Blood flow determination by the laser speckle method

Blood flow within the skin is measured by evaluating the dynamics of the laser speckle pattern. Laser light scattered from an object with a rough surface forms a granular structure--the speckles. When the object is moving, the speckle pattern becomes dependent on time. The measurements are performed at a distance of 6 cm which is adjusted by an auxiliary beam. The laser beam forms a spot on the skin with a diameter of approximately 1.5 mm and penetrates the skin. Part of the light is scattered back to the surface by the blood cells in the capillaries. The time dependent speckle intensity I(t) is determined by a photomultiplier. The comparison of spectra of I(t) obtained from measurements on the skin and on adhesive tape attached to the skin shows that there is a "tissue movement", the velocity of which has the same order of magnitude as the blood velocity in the capillaries. This has to be considered when measuring blood flow by the speckle method. Electronic signal processing reduces the influence from tissue movement and yields a value M being a relative measure of the blood flow. The time course of M during ischemia and reactive hyperaemia is compared with concurrent measurements of the skin temperature, the transcutaneous oxygen tension, and the laser Doppler signal. They exhibit similar tracings. Investigations in patients with leg ulcers show that measurements in open wounds can be performed.