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- 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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- 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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| 6. |
- Lindén, Maria, 1965-
(författare)
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High resolution laser doppler imaging for microvascular blood flow measurements
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Techniques for functional assessment of blood flow dynamics in individual microvessels are likely to become tools of increasing importance, for example in the evaluation of new vasoactive drugs. Laser Doppler perfusion Imaging (LDI) is a non- contact method for visualization of spatial and temporal blood flow dynamics. In this thesis the LDI technique was adapted for investigation of flow dynamics in separate microvessels. The technique was evaluated and used for flow studies during microdialysis in human skin, in the rabbit tenuissimus muscle and in the hamster cheek pouch model. Furthermore, an algorithm was introduced, relating the technique to quantitative flow assessment.For investigations of individual structures of microvascular networks, a resolution higher than that in standard LDI is required. This can be achieved by focusing the laser beam and reducing the step length between adjacent measurement sites to a degree determined by the requirement of the application. In High Resolution LDI (HR-LDI) the laser spot is reduced to a diameter of 100 μm in the focal plane situated 7 cm beneath the scanner head. The laser beam is moved in steps of 125 or 250 μm in this plane, resulting in full format images of 8 mm x 8 mm or 16 mm x 16 mm. Enhanced High Resolution LDI (EHR-LDI) reduces the diameter of the laser beam to 40 μm in the focal plane, positioned 40 mm beneath the scanner head. The step length in this plane is 25 or 50 μm, which corresponds to full format images of 1.5 mm x 1.5 mm or 3 mm x 3 mm respectively. Thus blood flow variations within an area of a single measurement site in standard LDI are visualized by EHR-LDI.Inside separate micro vessels a high concentration of blood cells is present and the prerequisite of a low density of moving scatterers usually assumed in laser Doppler theory is not valid. Many of the detected photons originating from such vessels can thus be expected to have suffered multiple Doppler shifts. To further investigate this situation, an in vitro model of plastic tubes perfused with human blood was used. The LDI signal was found to scale linearly with average flow velocity (0 - 9 mm/s) and was not influenced by haematocrit variations (16 - 44 %). An underestimation of the LDI signal was observed as the tube diameter increased, interpreted as being caused by the limited depth of laser light penetration. By an algorithm considering both the Doppler shifts and the tube diameter, this effect could be compensated for. Furthermore, volume blood flow in tubes of diameters 500 μm, 750 μm and 1.4 mm were predicted by correlation coefficients of 0.994, 0.993 and 0.996.In applications based on high resolution LDI, the textures of the vascular structures in the rabbit tenuissimus muscle and the hamster cheek pouch preparation were rendered in good agreement with corresponding microscopic images. The vascular structures showed their sensitivity to vasoactive substances by changes in flow. The spatial heterogeneity in these changes and in flow redistribution occurring after a period of ischemia were visualized by the images, whereas the temporal flow changes inside separate microvessels were captured by single point recordings. The muscle tissue reacted to ambient air oxygen tension by a reduction in blood flow. Further, blood flow changes in the human skin following microdialysis probe insertion could be followed in detail. 60 minutes after probe insertion skin blood perfusion had returned towards pre-insertion levels. Individual variations, which might be of importance for the interpretation of microdialysis data were, however, observed.
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