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| Untersuchte Arbeit: Seite: 20, Zeilen: 3-26 |
Quelle: Moor instruments 2006 Seite(n): 1, 2, Zeilen: 1: 4ff; 2: 1ff |
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| Laser Doppler is a standard technique for the non-invasive blood flow monitoring and measurement of blood flow in the microcirculatory system. The strength of the technique is in looking at changes in flow - either over time or differences in flow over an area of skin or other exposed tissue.
5.2. Operating principles The laser Doppler technique measures blood flow in the very small blood vessels of the microvasculature, such as the low-speed flows associated with nutritional blood flow in capillaries close to the skin surface and flow in the underlying arterioles and venules involved in regulation of skin temperature. The tissue thickness sampled is typically 1mm, the capillary diameters 10 microns and the velocity spectrum measurement typically 0.01 to 10mm/s. The technique depends on the Doppler principle whereby low power light from a monochromatic stable laser, e.g. a helium neon gas laser or a single mode laser diode, incident on tissue is scattered by moving red blood cells and as a consequence is frequency broadened. The frequency broadened light, together with laser light scattered from static tissue, is photo-detected and the resulting photocurrent processed to provide a blood flow measurement. Please note, where laser light is scattered for tissue with a low red blood cell concentration, the average Doppler frequency shift is proportional to the average speed of red blood cells. Laser light can be directed to the tissue surface either via an optic fibre (Fig.1.8.a) or as a light beam (Fig.1.8.b). For ‘fibre optic’ monitors (LDF instruments) the optic fibre terminates in an optic probe which can be attached to the tissue surface. One or more light collecting fibres also terminate in the probe head and these fibres transmit a proportion of the scattered light to a photo-detector and the electronic signal processing [system.] |
Laser Doppler is a standard technique for the non-invasive blood flow monitoring and measurement of blood flow in the microcirculation. The strength of the technique is in looking at changes in flow - either over time or differences in flow over an area of skin or other exposed tissue.
[...] Operating Principles The laser Doppler technique measures blood flow in the very small blood vessels of the microvasculature, such as the low-speed flows associated with nutritional blood flow in capillaries close to the skin surface and flow in the underlying arterioles and venules involved in regulation of skin temperature. The tissue thickness sampled is typically 1mm, the capillary diameters 10 microns and the velocity spectrum measurement typically 0.01 to 10mm/s. The technique depends on the Doppler principle whereby low power light from a monochromatic stable laser (a), e.g. a Helium Neon gas laser or a single mode laser diode, incident on tissue is scattered by moving red blood cells and as a consequence is frequency broadened (b). The frequency broadened light, together with laser light scattered from static tissue, is photodetected and the resulting photocurrent processed to provide a blood flow measurement. Please note, where laser light is scattered for tissue with a low red blood cell concentration the average Doppler frequency shift is proportional to the average speed of red blood cells. [Seite 2] Laser light can be directed to the tissue surface either via an optic fibre (c) or as a light beam (d). For ‘fibre optic’ monitors (LDF instruments) the optic fibre terminates in an optic probe which can be attached to the tissue surface. One or more light collecting fibres also terminate in the probe head and these fibres transmit a proportion of the scattered light to a photodetector and the signal processing electronics. |
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