Variable hyperemia of biological tissue as a noise source in the input optical signal of a medical laser Doppler flowmeter
As applied to the problems of medical laser Doppler flowmetry and based on a modified Kubelka Munk two flow model, analytic expressions have been obtained for the radiation power backscattered by biological tissue, taking into account the variable hyperemia of its microvasculature. An estimate is made of the power contribution of the Doppler component of the flow to the overall backscattered radiation signal recorded by the device, which appears when light is scattered at moving erythrocytes. It is shown that the power contribution of the Doppler component to the overall backscattered radiation flux is no greater than 5% on average. The variable hyperemia that results from various physiological processes causes the radiation flux recorded by the Doppler flowmeter to be amplitude modulated. The power of the amplitude modulated component can be of the same order of magnitude as, and in certain cases even greater than, the power of the useful Doppler signal, creating noise in the input signal of the device.