| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Nilsson, Gert, 1947-
(författare)
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High resolution
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)
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| 8. |
- 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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| 9. |
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| 10. |
- Nilsson, Gert, 1947-, et al.
(författare)
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Laser Doppler perfusion,monitoring and imaging
- 2003
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Ingår i: Biomedical Photonics Handbook. - London : CRC Press. - 0849311160 - 9780849311161 ; , s. 15-1-15-23
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Integrates interdisciplinary research and development on instrumentation, methods, and clinical applications. This book is of interest to scientists, engineers, manufacturers, teachers, students, and clinical providers.
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