Surgery – Truss – Pad
Patent
1993-04-21
1994-11-08
Smith, Ruth S.
Surgery
Truss
Pad
128691, 356 28, A61B 5026
Patent
active
053617690
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a method and to a system for reducing the distance-dependent amplification factor when measuring fluid flow movements with an image-producing laser-Doppler technique, particularly when measuring blood perfusion through tissue. The system includes a laser beam generating source and means for directing the laser beam onto a measurement object which scatters and reflects the light beam. The light reflected is received by a detector which detects broadening of the frequency caused by the Doppler effect.
BACKGROUND OF THE INVENTION
The invention is based on the use of the known laser-Doppler technique for measuring the superficial circulation of blood in cutaneous tissue. This technique is described, for instance, in U.S. Pat. Nos. 3,511,227, 4,109,647, SE 419 678 and tile articles "In Vivo Evaluation of Microcirculation by Coherent Light Scattering", Stern, N. D., Nature, Vol. 254, pp. 56-58, 1975; "A New Instrument for Continuous Measurement of Tissue Blood Flow by Light Beating Spectroscopy", Nilsson, G. E., Tenland, T. and Oberg, P. A., IEE trans., BME-27, pp. 12-19, 1980, and "Evaluation of a Laser Doppler Flow Meter for Measurement of Tissue Blood Flow", Nilsson, G. E., Tenland, T. and Oberg, P. A., IEE trans., BME-27, pp. 597-604, 1980. In principle, this technique involves directing a laser beam onto a part of the tissue and receiving, with the aid of an appropriate photodetector, part of the light scattered and reflected back by that part of the tissue that is irradiated by the laser beam. As a result of the Doppler effect, the frequency of the reflected and scattered light is broadened and the frequency spectrum of the light will thus be broader than the frequency spectrum of the original laser beam, this broadening of the light frequency being due to the influence of movement of blood cells in the superficial part of the irradiated tissue. The extent to which the frequency is broadened and the intensity of light within different parts of this broader frequency spectrum constitute a measurement of the superficial blood circulation in the irradiated part of the examined tissue and can be determined or evaluated by appropriate processing of the photodetector output signal.
Swedish Patent Application No. 8903641-2 describes how this technique is used in a system for measuring and visually presenting the extent of superficial blood circulation over a large area of a part of the body, for instance a complete hand or foot or a part of a hand or foot or a part of a leg. The superficial blood circulation can vary quite considerably within different regions of a body part, and the described system enables the course taken by an illness, disease or healing process to be studied effectively. This known system includes a laser light source for generating a laser beam and means for directing the laser beam onto the body part to be examined and for guided movement of the laser beam over said body part in accordance with a predetermined scanning pattern. The system also includes means for receiving light reflected from said body part and for detecting the broadening in frequency of the reflected light caused by the Doppler effect, and also for registering this broadening of the frequency over a large number of points along the path scanned by the laser as a measurement of the superficial blood circulation in said body part at said points. The system also includes means for visual presentation on a color screen of the magnitude of the superficial blood circulation at the scanned points, using mutually different colors for mutually different blood circulation magnitude intervals.
When practicing the light-fiber-based Doppler effect described in the introduction, registration of the superficial blood circulation is effected solely with the aid of a punctiform measuring process. In the technique described in Swedish Patent Application No. 8903641-2, the laser beam scans different measuring points over a wide surface area, so as finally to generate an image or pictu
REFERENCES:
patent: 4862894 (1989-09-01), Fuji
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