |
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| 35. |
- Nilsson, Gert, 1947-, et al.
(författare)
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Assessment of tissue viability by polarization spectroscopy
- 2008
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Ingår i: Opto-Electronics Review. - : SpringerLink. - 1230-3402 .- 1896-3757. ; 16:3, s. 309-313
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Tidskriftsartikel (refereegranskat)abstract
- A new and versatile method for tissue viability imaging based on polarization spectroscopy of blood in superficial tissue structures such as the skin is presented in this paper. Linearly polarized light in the visible wavelength region is partly reflected directly by the skin surface and partly diffusely backscattered from the dermal tissue matrix. Most of the directly reflected light preserves its polarization state while the light returning from the deeper tissue layers is depolarized. By the use of a polarization filter positioned in front of a sensitive CCD-array, the light directly reflected from the tissue surface is blocked, while the depolarized light returning from the deeper tissue layers reaches the detector array. By separating the colour planes of the detected image, spectroscopic information about the amount of red blood cells (RBCs) in the microvascular network of the tissue under investigation can be derived. A theory that utilizes the differences in light absorption of RBCs and bloodless tissue in the red and green wavelength region forms the basis of an algorithm for displaying a colour coded map of the RBC distribution in a tissue. Using a fluid model, a linear relationship (cc. = 0.99) between RBC concentration and the output signal was demonstrated within the physiological range 0–4%. In-vivo evaluation using transepidermal application of acetylcholine by the way of iontophoresis displayed the heterogeneity pattern of the vasodilatation produced by the vasoactive agent. Applications of this novel technology are likely to be found in drug and skin care product development as well as in the assessment of skin irritation and tissue repair processes and even ultimately in a clinic case situation.
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| 36. |
- Nilsson, Gert, 1947-, et al.
(författare)
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Biomedical Applications of Laser-Light Scattering
- 1982
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Ingår i: Biomedical Applications of Laser-Light Scattering. - Amsterdam : Elsevier Biomedical press. - 0444804560 ; , s. 335-348
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 43. |
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| 44. |
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| 45. |
- Nilsson, Gert, 1947-
(författare)
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High resolution
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)
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| 46. |
- Nilsson, Gert, 1947-
(författare)
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History of laser Doppler technology
- 2000
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Ingår i: European Conference on Microcirculation,2000. - : S. Karger AG. - 9783805571227 - 9783318006209
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Konferensbidrag (refereegranskat)
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| 47. |
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