Non-contact laser tissue blood flow measurement using polarization to reduce the specular reflection artefact

Abstract

A non-contact laser (tissue) blood flowmeter capable of measuring ‘tissue blood flow’ (local blood flow per unit tissue volume) is proposed. The non-contact flowmeter utilizes the polarization of laser light to eliminate the light specularly reflected from the tissue surface, and an electronic circuit to reduce artefacts caused by temporal changes in the distance between the probe and tissue. The probe of the non-contact laser blood flowmeter (LBF) consists of optical fibres and a special polarizer. The tissue sample is illuminated by linearly polarized light, and the light, which is polarized perpendicularly with respect to the polarization of the incident light, is detected by the probe. The non-contact LBF was evaluated using a tissue blood flow model and human fingers. The results show that the values obtained by the non-contact LBF were not influenced by the intensity of the light reflected from the model surface and were hardly affected by temporal changes in the distance between the probe and model. In addition, the values obtained by the non-contact LBF agreed very well with those of a conventional LBF instrument for measurements on human fingers.